ARK-OS/arkos/system/sysrootaarch64/usr/share/info/libc.info-7

This is libc.info, produced by makeinfo version 7.3 from libc.texinfo.

This is ‘The GNU C Library Reference Manual’, for version 2.43.

   Copyright © 1993-2026 Free Software Foundation, Inc.

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "Free Software Needs Free Documentation" and
"GNU Lesser General Public License", the Front-Cover texts being "A GNU
Manual", and with the Back-Cover Texts as in (a) below.  A copy of the
license is included in the section entitled "GNU Free Documentation
License".

   (a) The FSF's Back-Cover Text is: "You have the freedom to copy and
modify this GNU manual.  Buying copies from the FSF supports it in
developing GNU and promoting software freedom."
INFO-DIR-SECTION Software libraries
START-INFO-DIR-ENTRY
* Libc: (libc).                 C library.
END-INFO-DIR-ENTRY

INFO-DIR-SECTION GNU C library functions and macros
START-INFO-DIR-ENTRY
* ALTWERASE: (libc)Local Modes.
* ARGP_ERR_UNKNOWN: (libc)Argp Parser Functions.
* ARG_MAX: (libc)General Limits.
* BAUD_MAX: (libc)Line Speed.
* BC_BASE_MAX: (libc)Utility Limits.
* BC_DIM_MAX: (libc)Utility Limits.
* BC_SCALE_MAX: (libc)Utility Limits.
* BC_STRING_MAX: (libc)Utility Limits.
* BRKINT: (libc)Input Modes.
* BUFSIZ: (libc)Controlling Buffering.
* CCTS_OFLOW: (libc)Control Modes.
* CHAR_BIT: (libc)Width of Type.
* CHILD_MAX: (libc)General Limits.
* CIGNORE: (libc)Control Modes.
* CLK_TCK: (libc)Processor Time.
* CLOCAL: (libc)Control Modes.
* CLOCKS_PER_SEC: (libc)CPU Time.
* CLOCK_BOOTTIME: (libc)Getting the Time.
* CLOCK_BOOTTIME_ALARM: (libc)Getting the Time.
* CLOCK_MONOTONIC: (libc)Getting the Time.
* CLOCK_MONOTONIC_COARSE: (libc)Getting the Time.
* CLOCK_MONOTONIC_RAW: (libc)Getting the Time.
* CLOCK_PROCESS_CPUTIME_ID: (libc)Getting the Time.
* CLOCK_REALTIME: (libc)Getting the Time.
* CLOCK_REALTIME_ALARM: (libc)Getting the Time.
* CLOCK_REALTIME_COARSE: (libc)Getting the Time.
* CLOCK_TAI: (libc)Getting the Time.
* CLOCK_THREAD_CPUTIME_ID: (libc)Getting the Time.
* COLL_WEIGHTS_MAX: (libc)Utility Limits.
* CPU_ALLOC: (libc)CPU Affinity.
* CPU_ALLOC_SIZE: (libc)CPU Affinity.
* CPU_AND: (libc)CPU Affinity.
* CPU_AND_S: (libc)CPU Affinity.
* CPU_CLR: (libc)CPU Affinity.
* CPU_CLR_S: (libc)CPU Affinity.
* CPU_COUNT: (libc)CPU Affinity.
* CPU_COUNT_S: (libc)CPU Affinity.
* CPU_EQUAL: (libc)CPU Affinity.
* CPU_EQUAL_S: (libc)CPU Affinity.
* CPU_FEATURE_ACTIVE: (libc)X86.
* CPU_FEATURE_PRESENT: (libc)X86.
* CPU_FREE: (libc)CPU Affinity.
* CPU_ISSET: (libc)CPU Affinity.
* CPU_ISSET_S: (libc)CPU Affinity.
* CPU_OR: (libc)CPU Affinity.
* CPU_OR_S: (libc)CPU Affinity.
* CPU_SET: (libc)CPU Affinity.
* CPU_SETSIZE: (libc)CPU Affinity.
* CPU_SET_S: (libc)CPU Affinity.
* CPU_XOR: (libc)CPU Affinity.
* CPU_XOR_S: (libc)CPU Affinity.
* CPU_ZERO: (libc)CPU Affinity.
* CPU_ZERO_S: (libc)CPU Affinity.
* CREAD: (libc)Control Modes.
* CRTS_IFLOW: (libc)Control Modes.
* CS5: (libc)Control Modes.
* CS6: (libc)Control Modes.
* CS7: (libc)Control Modes.
* CS8: (libc)Control Modes.
* CSIZE: (libc)Control Modes.
* CSTOPB: (libc)Control Modes.
* DLFO_EH_SEGMENT_TYPE: (libc)Dynamic Linker Introspection.
* DLFO_STRUCT_HAS_EH_COUNT: (libc)Dynamic Linker Introspection.
* DLFO_STRUCT_HAS_EH_DBASE: (libc)Dynamic Linker Introspection.
* DTTOIF: (libc)Directory Entries.
* E2BIG: (libc)Error Codes.
* EACCES: (libc)Error Codes.
* EADDRINUSE: (libc)Error Codes.
* EADDRNOTAVAIL: (libc)Error Codes.
* EADV: (libc)Error Codes.
* EAFNOSUPPORT: (libc)Error Codes.
* EAGAIN: (libc)Error Codes.
* EALREADY: (libc)Error Codes.
* EAUTH: (libc)Error Codes.
* EBACKGROUND: (libc)Error Codes.
* EBADE: (libc)Error Codes.
* EBADF: (libc)Error Codes.
* EBADFD: (libc)Error Codes.
* EBADMSG: (libc)Error Codes.
* EBADR: (libc)Error Codes.
* EBADRPC: (libc)Error Codes.
* EBADRQC: (libc)Error Codes.
* EBADSLT: (libc)Error Codes.
* EBFONT: (libc)Error Codes.
* EBUSY: (libc)Error Codes.
* ECANCELED: (libc)Error Codes.
* ECHILD: (libc)Error Codes.
* ECHO: (libc)Local Modes.
* ECHOCTL: (libc)Local Modes.
* ECHOE: (libc)Local Modes.
* ECHOK: (libc)Local Modes.
* ECHOKE: (libc)Local Modes.
* ECHONL: (libc)Local Modes.
* ECHOPRT: (libc)Local Modes.
* ECHRNG: (libc)Error Codes.
* ECOMM: (libc)Error Codes.
* ECONNABORTED: (libc)Error Codes.
* ECONNREFUSED: (libc)Error Codes.
* ECONNRESET: (libc)Error Codes.
* ED: (libc)Error Codes.
* EDEADLK: (libc)Error Codes.
* EDEADLOCK: (libc)Error Codes.
* EDESTADDRREQ: (libc)Error Codes.
* EDIED: (libc)Error Codes.
* EDOM: (libc)Error Codes.
* EDOTDOT: (libc)Error Codes.
* EDQUOT: (libc)Error Codes.
* EEXIST: (libc)Error Codes.
* EFAULT: (libc)Error Codes.
* EFBIG: (libc)Error Codes.
* EFTYPE: (libc)Error Codes.
* EGRATUITOUS: (libc)Error Codes.
* EGREGIOUS: (libc)Error Codes.
* EHOSTDOWN: (libc)Error Codes.
* EHOSTUNREACH: (libc)Error Codes.
* EHWPOISON: (libc)Error Codes.
* EIDRM: (libc)Error Codes.
* EIEIO: (libc)Error Codes.
* EILSEQ: (libc)Error Codes.
* EINPROGRESS: (libc)Error Codes.
* EINTR: (libc)Error Codes.
* EINVAL: (libc)Error Codes.
* EIO: (libc)Error Codes.
* EISCONN: (libc)Error Codes.
* EISDIR: (libc)Error Codes.
* EISNAM: (libc)Error Codes.
* EKEYEXPIRED: (libc)Error Codes.
* EKEYREJECTED: (libc)Error Codes.
* EKEYREVOKED: (libc)Error Codes.
* EL2HLT: (libc)Error Codes.
* EL2NSYNC: (libc)Error Codes.
* EL3HLT: (libc)Error Codes.
* EL3RST: (libc)Error Codes.
* ELIBACC: (libc)Error Codes.
* ELIBBAD: (libc)Error Codes.
* ELIBEXEC: (libc)Error Codes.
* ELIBMAX: (libc)Error Codes.
* ELIBSCN: (libc)Error Codes.
* ELNRNG: (libc)Error Codes.
* ELOOP: (libc)Error Codes.
* EMEDIUMTYPE: (libc)Error Codes.
* EMFILE: (libc)Error Codes.
* EMLINK: (libc)Error Codes.
* EMSGSIZE: (libc)Error Codes.
* EMULTIHOP: (libc)Error Codes.
* ENAMETOOLONG: (libc)Error Codes.
* ENAVAIL: (libc)Error Codes.
* ENEEDAUTH: (libc)Error Codes.
* ENETDOWN: (libc)Error Codes.
* ENETRESET: (libc)Error Codes.
* ENETUNREACH: (libc)Error Codes.
* ENFILE: (libc)Error Codes.
* ENOANO: (libc)Error Codes.
* ENOBUFS: (libc)Error Codes.
* ENOCSI: (libc)Error Codes.
* ENODATA: (libc)Error Codes.
* ENODEV: (libc)Error Codes.
* ENOENT: (libc)Error Codes.
* ENOEXEC: (libc)Error Codes.
* ENOKEY: (libc)Error Codes.
* ENOLCK: (libc)Error Codes.
* ENOLINK: (libc)Error Codes.
* ENOMEDIUM: (libc)Error Codes.
* ENOMEM: (libc)Error Codes.
* ENOMSG: (libc)Error Codes.
* ENONET: (libc)Error Codes.
* ENOPKG: (libc)Error Codes.
* ENOPROTOOPT: (libc)Error Codes.
* ENOSPC: (libc)Error Codes.
* ENOSR: (libc)Error Codes.
* ENOSTR: (libc)Error Codes.
* ENOSYS: (libc)Error Codes.
* ENOTBLK: (libc)Error Codes.
* ENOTCONN: (libc)Error Codes.
* ENOTDIR: (libc)Error Codes.
* ENOTEMPTY: (libc)Error Codes.
* ENOTNAM: (libc)Error Codes.
* ENOTRECOVERABLE: (libc)Error Codes.
* ENOTSOCK: (libc)Error Codes.
* ENOTSUP: (libc)Error Codes.
* ENOTTY: (libc)Error Codes.
* ENOTUNIQ: (libc)Error Codes.
* ENXIO: (libc)Error Codes.
* EOF: (libc)EOF and Errors.
* EOPNOTSUPP: (libc)Error Codes.
* EOVERFLOW: (libc)Error Codes.
* EOWNERDEAD: (libc)Error Codes.
* EPERM: (libc)Error Codes.
* EPFNOSUPPORT: (libc)Error Codes.
* EPIPE: (libc)Error Codes.
* EPROCLIM: (libc)Error Codes.
* EPROCUNAVAIL: (libc)Error Codes.
* EPROGMISMATCH: (libc)Error Codes.
* EPROGUNAVAIL: (libc)Error Codes.
* EPROTO: (libc)Error Codes.
* EPROTONOSUPPORT: (libc)Error Codes.
* EPROTOTYPE: (libc)Error Codes.
* EQUIV_CLASS_MAX: (libc)Utility Limits.
* ERANGE: (libc)Error Codes.
* EREMCHG: (libc)Error Codes.
* EREMOTE: (libc)Error Codes.
* EREMOTEIO: (libc)Error Codes.
* ERESTART: (libc)Error Codes.
* ERFKILL: (libc)Error Codes.
* EROFS: (libc)Error Codes.
* ERPCMISMATCH: (libc)Error Codes.
* ESHUTDOWN: (libc)Error Codes.
* ESOCKTNOSUPPORT: (libc)Error Codes.
* ESPIPE: (libc)Error Codes.
* ESRCH: (libc)Error Codes.
* ESRMNT: (libc)Error Codes.
* ESTALE: (libc)Error Codes.
* ESTRPIPE: (libc)Error Codes.
* ETIME: (libc)Error Codes.
* ETIMEDOUT: (libc)Error Codes.
* ETOOMANYREFS: (libc)Error Codes.
* ETXTBSY: (libc)Error Codes.
* EUCLEAN: (libc)Error Codes.
* EUNATCH: (libc)Error Codes.
* EUSERS: (libc)Error Codes.
* EWOULDBLOCK: (libc)Error Codes.
* EXDEV: (libc)Error Codes.
* EXFULL: (libc)Error Codes.
* EXIT_FAILURE: (libc)Exit Status.
* EXIT_SUCCESS: (libc)Exit Status.
* EXPR_NEST_MAX: (libc)Utility Limits.
* FD_CLOEXEC: (libc)Descriptor Flags.
* FD_CLR: (libc)Waiting for I/O.
* FD_ISSET: (libc)Waiting for I/O.
* FD_SET: (libc)Waiting for I/O.
* FD_SETSIZE: (libc)Waiting for I/O.
* FD_ZERO: (libc)Waiting for I/O.
* FE_SNANS_ALWAYS_SIGNAL: (libc)Infinity and NaN.
* FILENAME_MAX: (libc)Limits for Files.
* FLUSHO: (libc)Local Modes.
* FOPEN_MAX: (libc)Opening Streams.
* FP_ILOGB0: (libc)Exponents and Logarithms.
* FP_ILOGBNAN: (libc)Exponents and Logarithms.
* FP_LLOGB0: (libc)Exponents and Logarithms.
* FP_LLOGBNAN: (libc)Exponents and Logarithms.
* F_DUPFD: (libc)Duplicating Descriptors.
* F_GETFD: (libc)Descriptor Flags.
* F_GETFL: (libc)Getting File Status Flags.
* F_GETLK: (libc)File Locks.
* F_GETOWN: (libc)Interrupt Input.
* F_OFD_GETLK: (libc)Open File Description Locks.
* F_OFD_SETLK: (libc)Open File Description Locks.
* F_OFD_SETLKW: (libc)Open File Description Locks.
* F_OK: (libc)Testing File Access.
* F_SETFD: (libc)Descriptor Flags.
* F_SETFL: (libc)Getting File Status Flags.
* F_SETLK: (libc)File Locks.
* F_SETLKW: (libc)File Locks.
* F_SETOWN: (libc)Interrupt Input.
* HUGE_VAL: (libc)Math Error Reporting.
* HUGE_VALF: (libc)Math Error Reporting.
* HUGE_VALL: (libc)Math Error Reporting.
* HUGE_VAL_FN: (libc)Math Error Reporting.
* HUGE_VAL_FNx: (libc)Math Error Reporting.
* HUPCL: (libc)Control Modes.
* I: (libc)Complex Numbers.
* ICANON: (libc)Local Modes.
* ICRNL: (libc)Input Modes.
* IEXTEN: (libc)Local Modes.
* IFNAMSIZ: (libc)Interface Naming.
* IFTODT: (libc)Directory Entries.
* IGNBRK: (libc)Input Modes.
* IGNCR: (libc)Input Modes.
* IGNPAR: (libc)Input Modes.
* IMAXBEL: (libc)Input Modes.
* INADDR_ANY: (libc)Host Address Data Type.
* INADDR_BROADCAST: (libc)Host Address Data Type.
* INADDR_LOOPBACK: (libc)Host Address Data Type.
* INADDR_NONE: (libc)Host Address Data Type.
* INFINITY: (libc)Infinity and NaN.
* INLCR: (libc)Input Modes.
* INPCK: (libc)Input Modes.
* IPPORT_RESERVED: (libc)Ports.
* IPPORT_USERRESERVED: (libc)Ports.
* ISIG: (libc)Local Modes.
* ISTRIP: (libc)Input Modes.
* IXANY: (libc)Input Modes.
* IXOFF: (libc)Input Modes.
* IXON: (libc)Input Modes.
* LINE_MAX: (libc)Utility Limits.
* LINK_MAX: (libc)Limits for Files.
* L_ctermid: (libc)Identifying the Terminal.
* L_cuserid: (libc)Who Logged In.
* L_tmpnam: (libc)Temporary Files.
* MAXNAMLEN: (libc)Limits for Files.
* MAXSYMLINKS: (libc)Symbolic Links.
* MAX_CANON: (libc)Limits for Files.
* MAX_INPUT: (libc)Limits for Files.
* MB_CUR_MAX: (libc)Selecting the Conversion.
* MB_LEN_MAX: (libc)Selecting the Conversion.
* MDMBUF: (libc)Control Modes.
* MSG_DONTROUTE: (libc)Socket Data Options.
* MSG_OOB: (libc)Socket Data Options.
* MSG_PEEK: (libc)Socket Data Options.
* NAME_MAX: (libc)Limits for Files.
* NAN: (libc)Infinity and NaN.
* NCCS: (libc)Mode Data Types.
* NGROUPS_MAX: (libc)General Limits.
* NOFLSH: (libc)Local Modes.
* NOKERNINFO: (libc)Local Modes.
* NSIG: (libc)Standard Signals.
* NULL: (libc)Null Pointer Constant.
* ONLCR: (libc)Output Modes.
* ONOEOT: (libc)Output Modes.
* OPEN_MAX: (libc)General Limits.
* OPOST: (libc)Output Modes.
* OXTABS: (libc)Output Modes.
* O_ACCMODE: (libc)Access Modes.
* O_APPEND: (libc)Operating Modes.
* O_ASYNC: (libc)Operating Modes.
* O_CREAT: (libc)Open-time Flags.
* O_DIRECTORY: (libc)Open-time Flags.
* O_EXCL: (libc)Open-time Flags.
* O_EXEC: (libc)Access Modes.
* O_EXLOCK: (libc)Open-time Flags.
* O_FSYNC: (libc)Operating Modes.
* O_IGNORE_CTTY: (libc)Open-time Flags.
* O_NDELAY: (libc)Operating Modes.
* O_NOATIME: (libc)Operating Modes.
* O_NOCTTY: (libc)Open-time Flags.
* O_NOFOLLOW: (libc)Open-time Flags.
* O_NOLINK: (libc)Open-time Flags.
* O_NONBLOCK: (libc)Open-time Flags.
* O_NONBLOCK: (libc)Operating Modes.
* O_NOTRANS: (libc)Open-time Flags.
* O_PATH: (libc)Access Modes.
* O_RDONLY: (libc)Access Modes.
* O_RDWR: (libc)Access Modes.
* O_READ: (libc)Access Modes.
* O_SHLOCK: (libc)Open-time Flags.
* O_SYNC: (libc)Operating Modes.
* O_TMPFILE: (libc)Open-time Flags.
* O_TRUNC: (libc)Open-time Flags.
* O_WRITE: (libc)Access Modes.
* O_WRONLY: (libc)Access Modes.
* PARENB: (libc)Control Modes.
* PARMRK: (libc)Input Modes.
* PARODD: (libc)Control Modes.
* PATH_MAX: (libc)Limits for Files.
* PA_FLAG_MASK: (libc)Parsing a Template String.
* PENDIN: (libc)Local Modes.
* PF_FILE: (libc)Local Namespace Details.
* PF_INET6: (libc)Internet Namespace.
* PF_INET: (libc)Internet Namespace.
* PF_LOCAL: (libc)Local Namespace Details.
* PF_UNIX: (libc)Local Namespace Details.
* PIPE_BUF: (libc)Limits for Files.
* PTHREAD_ATTR_NO_SIGMASK_NP: (libc)Initial Thread Signal Mask.
* P_tmpdir: (libc)Temporary Files.
* RAND_MAX: (libc)ISO Random.
* RE_DUP_MAX: (libc)General Limits.
* RLIM_INFINITY: (libc)Limits on Resources.
* RSEQ_SIG: (libc)Restartable Sequences.
* R_OK: (libc)Testing File Access.
* SA_NOCLDSTOP: (libc)Flags for Sigaction.
* SA_NOCLDWAIT: (libc)Flags for Sigaction.
* SA_NODEFER: (libc)Flags for Sigaction.
* SA_ONSTACK: (libc)Flags for Sigaction.
* SA_RESETHAND: (libc)Flags for Sigaction.
* SA_RESTART: (libc)Flags for Sigaction.
* SA_SIGINFO: (libc)Flags for Sigaction.
* SEEK_CUR: (libc)File Positioning.
* SEEK_END: (libc)File Positioning.
* SEEK_SET: (libc)File Positioning.
* SIGABRT: (libc)Program Error Signals.
* SIGALRM: (libc)Alarm Signals.
* SIGBUS: (libc)Program Error Signals.
* SIGCHLD: (libc)Job Control Signals.
* SIGCLD: (libc)Job Control Signals.
* SIGCONT: (libc)Job Control Signals.
* SIGEMT: (libc)Program Error Signals.
* SIGFPE: (libc)Program Error Signals.
* SIGHUP: (libc)Termination Signals.
* SIGILL: (libc)Program Error Signals.
* SIGINFO: (libc)Miscellaneous Signals.
* SIGINT: (libc)Termination Signals.
* SIGIO: (libc)Asynchronous I/O Signals.
* SIGIOT: (libc)Program Error Signals.
* SIGKILL: (libc)Termination Signals.
* SIGLOST: (libc)Operation Error Signals.
* SIGPIPE: (libc)Operation Error Signals.
* SIGPOLL: (libc)Asynchronous I/O Signals.
* SIGPROF: (libc)Alarm Signals.
* SIGPWR: (libc)Miscellaneous Signals.
* SIGQUIT: (libc)Termination Signals.
* SIGSEGV: (libc)Program Error Signals.
* SIGSTKFLT: (libc)Program Error Signals.
* SIGSTOP: (libc)Job Control Signals.
* SIGSYS: (libc)Program Error Signals.
* SIGTERM: (libc)Termination Signals.
* SIGTRAP: (libc)Program Error Signals.
* SIGTSTP: (libc)Job Control Signals.
* SIGTTIN: (libc)Job Control Signals.
* SIGTTOU: (libc)Job Control Signals.
* SIGURG: (libc)Asynchronous I/O Signals.
* SIGUSR1: (libc)Miscellaneous Signals.
* SIGUSR2: (libc)Miscellaneous Signals.
* SIGVTALRM: (libc)Alarm Signals.
* SIGWINCH: (libc)Miscellaneous Signals.
* SIGXCPU: (libc)Operation Error Signals.
* SIGXFSZ: (libc)Operation Error Signals.
* SIG_ERR: (libc)Basic Signal Handling.
* SNAN: (libc)Infinity and NaN.
* SNANF: (libc)Infinity and NaN.
* SNANFN: (libc)Infinity and NaN.
* SNANFNx: (libc)Infinity and NaN.
* SNANL: (libc)Infinity and NaN.
* SOCK_DGRAM: (libc)Communication Styles.
* SOCK_RAW: (libc)Communication Styles.
* SOCK_RDM: (libc)Communication Styles.
* SOCK_SEQPACKET: (libc)Communication Styles.
* SOCK_STREAM: (libc)Communication Styles.
* SOL_SOCKET: (libc)Socket-Level Options.
* SPEED_MAX: (libc)Line Speed.
* SSIZE_MAX: (libc)General Limits.
* STREAM_MAX: (libc)General Limits.
* SUN_LEN: (libc)Local Namespace Details.
* S_IFMT: (libc)Testing File Type.
* S_ISBLK: (libc)Testing File Type.
* S_ISCHR: (libc)Testing File Type.
* S_ISDIR: (libc)Testing File Type.
* S_ISFIFO: (libc)Testing File Type.
* S_ISLNK: (libc)Testing File Type.
* S_ISREG: (libc)Testing File Type.
* S_ISSOCK: (libc)Testing File Type.
* S_TYPEISMQ: (libc)Testing File Type.
* S_TYPEISSEM: (libc)Testing File Type.
* S_TYPEISSHM: (libc)Testing File Type.
* TIME_UTC: (libc)Getting the Time.
* TMP_MAX: (libc)Temporary Files.
* TOSTOP: (libc)Local Modes.
* TZNAME_MAX: (libc)General Limits.
* VDISCARD: (libc)Other Special.
* VDSUSP: (libc)Signal Characters.
* VEOF: (libc)Editing Characters.
* VEOL2: (libc)Editing Characters.
* VEOL: (libc)Editing Characters.
* VERASE: (libc)Editing Characters.
* VINTR: (libc)Signal Characters.
* VKILL: (libc)Editing Characters.
* VLNEXT: (libc)Other Special.
* VMIN: (libc)Noncanonical Input.
* VQUIT: (libc)Signal Characters.
* VREPRINT: (libc)Editing Characters.
* VSTART: (libc)Start/Stop Characters.
* VSTATUS: (libc)Other Special.
* VSTOP: (libc)Start/Stop Characters.
* VSUSP: (libc)Signal Characters.
* VTIME: (libc)Noncanonical Input.
* VWERASE: (libc)Editing Characters.
* WCHAR_MAX: (libc)Extended Char Intro.
* WCHAR_MIN: (libc)Extended Char Intro.
* WCOREDUMP: (libc)Process Completion Status.
* WEOF: (libc)EOF and Errors.
* WEOF: (libc)Extended Char Intro.
* WEXITSTATUS: (libc)Process Completion Status.
* WIFEXITED: (libc)Process Completion Status.
* WIFSIGNALED: (libc)Process Completion Status.
* WIFSTOPPED: (libc)Process Completion Status.
* WSTOPSIG: (libc)Process Completion Status.
* WTERMSIG: (libc)Process Completion Status.
* W_OK: (libc)Testing File Access.
* X_OK: (libc)Testing File Access.
* _Complex_I: (libc)Complex Numbers.
* _Exit: (libc)Termination Internals.
* _Fork: (libc)Creating a Process.
* _IOFBF: (libc)Controlling Buffering.
* _IOLBF: (libc)Controlling Buffering.
* _IONBF: (libc)Controlling Buffering.
* _Imaginary_I: (libc)Complex Numbers.
* _PATH_UTMP: (libc)Manipulating the Database.
* _PATH_WTMP: (libc)Manipulating the Database.
* _POSIX2_C_DEV: (libc)System Options.
* _POSIX2_C_VERSION: (libc)Version Supported.
* _POSIX2_FORT_DEV: (libc)System Options.
* _POSIX2_FORT_RUN: (libc)System Options.
* _POSIX2_LOCALEDEF: (libc)System Options.
* _POSIX2_SW_DEV: (libc)System Options.
* _POSIX_CHOWN_RESTRICTED: (libc)Options for Files.
* _POSIX_JOB_CONTROL: (libc)System Options.
* _POSIX_NO_TRUNC: (libc)Options for Files.
* _POSIX_SAVED_IDS: (libc)System Options.
* _POSIX_VDISABLE: (libc)Options for Files.
* _POSIX_VERSION: (libc)Version Supported.
* __fbufsize: (libc)Controlling Buffering.
* __flbf: (libc)Controlling Buffering.
* __fpending: (libc)Controlling Buffering.
* __fpurge: (libc)Flushing Buffers.
* __freadable: (libc)Opening Streams.
* __freading: (libc)Opening Streams.
* __fsetlocking: (libc)Streams and Threads.
* __fwritable: (libc)Opening Streams.
* __fwriting: (libc)Opening Streams.
* __gconv_end_fct: (libc)glibc iconv Implementation.
* __gconv_fct: (libc)glibc iconv Implementation.
* __gconv_init_fct: (libc)glibc iconv Implementation.
* __ppc_get_timebase: (libc)PowerPC.
* __ppc_get_timebase_freq: (libc)PowerPC.
* __ppc_mdoio: (libc)PowerPC.
* __ppc_mdoom: (libc)PowerPC.
* __ppc_set_ppr_low: (libc)PowerPC.
* __ppc_set_ppr_med: (libc)PowerPC.
* __ppc_set_ppr_med_high: (libc)PowerPC.
* __ppc_set_ppr_med_low: (libc)PowerPC.
* __ppc_set_ppr_very_low: (libc)PowerPC.
* __ppc_yield: (libc)PowerPC.
* __riscv_flush_icache: (libc)RISC-V.
* __va_copy: (libc)Argument Macros.
* __x86_get_cpuid_feature_leaf: (libc)X86.
* _dl_find_object: (libc)Dynamic Linker Introspection.
* _exit: (libc)Termination Internals.
* _flushlbf: (libc)Flushing Buffers.
* _tolower: (libc)Case Conversion.
* _toupper: (libc)Case Conversion.
* a64l: (libc)Encode Binary Data.
* abort: (libc)Aborting a Program.
* abs: (libc)Absolute Value.
* accept: (libc)Accepting Connections.
* access: (libc)Testing File Access.
* acos: (libc)Inverse Trig Functions.
* acosf: (libc)Inverse Trig Functions.
* acosfN: (libc)Inverse Trig Functions.
* acosfNx: (libc)Inverse Trig Functions.
* acosh: (libc)Hyperbolic Functions.
* acoshf: (libc)Hyperbolic Functions.
* acoshfN: (libc)Hyperbolic Functions.
* acoshfNx: (libc)Hyperbolic Functions.
* acoshl: (libc)Hyperbolic Functions.
* acosl: (libc)Inverse Trig Functions.
* acospi: (libc)Inverse Trig Functions.
* acospif: (libc)Inverse Trig Functions.
* acospifN: (libc)Inverse Trig Functions.
* acospifNx: (libc)Inverse Trig Functions.
* acospil: (libc)Inverse Trig Functions.
* addmntent: (libc)mtab.
* addseverity: (libc)Adding Severity Classes.
* adjtime: (libc)Setting and Adjusting the Time.
* adjtimex: (libc)Setting and Adjusting the Time.
* aio_cancel64: (libc)Cancel AIO Operations.
* aio_cancel: (libc)Cancel AIO Operations.
* aio_error64: (libc)Status of AIO Operations.
* aio_error: (libc)Status of AIO Operations.
* aio_fsync64: (libc)Synchronizing AIO Operations.
* aio_fsync: (libc)Synchronizing AIO Operations.
* aio_init: (libc)Configuration of AIO.
* aio_read64: (libc)Asynchronous Reads/Writes.
* aio_read: (libc)Asynchronous Reads/Writes.
* aio_return64: (libc)Status of AIO Operations.
* aio_return: (libc)Status of AIO Operations.
* aio_suspend64: (libc)Synchronizing AIO Operations.
* aio_suspend: (libc)Synchronizing AIO Operations.
* aio_write64: (libc)Asynchronous Reads/Writes.
* aio_write: (libc)Asynchronous Reads/Writes.
* alarm: (libc)Setting an Alarm.
* aligned_alloc: (libc)Aligned Memory Blocks.
* alloca: (libc)Variable Size Automatic.
* alphasort64: (libc)Scanning Directory Content.
* alphasort: (libc)Scanning Directory Content.
* arc4random: (libc)High Quality Random.
* arc4random_buf: (libc)High Quality Random.
* arc4random_uniform: (libc)High Quality Random.
* argp_error: (libc)Argp Helper Functions.
* argp_failure: (libc)Argp Helper Functions.
* argp_help: (libc)Argp Help.
* argp_parse: (libc)Argp.
* argp_state_help: (libc)Argp Helper Functions.
* argp_usage: (libc)Argp Helper Functions.
* argz_add: (libc)Argz Functions.
* argz_add_sep: (libc)Argz Functions.
* argz_append: (libc)Argz Functions.
* argz_count: (libc)Argz Functions.
* argz_create: (libc)Argz Functions.
* argz_create_sep: (libc)Argz Functions.
* argz_delete: (libc)Argz Functions.
* argz_extract: (libc)Argz Functions.
* argz_insert: (libc)Argz Functions.
* argz_next: (libc)Argz Functions.
* argz_replace: (libc)Argz Functions.
* argz_stringify: (libc)Argz Functions.
* asctime: (libc)Formatting Calendar Time.
* asctime_r: (libc)Formatting Calendar Time.
* asin: (libc)Inverse Trig Functions.
* asinf: (libc)Inverse Trig Functions.
* asinfN: (libc)Inverse Trig Functions.
* asinfNx: (libc)Inverse Trig Functions.
* asinh: (libc)Hyperbolic Functions.
* asinhf: (libc)Hyperbolic Functions.
* asinhfN: (libc)Hyperbolic Functions.
* asinhfNx: (libc)Hyperbolic Functions.
* asinhl: (libc)Hyperbolic Functions.
* asinl: (libc)Inverse Trig Functions.
* asinpi: (libc)Inverse Trig Functions.
* asinpif: (libc)Inverse Trig Functions.
* asinpifN: (libc)Inverse Trig Functions.
* asinpifNx: (libc)Inverse Trig Functions.
* asinpil: (libc)Inverse Trig Functions.
* asprintf: (libc)Dynamic Output.
* assert: (libc)Consistency Checking.
* assert_perror: (libc)Consistency Checking.
* atan2: (libc)Inverse Trig Functions.
* atan2f: (libc)Inverse Trig Functions.
* atan2fN: (libc)Inverse Trig Functions.
* atan2fNx: (libc)Inverse Trig Functions.
* atan2l: (libc)Inverse Trig Functions.
* atan2pi: (libc)Inverse Trig Functions.
* atan2pif: (libc)Inverse Trig Functions.
* atan2pifN: (libc)Inverse Trig Functions.
* atan2pifNx: (libc)Inverse Trig Functions.
* atan2pil: (libc)Inverse Trig Functions.
* atan: (libc)Inverse Trig Functions.
* atanf: (libc)Inverse Trig Functions.
* atanfN: (libc)Inverse Trig Functions.
* atanfNx: (libc)Inverse Trig Functions.
* atanh: (libc)Hyperbolic Functions.
* atanhf: (libc)Hyperbolic Functions.
* atanhfN: (libc)Hyperbolic Functions.
* atanhfNx: (libc)Hyperbolic Functions.
* atanhl: (libc)Hyperbolic Functions.
* atanl: (libc)Inverse Trig Functions.
* atanpi: (libc)Inverse Trig Functions.
* atanpif: (libc)Inverse Trig Functions.
* atanpifN: (libc)Inverse Trig Functions.
* atanpifNx: (libc)Inverse Trig Functions.
* atanpil: (libc)Inverse Trig Functions.
* atexit: (libc)Cleanups on Exit.
* atof: (libc)Parsing of Floats.
* atoi: (libc)Parsing of Integers.
* atol: (libc)Parsing of Integers.
* atoll: (libc)Parsing of Integers.
* backtrace: (libc)Backtraces.
* backtrace_symbols: (libc)Backtraces.
* backtrace_symbols_fd: (libc)Backtraces.
* basename: (libc)Finding Tokens in a String.
* basename: (libc)Finding Tokens in a String.
* bcmp: (libc)String/Array Comparison.
* bcopy: (libc)Copying Strings and Arrays.
* bind: (libc)Setting Address.
* bind_textdomain_codeset: (libc)Charset conversion in gettext.
* bindtextdomain: (libc)Locating gettext catalog.
* brk: (libc)Resizing the Data Segment.
* bsearch: (libc)Array Search Function.
* btowc: (libc)Converting a Character.
* bzero: (libc)Copying Strings and Arrays.
* cabs: (libc)Absolute Value.
* cabsf: (libc)Absolute Value.
* cabsfN: (libc)Absolute Value.
* cabsfNx: (libc)Absolute Value.
* cabsl: (libc)Absolute Value.
* cacos: (libc)Inverse Trig Functions.
* cacosf: (libc)Inverse Trig Functions.
* cacosfN: (libc)Inverse Trig Functions.
* cacosfNx: (libc)Inverse Trig Functions.
* cacosh: (libc)Hyperbolic Functions.
* cacoshf: (libc)Hyperbolic Functions.
* cacoshfN: (libc)Hyperbolic Functions.
* cacoshfNx: (libc)Hyperbolic Functions.
* cacoshl: (libc)Hyperbolic Functions.
* cacosl: (libc)Inverse Trig Functions.
* call_once: (libc)Call Once.
* calloc: (libc)Allocating Cleared Space.
* canonicalize: (libc)FP Bit Twiddling.
* canonicalize_file_name: (libc)Symbolic Links.
* canonicalizef: (libc)FP Bit Twiddling.
* canonicalizefN: (libc)FP Bit Twiddling.
* canonicalizefNx: (libc)FP Bit Twiddling.
* canonicalizel: (libc)FP Bit Twiddling.
* carg: (libc)Operations on Complex.
* cargf: (libc)Operations on Complex.
* cargfN: (libc)Operations on Complex.
* cargfNx: (libc)Operations on Complex.
* cargl: (libc)Operations on Complex.
* casin: (libc)Inverse Trig Functions.
* casinf: (libc)Inverse Trig Functions.
* casinfN: (libc)Inverse Trig Functions.
* casinfNx: (libc)Inverse Trig Functions.
* casinh: (libc)Hyperbolic Functions.
* casinhf: (libc)Hyperbolic Functions.
* casinhfN: (libc)Hyperbolic Functions.
* casinhfNx: (libc)Hyperbolic Functions.
* casinhl: (libc)Hyperbolic Functions.
* casinl: (libc)Inverse Trig Functions.
* catan: (libc)Inverse Trig Functions.
* catanf: (libc)Inverse Trig Functions.
* catanfN: (libc)Inverse Trig Functions.
* catanfNx: (libc)Inverse Trig Functions.
* catanh: (libc)Hyperbolic Functions.
* catanhf: (libc)Hyperbolic Functions.
* catanhfN: (libc)Hyperbolic Functions.
* catanhfNx: (libc)Hyperbolic Functions.
* catanhl: (libc)Hyperbolic Functions.
* catanl: (libc)Inverse Trig Functions.
* catclose: (libc)The catgets Functions.
* catgets: (libc)The catgets Functions.
* catopen: (libc)The catgets Functions.
* cbrt: (libc)Exponents and Logarithms.
* cbrtf: (libc)Exponents and Logarithms.
* cbrtfN: (libc)Exponents and Logarithms.
* cbrtfNx: (libc)Exponents and Logarithms.
* cbrtl: (libc)Exponents and Logarithms.
* ccos: (libc)Trig Functions.
* ccosf: (libc)Trig Functions.
* ccosfN: (libc)Trig Functions.
* ccosfNx: (libc)Trig Functions.
* ccosh: (libc)Hyperbolic Functions.
* ccoshf: (libc)Hyperbolic Functions.
* ccoshfN: (libc)Hyperbolic Functions.
* ccoshfNx: (libc)Hyperbolic Functions.
* ccoshl: (libc)Hyperbolic Functions.
* ccosl: (libc)Trig Functions.
* ceil: (libc)Rounding Functions.
* ceilf: (libc)Rounding Functions.
* ceilfN: (libc)Rounding Functions.
* ceilfNx: (libc)Rounding Functions.
* ceill: (libc)Rounding Functions.
* cexp: (libc)Exponents and Logarithms.
* cexpf: (libc)Exponents and Logarithms.
* cexpfN: (libc)Exponents and Logarithms.
* cexpfNx: (libc)Exponents and Logarithms.
* cexpl: (libc)Exponents and Logarithms.
* cfgetibaud: (libc)Line Speed.
* cfgetispeed: (libc)Line Speed.
* cfgetobaud: (libc)Line Speed.
* cfgetospeed: (libc)Line Speed.
* cfmakeraw: (libc)Noncanonical Input.
* cfsetbaud: (libc)Line Speed.
* cfsetibaud: (libc)Line Speed.
* cfsetispeed: (libc)Line Speed.
* cfsetobaud: (libc)Line Speed.
* cfsetospeed: (libc)Line Speed.
* cfsetspeed: (libc)Line Speed.
* chdir: (libc)Working Directory.
* chmod: (libc)Setting Permissions.
* chown: (libc)File Owner.
* cimag: (libc)Operations on Complex.
* cimagf: (libc)Operations on Complex.
* cimagfN: (libc)Operations on Complex.
* cimagfNx: (libc)Operations on Complex.
* cimagl: (libc)Operations on Complex.
* clearenv: (libc)Environment Access.
* clearerr: (libc)Error Recovery.
* clearerr_unlocked: (libc)Error Recovery.
* clock: (libc)CPU Time.
* clock_getres: (libc)Getting the Time.
* clock_gettime: (libc)Getting the Time.
* clock_nanosleep: (libc)Sleeping.
* clock_settime: (libc)Setting and Adjusting the Time.
* clog10: (libc)Exponents and Logarithms.
* clog10f: (libc)Exponents and Logarithms.
* clog10fN: (libc)Exponents and Logarithms.
* clog10fNx: (libc)Exponents and Logarithms.
* clog10l: (libc)Exponents and Logarithms.
* clog: (libc)Exponents and Logarithms.
* clogf: (libc)Exponents and Logarithms.
* clogfN: (libc)Exponents and Logarithms.
* clogfNx: (libc)Exponents and Logarithms.
* clogl: (libc)Exponents and Logarithms.
* close: (libc)Opening and Closing Files.
* close_range: (libc)Opening and Closing Files.
* closedir: (libc)Reading/Closing Directory.
* closefrom: (libc)Opening and Closing Files.
* closelog: (libc)closelog.
* cnd_broadcast: (libc)ISO C Condition Variables.
* cnd_destroy: (libc)ISO C Condition Variables.
* cnd_init: (libc)ISO C Condition Variables.
* cnd_signal: (libc)ISO C Condition Variables.
* cnd_timedwait: (libc)ISO C Condition Variables.
* cnd_wait: (libc)ISO C Condition Variables.
* compoundn: (libc)Exponents and Logarithms.
* compoundnf: (libc)Exponents and Logarithms.
* compoundnfN: (libc)Exponents and Logarithms.
* compoundnfNx: (libc)Exponents and Logarithms.
* compoundnl: (libc)Exponents and Logarithms.
* confstr: (libc)String Parameters.
* conj: (libc)Operations on Complex.
* conjf: (libc)Operations on Complex.
* conjfN: (libc)Operations on Complex.
* conjfNx: (libc)Operations on Complex.
* conjl: (libc)Operations on Complex.
* connect: (libc)Connecting.
* copy_file_range: (libc)Copying File Data.
* copysign: (libc)FP Bit Twiddling.
* copysignf: (libc)FP Bit Twiddling.
* copysignfN: (libc)FP Bit Twiddling.
* copysignfNx: (libc)FP Bit Twiddling.
* copysignl: (libc)FP Bit Twiddling.
* cos: (libc)Trig Functions.
* cosf: (libc)Trig Functions.
* cosfN: (libc)Trig Functions.
* cosfNx: (libc)Trig Functions.
* cosh: (libc)Hyperbolic Functions.
* coshf: (libc)Hyperbolic Functions.
* coshfN: (libc)Hyperbolic Functions.
* coshfNx: (libc)Hyperbolic Functions.
* coshl: (libc)Hyperbolic Functions.
* cosl: (libc)Trig Functions.
* cospi: (libc)Trig Functions.
* cospif: (libc)Trig Functions.
* cospifN: (libc)Trig Functions.
* cospifNx: (libc)Trig Functions.
* cospil: (libc)Trig Functions.
* cpow: (libc)Exponents and Logarithms.
* cpowf: (libc)Exponents and Logarithms.
* cpowfN: (libc)Exponents and Logarithms.
* cpowfNx: (libc)Exponents and Logarithms.
* cpowl: (libc)Exponents and Logarithms.
* cproj: (libc)Operations on Complex.
* cprojf: (libc)Operations on Complex.
* cprojfN: (libc)Operations on Complex.
* cprojfNx: (libc)Operations on Complex.
* cprojl: (libc)Operations on Complex.
* creal: (libc)Operations on Complex.
* crealf: (libc)Operations on Complex.
* crealfN: (libc)Operations on Complex.
* crealfNx: (libc)Operations on Complex.
* creall: (libc)Operations on Complex.
* creat64: (libc)Opening and Closing Files.
* creat: (libc)Opening and Closing Files.
* csin: (libc)Trig Functions.
* csinf: (libc)Trig Functions.
* csinfN: (libc)Trig Functions.
* csinfNx: (libc)Trig Functions.
* csinh: (libc)Hyperbolic Functions.
* csinhf: (libc)Hyperbolic Functions.
* csinhfN: (libc)Hyperbolic Functions.
* csinhfNx: (libc)Hyperbolic Functions.
* csinhl: (libc)Hyperbolic Functions.
* csinl: (libc)Trig Functions.
* csqrt: (libc)Exponents and Logarithms.
* csqrtf: (libc)Exponents and Logarithms.
* csqrtfN: (libc)Exponents and Logarithms.
* csqrtfNx: (libc)Exponents and Logarithms.
* csqrtl: (libc)Exponents and Logarithms.
* ctan: (libc)Trig Functions.
* ctanf: (libc)Trig Functions.
* ctanfN: (libc)Trig Functions.
* ctanfNx: (libc)Trig Functions.
* ctanh: (libc)Hyperbolic Functions.
* ctanhf: (libc)Hyperbolic Functions.
* ctanhfN: (libc)Hyperbolic Functions.
* ctanhfNx: (libc)Hyperbolic Functions.
* ctanhl: (libc)Hyperbolic Functions.
* ctanl: (libc)Trig Functions.
* ctermid: (libc)Identifying the Terminal.
* ctime: (libc)Formatting Calendar Time.
* ctime_r: (libc)Formatting Calendar Time.
* cuserid: (libc)Who Logged In.
* daddl: (libc)Misc FP Arithmetic.
* dcgettext: (libc)Translation with gettext.
* dcngettext: (libc)Advanced gettext functions.
* ddivl: (libc)Misc FP Arithmetic.
* dfmal: (libc)Misc FP Arithmetic.
* dgettext: (libc)Translation with gettext.
* difftime: (libc)Calculating Elapsed Time.
* dirfd: (libc)Opening a Directory.
* dirname: (libc)Finding Tokens in a String.
* div: (libc)Integer Division.
* dlinfo: (libc)Dynamic Linker Introspection.
* dmull: (libc)Misc FP Arithmetic.
* dngettext: (libc)Advanced gettext functions.
* dprintf: (libc)Formatted Output Functions.
* drand48: (libc)SVID Random.
* drand48_r: (libc)SVID Random.
* drem: (libc)Remainder Functions.
* dremf: (libc)Remainder Functions.
* dreml: (libc)Remainder Functions.
* dsqrtl: (libc)Misc FP Arithmetic.
* dsubl: (libc)Misc FP Arithmetic.
* dup2: (libc)Duplicating Descriptors.
* dup3: (libc)Duplicating Descriptors.
* dup: (libc)Duplicating Descriptors.
* ecvt: (libc)System V Number Conversion.
* ecvt_r: (libc)System V Number Conversion.
* endfsent: (libc)fstab.
* endgrent: (libc)Scanning All Groups.
* endhostent: (libc)Host Names.
* endmntent: (libc)mtab.
* endnetent: (libc)Networks Database.
* endnetgrent: (libc)Lookup Netgroup.
* endprotoent: (libc)Protocols Database.
* endpwent: (libc)Scanning All Users.
* endservent: (libc)Services Database.
* endutent: (libc)Manipulating the Database.
* endutxent: (libc)XPG Functions.
* envz_add: (libc)Envz Functions.
* envz_entry: (libc)Envz Functions.
* envz_get: (libc)Envz Functions.
* envz_merge: (libc)Envz Functions.
* envz_remove: (libc)Envz Functions.
* envz_strip: (libc)Envz Functions.
* epoll_create: (libc)Other Low-Level I/O APIs.
* epoll_wait: (libc)Other Low-Level I/O APIs.
* erand48: (libc)SVID Random.
* erand48_r: (libc)SVID Random.
* erf: (libc)Special Functions.
* erfc: (libc)Special Functions.
* erfcf: (libc)Special Functions.
* erfcfN: (libc)Special Functions.
* erfcfNx: (libc)Special Functions.
* erfcl: (libc)Special Functions.
* erff: (libc)Special Functions.
* erffN: (libc)Special Functions.
* erffNx: (libc)Special Functions.
* erfl: (libc)Special Functions.
* err: (libc)Error Messages.
* errno: (libc)Checking for Errors.
* error: (libc)Error Messages.
* error_at_line: (libc)Error Messages.
* errx: (libc)Error Messages.
* execl: (libc)Executing a File.
* execle: (libc)Executing a File.
* execlp: (libc)Executing a File.
* execv: (libc)Executing a File.
* execve: (libc)Executing a File.
* execvp: (libc)Executing a File.
* exit: (libc)Normal Termination.
* exp10: (libc)Exponents and Logarithms.
* exp10f: (libc)Exponents and Logarithms.
* exp10fN: (libc)Exponents and Logarithms.
* exp10fNx: (libc)Exponents and Logarithms.
* exp10l: (libc)Exponents and Logarithms.
* exp10m1: (libc)Exponents and Logarithms.
* exp10m1f: (libc)Exponents and Logarithms.
* exp10m1fN: (libc)Exponents and Logarithms.
* exp10m1fNx: (libc)Exponents and Logarithms.
* exp10m1l: (libc)Exponents and Logarithms.
* exp2: (libc)Exponents and Logarithms.
* exp2f: (libc)Exponents and Logarithms.
* exp2fN: (libc)Exponents and Logarithms.
* exp2fNx: (libc)Exponents and Logarithms.
* exp2l: (libc)Exponents and Logarithms.
* exp2m1: (libc)Exponents and Logarithms.
* exp2m1f: (libc)Exponents and Logarithms.
* exp2m1fN: (libc)Exponents and Logarithms.
* exp2m1fNx: (libc)Exponents and Logarithms.
* exp2m1l: (libc)Exponents and Logarithms.
* exp: (libc)Exponents and Logarithms.
* expf: (libc)Exponents and Logarithms.
* expfN: (libc)Exponents and Logarithms.
* expfNx: (libc)Exponents and Logarithms.
* expl: (libc)Exponents and Logarithms.
* explicit_bzero: (libc)Erasing Sensitive Data.
* expm1: (libc)Exponents and Logarithms.
* expm1f: (libc)Exponents and Logarithms.
* expm1fN: (libc)Exponents and Logarithms.
* expm1fNx: (libc)Exponents and Logarithms.
* expm1l: (libc)Exponents and Logarithms.
* fMaddfN: (libc)Misc FP Arithmetic.
* fMaddfNx: (libc)Misc FP Arithmetic.
* fMdivfN: (libc)Misc FP Arithmetic.
* fMdivfNx: (libc)Misc FP Arithmetic.
* fMfmafN: (libc)Misc FP Arithmetic.
* fMfmafNx: (libc)Misc FP Arithmetic.
* fMmulfN: (libc)Misc FP Arithmetic.
* fMmulfNx: (libc)Misc FP Arithmetic.
* fMsqrtfN: (libc)Misc FP Arithmetic.
* fMsqrtfNx: (libc)Misc FP Arithmetic.
* fMsubfN: (libc)Misc FP Arithmetic.
* fMsubfNx: (libc)Misc FP Arithmetic.
* fMxaddfN: (libc)Misc FP Arithmetic.
* fMxaddfNx: (libc)Misc FP Arithmetic.
* fMxdivfN: (libc)Misc FP Arithmetic.
* fMxdivfNx: (libc)Misc FP Arithmetic.
* fMxfmafN: (libc)Misc FP Arithmetic.
* fMxfmafNx: (libc)Misc FP Arithmetic.
* fMxmulfN: (libc)Misc FP Arithmetic.
* fMxmulfNx: (libc)Misc FP Arithmetic.
* fMxsqrtfN: (libc)Misc FP Arithmetic.
* fMxsqrtfNx: (libc)Misc FP Arithmetic.
* fMxsubfN: (libc)Misc FP Arithmetic.
* fMxsubfNx: (libc)Misc FP Arithmetic.
* fabs: (libc)Absolute Value.
* fabsf: (libc)Absolute Value.
* fabsfN: (libc)Absolute Value.
* fabsfNx: (libc)Absolute Value.
* fabsl: (libc)Absolute Value.
* faccessat: (libc)Testing File Access.
* fadd: (libc)Misc FP Arithmetic.
* faddl: (libc)Misc FP Arithmetic.
* fchdir: (libc)Working Directory.
* fchmod: (libc)Setting Permissions.
* fchown: (libc)File Owner.
* fclose: (libc)Closing Streams.
* fcloseall: (libc)Closing Streams.
* fcntl: (libc)Control Operations.
* fcvt: (libc)System V Number Conversion.
* fcvt_r: (libc)System V Number Conversion.
* fdatasync: (libc)Synchronizing I/O.
* fdim: (libc)Misc FP Arithmetic.
* fdimf: (libc)Misc FP Arithmetic.
* fdimfN: (libc)Misc FP Arithmetic.
* fdimfNx: (libc)Misc FP Arithmetic.
* fdiml: (libc)Misc FP Arithmetic.
* fdiv: (libc)Misc FP Arithmetic.
* fdivl: (libc)Misc FP Arithmetic.
* fdopen: (libc)Descriptors and Streams.
* fdopendir: (libc)Opening a Directory.
* feclearexcept: (libc)Status bit operations.
* fedisableexcept: (libc)Control Functions.
* feenableexcept: (libc)Control Functions.
* fegetenv: (libc)Control Functions.
* fegetexcept: (libc)Control Functions.
* fegetexceptflag: (libc)Status bit operations.
* fegetmode: (libc)Control Functions.
* fegetround: (libc)Rounding.
* feholdexcept: (libc)Control Functions.
* feof: (libc)EOF and Errors.
* feof_unlocked: (libc)EOF and Errors.
* feraiseexcept: (libc)Status bit operations.
* ferror: (libc)EOF and Errors.
* ferror_unlocked: (libc)EOF and Errors.
* fesetenv: (libc)Control Functions.
* fesetexcept: (libc)Status bit operations.
* fesetexceptflag: (libc)Status bit operations.
* fesetmode: (libc)Control Functions.
* fesetround: (libc)Rounding.
* fetestexcept: (libc)Status bit operations.
* fetestexceptflag: (libc)Status bit operations.
* feupdateenv: (libc)Control Functions.
* fexecve: (libc)Executing a File.
* fflush: (libc)Flushing Buffers.
* fflush_unlocked: (libc)Flushing Buffers.
* ffma: (libc)Misc FP Arithmetic.
* ffmal: (libc)Misc FP Arithmetic.
* fgetc: (libc)Character Input.
* fgetc_unlocked: (libc)Character Input.
* fgetgrent: (libc)Scanning All Groups.
* fgetgrent_r: (libc)Scanning All Groups.
* fgetpos64: (libc)Portable Positioning.
* fgetpos: (libc)Portable Positioning.
* fgetpwent: (libc)Scanning All Users.
* fgetpwent_r: (libc)Scanning All Users.
* fgets: (libc)Line Input.
* fgets_unlocked: (libc)Line Input.
* fgetwc: (libc)Character Input.
* fgetwc_unlocked: (libc)Character Input.
* fgetws: (libc)Line Input.
* fgetws_unlocked: (libc)Line Input.
* fileno: (libc)Descriptors and Streams.
* fileno_unlocked: (libc)Descriptors and Streams.
* finite: (libc)Floating Point Classes.
* finitef: (libc)Floating Point Classes.
* finitel: (libc)Floating Point Classes.
* flockfile: (libc)Streams and Threads.
* floor: (libc)Rounding Functions.
* floorf: (libc)Rounding Functions.
* floorfN: (libc)Rounding Functions.
* floorfNx: (libc)Rounding Functions.
* floorl: (libc)Rounding Functions.
* fma: (libc)Misc FP Arithmetic.
* fmaf: (libc)Misc FP Arithmetic.
* fmafN: (libc)Misc FP Arithmetic.
* fmafNx: (libc)Misc FP Arithmetic.
* fmal: (libc)Misc FP Arithmetic.
* fmax: (libc)Misc FP Arithmetic.
* fmaxf: (libc)Misc FP Arithmetic.
* fmaxfN: (libc)Misc FP Arithmetic.
* fmaxfNx: (libc)Misc FP Arithmetic.
* fmaximum: (libc)Misc FP Arithmetic.
* fmaximum_mag: (libc)Misc FP Arithmetic.
* fmaximum_mag_num: (libc)Misc FP Arithmetic.
* fmaximum_mag_numf: (libc)Misc FP Arithmetic.
* fmaximum_mag_numfN: (libc)Misc FP Arithmetic.
* fmaximum_mag_numfNx: (libc)Misc FP Arithmetic.
* fmaximum_mag_numl: (libc)Misc FP Arithmetic.
* fmaximum_magf: (libc)Misc FP Arithmetic.
* fmaximum_magfN: (libc)Misc FP Arithmetic.
* fmaximum_magfNx: (libc)Misc FP Arithmetic.
* fmaximum_magl: (libc)Misc FP Arithmetic.
* fmaximum_num: (libc)Misc FP Arithmetic.
* fmaximum_numf: (libc)Misc FP Arithmetic.
* fmaximum_numfN: (libc)Misc FP Arithmetic.
* fmaximum_numfNx: (libc)Misc FP Arithmetic.
* fmaximum_numl: (libc)Misc FP Arithmetic.
* fmaximumf: (libc)Misc FP Arithmetic.
* fmaximumfN: (libc)Misc FP Arithmetic.
* fmaximumfNx: (libc)Misc FP Arithmetic.
* fmaximuml: (libc)Misc FP Arithmetic.
* fmaxl: (libc)Misc FP Arithmetic.
* fmaxmag: (libc)Misc FP Arithmetic.
* fmaxmagf: (libc)Misc FP Arithmetic.
* fmaxmagfN: (libc)Misc FP Arithmetic.
* fmaxmagfNx: (libc)Misc FP Arithmetic.
* fmaxmagl: (libc)Misc FP Arithmetic.
* fmemopen: (libc)String Streams.
* fmin: (libc)Misc FP Arithmetic.
* fminf: (libc)Misc FP Arithmetic.
* fminfN: (libc)Misc FP Arithmetic.
* fminfNx: (libc)Misc FP Arithmetic.
* fminimum: (libc)Misc FP Arithmetic.
* fminimum_mag: (libc)Misc FP Arithmetic.
* fminimum_mag_num: (libc)Misc FP Arithmetic.
* fminimum_mag_numf: (libc)Misc FP Arithmetic.
* fminimum_mag_numfN: (libc)Misc FP Arithmetic.
* fminimum_mag_numfNx: (libc)Misc FP Arithmetic.
* fminimum_mag_numl: (libc)Misc FP Arithmetic.
* fminimum_magf: (libc)Misc FP Arithmetic.
* fminimum_magfN: (libc)Misc FP Arithmetic.
* fminimum_magfNx: (libc)Misc FP Arithmetic.
* fminimum_magl: (libc)Misc FP Arithmetic.
* fminimum_num: (libc)Misc FP Arithmetic.
* fminimum_numf: (libc)Misc FP Arithmetic.
* fminimum_numfN: (libc)Misc FP Arithmetic.
* fminimum_numfNx: (libc)Misc FP Arithmetic.
* fminimum_numl: (libc)Misc FP Arithmetic.
* fminimumf: (libc)Misc FP Arithmetic.
* fminimumfN: (libc)Misc FP Arithmetic.
* fminimumfNx: (libc)Misc FP Arithmetic.
* fminimuml: (libc)Misc FP Arithmetic.
* fminl: (libc)Misc FP Arithmetic.
* fminmag: (libc)Misc FP Arithmetic.
* fminmagf: (libc)Misc FP Arithmetic.
* fminmagfN: (libc)Misc FP Arithmetic.
* fminmagfNx: (libc)Misc FP Arithmetic.
* fminmagl: (libc)Misc FP Arithmetic.
* fmod: (libc)Remainder Functions.
* fmodf: (libc)Remainder Functions.
* fmodfN: (libc)Remainder Functions.
* fmodfNx: (libc)Remainder Functions.
* fmodl: (libc)Remainder Functions.
* fmtmsg: (libc)Printing Formatted Messages.
* fmul: (libc)Misc FP Arithmetic.
* fmull: (libc)Misc FP Arithmetic.
* fnmatch: (libc)Wildcard Matching.
* fopen64: (libc)Opening Streams.
* fopen: (libc)Opening Streams.
* fopencookie: (libc)Streams and Cookies.
* fork: (libc)Creating a Process.
* forkpty: (libc)Pseudo-Terminal Pairs.
* fpathconf: (libc)Pathconf.
* fpclassify: (libc)Floating Point Classes.
* fprintf: (libc)Formatted Output Functions.
* fputc: (libc)Simple Output.
* fputc_unlocked: (libc)Simple Output.
* fputs: (libc)Simple Output.
* fputs_unlocked: (libc)Simple Output.
* fputwc: (libc)Simple Output.
* fputwc_unlocked: (libc)Simple Output.
* fputws: (libc)Simple Output.
* fputws_unlocked: (libc)Simple Output.
* fread: (libc)Block Input/Output.
* fread_unlocked: (libc)Block Input/Output.
* free: (libc)Freeing after Malloc.
* free_aligned_sized: (libc)Freeing after Malloc.
* free_sized: (libc)Freeing after Malloc.
* freopen64: (libc)Opening Streams.
* freopen: (libc)Opening Streams.
* frexp: (libc)Normalization Functions.
* frexpf: (libc)Normalization Functions.
* frexpfN: (libc)Normalization Functions.
* frexpfNx: (libc)Normalization Functions.
* frexpl: (libc)Normalization Functions.
* fromfp: (libc)Rounding Functions.
* fromfpf: (libc)Rounding Functions.
* fromfpfN: (libc)Rounding Functions.
* fromfpfNx: (libc)Rounding Functions.
* fromfpl: (libc)Rounding Functions.
* fromfpx: (libc)Rounding Functions.
* fromfpxf: (libc)Rounding Functions.
* fromfpxfN: (libc)Rounding Functions.
* fromfpxfNx: (libc)Rounding Functions.
* fromfpxl: (libc)Rounding Functions.
* fscanf: (libc)Formatted Input Functions.
* fseek: (libc)File Positioning.
* fseeko64: (libc)File Positioning.
* fseeko: (libc)File Positioning.
* fsetpos64: (libc)Portable Positioning.
* fsetpos: (libc)Portable Positioning.
* fsqrt: (libc)Misc FP Arithmetic.
* fsqrtl: (libc)Misc FP Arithmetic.
* fstat64: (libc)Reading Attributes.
* fstat: (libc)Reading Attributes.
* fstatat64: (libc)Reading Attributes.
* fstatat: (libc)Reading Attributes.
* fsub: (libc)Misc FP Arithmetic.
* fsubl: (libc)Misc FP Arithmetic.
* fsync: (libc)Synchronizing I/O.
* ftell: (libc)File Positioning.
* ftello64: (libc)File Positioning.
* ftello: (libc)File Positioning.
* ftruncate64: (libc)File Size.
* ftruncate: (libc)File Size.
* ftrylockfile: (libc)Streams and Threads.
* ftw64: (libc)Working with Directory Trees.
* ftw: (libc)Working with Directory Trees.
* funlockfile: (libc)Streams and Threads.
* futimens: (libc)File Times.
* futimes: (libc)File Times.
* fwide: (libc)Streams and I18N.
* fwprintf: (libc)Formatted Output Functions.
* fwrite: (libc)Block Input/Output.
* fwrite_unlocked: (libc)Block Input/Output.
* fwscanf: (libc)Formatted Input Functions.
* gamma: (libc)Special Functions.
* gammaf: (libc)Special Functions.
* gammal: (libc)Special Functions.
* gcvt: (libc)System V Number Conversion.
* get_avphys_pages: (libc)Query Memory Parameters.
* get_current_dir_name: (libc)Working Directory.
* get_nprocs: (libc)Processor Resources.
* get_nprocs_conf: (libc)Processor Resources.
* get_phys_pages: (libc)Query Memory Parameters.
* getauxval: (libc)Auxiliary Vector.
* getc: (libc)Character Input.
* getc_unlocked: (libc)Character Input.
* getchar: (libc)Character Input.
* getchar_unlocked: (libc)Character Input.
* getcontext: (libc)System V contexts.
* getcpu: (libc)CPU Affinity.
* getcwd: (libc)Working Directory.
* getdate: (libc)General Time String Parsing.
* getdate_r: (libc)General Time String Parsing.
* getdelim: (libc)Line Input.
* getdents64: (libc)Low-level Directory Access.
* getdomainname: (libc)Host Identification.
* getegid: (libc)Reading Persona.
* getentropy: (libc)Unpredictable Bytes.
* getenv: (libc)Environment Access.
* geteuid: (libc)Reading Persona.
* getfsent: (libc)fstab.
* getfsfile: (libc)fstab.
* getfsspec: (libc)fstab.
* getgid: (libc)Reading Persona.
* getgrent: (libc)Scanning All Groups.
* getgrent_r: (libc)Scanning All Groups.
* getgrgid: (libc)Lookup Group.
* getgrgid_r: (libc)Lookup Group.
* getgrnam: (libc)Lookup Group.
* getgrnam_r: (libc)Lookup Group.
* getgrouplist: (libc)Setting Groups.
* getgroups: (libc)Reading Persona.
* gethostbyaddr: (libc)Host Names.
* gethostbyaddr_r: (libc)Host Names.
* gethostbyname2: (libc)Host Names.
* gethostbyname2_r: (libc)Host Names.
* gethostbyname: (libc)Host Names.
* gethostbyname_r: (libc)Host Names.
* gethostent: (libc)Host Names.
* gethostid: (libc)Host Identification.
* gethostname: (libc)Host Identification.
* getitimer: (libc)Setting an Alarm.
* getline: (libc)Line Input.
* getloadavg: (libc)Processor Resources.
* getlogin: (libc)Who Logged In.
* getmntent: (libc)mtab.
* getmntent_r: (libc)mtab.
* getnetbyaddr: (libc)Networks Database.
* getnetbyname: (libc)Networks Database.
* getnetent: (libc)Networks Database.
* getnetgrent: (libc)Lookup Netgroup.
* getnetgrent_r: (libc)Lookup Netgroup.
* getopt: (libc)Using Getopt.
* getopt_long: (libc)Getopt Long Options.
* getopt_long_only: (libc)Getopt Long Options.
* getpagesize: (libc)Query Memory Parameters.
* getpass: (libc)getpass.
* getpayload: (libc)FP Bit Twiddling.
* getpayloadf: (libc)FP Bit Twiddling.
* getpayloadfN: (libc)FP Bit Twiddling.
* getpayloadfNx: (libc)FP Bit Twiddling.
* getpayloadl: (libc)FP Bit Twiddling.
* getpeername: (libc)Who is Connected.
* getpgid: (libc)Process Group Functions.
* getpgrp: (libc)Process Group Functions.
* getpid: (libc)Process Identification.
* getppid: (libc)Process Identification.
* getpriority: (libc)Traditional Scheduling Functions.
* getprotobyname: (libc)Protocols Database.
* getprotobynumber: (libc)Protocols Database.
* getprotoent: (libc)Protocols Database.
* getpt: (libc)Allocation.
* getpwent: (libc)Scanning All Users.
* getpwent_r: (libc)Scanning All Users.
* getpwnam: (libc)Lookup User.
* getpwnam_r: (libc)Lookup User.
* getpwuid: (libc)Lookup User.
* getpwuid_r: (libc)Lookup User.
* getrandom: (libc)Unpredictable Bytes.
* getrlimit64: (libc)Limits on Resources.
* getrlimit: (libc)Limits on Resources.
* getrusage: (libc)Resource Usage.
* gets: (libc)Line Input.
* getservbyname: (libc)Services Database.
* getservbyport: (libc)Services Database.
* getservent: (libc)Services Database.
* getsid: (libc)Process Group Functions.
* getsockname: (libc)Reading Address.
* getsockopt: (libc)Socket Option Functions.
* getsubopt: (libc)Suboptions.
* gettext: (libc)Translation with gettext.
* gettid: (libc)Process Identification.
* gettimeofday: (libc)Getting the Time.
* getuid: (libc)Reading Persona.
* getumask: (libc)Setting Permissions.
* getutent: (libc)Manipulating the Database.
* getutent_r: (libc)Manipulating the Database.
* getutid: (libc)Manipulating the Database.
* getutid_r: (libc)Manipulating the Database.
* getutline: (libc)Manipulating the Database.
* getutline_r: (libc)Manipulating the Database.
* getutmp: (libc)XPG Functions.
* getutmpx: (libc)XPG Functions.
* getutxent: (libc)XPG Functions.
* getutxid: (libc)XPG Functions.
* getutxline: (libc)XPG Functions.
* getw: (libc)Character Input.
* getwc: (libc)Character Input.
* getwc_unlocked: (libc)Character Input.
* getwchar: (libc)Character Input.
* getwchar_unlocked: (libc)Character Input.
* getwd: (libc)Working Directory.
* glob64: (libc)Calling Glob.
* glob: (libc)Calling Glob.
* globfree64: (libc)More Flags for Globbing.
* globfree: (libc)More Flags for Globbing.
* gmtime: (libc)Broken-down Time.
* gmtime_r: (libc)Broken-down Time.
* grantpt: (libc)Allocation.
* gsignal: (libc)Signaling Yourself.
* gtty: (libc)BSD Terminal Modes.
* hasmntopt: (libc)mtab.
* hcreate: (libc)Hash Search Function.
* hcreate_r: (libc)Hash Search Function.
* hdestroy: (libc)Hash Search Function.
* hdestroy_r: (libc)Hash Search Function.
* hsearch: (libc)Hash Search Function.
* hsearch_r: (libc)Hash Search Function.
* htonl: (libc)Byte Order.
* htons: (libc)Byte Order.
* hypot: (libc)Exponents and Logarithms.
* hypotf: (libc)Exponents and Logarithms.
* hypotfN: (libc)Exponents and Logarithms.
* hypotfNx: (libc)Exponents and Logarithms.
* hypotl: (libc)Exponents and Logarithms.
* iconv: (libc)Generic Conversion Interface.
* iconv_close: (libc)Generic Conversion Interface.
* iconv_open: (libc)Generic Conversion Interface.
* if_freenameindex: (libc)Interface Naming.
* if_indextoname: (libc)Interface Naming.
* if_nameindex: (libc)Interface Naming.
* if_nametoindex: (libc)Interface Naming.
* ilogb: (libc)Exponents and Logarithms.
* ilogbf: (libc)Exponents and Logarithms.
* ilogbfN: (libc)Exponents and Logarithms.
* ilogbfNx: (libc)Exponents and Logarithms.
* ilogbl: (libc)Exponents and Logarithms.
* imaxabs: (libc)Absolute Value.
* imaxdiv: (libc)Integer Division.
* in6addr_any: (libc)Host Address Data Type.
* in6addr_loopback: (libc)Host Address Data Type.
* index: (libc)Search Functions.
* inet_addr: (libc)Host Address Functions.
* inet_aton: (libc)Host Address Functions.
* inet_lnaof: (libc)Host Address Functions.
* inet_makeaddr: (libc)Host Address Functions.
* inet_netof: (libc)Host Address Functions.
* inet_network: (libc)Host Address Functions.
* inet_ntoa: (libc)Host Address Functions.
* inet_ntop: (libc)Host Address Functions.
* inet_pton: (libc)Host Address Functions.
* initgroups: (libc)Setting Groups.
* initstate: (libc)BSD Random.
* initstate_r: (libc)BSD Random.
* innetgr: (libc)Netgroup Membership.
* ioctl: (libc)IOCTLs.
* isalnum: (libc)Classification of Characters.
* isalpha: (libc)Classification of Characters.
* isascii: (libc)Classification of Characters.
* isatty: (libc)Is It a Terminal.
* isblank: (libc)Classification of Characters.
* iscanonical: (libc)Floating Point Classes.
* iscntrl: (libc)Classification of Characters.
* isdigit: (libc)Classification of Characters.
* iseqsig: (libc)FP Comparison Functions.
* isfinite: (libc)Floating Point Classes.
* isgraph: (libc)Classification of Characters.
* isgreater: (libc)FP Comparison Functions.
* isgreaterequal: (libc)FP Comparison Functions.
* isinf: (libc)Floating Point Classes.
* isinff: (libc)Floating Point Classes.
* isinfl: (libc)Floating Point Classes.
* isless: (libc)FP Comparison Functions.
* islessequal: (libc)FP Comparison Functions.
* islessgreater: (libc)FP Comparison Functions.
* islower: (libc)Classification of Characters.
* isnan: (libc)Floating Point Classes.
* isnan: (libc)Floating Point Classes.
* isnanf: (libc)Floating Point Classes.
* isnanl: (libc)Floating Point Classes.
* isnormal: (libc)Floating Point Classes.
* isprint: (libc)Classification of Characters.
* ispunct: (libc)Classification of Characters.
* issignaling: (libc)Floating Point Classes.
* isspace: (libc)Classification of Characters.
* issubnormal: (libc)Floating Point Classes.
* isunordered: (libc)FP Comparison Functions.
* isupper: (libc)Classification of Characters.
* iswalnum: (libc)Classification of Wide Characters.
* iswalpha: (libc)Classification of Wide Characters.
* iswblank: (libc)Classification of Wide Characters.
* iswcntrl: (libc)Classification of Wide Characters.
* iswctype: (libc)Classification of Wide Characters.
* iswdigit: (libc)Classification of Wide Characters.
* iswgraph: (libc)Classification of Wide Characters.
* iswlower: (libc)Classification of Wide Characters.
* iswprint: (libc)Classification of Wide Characters.
* iswpunct: (libc)Classification of Wide Characters.
* iswspace: (libc)Classification of Wide Characters.
* iswupper: (libc)Classification of Wide Characters.
* iswxdigit: (libc)Classification of Wide Characters.
* isxdigit: (libc)Classification of Characters.
* iszero: (libc)Floating Point Classes.
* j0: (libc)Special Functions.
* j0f: (libc)Special Functions.
* j0fN: (libc)Special Functions.
* j0fNx: (libc)Special Functions.
* j0l: (libc)Special Functions.
* j1: (libc)Special Functions.
* j1f: (libc)Special Functions.
* j1fN: (libc)Special Functions.
* j1fNx: (libc)Special Functions.
* j1l: (libc)Special Functions.
* jn: (libc)Special Functions.
* jnf: (libc)Special Functions.
* jnfN: (libc)Special Functions.
* jnfNx: (libc)Special Functions.
* jnl: (libc)Special Functions.
* jrand48: (libc)SVID Random.
* jrand48_r: (libc)SVID Random.
* kill: (libc)Signaling Another Process.
* killpg: (libc)Signaling Another Process.
* l64a: (libc)Encode Binary Data.
* labs: (libc)Absolute Value.
* lcong48: (libc)SVID Random.
* lcong48_r: (libc)SVID Random.
* ldexp: (libc)Normalization Functions.
* ldexpf: (libc)Normalization Functions.
* ldexpfN: (libc)Normalization Functions.
* ldexpfNx: (libc)Normalization Functions.
* ldexpl: (libc)Normalization Functions.
* ldiv: (libc)Integer Division.
* lfind: (libc)Array Search Function.
* lgamma: (libc)Special Functions.
* lgamma_r: (libc)Special Functions.
* lgammaf: (libc)Special Functions.
* lgammafN: (libc)Special Functions.
* lgammafN_r: (libc)Special Functions.
* lgammafNx: (libc)Special Functions.
* lgammafNx_r: (libc)Special Functions.
* lgammaf_r: (libc)Special Functions.
* lgammal: (libc)Special Functions.
* lgammal_r: (libc)Special Functions.
* link: (libc)Hard Links.
* linkat: (libc)Hard Links.
* lio_listio64: (libc)Asynchronous Reads/Writes.
* lio_listio: (libc)Asynchronous Reads/Writes.
* listen: (libc)Listening.
* llabs: (libc)Absolute Value.
* lldiv: (libc)Integer Division.
* llogb: (libc)Exponents and Logarithms.
* llogbf: (libc)Exponents and Logarithms.
* llogbfN: (libc)Exponents and Logarithms.
* llogbfNx: (libc)Exponents and Logarithms.
* llogbl: (libc)Exponents and Logarithms.
* llrint: (libc)Rounding Functions.
* llrintf: (libc)Rounding Functions.
* llrintfN: (libc)Rounding Functions.
* llrintfNx: (libc)Rounding Functions.
* llrintl: (libc)Rounding Functions.
* llround: (libc)Rounding Functions.
* llroundf: (libc)Rounding Functions.
* llroundfN: (libc)Rounding Functions.
* llroundfNx: (libc)Rounding Functions.
* llroundl: (libc)Rounding Functions.
* localeconv: (libc)The Lame Way to Locale Data.
* localtime: (libc)Broken-down Time.
* localtime_r: (libc)Broken-down Time.
* log10: (libc)Exponents and Logarithms.
* log10f: (libc)Exponents and Logarithms.
* log10fN: (libc)Exponents and Logarithms.
* log10fNx: (libc)Exponents and Logarithms.
* log10l: (libc)Exponents and Logarithms.
* log10p1: (libc)Exponents and Logarithms.
* log10p1f: (libc)Exponents and Logarithms.
* log10p1fN: (libc)Exponents and Logarithms.
* log10p1fNx: (libc)Exponents and Logarithms.
* log10p1l: (libc)Exponents and Logarithms.
* log1p: (libc)Exponents and Logarithms.
* log1pf: (libc)Exponents and Logarithms.
* log1pfN: (libc)Exponents and Logarithms.
* log1pfNx: (libc)Exponents and Logarithms.
* log1pl: (libc)Exponents and Logarithms.
* log2: (libc)Exponents and Logarithms.
* log2f: (libc)Exponents and Logarithms.
* log2fN: (libc)Exponents and Logarithms.
* log2fNx: (libc)Exponents and Logarithms.
* log2l: (libc)Exponents and Logarithms.
* log2p1: (libc)Exponents and Logarithms.
* log2p1f: (libc)Exponents and Logarithms.
* log2p1fN: (libc)Exponents and Logarithms.
* log2p1fNx: (libc)Exponents and Logarithms.
* log2p1l: (libc)Exponents and Logarithms.
* log: (libc)Exponents and Logarithms.
* logb: (libc)Exponents and Logarithms.
* logbf: (libc)Exponents and Logarithms.
* logbfN: (libc)Exponents and Logarithms.
* logbfNx: (libc)Exponents and Logarithms.
* logbl: (libc)Exponents and Logarithms.
* logf: (libc)Exponents and Logarithms.
* logfN: (libc)Exponents and Logarithms.
* logfNx: (libc)Exponents and Logarithms.
* login: (libc)Logging In and Out.
* login_tty: (libc)Logging In and Out.
* logl: (libc)Exponents and Logarithms.
* logout: (libc)Logging In and Out.
* logp1: (libc)Exponents and Logarithms.
* logp1f: (libc)Exponents and Logarithms.
* logp1fN: (libc)Exponents and Logarithms.
* logp1fNx: (libc)Exponents and Logarithms.
* logp1l: (libc)Exponents and Logarithms.
* logwtmp: (libc)Logging In and Out.
* longjmp: (libc)Non-Local Details.
* lrand48: (libc)SVID Random.
* lrand48_r: (libc)SVID Random.
* lrint: (libc)Rounding Functions.
* lrintf: (libc)Rounding Functions.
* lrintfN: (libc)Rounding Functions.
* lrintfNx: (libc)Rounding Functions.
* lrintl: (libc)Rounding Functions.
* lround: (libc)Rounding Functions.
* lroundf: (libc)Rounding Functions.
* lroundfN: (libc)Rounding Functions.
* lroundfNx: (libc)Rounding Functions.
* lroundl: (libc)Rounding Functions.
* lsearch: (libc)Array Search Function.
* lseek64: (libc)File Position Primitive.
* lseek: (libc)File Position Primitive.
* lstat64: (libc)Reading Attributes.
* lstat: (libc)Reading Attributes.
* lutimes: (libc)File Times.
* madvise: (libc)Memory-mapped I/O.
* makecontext: (libc)System V contexts.
* mallinfo2: (libc)Statistics of Malloc.
* malloc: (libc)Basic Allocation.
* mallopt: (libc)Malloc Tunable Parameters.
* mblen: (libc)Non-reentrant Character Conversion.
* mbrlen: (libc)Converting a Character.
* mbrtowc: (libc)Converting a Character.
* mbsinit: (libc)Keeping the state.
* mbsnrtowcs: (libc)Converting Strings.
* mbsrtowcs: (libc)Converting Strings.
* mbstowcs: (libc)Non-reentrant String Conversion.
* mbtowc: (libc)Non-reentrant Character Conversion.
* mcheck: (libc)Heap Consistency Checking.
* memalign: (libc)Aligned Memory Blocks.
* memalignment: (libc)Aligned Memory Blocks.
* memccpy: (libc)Copying Strings and Arrays.
* memchr: (libc)Search Functions.
* memcmp: (libc)String/Array Comparison.
* memcpy: (libc)Copying Strings and Arrays.
* memfd_create: (libc)Memory-mapped I/O.
* memfrob: (libc)Obfuscating Data.
* memmem: (libc)Search Functions.
* memmove: (libc)Copying Strings and Arrays.
* mempcpy: (libc)Copying Strings and Arrays.
* memrchr: (libc)Search Functions.
* memset: (libc)Copying Strings and Arrays.
* memset_explicit: (libc)Erasing Sensitive Data.
* mkdir: (libc)Creating Directories.
* mkdirat: (libc)Creating Directories.
* mkdtemp: (libc)Temporary Files.
* mkfifo: (libc)FIFO Special Files.
* mknod: (libc)Making Special Files.
* mkstemp: (libc)Temporary Files.
* mktemp: (libc)Temporary Files.
* mktime: (libc)Broken-down Time.
* mlock2: (libc)Page Lock Functions.
* mlock: (libc)Page Lock Functions.
* mlockall: (libc)Page Lock Functions.
* mmap64: (libc)Memory-mapped I/O.
* mmap: (libc)Memory-mapped I/O.
* modf: (libc)Rounding Functions.
* modff: (libc)Rounding Functions.
* modffN: (libc)Rounding Functions.
* modffNx: (libc)Rounding Functions.
* modfl: (libc)Rounding Functions.
* mount: (libc)Mount-Unmount-Remount.
* mprobe: (libc)Heap Consistency Checking.
* mprotect: (libc)Memory Protection.
* mrand48: (libc)SVID Random.
* mrand48_r: (libc)SVID Random.
* mremap: (libc)Memory-mapped I/O.
* mseal: (libc)Memory Protection.
* msync: (libc)Memory-mapped I/O.
* mtrace: (libc)Tracing malloc.
* mtx_destroy: (libc)ISO C Mutexes.
* mtx_init: (libc)ISO C Mutexes.
* mtx_lock: (libc)ISO C Mutexes.
* mtx_timedlock: (libc)ISO C Mutexes.
* mtx_trylock: (libc)ISO C Mutexes.
* mtx_unlock: (libc)ISO C Mutexes.
* munlock: (libc)Page Lock Functions.
* munlockall: (libc)Page Lock Functions.
* munmap: (libc)Memory-mapped I/O.
* muntrace: (libc)Tracing malloc.
* nan: (libc)FP Bit Twiddling.
* nanf: (libc)FP Bit Twiddling.
* nanfN: (libc)FP Bit Twiddling.
* nanfNx: (libc)FP Bit Twiddling.
* nanl: (libc)FP Bit Twiddling.
* nanosleep: (libc)Sleeping.
* nearbyint: (libc)Rounding Functions.
* nearbyintf: (libc)Rounding Functions.
* nearbyintfN: (libc)Rounding Functions.
* nearbyintfNx: (libc)Rounding Functions.
* nearbyintl: (libc)Rounding Functions.
* nextafter: (libc)FP Bit Twiddling.
* nextafterf: (libc)FP Bit Twiddling.
* nextafterfN: (libc)FP Bit Twiddling.
* nextafterfNx: (libc)FP Bit Twiddling.
* nextafterl: (libc)FP Bit Twiddling.
* nextdown: (libc)FP Bit Twiddling.
* nextdownf: (libc)FP Bit Twiddling.
* nextdownfN: (libc)FP Bit Twiddling.
* nextdownfNx: (libc)FP Bit Twiddling.
* nextdownl: (libc)FP Bit Twiddling.
* nexttoward: (libc)FP Bit Twiddling.
* nexttowardf: (libc)FP Bit Twiddling.
* nexttowardl: (libc)FP Bit Twiddling.
* nextup: (libc)FP Bit Twiddling.
* nextupf: (libc)FP Bit Twiddling.
* nextupfN: (libc)FP Bit Twiddling.
* nextupfNx: (libc)FP Bit Twiddling.
* nextupl: (libc)FP Bit Twiddling.
* nftw64: (libc)Working with Directory Trees.
* nftw: (libc)Working with Directory Trees.
* ngettext: (libc)Advanced gettext functions.
* nice: (libc)Traditional Scheduling Functions.
* nl_langinfo: (libc)The Elegant and Fast Way.
* nrand48: (libc)SVID Random.
* nrand48_r: (libc)SVID Random.
* ntohl: (libc)Byte Order.
* ntohs: (libc)Byte Order.
* ntp_adjtime: (libc)Setting and Adjusting the Time.
* ntp_gettime: (libc)Setting and Adjusting the Time.
* obstack_1grow: (libc)Growing Objects.
* obstack_1grow_fast: (libc)Extra Fast Growing.
* obstack_alignment_mask: (libc)Obstacks Data Alignment.
* obstack_alloc: (libc)Allocation in an Obstack.
* obstack_base: (libc)Status of an Obstack.
* obstack_blank: (libc)Growing Objects.
* obstack_blank_fast: (libc)Extra Fast Growing.
* obstack_chunk_size: (libc)Obstack Chunks.
* obstack_copy0: (libc)Allocation in an Obstack.
* obstack_copy: (libc)Allocation in an Obstack.
* obstack_finish: (libc)Growing Objects.
* obstack_free: (libc)Freeing Obstack Objects.
* obstack_grow0: (libc)Growing Objects.
* obstack_grow: (libc)Growing Objects.
* obstack_init: (libc)Preparing for Obstacks.
* obstack_int_grow: (libc)Growing Objects.
* obstack_int_grow_fast: (libc)Extra Fast Growing.
* obstack_next_free: (libc)Status of an Obstack.
* obstack_object_size: (libc)Growing Objects.
* obstack_object_size: (libc)Status of an Obstack.
* obstack_printf: (libc)Dynamic Output.
* obstack_ptr_grow: (libc)Growing Objects.
* obstack_ptr_grow_fast: (libc)Extra Fast Growing.
* obstack_room: (libc)Extra Fast Growing.
* obstack_vprintf: (libc)Variable Arguments Output.
* offsetof: (libc)Structure Measurement.
* on_exit: (libc)Cleanups on Exit.
* open64: (libc)Opening and Closing Files.
* open: (libc)Opening and Closing Files.
* open_memstream: (libc)String Streams.
* openat2: (libc)Opening and Closing Files.
* openat64: (libc)Opening and Closing Files.
* openat: (libc)Opening and Closing Files.
* opendir: (libc)Opening a Directory.
* openlog: (libc)openlog.
* openpty: (libc)Pseudo-Terminal Pairs.
* parse_printf_format: (libc)Parsing a Template String.
* pathconf: (libc)Pathconf.
* pause: (libc)Using Pause.
* pclose: (libc)Pipe to a Subprocess.
* perror: (libc)Error Messages.
* pidfd_getpid: (libc)Querying a Process.
* pipe: (libc)Creating a Pipe.
* pkey_alloc: (libc)Memory Protection.
* pkey_free: (libc)Memory Protection.
* pkey_get: (libc)Memory Protection.
* pkey_mprotect: (libc)Memory Protection.
* pkey_set: (libc)Memory Protection.
* poll: (libc)Other Low-Level I/O APIs.
* popen: (libc)Pipe to a Subprocess.
* posix_fallocate64: (libc)Storage Allocation.
* posix_fallocate: (libc)Storage Allocation.
* posix_memalign: (libc)Aligned Memory Blocks.
* posix_openpt: (libc)Allocation.
* pow: (libc)Exponents and Logarithms.
* powf: (libc)Exponents and Logarithms.
* powfN: (libc)Exponents and Logarithms.
* powfNx: (libc)Exponents and Logarithms.
* powl: (libc)Exponents and Logarithms.
* pown: (libc)Exponents and Logarithms.
* pownf: (libc)Exponents and Logarithms.
* pownfN: (libc)Exponents and Logarithms.
* pownfNx: (libc)Exponents and Logarithms.
* pownl: (libc)Exponents and Logarithms.
* powr: (libc)Exponents and Logarithms.
* powrf: (libc)Exponents and Logarithms.
* powrfN: (libc)Exponents and Logarithms.
* powrfNx: (libc)Exponents and Logarithms.
* powrl: (libc)Exponents and Logarithms.
* pread64: (libc)I/O Primitives.
* pread: (libc)I/O Primitives.
* preadv2: (libc)Scatter-Gather.
* preadv64: (libc)Scatter-Gather.
* preadv64v2: (libc)Scatter-Gather.
* preadv: (libc)Scatter-Gather.
* printf: (libc)Formatted Output Functions.
* printf_size: (libc)Predefined Printf Handlers.
* printf_size_info: (libc)Predefined Printf Handlers.
* psignal: (libc)Signal Messages.
* pthread_attr_destroy: (libc)Creating and Destroying Threads.
* pthread_attr_getaffinity_np: (libc)Thread CPU Affinity.
* pthread_attr_getdetachstate: (libc)Creating and Destroying Threads.
* pthread_attr_getsigmask_np: (libc)Initial Thread Signal Mask.
* pthread_attr_init: (libc)Creating and Destroying Threads.
* pthread_attr_setaffinity_np: (libc)Thread CPU Affinity.
* pthread_attr_setdetachstate: (libc)Creating and Destroying Threads.
* pthread_attr_setsigmask_np: (libc)Initial Thread Signal Mask.
* pthread_barrier_destroy: (libc)POSIX Barriers.
* pthread_barrier_init: (libc)POSIX Barriers.
* pthread_barrier_wait: (libc)POSIX Barriers.
* pthread_clockjoin_np: (libc)Joining Threads.
* pthread_cond_clockwait: (libc)Waiting with Explicit Clocks.
* pthread_create: (libc)Creating and Destroying Threads.
* pthread_detach: (libc)Creating and Destroying Threads.
* pthread_equal: (libc)POSIX Threads Other APIs.
* pthread_getaffinity_np: (libc)Thread CPU Affinity.
* pthread_getattr_default_np: (libc)Default Thread Attributes.
* pthread_getcpuclockid: (libc)POSIX Threads Other APIs.
* pthread_getname_np: (libc)Thread Names.
* pthread_getspecific: (libc)Thread-specific Data.
* pthread_gettid_np: (libc)Process Identification.
* pthread_join: (libc)Creating and Destroying Threads.
* pthread_key_create: (libc)Thread-specific Data.
* pthread_key_delete: (libc)Thread-specific Data.
* pthread_kill: (libc)Creating and Destroying Threads.
* pthread_mutex_clocklock: (libc)POSIX Mutexes.
* pthread_mutex_destroy: (libc)POSIX Mutexes.
* pthread_mutex_init: (libc)POSIX Mutexes.
* pthread_mutex_lock: (libc)POSIX Mutexes.
* pthread_mutex_timedlock: (libc)POSIX Mutexes.
* pthread_mutex_trylock: (libc)POSIX Mutexes.
* pthread_mutex_unlock: (libc)POSIX Mutexes.
* pthread_mutexattr_destroy: (libc)POSIX Mutexes.
* pthread_mutexattr_gettype: (libc)POSIX Mutexes.
* pthread_mutexattr_init: (libc)POSIX Mutexes.
* pthread_mutexattr_settype: (libc)POSIX Mutexes.
* pthread_once: (libc)POSIX Threads Other APIs.
* pthread_rwlock_clockrdlock: (libc)Waiting with Explicit Clocks.
* pthread_rwlock_clockwrlock: (libc)Waiting with Explicit Clocks.
* pthread_self: (libc)Creating and Destroying Threads.
* pthread_setaffinity_np: (libc)Thread CPU Affinity.
* pthread_setattr_default_np: (libc)Default Thread Attributes.
* pthread_setname_np: (libc)Thread Names.
* pthread_setspecific: (libc)Thread-specific Data.
* pthread_sigmask: (libc)POSIX Threads Other APIs.
* pthread_spin_destroy: (libc)POSIX Spin Locks.
* pthread_spin_init: (libc)POSIX Spin Locks.
* pthread_spin_lock: (libc)POSIX Spin Locks.
* pthread_spin_trylock: (libc)POSIX Spin Locks.
* pthread_spin_unlock: (libc)POSIX Spin Locks.
* pthread_timedjoin_np: (libc)Joining Threads.
* pthread_tryjoin_np: (libc)Joining Threads.
* ptsname: (libc)Allocation.
* ptsname_r: (libc)Allocation.
* putc: (libc)Simple Output.
* putc_unlocked: (libc)Simple Output.
* putchar: (libc)Simple Output.
* putchar_unlocked: (libc)Simple Output.
* putenv: (libc)Environment Access.
* putpwent: (libc)Writing a User Entry.
* puts: (libc)Simple Output.
* pututline: (libc)Manipulating the Database.
* pututxline: (libc)XPG Functions.
* putw: (libc)Simple Output.
* putwc: (libc)Simple Output.
* putwc_unlocked: (libc)Simple Output.
* putwchar: (libc)Simple Output.
* putwchar_unlocked: (libc)Simple Output.
* pwrite64: (libc)I/O Primitives.
* pwrite: (libc)I/O Primitives.
* pwritev2: (libc)Scatter-Gather.
* pwritev64: (libc)Scatter-Gather.
* pwritev64v2: (libc)Scatter-Gather.
* pwritev: (libc)Scatter-Gather.
* qecvt: (libc)System V Number Conversion.
* qecvt_r: (libc)System V Number Conversion.
* qfcvt: (libc)System V Number Conversion.
* qfcvt_r: (libc)System V Number Conversion.
* qgcvt: (libc)System V Number Conversion.
* qsort: (libc)Array Sort Function.
* raise: (libc)Signaling Yourself.
* rand: (libc)ISO Random.
* rand_r: (libc)ISO Random.
* random: (libc)BSD Random.
* random_r: (libc)BSD Random.
* rawmemchr: (libc)Search Functions.
* read: (libc)I/O Primitives.
* readdir64: (libc)Reading/Closing Directory.
* readdir64_r: (libc)Reading/Closing Directory.
* readdir: (libc)Reading/Closing Directory.
* readdir_r: (libc)Reading/Closing Directory.
* readlink: (libc)Symbolic Links.
* readv: (libc)Scatter-Gather.
* realloc: (libc)Changing Block Size.
* reallocarray: (libc)Changing Block Size.
* realpath: (libc)Symbolic Links.
* recv: (libc)Receiving Data.
* recvfrom: (libc)Receiving Datagrams.
* recvmsg: (libc)Other Socket APIs.
* regcomp: (libc)POSIX Regexp Compilation.
* regerror: (libc)Regexp Cleanup.
* regexec: (libc)Matching POSIX Regexps.
* regfree: (libc)Regexp Cleanup.
* register_printf_function: (libc)Registering New Conversions.
* remainder: (libc)Remainder Functions.
* remainderf: (libc)Remainder Functions.
* remainderfN: (libc)Remainder Functions.
* remainderfNx: (libc)Remainder Functions.
* remainderl: (libc)Remainder Functions.
* remove: (libc)Deleting Files.
* rename: (libc)Renaming Files.
* renameat: (libc)Renaming Files.
* rewind: (libc)File Positioning.
* rewinddir: (libc)Random Access Directory.
* rindex: (libc)Search Functions.
* rint: (libc)Rounding Functions.
* rintf: (libc)Rounding Functions.
* rintfN: (libc)Rounding Functions.
* rintfNx: (libc)Rounding Functions.
* rintl: (libc)Rounding Functions.
* rmdir: (libc)Deleting Files.
* rootn: (libc)Exponents and Logarithms.
* rootnf: (libc)Exponents and Logarithms.
* rootnfN: (libc)Exponents and Logarithms.
* rootnfNx: (libc)Exponents and Logarithms.
* rootnl: (libc)Exponents and Logarithms.
* round: (libc)Rounding Functions.
* roundeven: (libc)Rounding Functions.
* roundevenf: (libc)Rounding Functions.
* roundevenfN: (libc)Rounding Functions.
* roundevenfNx: (libc)Rounding Functions.
* roundevenl: (libc)Rounding Functions.
* roundf: (libc)Rounding Functions.
* roundfN: (libc)Rounding Functions.
* roundfNx: (libc)Rounding Functions.
* roundl: (libc)Rounding Functions.
* rpmatch: (libc)Yes-or-No Questions.
* rsqrt: (libc)Exponents and Logarithms.
* rsqrtf: (libc)Exponents and Logarithms.
* rsqrtfN: (libc)Exponents and Logarithms.
* rsqrtfNx: (libc)Exponents and Logarithms.
* rsqrtl: (libc)Exponents and Logarithms.
* sbrk: (libc)Resizing the Data Segment.
* scalb: (libc)Normalization Functions.
* scalbf: (libc)Normalization Functions.
* scalbl: (libc)Normalization Functions.
* scalbln: (libc)Normalization Functions.
* scalblnf: (libc)Normalization Functions.
* scalblnfN: (libc)Normalization Functions.
* scalblnfNx: (libc)Normalization Functions.
* scalblnl: (libc)Normalization Functions.
* scalbn: (libc)Normalization Functions.
* scalbnf: (libc)Normalization Functions.
* scalbnfN: (libc)Normalization Functions.
* scalbnfNx: (libc)Normalization Functions.
* scalbnl: (libc)Normalization Functions.
* scandir64: (libc)Scanning Directory Content.
* scandir: (libc)Scanning Directory Content.
* scanf: (libc)Formatted Input Functions.
* sched_get_priority_max: (libc)Basic Scheduling Functions.
* sched_get_priority_min: (libc)Basic Scheduling Functions.
* sched_getaffinity: (libc)CPU Affinity.
* sched_getattr: (libc)Extensible Scheduling.
* sched_getcpu: (libc)CPU Affinity.
* sched_getparam: (libc)Basic Scheduling Functions.
* sched_getscheduler: (libc)Basic Scheduling Functions.
* sched_rr_get_interval: (libc)Basic Scheduling Functions.
* sched_setaffinity: (libc)CPU Affinity.
* sched_setattr: (libc)Extensible Scheduling.
* sched_setparam: (libc)Basic Scheduling Functions.
* sched_setscheduler: (libc)Basic Scheduling Functions.
* sched_yield: (libc)Basic Scheduling Functions.
* secure_getenv: (libc)Environment Access.
* seed48: (libc)SVID Random.
* seed48_r: (libc)SVID Random.
* seekdir: (libc)Random Access Directory.
* select: (libc)Waiting for I/O.
* sem_clockwait: (libc)POSIX Semaphores.
* sem_close: (libc)POSIX Semaphores.
* sem_destroy: (libc)POSIX Semaphores.
* sem_getvalue: (libc)POSIX Semaphores.
* sem_init: (libc)POSIX Semaphores.
* sem_open: (libc)POSIX Semaphores.
* sem_post: (libc)POSIX Semaphores.
* sem_timedwait: (libc)POSIX Semaphores.
* sem_trywait: (libc)POSIX Semaphores.
* sem_unlink: (libc)POSIX Semaphores.
* sem_wait: (libc)POSIX Semaphores.
* semctl: (libc)Semaphores.
* semget: (libc)Semaphores.
* semop: (libc)Semaphores.
* semtimedop: (libc)Semaphores.
* send: (libc)Sending Data.
* sendmsg: (libc)Other Socket APIs.
* sendto: (libc)Sending Datagrams.
* setbuf: (libc)Controlling Buffering.
* setbuffer: (libc)Controlling Buffering.
* setcontext: (libc)System V contexts.
* setdomainname: (libc)Host Identification.
* setegid: (libc)Setting Groups.
* setenv: (libc)Environment Access.
* seteuid: (libc)Setting User ID.
* setfsent: (libc)fstab.
* setgid: (libc)Setting Groups.
* setgrent: (libc)Scanning All Groups.
* setgroups: (libc)Setting Groups.
* sethostent: (libc)Host Names.
* sethostid: (libc)Host Identification.
* sethostname: (libc)Host Identification.
* setitimer: (libc)Setting an Alarm.
* setjmp: (libc)Non-Local Details.
* setlinebuf: (libc)Controlling Buffering.
* setlocale: (libc)Setting the Locale.
* setlogmask: (libc)setlogmask.
* setmntent: (libc)mtab.
* setnetent: (libc)Networks Database.
* setnetgrent: (libc)Lookup Netgroup.
* setpayload: (libc)FP Bit Twiddling.
* setpayloadf: (libc)FP Bit Twiddling.
* setpayloadfN: (libc)FP Bit Twiddling.
* setpayloadfNx: (libc)FP Bit Twiddling.
* setpayloadl: (libc)FP Bit Twiddling.
* setpayloadsig: (libc)FP Bit Twiddling.
* setpayloadsigf: (libc)FP Bit Twiddling.
* setpayloadsigfN: (libc)FP Bit Twiddling.
* setpayloadsigfNx: (libc)FP Bit Twiddling.
* setpayloadsigl: (libc)FP Bit Twiddling.
* setpgid: (libc)Process Group Functions.
* setpgrp: (libc)Process Group Functions.
* setpriority: (libc)Traditional Scheduling Functions.
* setprotoent: (libc)Protocols Database.
* setpwent: (libc)Scanning All Users.
* setregid: (libc)Setting Groups.
* setreuid: (libc)Setting User ID.
* setrlimit64: (libc)Limits on Resources.
* setrlimit: (libc)Limits on Resources.
* setservent: (libc)Services Database.
* setsid: (libc)Process Group Functions.
* setsockopt: (libc)Socket Option Functions.
* setstate: (libc)BSD Random.
* setstate_r: (libc)BSD Random.
* settimeofday: (libc)Setting and Adjusting the Time.
* setuid: (libc)Setting User ID.
* setutent: (libc)Manipulating the Database.
* setutxent: (libc)XPG Functions.
* setvbuf: (libc)Controlling Buffering.
* shm_open: (libc)Memory-mapped I/O.
* shm_unlink: (libc)Memory-mapped I/O.
* shutdown: (libc)Closing a Socket.
* sigabbrev_np: (libc)Signal Messages.
* sigaction: (libc)Advanced Signal Handling.
* sigaddset: (libc)Signal Sets.
* sigaltstack: (libc)Signal Stack.
* sigblock: (libc)BSD Signal Handling.
* sigdelset: (libc)Signal Sets.
* sigdescr_np: (libc)Signal Messages.
* sigemptyset: (libc)Signal Sets.
* sigfillset: (libc)Signal Sets.
* siginterrupt: (libc)BSD Signal Handling.
* sigismember: (libc)Signal Sets.
* siglongjmp: (libc)Non-Local Exits and Signals.
* sigmask: (libc)BSD Signal Handling.
* signal: (libc)Basic Signal Handling.
* signbit: (libc)FP Bit Twiddling.
* significand: (libc)Normalization Functions.
* significandf: (libc)Normalization Functions.
* significandl: (libc)Normalization Functions.
* sigpause: (libc)BSD Signal Handling.
* sigpending: (libc)Checking for Pending Signals.
* sigprocmask: (libc)Process Signal Mask.
* sigsetjmp: (libc)Non-Local Exits and Signals.
* sigsetmask: (libc)BSD Signal Handling.
* sigstack: (libc)Signal Stack.
* sigsuspend: (libc)Sigsuspend.
* sin: (libc)Trig Functions.
* sincos: (libc)Trig Functions.
* sincosf: (libc)Trig Functions.
* sincosfN: (libc)Trig Functions.
* sincosfNx: (libc)Trig Functions.
* sincosl: (libc)Trig Functions.
* sinf: (libc)Trig Functions.
* sinfN: (libc)Trig Functions.
* sinfNx: (libc)Trig Functions.
* sinh: (libc)Hyperbolic Functions.
* sinhf: (libc)Hyperbolic Functions.
* sinhfN: (libc)Hyperbolic Functions.
* sinhfNx: (libc)Hyperbolic Functions.
* sinhl: (libc)Hyperbolic Functions.
* sinl: (libc)Trig Functions.
* sinpi: (libc)Trig Functions.
* sinpif: (libc)Trig Functions.
* sinpifN: (libc)Trig Functions.
* sinpifNx: (libc)Trig Functions.
* sinpil: (libc)Trig Functions.
* sleep: (libc)Sleeping.
* snprintf: (libc)Formatted Output Functions.
* socket: (libc)Creating a Socket.
* socketpair: (libc)Socket Pairs.
* sprintf: (libc)Formatted Output Functions.
* sqrt: (libc)Exponents and Logarithms.
* sqrtf: (libc)Exponents and Logarithms.
* sqrtfN: (libc)Exponents and Logarithms.
* sqrtfNx: (libc)Exponents and Logarithms.
* sqrtl: (libc)Exponents and Logarithms.
* srand48: (libc)SVID Random.
* srand48_r: (libc)SVID Random.
* srand: (libc)ISO Random.
* srandom: (libc)BSD Random.
* srandom_r: (libc)BSD Random.
* sscanf: (libc)Formatted Input Functions.
* ssignal: (libc)Basic Signal Handling.
* stat64: (libc)Reading Attributes.
* stat: (libc)Reading Attributes.
* stdc_bit_ceil_uc: (libc)Bit Manipulation.
* stdc_bit_ceil_ui: (libc)Bit Manipulation.
* stdc_bit_ceil_ul: (libc)Bit Manipulation.
* stdc_bit_ceil_ull: (libc)Bit Manipulation.
* stdc_bit_ceil_us: (libc)Bit Manipulation.
* stdc_bit_floor_uc: (libc)Bit Manipulation.
* stdc_bit_floor_ui: (libc)Bit Manipulation.
* stdc_bit_floor_ul: (libc)Bit Manipulation.
* stdc_bit_floor_ull: (libc)Bit Manipulation.
* stdc_bit_floor_us: (libc)Bit Manipulation.
* stdc_bit_width_uc: (libc)Bit Manipulation.
* stdc_bit_width_ui: (libc)Bit Manipulation.
* stdc_bit_width_ul: (libc)Bit Manipulation.
* stdc_bit_width_ull: (libc)Bit Manipulation.
* stdc_bit_width_us: (libc)Bit Manipulation.
* stdc_count_ones_uc: (libc)Bit Manipulation.
* stdc_count_ones_ui: (libc)Bit Manipulation.
* stdc_count_ones_ul: (libc)Bit Manipulation.
* stdc_count_ones_ull: (libc)Bit Manipulation.
* stdc_count_ones_us: (libc)Bit Manipulation.
* stdc_count_zeros_uc: (libc)Bit Manipulation.
* stdc_count_zeros_ui: (libc)Bit Manipulation.
* stdc_count_zeros_ul: (libc)Bit Manipulation.
* stdc_count_zeros_ull: (libc)Bit Manipulation.
* stdc_count_zeros_us: (libc)Bit Manipulation.
* stdc_first_leading_one_uc: (libc)Bit Manipulation.
* stdc_first_leading_one_ui: (libc)Bit Manipulation.
* stdc_first_leading_one_ul: (libc)Bit Manipulation.
* stdc_first_leading_one_ull: (libc)Bit Manipulation.
* stdc_first_leading_one_us: (libc)Bit Manipulation.
* stdc_first_leading_zero_uc: (libc)Bit Manipulation.
* stdc_first_leading_zero_ui: (libc)Bit Manipulation.
* stdc_first_leading_zero_ul: (libc)Bit Manipulation.
* stdc_first_leading_zero_ull: (libc)Bit Manipulation.
* stdc_first_leading_zero_us: (libc)Bit Manipulation.
* stdc_first_trailing_one_uc: (libc)Bit Manipulation.
* stdc_first_trailing_one_ui: (libc)Bit Manipulation.
* stdc_first_trailing_one_ul: (libc)Bit Manipulation.
* stdc_first_trailing_one_ull: (libc)Bit Manipulation.
* stdc_first_trailing_one_us: (libc)Bit Manipulation.
* stdc_first_trailing_zero_uc: (libc)Bit Manipulation.
* stdc_first_trailing_zero_ui: (libc)Bit Manipulation.
* stdc_first_trailing_zero_ul: (libc)Bit Manipulation.
* stdc_first_trailing_zero_ull: (libc)Bit Manipulation.
* stdc_first_trailing_zero_us: (libc)Bit Manipulation.
* stdc_has_single_bit_uc: (libc)Bit Manipulation.
* stdc_has_single_bit_ui: (libc)Bit Manipulation.
* stdc_has_single_bit_ul: (libc)Bit Manipulation.
* stdc_has_single_bit_ull: (libc)Bit Manipulation.
* stdc_has_single_bit_us: (libc)Bit Manipulation.
* stdc_leading_ones_uc: (libc)Bit Manipulation.
* stdc_leading_ones_ui: (libc)Bit Manipulation.
* stdc_leading_ones_ul: (libc)Bit Manipulation.
* stdc_leading_ones_ull: (libc)Bit Manipulation.
* stdc_leading_ones_us: (libc)Bit Manipulation.
* stdc_leading_zeros_uc: (libc)Bit Manipulation.
* stdc_leading_zeros_ui: (libc)Bit Manipulation.
* stdc_leading_zeros_ul: (libc)Bit Manipulation.
* stdc_leading_zeros_ull: (libc)Bit Manipulation.
* stdc_leading_zeros_us: (libc)Bit Manipulation.
* stdc_trailing_ones_uc: (libc)Bit Manipulation.
* stdc_trailing_ones_ui: (libc)Bit Manipulation.
* stdc_trailing_ones_ul: (libc)Bit Manipulation.
* stdc_trailing_ones_ull: (libc)Bit Manipulation.
* stdc_trailing_ones_us: (libc)Bit Manipulation.
* stdc_trailing_zeros_uc: (libc)Bit Manipulation.
* stdc_trailing_zeros_ui: (libc)Bit Manipulation.
* stdc_trailing_zeros_ul: (libc)Bit Manipulation.
* stdc_trailing_zeros_ull: (libc)Bit Manipulation.
* stdc_trailing_zeros_us: (libc)Bit Manipulation.
* stime: (libc)Setting and Adjusting the Time.
* stpcpy: (libc)Copying Strings and Arrays.
* stpncpy: (libc)Truncating Strings.
* strcasecmp: (libc)String/Array Comparison.
* strcasestr: (libc)Search Functions.
* strcat: (libc)Concatenating Strings.
* strchr: (libc)Search Functions.
* strchrnul: (libc)Search Functions.
* strcmp: (libc)String/Array Comparison.
* strcoll: (libc)Collation Functions.
* strcpy: (libc)Copying Strings and Arrays.
* strcspn: (libc)Search Functions.
* strdup: (libc)Copying Strings and Arrays.
* strdupa: (libc)Copying Strings and Arrays.
* strerror: (libc)Error Messages.
* strerror_l: (libc)Error Messages.
* strerror_r: (libc)Error Messages.
* strerror_r: (libc)Error Messages.
* strerrordesc_np: (libc)Error Messages.
* strerrorname_np: (libc)Error Messages.
* strfmon: (libc)Formatting Numbers.
* strfromd: (libc)Printing of Floats.
* strfromf: (libc)Printing of Floats.
* strfromfN: (libc)Printing of Floats.
* strfromfNx: (libc)Printing of Floats.
* strfroml: (libc)Printing of Floats.
* strfry: (libc)Shuffling Bytes.
* strftime: (libc)Formatting Calendar Time.
* strftime_l: (libc)Formatting Calendar Time.
* strlcat: (libc)Truncating Strings.
* strlcpy: (libc)Truncating Strings.
* strlen: (libc)String Length.
* strncasecmp: (libc)String/Array Comparison.
* strncat: (libc)Truncating Strings.
* strncmp: (libc)String/Array Comparison.
* strncpy: (libc)Truncating Strings.
* strndup: (libc)Truncating Strings.
* strndupa: (libc)Truncating Strings.
* strnlen: (libc)String Length.
* strpbrk: (libc)Search Functions.
* strptime: (libc)Low-Level Time String Parsing.
* strrchr: (libc)Search Functions.
* strsep: (libc)Finding Tokens in a String.
* strsignal: (libc)Signal Messages.
* strspn: (libc)Search Functions.
* strstr: (libc)Search Functions.
* strtod: (libc)Parsing of Floats.
* strtof: (libc)Parsing of Floats.
* strtofN: (libc)Parsing of Floats.
* strtofNx: (libc)Parsing of Floats.
* strtoimax: (libc)Parsing of Integers.
* strtok: (libc)Finding Tokens in a String.
* strtok_r: (libc)Finding Tokens in a String.
* strtol: (libc)Parsing of Integers.
* strtold: (libc)Parsing of Floats.
* strtoll: (libc)Parsing of Integers.
* strtoq: (libc)Parsing of Integers.
* strtoul: (libc)Parsing of Integers.
* strtoull: (libc)Parsing of Integers.
* strtoumax: (libc)Parsing of Integers.
* strtouq: (libc)Parsing of Integers.
* strverscmp: (libc)String/Array Comparison.
* strxfrm: (libc)Collation Functions.
* stty: (libc)BSD Terminal Modes.
* swapcontext: (libc)System V contexts.
* swprintf: (libc)Formatted Output Functions.
* swscanf: (libc)Formatted Input Functions.
* symlink: (libc)Symbolic Links.
* sync: (libc)Synchronizing I/O.
* syscall: (libc)System Calls.
* sysconf: (libc)Sysconf Definition.
* syslog: (libc)syslog; vsyslog.
* system: (libc)Running a Command.
* sysv_signal: (libc)Basic Signal Handling.
* tan: (libc)Trig Functions.
* tanf: (libc)Trig Functions.
* tanfN: (libc)Trig Functions.
* tanfNx: (libc)Trig Functions.
* tanh: (libc)Hyperbolic Functions.
* tanhf: (libc)Hyperbolic Functions.
* tanhfN: (libc)Hyperbolic Functions.
* tanhfNx: (libc)Hyperbolic Functions.
* tanhl: (libc)Hyperbolic Functions.
* tanl: (libc)Trig Functions.
* tanpi: (libc)Trig Functions.
* tanpif: (libc)Trig Functions.
* tanpifN: (libc)Trig Functions.
* tanpifNx: (libc)Trig Functions.
* tanpil: (libc)Trig Functions.
* tcdrain: (libc)Line Control.
* tcflow: (libc)Line Control.
* tcflush: (libc)Line Control.
* tcgetattr: (libc)Mode Functions.
* tcgetpgrp: (libc)Terminal Access Functions.
* tcgetsid: (libc)Terminal Access Functions.
* tcsendbreak: (libc)Line Control.
* tcsetattr: (libc)Mode Functions.
* tcsetpgrp: (libc)Terminal Access Functions.
* tdelete: (libc)Tree Search Function.
* tdestroy: (libc)Tree Search Function.
* telldir: (libc)Random Access Directory.
* tempnam: (libc)Temporary Files.
* textdomain: (libc)Locating gettext catalog.
* tfind: (libc)Tree Search Function.
* tgamma: (libc)Special Functions.
* tgammaf: (libc)Special Functions.
* tgammafN: (libc)Special Functions.
* tgammafNx: (libc)Special Functions.
* tgammal: (libc)Special Functions.
* tgkill: (libc)Signaling Another Process.
* thrd_create: (libc)ISO C Thread Management.
* thrd_current: (libc)ISO C Thread Management.
* thrd_detach: (libc)ISO C Thread Management.
* thrd_equal: (libc)ISO C Thread Management.
* thrd_exit: (libc)ISO C Thread Management.
* thrd_join: (libc)ISO C Thread Management.
* thrd_sleep: (libc)ISO C Thread Management.
* thrd_yield: (libc)ISO C Thread Management.
* time: (libc)Getting the Time.
* timegm: (libc)Broken-down Time.
* timelocal: (libc)Broken-down Time.
* times: (libc)Processor Time.
* timespec_get: (libc)Getting the Time.
* timespec_getres: (libc)Getting the Time.
* tmpfile64: (libc)Temporary Files.
* tmpfile: (libc)Temporary Files.
* tmpnam: (libc)Temporary Files.
* tmpnam_r: (libc)Temporary Files.
* toascii: (libc)Case Conversion.
* tolower: (libc)Case Conversion.
* totalorder: (libc)FP Comparison Functions.
* totalorderf: (libc)FP Comparison Functions.
* totalorderfN: (libc)FP Comparison Functions.
* totalorderfNx: (libc)FP Comparison Functions.
* totalorderl: (libc)FP Comparison Functions.
* totalordermag: (libc)FP Comparison Functions.
* totalordermagf: (libc)FP Comparison Functions.
* totalordermagfN: (libc)FP Comparison Functions.
* totalordermagfNx: (libc)FP Comparison Functions.
* totalordermagl: (libc)FP Comparison Functions.
* toupper: (libc)Case Conversion.
* towctrans: (libc)Wide Character Case Conversion.
* towlower: (libc)Wide Character Case Conversion.
* towupper: (libc)Wide Character Case Conversion.
* trunc: (libc)Rounding Functions.
* truncate64: (libc)File Size.
* truncate: (libc)File Size.
* truncf: (libc)Rounding Functions.
* truncfN: (libc)Rounding Functions.
* truncfNx: (libc)Rounding Functions.
* truncl: (libc)Rounding Functions.
* tsearch: (libc)Tree Search Function.
* tss_create: (libc)ISO C Thread-local Storage.
* tss_delete: (libc)ISO C Thread-local Storage.
* tss_get: (libc)ISO C Thread-local Storage.
* tss_set: (libc)ISO C Thread-local Storage.
* ttyname: (libc)Is It a Terminal.
* ttyname_r: (libc)Is It a Terminal.
* twalk: (libc)Tree Search Function.
* twalk_r: (libc)Tree Search Function.
* tzset: (libc)Time Zone State.
* uabs: (libc)Absolute Value.
* ufromfp: (libc)Rounding Functions.
* ufromfpf: (libc)Rounding Functions.
* ufromfpfN: (libc)Rounding Functions.
* ufromfpfNx: (libc)Rounding Functions.
* ufromfpl: (libc)Rounding Functions.
* ufromfpx: (libc)Rounding Functions.
* ufromfpxf: (libc)Rounding Functions.
* ufromfpxfN: (libc)Rounding Functions.
* ufromfpxfNx: (libc)Rounding Functions.
* ufromfpxl: (libc)Rounding Functions.
* ulabs: (libc)Absolute Value.
* ulimit: (libc)Limits on Resources.
* ullabs: (libc)Absolute Value.
* umask: (libc)Setting Permissions.
* umaxabs: (libc)Absolute Value.
* umount2: (libc)Mount-Unmount-Remount.
* umount: (libc)Mount-Unmount-Remount.
* uname: (libc)Platform Type.
* ungetc: (libc)How Unread.
* ungetwc: (libc)How Unread.
* unlink: (libc)Deleting Files.
* unlinkat: (libc)Deleting Files.
* unlockpt: (libc)Allocation.
* unsetenv: (libc)Environment Access.
* updwtmp: (libc)Manipulating the Database.
* utime: (libc)File Times.
* utimensat: (libc)File Times.
* utimes: (libc)File Times.
* utmpname: (libc)Manipulating the Database.
* utmpxname: (libc)XPG Functions.
* va_arg: (libc)Argument Macros.
* va_copy: (libc)Argument Macros.
* va_end: (libc)Argument Macros.
* va_start: (libc)Argument Macros.
* valloc: (libc)Aligned Memory Blocks.
* vasprintf: (libc)Variable Arguments Output.
* vdprintf: (libc)Variable Arguments Output.
* verr: (libc)Error Messages.
* verrx: (libc)Error Messages.
* versionsort64: (libc)Scanning Directory Content.
* versionsort: (libc)Scanning Directory Content.
* vfork: (libc)Creating a Process.
* vfprintf: (libc)Variable Arguments Output.
* vfscanf: (libc)Variable Arguments Input.
* vfwprintf: (libc)Variable Arguments Output.
* vfwscanf: (libc)Variable Arguments Input.
* vlimit: (libc)Limits on Resources.
* vprintf: (libc)Variable Arguments Output.
* vscanf: (libc)Variable Arguments Input.
* vsnprintf: (libc)Variable Arguments Output.
* vsprintf: (libc)Variable Arguments Output.
* vsscanf: (libc)Variable Arguments Input.
* vswprintf: (libc)Variable Arguments Output.
* vswscanf: (libc)Variable Arguments Input.
* vsyslog: (libc)syslog; vsyslog.
* vwarn: (libc)Error Messages.
* vwarnx: (libc)Error Messages.
* vwprintf: (libc)Variable Arguments Output.
* vwscanf: (libc)Variable Arguments Input.
* wait3: (libc)BSD Wait Functions.
* wait4: (libc)Process Completion.
* wait: (libc)Process Completion.
* waitpid: (libc)Process Completion.
* warn: (libc)Error Messages.
* warnx: (libc)Error Messages.
* wcpcpy: (libc)Copying Strings and Arrays.
* wcpncpy: (libc)Truncating Strings.
* wcrtomb: (libc)Converting a Character.
* wcscasecmp: (libc)String/Array Comparison.
* wcscat: (libc)Concatenating Strings.
* wcschr: (libc)Search Functions.
* wcschrnul: (libc)Search Functions.
* wcscmp: (libc)String/Array Comparison.
* wcscoll: (libc)Collation Functions.
* wcscpy: (libc)Copying Strings and Arrays.
* wcscspn: (libc)Search Functions.
* wcsdup: (libc)Copying Strings and Arrays.
* wcsftime: (libc)Formatting Calendar Time.
* wcslcat: (libc)Truncating Strings.
* wcslcpy: (libc)Truncating Strings.
* wcslen: (libc)String Length.
* wcsncasecmp: (libc)String/Array Comparison.
* wcsncat: (libc)Truncating Strings.
* wcsncmp: (libc)String/Array Comparison.
* wcsncpy: (libc)Truncating Strings.
* wcsnlen: (libc)String Length.
* wcsnrtombs: (libc)Converting Strings.
* wcspbrk: (libc)Search Functions.
* wcsrchr: (libc)Search Functions.
* wcsrtombs: (libc)Converting Strings.
* wcsspn: (libc)Search Functions.
* wcsstr: (libc)Search Functions.
* wcstod: (libc)Parsing of Floats.
* wcstof: (libc)Parsing of Floats.
* wcstofN: (libc)Parsing of Floats.
* wcstofNx: (libc)Parsing of Floats.
* wcstoimax: (libc)Parsing of Integers.
* wcstok: (libc)Finding Tokens in a String.
* wcstol: (libc)Parsing of Integers.
* wcstold: (libc)Parsing of Floats.
* wcstoll: (libc)Parsing of Integers.
* wcstombs: (libc)Non-reentrant String Conversion.
* wcstoq: (libc)Parsing of Integers.
* wcstoul: (libc)Parsing of Integers.
* wcstoull: (libc)Parsing of Integers.
* wcstoumax: (libc)Parsing of Integers.
* wcstouq: (libc)Parsing of Integers.
* wcswcs: (libc)Search Functions.
* wcsxfrm: (libc)Collation Functions.
* wctob: (libc)Converting a Character.
* wctomb: (libc)Non-reentrant Character Conversion.
* wctrans: (libc)Wide Character Case Conversion.
* wctype: (libc)Classification of Wide Characters.
* wmemchr: (libc)Search Functions.
* wmemcmp: (libc)String/Array Comparison.
* wmemcpy: (libc)Copying Strings and Arrays.
* wmemmove: (libc)Copying Strings and Arrays.
* wmempcpy: (libc)Copying Strings and Arrays.
* wmemset: (libc)Copying Strings and Arrays.
* wordexp: (libc)Calling Wordexp.
* wordfree: (libc)Calling Wordexp.
* wprintf: (libc)Formatted Output Functions.
* write: (libc)I/O Primitives.
* writev: (libc)Scatter-Gather.
* wscanf: (libc)Formatted Input Functions.
* y0: (libc)Special Functions.
* y0f: (libc)Special Functions.
* y0fN: (libc)Special Functions.
* y0fNx: (libc)Special Functions.
* y0l: (libc)Special Functions.
* y1: (libc)Special Functions.
* y1f: (libc)Special Functions.
* y1fN: (libc)Special Functions.
* y1fNx: (libc)Special Functions.
* y1l: (libc)Special Functions.
* yn: (libc)Special Functions.
* ynf: (libc)Special Functions.
* ynfN: (libc)Special Functions.
* ynfNx: (libc)Special Functions.
* ynl: (libc)Special Functions.
END-INFO-DIR-ENTRY


File: libc.info,  Node: Synchronizing AIO Operations,  Next: Cancel AIO Operations,  Prev: Status of AIO Operations,  Up: Asynchronous I/O

13.11.3 Getting into a Consistent State
---------------------------------------

When dealing with asynchronous operations it is sometimes necessary to
get into a consistent state.  This would mean for AIO that one wants to
know whether a certain request or a group of requests were processed.
This could be done by waiting for the notification sent by the system
after the operation terminated, but this sometimes would mean wasting
resources (mainly computation time).  Instead POSIX.1b defines two
functions which will help with most kinds of consistency.

   The ‘aio_fsync’ and ‘aio_fsync64’ functions are only available if the
symbol ‘_POSIX_SYNCHRONIZED_IO’ is defined in ‘unistd.h’.

 -- Function: int aio_fsync (int OP, struct aiocb *AIOCBP)

     Preliminary: | MT-Safe | AS-Unsafe lock heap | AC-Unsafe lock mem |
     *Note POSIX Safety Concepts::.

     Calling this function forces all I/O operations queued at the time
     of the function call operating on the file descriptor
     ‘aiocbp->aio_fildes’ into the synchronized I/O completion state
     (*note Synchronizing I/O::).  The ‘aio_fsync’ function returns
     immediately but the notification through the method described in
     ‘aiocbp->aio_sigevent’ will happen only after all requests for this
     file descriptor have terminated and the file is synchronized.  This
     also means that requests for this very same file descriptor which
     are queued after the synchronization request are not affected.

     If OP is ‘O_DSYNC’ the synchronization happens as with a call to
     ‘fdatasync’.  Otherwise OP should be ‘O_SYNC’ and the
     synchronization happens as with ‘fsync’.

     As long as the synchronization has not happened, a call to
     ‘aio_error’ with the reference to the object pointed to by AIOCBP
     returns ‘EINPROGRESS’.  Once the synchronization is done
     ‘aio_error’ return 0 if the synchronization was not successful.
     Otherwise the value returned is the value to which the ‘fsync’ or
     ‘fdatasync’ function would have set the ‘errno’ variable.  In this
     case nothing can be assumed about the consistency of the data
     written to this file descriptor.

     The return value of this function is 0 if the request was
     successfully enqueued.  Otherwise the return value is -1 and
     ‘errno’ is set to one of the following values:

     ‘EAGAIN’
          The request could not be enqueued due to temporary lack of
          resources.
     ‘EBADF’
          The file descriptor ‘AIOCBP->aio_fildes’ is not valid.
     ‘EINVAL’
          The implementation does not support I/O synchronization or the
          OP parameter is other than ‘O_DSYNC’ and ‘O_SYNC’.
     ‘ENOSYS’
          This function is not implemented.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     function is in fact ‘aio_fsync64’ since the LFS interface
     transparently replaces the normal implementation.

 -- Function: int aio_fsync64 (int OP, struct aiocb64 *AIOCBP)

     Preliminary: | MT-Safe | AS-Unsafe lock heap | AC-Unsafe lock mem |
     *Note POSIX Safety Concepts::.

     This function is similar to ‘aio_fsync’ with the only difference
     that the argument is a reference to a variable of type ‘struct
     aiocb64’.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     function is available under the name ‘aio_fsync’ and so
     transparently replaces the interface for small files on 32 bit
     machines.

   Another method of synchronization is to wait until one or more
requests of a specific set terminated.  This could be achieved by the
‘aio_*’ functions to notify the initiating process about the termination
but in some situations this is not the ideal solution.  In a program
which constantly updates clients somehow connected to the server it is
not always the best solution to go round robin since some connections
might be slow.  On the other hand letting the ‘aio_*’ functions notify
the caller might also be not the best solution since whenever the
process works on preparing data for a client it makes no sense to be
interrupted by a notification since the new client will not be handled
before the current client is served.  For situations like this
‘aio_suspend’ should be used.

 -- Function: int aio_suspend (const struct aiocb *const LIST[], int
          NENT, const struct timespec *TIMEOUT)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     When calling this function, the calling thread is suspended until
     at least one of the requests pointed to by the NENT elements of the
     array LIST has completed.  If any of the requests has already
     completed at the time ‘aio_suspend’ is called, the function returns
     immediately.  Whether a request has terminated or not is determined
     by comparing the error status of the request with ‘EINPROGRESS’.
     If an element of LIST is ‘NULL’, the entry is simply ignored.

     If no request has finished, the calling process is suspended.  If
     TIMEOUT is ‘NULL’, the process is not woken until a request has
     finished.  If TIMEOUT is not ‘NULL’, the process remains suspended
     at least as long as specified in TIMEOUT.  In this case,
     ‘aio_suspend’ returns with an error.

     The return value of the function is 0 if one or more requests from
     the LIST have terminated.  Otherwise the function returns -1 and
     ‘errno’ is set to one of the following values:

     ‘EAGAIN’
          None of the requests from the LIST completed in the time
          specified by TIMEOUT.
     ‘EINTR’
          A signal interrupted the ‘aio_suspend’ function.  This signal
          might also be sent by the AIO implementation while signalling
          the termination of one of the requests.
     ‘ENOSYS’
          The ‘aio_suspend’ function is not implemented.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     function is in fact ‘aio_suspend64’ since the LFS interface
     transparently replaces the normal implementation.

 -- Function: int aio_suspend64 (const struct aiocb64 *const LIST[], int
          NENT, const struct timespec *TIMEOUT)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     This function is similar to ‘aio_suspend’ with the only difference
     that the argument is a reference to a variable of type ‘struct
     aiocb64’.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     function is available under the name ‘aio_suspend’ and so
     transparently replaces the interface for small files on 32 bit
     machines.


File: libc.info,  Node: Cancel AIO Operations,  Next: Configuration of AIO,  Prev: Synchronizing AIO Operations,  Up: Asynchronous I/O

13.11.4 Cancellation of AIO Operations
--------------------------------------

When one or more requests are asynchronously processed, it might be
useful in some situations to cancel a selected operation, e.g., if it
becomes obvious that the written data is no longer accurate and would
have to be overwritten soon.  As an example, assume an application,
which writes data in files in a situation where new incoming data would
have to be written in a file which will be updated by an enqueued
request.  The POSIX AIO implementation provides such a function, but
this function is not capable of forcing the cancellation of the request.
It is up to the implementation to decide whether it is possible to
cancel the operation or not.  Therefore using this function is merely a
hint.

 -- Function: int aio_cancel (int FILDES, struct aiocb *AIOCBP)

     Preliminary: | MT-Safe | AS-Unsafe lock heap | AC-Unsafe lock mem |
     *Note POSIX Safety Concepts::.

     The ‘aio_cancel’ function can be used to cancel one or more
     outstanding requests.  If the AIOCBP parameter is ‘NULL’, the
     function tries to cancel all of the outstanding requests which
     would process the file descriptor FILDES (i.e., whose ‘aio_fildes’
     member is FILDES).  If AIOCBP is not ‘NULL’, ‘aio_cancel’ attempts
     to cancel the specific request pointed to by AIOCBP.

     For requests which were successfully canceled, the normal
     notification about the termination of the request should take
     place.  I.e., depending on the ‘struct sigevent’ object which
     controls this, nothing happens, a signal is sent or a thread is
     started.  If the request cannot be canceled, it terminates the
     usual way after performing the operation.

     After a request is successfully canceled, a call to ‘aio_error’
     with a reference to this request as the parameter will return
     ‘ECANCELED’ and a call to ‘aio_return’ will return -1.  If the
     request wasn't canceled and is still running the error status is
     still ‘EINPROGRESS’.

     The return value of the function is ‘AIO_CANCELED’ if there were
     requests which haven't terminated and which were successfully
     canceled.  If there is one or more requests left which couldn't be
     canceled, the return value is ‘AIO_NOTCANCELED’.  In this case
     ‘aio_error’ must be used to find out which of the, perhaps
     multiple, requests (if AIOCBP is ‘NULL’) weren't successfully
     canceled.  If all requests already terminated at the time
     ‘aio_cancel’ is called the return value is ‘AIO_ALLDONE’.

     If an error occurred during the execution of ‘aio_cancel’ the
     function returns -1 and sets ‘errno’ to one of the following
     values.

     ‘EBADF’
          The file descriptor FILDES is not valid.
     ‘ENOSYS’
          ‘aio_cancel’ is not implemented.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’, this
     function is in fact ‘aio_cancel64’ since the LFS interface
     transparently replaces the normal implementation.

 -- Function: int aio_cancel64 (int FILDES, struct aiocb64 *AIOCBP)

     Preliminary: | MT-Safe | AS-Unsafe lock heap | AC-Unsafe lock mem |
     *Note POSIX Safety Concepts::.

     This function is similar to ‘aio_cancel’ with the only difference
     that the argument is a reference to a variable of type ‘struct
     aiocb64’.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’, this
     function is available under the name ‘aio_cancel’ and so
     transparently replaces the interface for small files on 32 bit
     machines.


File: libc.info,  Node: Configuration of AIO,  Prev: Cancel AIO Operations,  Up: Asynchronous I/O

13.11.5 How to optimize the AIO implementation
----------------------------------------------

The POSIX standard does not specify how the AIO functions are
implemented.  They could be system calls, but it is also possible to
emulate them at userlevel.

   At the time of writing, the available implementation is a user-level
implementation which uses threads for handling the enqueued requests.
While this implementation requires making some decisions about
limitations, hard limitations are something best avoided in the GNU C
Library.  Therefore, the GNU C Library provides a means for tuning the
AIO implementation according to the individual use.

 -- Data Type: struct aioinit

     This data type is used to pass the configuration or tunable
     parameters to the implementation.  The program has to initialize
     the members of this struct and pass it to the implementation using
     the ‘aio_init’ function.

     ‘int aio_threads’
          This member specifies the maximal number of threads which may
          be used at any one time.
     ‘int aio_num’
          This number provides an estimate on the maximal number of
          simultaneously enqueued requests.
     ‘int aio_locks’
          Unused.
     ‘int aio_usedba’
          Unused.
     ‘int aio_debug’
          Unused.
     ‘int aio_numusers’
          Unused.
     ‘int aio_reserved[2]’
          Unused.

 -- Function: void aio_init (const struct aioinit *INIT)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     This function must be called before any other AIO function.
     Calling it is completely voluntary, as it is only meant to help the
     AIO implementation perform better.

     Before calling ‘aio_init’, the members of a variable of type
     ‘struct aioinit’ must be initialized.  Then a reference to this
     variable is passed as the parameter to ‘aio_init’ which itself may
     or may not pay attention to the hints.

     The function has no return value and no error cases are defined.
     It is an extension which follows a proposal from the SGI
     implementation in Irix 6.  It is not covered by POSIX.1b or Unix98.


File: libc.info,  Node: Control Operations,  Next: Duplicating Descriptors,  Prev: Asynchronous I/O,  Up: Low-Level I/O

13.12 Control Operations on Files
=================================

This section describes how you can perform various other operations on
file descriptors, such as inquiring about or setting flags describing
the status of the file descriptor, manipulating record locks, and the
like.  All of these operations are performed by the function ‘fcntl’.

   The second argument to the ‘fcntl’ function is a command that
specifies which operation to perform.  The function and macros that name
various flags that are used with it are declared in the header file
‘fcntl.h’.  Many of these flags are also used by the ‘open’ function;
see *note Opening and Closing Files::.

 -- Function: int fcntl (int FILEDES, int COMMAND, ...)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘fcntl’ function performs the operation specified by COMMAND on
     the file descriptor FILEDES.  Some commands require additional
     arguments to be supplied.  These additional arguments and the
     return value and error conditions are given in the detailed
     descriptions of the individual commands.

     Briefly, here is a list of what the various commands are.  For an
     exhaustive list of kernel-specific options, please see *Note System
     Calls::.

     ‘F_DUPFD’
          Duplicate the file descriptor (return another file descriptor
          pointing to the same open file).  *Note Duplicating
          Descriptors::.

     ‘F_GETFD’
          Get flags associated with the file descriptor.  *Note
          Descriptor Flags::.

     ‘F_SETFD’
          Set flags associated with the file descriptor.  *Note
          Descriptor Flags::.

     ‘F_GETFL’
          Get flags associated with the open file.  *Note File Status
          Flags::.

     ‘F_SETFL’
          Set flags associated with the open file.  *Note File Status
          Flags::.

     ‘F_GETLK’
          Test a file lock.  *Note File Locks::.

     ‘F_SETLK’
          Set or clear a file lock.  *Note File Locks::.

     ‘F_SETLKW’
          Like ‘F_SETLK’, but wait for completion.  *Note File Locks::.

     ‘F_OFD_GETLK’
          Test an open file description lock.  *Note Open File
          Description Locks::.  Specific to Linux.

     ‘F_OFD_SETLK’
          Set or clear an open file description lock.  *Note Open File
          Description Locks::.  Specific to Linux.

     ‘F_OFD_SETLKW’
          Like ‘F_OFD_SETLK’, but block until lock is acquired.  *Note
          Open File Description Locks::.  Specific to Linux.

     ‘F_GETOWN’
          Get process or process group ID to receive ‘SIGIO’ signals.
          *Note Interrupt Input::.

     ‘F_SETOWN’
          Set process or process group ID to receive ‘SIGIO’ signals.
          *Note Interrupt Input::.

     This function is a cancellation point in multi-threaded programs
     for the commands ‘F_SETLKW’ (and the LFS analogous ‘F_SETLKW64’)
     and ‘F_OFD_SETLKW’.  This is a problem if the thread allocates some
     resources (like memory, file descriptors, semaphores or whatever)
     at the time ‘fcntl’ is called.  If the thread gets canceled these
     resources stay allocated until the program ends.  To avoid this
     calls to ‘fcntl’ should be protected using cancellation handlers.


File: libc.info,  Node: Duplicating Descriptors,  Next: Descriptor Flags,  Prev: Control Operations,  Up: Low-Level I/O

13.13 Duplicating Descriptors
=============================

You can “duplicate” a file descriptor, or allocate another file
descriptor that refers to the same open file as the original.  Duplicate
descriptors share one file position and one set of file status flags
(*note File Status Flags::), but each has its own set of file descriptor
flags (*note Descriptor Flags::).

   The major use of duplicating a file descriptor is to implement
“redirection” of input or output: that is, to change the file or pipe
that a particular file descriptor corresponds to.

   You can perform this operation using the ‘fcntl’ function with the
‘F_DUPFD’ command, but there are also convenient functions ‘dup’ and
‘dup2’ for duplicating descriptors.

   The ‘fcntl’ function and flags are declared in ‘fcntl.h’, while
prototypes for ‘dup’ and ‘dup2’ are in the header file ‘unistd.h’.

 -- Function: int dup (int OLD)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function copies descriptor OLD to the first available
     descriptor number (the first number not currently open).  It is
     equivalent to ‘fcntl (OLD, F_DUPFD, 0)’.

 -- Function: int dup2 (int OLD, int NEW)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function copies the descriptor OLD to descriptor number NEW.

     If OLD is an invalid descriptor, then ‘dup2’ does nothing; it does
     not close NEW.  Otherwise, the new duplicate of OLD replaces any
     previous meaning of descriptor NEW, as if NEW were closed first.

     If OLD and NEW are different numbers, and OLD is a valid descriptor
     number, then ‘dup2’ is equivalent to:

          close (NEW);
          fcntl (OLD, F_DUPFD, NEW)

     However, ‘dup2’ does this atomically; there is no instant in the
     middle of calling ‘dup2’ at which NEW is closed and not yet a
     duplicate of OLD.

 -- Function: int dup3 (int OLD, int NEW, int FLAGS)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is the same as ‘dup2’ but creates the new descriptor
     as if it had been opened with flags FLAGS.  The only allowed flag
     is ‘O_CLOEXEC’.

     This function was originally a Linux extension, but was added in
     POSIX.1-2024.

 -- Macro: int F_DUPFD

     This macro is used as the COMMAND argument to ‘fcntl’, to copy the
     file descriptor given as the first argument.

     The form of the call in this case is:

          fcntl (OLD, F_DUPFD, NEXT-FILEDES)

     The NEXT-FILEDES argument is of type ‘int’ and specifies that the
     file descriptor returned should be the next available one greater
     than or equal to this value.

     The return value from ‘fcntl’ with this command is normally the
     value of the new file descriptor.  A return value of -1 indicates
     an error.  The following ‘errno’ error conditions are defined for
     this command:

     ‘EBADF’
          The OLD argument is invalid.

     ‘EINVAL’
          The NEXT-FILEDES argument is invalid.

     ‘EMFILE’
          There are no more file descriptors available--your program is
          already using the maximum.  In BSD and GNU, the maximum is
          controlled by a resource limit that can be changed; *note
          Limits on Resources::, for more information about the
          ‘RLIMIT_NOFILE’ limit.

     ‘ENFILE’ is not a possible error code for ‘dup2’ because ‘dup2’
     does not create a new opening of a file; duplicate descriptors do
     not count toward the limit which ‘ENFILE’ indicates.  ‘EMFILE’ is
     possible because it refers to the limit on distinct descriptor
     numbers in use in one process.

   Here is an example showing how to use ‘dup2’ to do redirection.
Typically, redirection of the standard streams (like ‘stdin’) is done by
a shell or shell-like program before calling one of the ‘exec’ functions
(*note Executing a File::) to execute a new program in a child process.
When the new program is executed, it creates and initializes the
standard streams to point to the corresponding file descriptors, before
its ‘main’ function is invoked.

   So, to redirect standard input to a file, the shell could do
something like:

     pid = fork ();
     if (pid == 0)
       {
         char *filename;
         char *program;
         int file;
         ...
         file = TEMP_FAILURE_RETRY (open (filename, O_RDONLY));
         dup2 (file, STDIN_FILENO);
         TEMP_FAILURE_RETRY (close (file));
         execv (program, NULL);
       }

   There is also a more detailed example showing how to implement
redirection in the context of a pipeline of processes in *note Launching
Jobs::.


File: libc.info,  Node: Descriptor Flags,  Next: File Status Flags,  Prev: Duplicating Descriptors,  Up: Low-Level I/O

13.14 File Descriptor Flags
===========================

“File descriptor flags” are miscellaneous attributes of a file
descriptor.  These flags are associated with particular file
descriptors, so that if you have created duplicate file descriptors from
a single opening of a file, each descriptor has its own set of flags.

   Currently there is just one file descriptor flag: ‘FD_CLOEXEC’, which
causes the descriptor to be closed if you use any of the ‘exec...’
functions (*note Executing a File::).

   The symbols in this section are defined in the header file ‘fcntl.h’.

 -- Macro: int F_GETFD

     This macro is used as the COMMAND argument to ‘fcntl’, to specify
     that it should return the file descriptor flags associated with the
     FILEDES argument.

     The normal return value from ‘fcntl’ with this command is a
     nonnegative number which can be interpreted as the bitwise OR of
     the individual flags (except that currently there is only one flag
     to use).

     In case of an error, ‘fcntl’ returns -1.  The following ‘errno’
     error conditions are defined for this command:

     ‘EBADF’
          The FILEDES argument is invalid.

 -- Macro: int F_SETFD

     This macro is used as the COMMAND argument to ‘fcntl’, to specify
     that it should set the file descriptor flags associated with the
     FILEDES argument.  This requires a third ‘int’ argument to specify
     the new flags, so the form of the call is:

          fcntl (FILEDES, F_SETFD, NEW-FLAGS)

     The normal return value from ‘fcntl’ with this command is an
     unspecified value other than -1, which indicates an error.  The
     flags and error conditions are the same as for the ‘F_GETFD’
     command.

   The following macro is defined for use as a file descriptor flag with
the ‘fcntl’ function.  The value is an integer constant usable as a bit
mask value.

 -- Macro: int FD_CLOEXEC

     This flag specifies that the file descriptor should be closed when
     an ‘exec’ function is invoked; see *note Executing a File::.  When
     a file descriptor is allocated (as with ‘open’ or ‘dup’), this bit
     is initially cleared on the new file descriptor, meaning that
     descriptor will survive into the new program after ‘exec’.

   If you want to modify the file descriptor flags, you should get the
current flags with ‘F_GETFD’ and modify the value.  Don't assume that
the flags listed here are the only ones that are implemented; your
program may be run years from now and more flags may exist then.  For
example, here is a function to set or clear the flag ‘FD_CLOEXEC’
without altering any other flags:

     /* Set the ‘FD_CLOEXEC’ flag of DESC if VALUE is nonzero,
        or clear the flag if VALUE is 0.
        Return 0 on success, or -1 on error with ‘errno’ set. */

     int
     set_cloexec_flag (int desc, int value)
     {
       int oldflags = fcntl (desc, F_GETFD, 0);
       /* If reading the flags failed, return error indication now. */
       if (oldflags < 0)
         return oldflags;
       /* Set just the flag we want to set. */
       if (value != 0)
         oldflags |= FD_CLOEXEC;
       else
         oldflags &= ~FD_CLOEXEC;
       /* Store modified flag word in the descriptor. */
       return fcntl (desc, F_SETFD, oldflags);
     }


File: libc.info,  Node: File Status Flags,  Next: File Locks,  Prev: Descriptor Flags,  Up: Low-Level I/O

13.15 File Status Flags
=======================

“File status flags” are used to specify attributes of the opening of a
file.  Unlike the file descriptor flags discussed in *note Descriptor
Flags::, the file status flags are shared by duplicated file descriptors
resulting from a single opening of the file.  The file status flags are
specified with the FLAGS argument to ‘open’; *note Opening and Closing
Files::.

   File status flags fall into three categories, which are described in
the following sections.

   • *note Access Modes::, specify what type of access is allowed to the
     file: reading, writing, or both.  They are set by ‘open’ and are
     returned by ‘fcntl’, but cannot be changed.

   • *note Open-time Flags::, control details of what ‘open’ will do.
     These flags are not preserved after the ‘open’ call.

   • *note Operating Modes::, affect how operations such as ‘read’ and
     ‘write’ are done.  They are set by ‘open’, and can be fetched or
     changed with ‘fcntl’.

   The symbols in this section are defined in the header file ‘fcntl.h’.

* Menu:

* Access Modes::                Whether the descriptor can read or write.
* Open-time Flags::             Details of ‘open’.
* Operating Modes::             Special modes to control I/O operations.
* Getting File Status Flags::   Fetching and changing these flags.


File: libc.info,  Node: Access Modes,  Next: Open-time Flags,  Up: File Status Flags

13.15.1 File Access Modes
-------------------------

The file access mode allows a file descriptor to be used for reading,
writing, both, or neither.  The access mode is determined when the file
is opened, and never change.

 -- Macro: int O_RDONLY

     Open the file for read access.

 -- Macro: int O_WRONLY

     Open the file for write access.

 -- Macro: int O_RDWR

     Open the file for both reading and writing.

 -- Macro: int O_PATH

     Obtain a file descriptor for the file, but do not open the file for
     reading or writing.  Permission checks for the file itself are
     skipped when the file is opened (but permission to access the
     directory that contains it is still needed), and permissions are
     checked when the descriptor is used later on.

     For example, such descriptors can be used with the ‘fexecve’
     function (*note Executing a File::).  Other applications involve
     the ‘*at’ function variants, along with the ‘AT_EMPTY_PATH’ flag.
     *Note Descriptor-Relative Access::.

     This access mode is specific to Linux.  On GNU/Hurd systems, it is
     possible to use ‘O_EXEC’ explicitly, or specify no access modes at
     all (see below).

   The portable file access modes ‘O_RDONLY’, ‘O_WRONLY’, and ‘O_RDWR’
may not correspond to individual bits.  To determine the file access
mode with ‘fcntl’, you must extract the access mode bits from the
retrieved file status flags, using the ‘O_ACCMODE’ mask.

 -- Macro: int O_ACCMODE

     This macro is a mask that can be bitwise-ANDed with the file status
     flag value to recover the file access mode, assuming that a
     standard file access mode is in use.

   If a non-standard file access mode is used (such as ‘O_PATH’ or
‘O_EXEC’), masking with ‘O_ACCMODE’ may give incorrect results.  These
non-standard access modes are identified by individual bits and have to
be checked directly (without masking with ‘O_ACCMODE’ first).

   On GNU/Hurd systems (but not on other systems), ‘O_RDONLY’ and
‘O_WRONLY’ are independent bits that can be bitwise-ORed together, and
it is valid for either bit to be set or clear.  This means that ‘O_RDWR’
is the same as ‘O_RDONLY|O_WRONLY’.  A file access mode of zero is
permissible; it allows no operations that do input or output to the
file, but does allow other operations such as ‘fchmod’.  On GNU/Hurd
systems, since "read-only" or "write-only" is a misnomer, ‘fcntl.h’
defines additional names for the file access modes.

 -- Macro: int O_READ

     Open the file for reading.  Same as ‘O_RDONLY’; only defined on
     GNU/Hurd.

 -- Macro: int O_WRITE

     Open the file for writing.  Same as ‘O_WRONLY’; only defined on
     GNU/Hurd.

 -- Macro: int O_EXEC

     Open the file for executing.  Only defined on GNU/Hurd.


File: libc.info,  Node: Open-time Flags,  Next: Operating Modes,  Prev: Access Modes,  Up: File Status Flags

13.15.2 Open-time Flags
-----------------------

The open-time flags specify options affecting how ‘open’ will behave.
These options are not preserved once the file is open.  The exception to
this is ‘O_NONBLOCK’, which is also an I/O operating mode and so it _is_
saved.  *Note Opening and Closing Files::, for how to call ‘open’.

   There are two sorts of options specified by open-time flags.

   • “File name translation flags” affect how ‘open’ looks up the file
     name to locate the file, and whether the file can be created.

   • “Open-time action flags” specify extra operations that ‘open’ will
     perform on the file once it is open.

   Here are the file name translation flags.

 -- Macro: int O_CREAT

     If set, the file will be created if it doesn't already exist.

 -- Macro: int O_EXCL

     If both ‘O_CREAT’ and ‘O_EXCL’ are set, then ‘open’ fails if the
     specified file already exists.  This is guaranteed to never clobber
     an existing file.

     The ‘O_EXCL’ flag has a special meaning in combination with
     ‘O_TMPFILE’; see below.

 -- Macro: int O_DIRECTORY

     If set, the open operation fails if the given name is not the name
     of a directory.  The ‘errno’ variable is set to ‘ENOTDIR’ for this
     error condition.

 -- Macro: int O_NOFOLLOW

     If set, the open operation fails if the final component of the file
     name refers to a symbolic link.  The ‘errno’ variable is set to
     ‘ELOOP’ for this error condition.

 -- Macro: int O_TMPFILE

     If this flag is specified, functions in the ‘open’ family create an
     unnamed temporary file.  In this case, the pathname argument to the
     ‘open’ family of functions (*note Opening and Closing Files::) is
     interpreted as the directory in which the temporary file is created
     (thus determining the file system which provides the storage for
     the file).  The ‘O_TMPFILE’ flag must be combined with ‘O_WRONLY’
     or ‘O_RDWR’, and the MODE argument is required.

     The temporary file can later be given a name using ‘linkat’,
     turning it into a regular file.  This allows the atomic creation of
     a file with the specific file attributes (mode and extended
     attributes) and file contents.  If, for security reasons, it is not
     desirable that a name can be given to the file, the ‘O_EXCL’ flag
     can be specified along with ‘O_TMPFILE’.

     Not all kernels support this open flag.  If this flag is
     unsupported, an attempt to create an unnamed temporary file fails
     with an error of ‘EINVAL’.  If the underlying file system does not
     support the ‘O_TMPFILE’ flag, an ‘EOPNOTSUPP’ error is the result.

     The ‘O_TMPFILE’ flag is a GNU extension.

 -- Macro: int O_NONBLOCK

     This prevents ‘open’ from blocking for a "long time" to open the
     file.  This is only meaningful for some kinds of files, usually
     devices such as serial ports; when it is not meaningful, it is
     harmless and ignored.  Often, opening a port to a modem blocks
     until the modem reports carrier detection; if ‘O_NONBLOCK’ is
     specified, ‘open’ will return immediately without a carrier.

     Note that the ‘O_NONBLOCK’ flag is overloaded as both an I/O
     operating mode and a file name translation flag.  This means that
     specifying ‘O_NONBLOCK’ in ‘open’ also sets nonblocking I/O mode;
     *note Operating Modes::.  To open the file without blocking but do
     normal I/O that blocks, you must call ‘open’ with ‘O_NONBLOCK’ set
     and then call ‘fcntl’ to turn the bit off.

 -- Macro: int O_NOCTTY

     If the named file is a terminal device, don't make it the
     controlling terminal for the process.  *Note Job Control::, for
     information about what it means to be the controlling terminal.

     On GNU/Hurd systems and 4.4 BSD, opening a file never makes it the
     controlling terminal and ‘O_NOCTTY’ is zero.  However, GNU/Linux
     systems and some other systems use a nonzero value for ‘O_NOCTTY’
     and set the controlling terminal when you open a file that is a
     terminal device; so to be portable, use ‘O_NOCTTY’ when it is
     important to avoid this.

   The following three file name translation flags exist only on
GNU/Hurd systems.

 -- Macro: int O_IGNORE_CTTY

     Do not recognize the named file as the controlling terminal, even
     if it refers to the process's existing controlling terminal device.
     Operations on the new file descriptor will never induce job control
     signals.  *Note Job Control::.

 -- Macro: int O_NOLINK

     If the named file is a symbolic link, open the link itself instead
     of the file it refers to.  (‘fstat’ on the new file descriptor will
     return the information returned by ‘lstat’ on the link's name.)

 -- Macro: int O_NOTRANS

     If the named file is specially translated, do not invoke the
     translator.  Open the bare file the translator itself sees.

   The open-time action flags tell ‘open’ to do additional operations
which are not really related to opening the file.  The reason to do them
as part of ‘open’ instead of in separate calls is that ‘open’ can do
them atomically.

 -- Macro: int O_TRUNC

     Truncate the file to zero length.  This option is only useful for
     regular files, not special files such as directories or FIFOs.
     POSIX.1 requires that you open the file for writing to use
     ‘O_TRUNC’.  In BSD and GNU you must have permission to write the
     file to truncate it, but you need not open for write access.

     This is the only open-time action flag specified by POSIX.1.  There
     is no good reason for truncation to be done by ‘open’, instead of
     by calling ‘ftruncate’ afterwards.  The ‘O_TRUNC’ flag existed in
     Unix before ‘ftruncate’ was invented, and is retained for backward
     compatibility.

   The remaining operating modes are BSD extensions.  They exist only on
some systems.  On other systems, these macros are not defined.

 -- Macro: int O_SHLOCK

     Acquire a shared lock on the file, as with ‘flock’.  *Note File
     Locks::.

     If ‘O_CREAT’ is specified, the locking is done atomically when
     creating the file.  You are guaranteed that no other process will
     get the lock on the new file first.

 -- Macro: int O_EXLOCK

     Acquire an exclusive lock on the file, as with ‘flock’.  *Note File
     Locks::.  This is atomic like ‘O_SHLOCK’.


File: libc.info,  Node: Operating Modes,  Next: Getting File Status Flags,  Prev: Open-time Flags,  Up: File Status Flags

13.15.3 I/O Operating Modes
---------------------------

The operating modes affect how input and output operations using a file
descriptor work.  These flags are set by ‘open’ and can be fetched and
changed with ‘fcntl’.

 -- Macro: int O_APPEND

     The bit that enables append mode for the file.  If set, then all
     ‘write’ operations write the data at the end of the file, extending
     it, regardless of the current file position.  This is the only
     reliable way to append to a file.  In append mode, you are
     guaranteed that the data you write will always go to the current
     end of the file, regardless of other processes writing to the file.
     Conversely, if you simply set the file position to the end of file
     and write, then another process can extend the file after you set
     the file position but before you write, resulting in your data
     appearing someplace before the real end of file.

 -- Macro: int O_NONBLOCK

     The bit that enables nonblocking mode for the file.  If this bit is
     set, ‘read’ requests on the file can return immediately with a
     failure status if there is no input immediately available, instead
     of blocking.  Likewise, ‘write’ requests can also return
     immediately with a failure status if the output can't be written
     immediately.

     Note that the ‘O_NONBLOCK’ flag is overloaded as both an I/O
     operating mode and a file name translation flag; *note Open-time
     Flags::.

 -- Macro: int O_NDELAY

     This is an obsolete name for ‘O_NONBLOCK’, provided for
     compatibility with BSD. It is not defined by the POSIX.1 standard.

   The remaining operating modes are BSD and GNU extensions.  They exist
only on some systems.  On other systems, these macros are not defined.

 -- Macro: int O_ASYNC

     The bit that enables asynchronous input mode.  If set, then ‘SIGIO’
     signals will be generated when input is available.  *Note Interrupt
     Input::.

     Asynchronous input mode is a BSD feature.

 -- Macro: int O_FSYNC

     The bit that enables synchronous writing for the file.  If set,
     each ‘write’ call will make sure the data is reliably stored on
     disk before returning.

     Synchronous writing is a BSD feature.

 -- Macro: int O_SYNC

     This is another name for ‘O_FSYNC’.  They have the same value.

 -- Macro: int O_NOATIME

     If this bit is set, ‘read’ will not update the access time of the
     file.  *Note File Times::.  This is used by programs that do
     backups, so that backing a file up does not count as reading it.
     Only the owner of the file or the superuser may use this bit.

     This is a GNU extension.


File: libc.info,  Node: Getting File Status Flags,  Prev: Operating Modes,  Up: File Status Flags

13.15.4 Getting and Setting File Status Flags
---------------------------------------------

The ‘fcntl’ function can fetch or change file status flags.

 -- Macro: int F_GETFL

     This macro is used as the COMMAND argument to ‘fcntl’, to read the
     file status flags for the open file with descriptor FILEDES.

     The normal return value from ‘fcntl’ with this command is a
     nonnegative number which can be interpreted as the bitwise OR of
     the individual flags.  Since the file access modes are not
     single-bit values, you can mask off other bits in the returned
     flags with ‘O_ACCMODE’ to compare them.

     In case of an error, ‘fcntl’ returns -1.  The following ‘errno’
     error conditions are defined for this command:

     ‘EBADF’
          The FILEDES argument is invalid.

 -- Macro: int F_SETFL

     This macro is used as the COMMAND argument to ‘fcntl’, to set the
     file status flags for the open file corresponding to the FILEDES
     argument.  This command requires a third ‘int’ argument to specify
     the new flags, so the call looks like this:

          fcntl (FILEDES, F_SETFL, NEW-FLAGS)

     You can't change the access mode for the file in this way; that is,
     whether the file descriptor was opened for reading or writing.

     The normal return value from ‘fcntl’ with this command is an
     unspecified value other than -1, which indicates an error.  The
     error conditions are the same as for the ‘F_GETFL’ command.

   If you want to modify the file status flags, you should get the
current flags with ‘F_GETFL’ and modify the value.  Don't assume that
the flags listed here are the only ones that are implemented; your
program may be run years from now and more flags may exist then.  For
example, here is a function to set or clear the flag ‘O_NONBLOCK’
without altering any other flags:

     /* Set the ‘O_NONBLOCK’ flag of DESC if VALUE is nonzero,
        or clear the flag if VALUE is 0.
        Return 0 on success, or -1 on error with ‘errno’ set. */

     int
     set_nonblock_flag (int desc, int value)
     {
       int oldflags = fcntl (desc, F_GETFL, 0);
       /* If reading the flags failed, return error indication now. */
       if (oldflags == -1)
         return -1;
       /* Set just the flag we want to set. */
       if (value != 0)
         oldflags |= O_NONBLOCK;
       else
         oldflags &= ~O_NONBLOCK;
       /* Store modified flag word in the descriptor. */
       return fcntl (desc, F_SETFL, oldflags);
     }


File: libc.info,  Node: File Locks,  Next: Open File Description Locks,  Prev: File Status Flags,  Up: Low-Level I/O

13.16 File Locks
================

This section describes record locks that are associated with the
process.  There is also a different type of record lock that is
associated with the open file description instead of the process.  *Note
Open File Description Locks::.

   The remaining ‘fcntl’ commands are used to support “record locking”,
which permits multiple cooperating programs to prevent each other from
simultaneously accessing parts of a file in error-prone ways.

   An “exclusive” or “write” lock gives a process exclusive access for
writing to the specified part of the file.  While a write lock is in
place, no other process can lock that part of the file.

   A “shared” or “read” lock prohibits any other process from requesting
a write lock on the specified part of the file.  However, other
processes can request read locks.

   The ‘read’ and ‘write’ functions do not actually check to see whether
there are any locks in place.  If you want to implement a locking
protocol for a file shared by multiple processes, your application must
do explicit ‘fcntl’ calls to request and clear locks at the appropriate
points.

   Locks are associated with processes.  A process can only have one
kind of lock set for each byte of a given file.  When any file
descriptor for that file is closed by the process, all of the locks that
process holds on that file are released, even if the locks were made
using other descriptors that remain open.  Likewise, locks are released
when a process exits, and are not inherited by child processes created
using ‘fork’ (*note Creating a Process::).

   When making a lock, use a ‘struct flock’ to specify what kind of lock
and where.  This data type and the associated macros for the ‘fcntl’
function are declared in the header file ‘fcntl.h’.

 -- Data Type: struct flock

     This structure is used with the ‘fcntl’ function to describe a file
     lock.  It has these members:

     ‘short int l_type’
          Specifies the type of the lock; one of ‘F_RDLCK’, ‘F_WRLCK’,
          or ‘F_UNLCK’.

     ‘short int l_whence’
          This corresponds to the WHENCE argument to ‘fseek’ or ‘lseek’,
          and specifies what the offset is relative to.  Its value can
          be one of ‘SEEK_SET’, ‘SEEK_CUR’, or ‘SEEK_END’.

     ‘off_t l_start’
          This specifies the offset of the start of the region to which
          the lock applies, and is given in bytes relative to the point
          specified by the ‘l_whence’ member.

     ‘off_t l_len’
          This specifies the length of the region to be locked.  A value
          of ‘0’ is treated specially; it means the region extends to
          the end of the file.

     ‘pid_t l_pid’
          This field is the process ID (*note Process Creation
          Concepts::) of the process holding the lock.  It is filled in
          by calling ‘fcntl’ with the ‘F_GETLK’ command, but is ignored
          when making a lock.  If the conflicting lock is an open file
          description lock (*note Open File Description Locks::), then
          this field will be set to -1.

 -- Macro: int F_GETLK

     This macro is used as the COMMAND argument to ‘fcntl’, to specify
     that it should get information about a lock.  This command requires
     a third argument of type ‘struct flock *’ to be passed to ‘fcntl’,
     so that the form of the call is:

          fcntl (FILEDES, F_GETLK, LOCKP)

     If there is a lock already in place that would block the lock
     described by the LOCKP argument, information about that lock
     overwrites ‘*LOCKP’.  Existing locks are not reported if they are
     compatible with making a new lock as specified.  Thus, you should
     specify a lock type of ‘F_WRLCK’ if you want to find out about both
     read and write locks, or ‘F_RDLCK’ if you want to find out about
     write locks only.

     There might be more than one lock affecting the region specified by
     the LOCKP argument, but ‘fcntl’ only returns information about one
     of them.  The ‘l_whence’ member of the LOCKP structure is set to
     ‘SEEK_SET’ and the ‘l_start’ and ‘l_len’ fields set to identify the
     locked region.

     If no lock applies, the only change to the LOCKP structure is to
     update the ‘l_type’ to a value of ‘F_UNLCK’.

     The normal return value from ‘fcntl’ with this command is an
     unspecified value other than -1, which is reserved to indicate an
     error.  The following ‘errno’ error conditions are defined for this
     command:

     ‘EBADF’
          The FILEDES argument is invalid.

     ‘EINVAL’
          Either the LOCKP argument doesn't specify valid lock
          information, or the file associated with FILEDES doesn't
          support locks.

 -- Macro: int F_SETLK

     This macro is used as the COMMAND argument to ‘fcntl’, to specify
     that it should set or clear a lock.  This command requires a third
     argument of type ‘struct flock *’ to be passed to ‘fcntl’, so that
     the form of the call is:

          fcntl (FILEDES, F_SETLK, LOCKP)

     If the process already has a lock on any part of the region, the
     old lock on that part is replaced with the new lock.  You can
     remove a lock by specifying a lock type of ‘F_UNLCK’.

     If the lock cannot be set, ‘fcntl’ returns immediately with a value
     of -1.  This function does not block while waiting for other
     processes to release locks.  If ‘fcntl’ succeeds, it returns a
     value other than -1.

     The following ‘errno’ error conditions are defined for this
     function:

     ‘EAGAIN’
     ‘EACCES’
          The lock cannot be set because it is blocked by an existing
          lock on the file.  Some systems use ‘EAGAIN’ in this case, and
          other systems use ‘EACCES’; your program should treat them
          alike, after ‘F_SETLK’.  (GNU/Linux and GNU/Hurd systems
          always use ‘EAGAIN’.)

     ‘EBADF’
          Either: the FILEDES argument is invalid; you requested a read
          lock but the FILEDES is not open for read access; or, you
          requested a write lock but the FILEDES is not open for write
          access.

     ‘EINVAL’
          Either the LOCKP argument doesn't specify valid lock
          information, or the file associated with FILEDES doesn't
          support locks.

     ‘ENOLCK’
          The system has run out of file lock resources; there are
          already too many file locks in place.

          Well-designed file systems never report this error, because
          they have no limitation on the number of locks.  However, you
          must still take account of the possibility of this error, as
          it could result from network access to a file system on
          another machine.

 -- Macro: int F_SETLKW

     This macro is used as the COMMAND argument to ‘fcntl’, to specify
     that it should set or clear a lock.  It is just like the ‘F_SETLK’
     command, but causes the process to block (or wait) until the
     request can be specified.

     This command requires a third argument of type ‘struct flock *’, as
     for the ‘F_SETLK’ command.

     The ‘fcntl’ return values and errors are the same as for the
     ‘F_SETLK’ command, but these additional ‘errno’ error conditions
     are defined for this command:

     ‘EINTR’
          The function was interrupted by a signal while it was waiting.
          *Note Interrupted Primitives::.

     ‘EDEADLK’
          The specified region is being locked by another process.  But
          that process is waiting to lock a region which the current
          process has locked, so waiting for the lock would result in
          deadlock.  The system does not guarantee that it will detect
          all such conditions, but it lets you know if it notices one.

   The following macros are defined for use as values for the ‘l_type’
member of the ‘flock’ structure.  The values are integer constants.

‘F_RDLCK’

     This macro is used to specify a read (or shared) lock.

‘F_WRLCK’

     This macro is used to specify a write (or exclusive) lock.

‘F_UNLCK’

     This macro is used to specify that the region is unlocked.

   As an example of a situation where file locking is useful, consider a
program that can be run simultaneously by several different users, that
logs status information to a common file.  One example of such a program
might be a game that uses a file to keep track of high scores.  Another
example might be a program that records usage or accounting information
for billing purposes.

   Having multiple copies of the program simultaneously writing to the
file could cause the contents of the file to become mixed up.  But you
can prevent this kind of problem by setting a write lock on the file
before actually writing to the file.

   If the program also needs to read the file and wants to make sure
that the contents of the file are in a consistent state, then it can
also use a read lock.  While the read lock is set, no other process can
lock that part of the file for writing.

   Remember that file locks are only an _advisory_ protocol for
controlling access to a file.  There is still potential for access to
the file by programs that don't use the lock protocol.


File: libc.info,  Node: Open File Description Locks,  Next: Open File Description Locks Example,  Prev: File Locks,  Up: Low-Level I/O

13.17 Open File Description Locks
=================================

In contrast to process-associated record locks (*note File Locks::),
open file description record locks are associated with an open file
description rather than a process.

   Using ‘fcntl’ to apply an open file description lock on a region that
already has an existing open file description lock that was created via
the same file descriptor will never cause a lock conflict.

   Open file description locks are also inherited by child processes
across ‘fork’, or ‘clone’ with ‘CLONE_FILES’ set (*note Creating a
Process::), along with the file descriptor.

   It is important to distinguish between the open file _description_
(an instance of an open file, usually created by a call to ‘open’) and
an open file _descriptor_, which is a numeric value that refers to the
open file description.  The locks described here are associated with the
open file _description_ and not the open file _descriptor_.

   Using ‘dup’ (*note Duplicating Descriptors::) to copy a file
descriptor does not give you a new open file description, but rather
copies a reference to an existing open file description and assigns it
to a new file descriptor.  Thus, open file description locks set on a
file descriptor cloned by ‘dup’ will never conflict with open file
description locks set on the original descriptor since they refer to the
same open file description.  Depending on the range and type of lock
involved, the original lock may be modified by a ‘F_OFD_SETLK’ or
‘F_OFD_SETLKW’ command in this situation however.

   Open file description locks always conflict with process-associated
locks, even if acquired by the same process or on the same open file
descriptor.

   Open file description locks use the same ‘struct flock’ as
process-associated locks as an argument (*note File Locks::) and the
macros for the ‘command’ values are also declared in the header file
‘fcntl.h’.  To use them, the macro ‘_GNU_SOURCE’ must be defined prior
to including any header file.

   In contrast to process-associated locks, any ‘struct flock’ used as
an argument to open file description lock commands must have the ‘l_pid’
value set to 0.  Also, when returning information about an open file
description lock in a ‘F_GETLK’ or ‘F_OFD_GETLK’ request, the ‘l_pid’
field in ‘struct flock’ will be set to -1 to indicate that the lock is
not associated with a process.

   When the same ‘struct flock’ is reused as an argument to a
‘F_OFD_SETLK’ or ‘F_OFD_SETLKW’ request after being used for an
‘F_OFD_GETLK’ request, it is necessary to inspect and reset the ‘l_pid’
field to 0.

 -- Macro: int F_OFD_GETLK
     This macro is used as the COMMAND argument to ‘fcntl’, to specify
     that it should get information about a lock.  This command requires
     a third argument of type ‘struct flock *’ to be passed to ‘fcntl’,
     so that the form of the call is:

          fcntl (FILEDES, F_OFD_GETLK, LOCKP)

     If there is a lock already in place that would block the lock
     described by the LOCKP argument, information about that lock is
     written to ‘*LOCKP’.  Existing locks are not reported if they are
     compatible with making a new lock as specified.  Thus, you should
     specify a lock type of ‘F_WRLCK’ if you want to find out about both
     read and write locks, or ‘F_RDLCK’ if you want to find out about
     write locks only.

     There might be more than one lock affecting the region specified by
     the LOCKP argument, but ‘fcntl’ only returns information about one
     of them.  Which lock is returned in this situation is undefined.

     The ‘l_whence’ member of the LOCKP structure are set to ‘SEEK_SET’
     and the ‘l_start’ and ‘l_len’ fields are set to identify the locked
     region.

     If no conflicting lock exists, the only change to the LOCKP
     structure is to update the ‘l_type’ field to the value ‘F_UNLCK’.

     The normal return value from ‘fcntl’ with this command is either 0
     on success or -1, which indicates an error.  The following ‘errno’
     error conditions are defined for this command:

     ‘EBADF’
          The FILEDES argument is invalid.

     ‘EINVAL’
          Either the LOCKP argument doesn't specify valid lock
          information, the operating system kernel doesn't support open
          file description locks, or the file associated with FILEDES
          doesn't support locks.

 -- Macro: int F_OFD_SETLK

     This macro is used as the COMMAND argument to ‘fcntl’, to specify
     that it should set or clear a lock.  This command requires a third
     argument of type ‘struct flock *’ to be passed to ‘fcntl’, so that
     the form of the call is:

          fcntl (FILEDES, F_OFD_SETLK, LOCKP)

     If the open file already has a lock on any part of the region, the
     old lock on that part is replaced with the new lock.  You can
     remove a lock by specifying a lock type of ‘F_UNLCK’.

     If the lock cannot be set, ‘fcntl’ returns immediately with a value
     of -1.  This command does not wait for other tasks to release
     locks.  If ‘fcntl’ succeeds, it returns 0.

     The following ‘errno’ error conditions are defined for this
     command:

     ‘EAGAIN’
          The lock cannot be set because it is blocked by an existing
          lock on the file.

     ‘EBADF’
          Either: the FILEDES argument is invalid; you requested a read
          lock but the FILEDES is not open for read access; or, you
          requested a write lock but the FILEDES is not open for write
          access.

     ‘EINVAL’
          Either the LOCKP argument doesn't specify valid lock
          information, the operating system kernel doesn't support open
          file description locks, or the file associated with FILEDES
          doesn't support locks.

     ‘ENOLCK’
          The system has run out of file lock resources; there are
          already too many file locks in place.

          Well-designed file systems never report this error, because
          they have no limitation on the number of locks.  However, you
          must still take account of the possibility of this error, as
          it could result from network access to a file system on
          another machine.

 -- Macro: int F_OFD_SETLKW

     This macro is used as the COMMAND argument to ‘fcntl’, to specify
     that it should set or clear a lock.  It is just like the
     ‘F_OFD_SETLK’ command, but causes the process to wait until the
     request can be completed.

     This command requires a third argument of type ‘struct flock *’, as
     for the ‘F_OFD_SETLK’ command.

     The ‘fcntl’ return values and errors are the same as for the
     ‘F_OFD_SETLK’ command, but these additional ‘errno’ error
     conditions are defined for this command:

     ‘EINTR’
          The function was interrupted by a signal while it was waiting.
          *Note Interrupted Primitives::.

   Open file description locks are useful in the same sorts of
situations as process-associated locks.  They can also be used to
synchronize file access between threads within the same process by
having each thread perform its own ‘open’ of the file, to obtain its own
open file description.

   Because open file description locks are automatically freed only upon
closing the last file descriptor that refers to the open file
description, this locking mechanism avoids the possibility that locks
are inadvertently released due to a library routine opening and closing
a file without the application being aware.

   As with process-associated locks, open file description locks are
advisory.


File: libc.info,  Node: Open File Description Locks Example,  Next: Interrupt Input,  Prev: Open File Description Locks,  Up: Low-Level I/O

13.18 Open File Description Locks Example
=========================================

Here is an example of using open file description locks in a threaded
program.  If this program used process-associated locks, then it would
be subject to data corruption because process-associated locks are
shared by the threads inside a process, and thus cannot be used by one
thread to lock out another thread in the same process.

   Proper error handling has been omitted in the following program for
brevity.


     #define _GNU_SOURCE
     #include <stdio.h>
     #include <sys/types.h>
     #include <sys/stat.h>
     #include <unistd.h>
     #include <fcntl.h>
     #include <pthread.h>

     #define FILENAME        "/tmp/foo"
     #define NUM_THREADS     3
     #define ITERATIONS      5

     void *
     thread_start (void *arg)
     {
       int i, fd, len;
       long tid = (long) arg;
       char buf[256];
       struct flock lck = {
         .l_whence = SEEK_SET,
         .l_start = 0,
         .l_len = 1,
       };

       fd = open ("/tmp/foo", O_RDWR | O_CREAT, 0666);

       for (i = 0; i < ITERATIONS; i++)
         {
           lck.l_type = F_WRLCK;
           fcntl (fd, F_OFD_SETLKW, &lck);

           len = sprintf (buf, "%d: tid=%ld fd=%d\n", i, tid, fd);

           lseek (fd, 0, SEEK_END);
           write (fd, buf, len);
           fsync (fd);

           lck.l_type = F_UNLCK;
           fcntl (fd, F_OFD_SETLK, &lck);

           /* sleep to ensure lock is yielded to another thread */
           usleep (1);
         }
       pthread_exit (NULL);
     }

     int
     main (int argc, char **argv)
     {
       long i;
       pthread_t threads[NUM_THREADS];

       truncate (FILENAME, 0);

       for (i = 0; i < NUM_THREADS; i++)
         pthread_create (&threads[i], NULL, thread_start, (void *) i);

       pthread_exit (NULL);
       return 0;
     }

   This example creates three threads each of which loops five times,
appending to the file.  Access to the file is serialized via open file
description locks.  If we compile and run the above program, we'll end
up with /tmp/foo that has 15 lines in it.

   If we, however, were to replace the ‘F_OFD_SETLK’ and ‘F_OFD_SETLKW’
commands with their process-associated lock equivalents, the locking
essentially becomes a noop since it is all done within the context of
the same process.  That leads to data corruption (typically manifested
as missing lines) as some threads race in and overwrite the data written
by others.


File: libc.info,  Node: Interrupt Input,  Next: IOCTLs,  Prev: Open File Description Locks Example,  Up: Low-Level I/O

13.19 Interrupt-Driven Input
============================

If you set the ‘O_ASYNC’ status flag on a file descriptor (*note File
Status Flags::), a ‘SIGIO’ signal is sent whenever input or output
becomes possible on that file descriptor.  The process or process group
to receive the signal can be selected by using the ‘F_SETOWN’ command to
the ‘fcntl’ function.  If the file descriptor is a socket, this also
selects the recipient of ‘SIGURG’ signals that are delivered when
out-of-band data arrives on that socket; see *note Out-of-Band Data::.
(‘SIGURG’ is sent in any situation where ‘select’ would report the
socket as having an "exceptional condition".  *Note Waiting for I/O::.)

   If the file descriptor corresponds to a terminal device, then ‘SIGIO’
signals are sent to the foreground process group of the terminal.  *Note
Job Control::.

   The symbols in this section are defined in the header file ‘fcntl.h’.

 -- Macro: int F_GETOWN

     This macro is used as the COMMAND argument to ‘fcntl’, to specify
     that it should get information about the process or process group
     to which ‘SIGIO’ signals are sent.  (For a terminal, this is
     actually the foreground process group ID, which you can get using
     ‘tcgetpgrp’; see *note Terminal Access Functions::.)

     The return value is interpreted as a process ID; if negative, its
     absolute value is the process group ID.

     The following ‘errno’ error condition is defined for this command:

     ‘EBADF’
          The FILEDES argument is invalid.

 -- Macro: int F_SETOWN

     This macro is used as the COMMAND argument to ‘fcntl’, to specify
     that it should set the process or process group to which ‘SIGIO’
     signals are sent.  This command requires a third argument of type
     ‘pid_t’ to be passed to ‘fcntl’, so that the form of the call is:

          fcntl (FILEDES, F_SETOWN, PID)

     The PID argument should be a process ID. You can also pass a
     negative number whose absolute value is a process group ID.

     The return value from ‘fcntl’ with this command is -1 in case of
     error and some other value if successful.  The following ‘errno’
     error conditions are defined for this command:

     ‘EBADF’
          The FILEDES argument is invalid.

     ‘ESRCH’
          There is no process or process group corresponding to PID.


File: libc.info,  Node: IOCTLs,  Next: Other Low-Level I/O APIs,  Prev: Interrupt Input,  Up: Low-Level I/O

13.20 Generic I/O Control operations
====================================

GNU systems can handle most input/output operations on many different
devices and objects in terms of a few file primitives - ‘read’, ‘write’
and ‘lseek’.  However, most devices also have a few peculiar operations
which do not fit into this model.  Such as:

   • Changing the character font used on a terminal.

   • Telling a magnetic tape system to rewind or fast forward.  (Since
     they cannot move in byte increments, ‘lseek’ is inapplicable).

   • Ejecting a disk from a drive.

   • Playing an audio track from a CD-ROM drive.

   • Maintaining routing tables for a network.

   Although some such objects such as sockets and terminals (1) have
special functions of their own, it would not be practical to create
functions for all these cases.

   Instead these minor operations, known as “IOCTL”s, are assigned code
numbers and multiplexed through the ‘ioctl’ function, defined in
‘sys/ioctl.h’.  The code numbers themselves are defined in many
different headers.

 -- Function: int ioctl (int FILEDES, int COMMAND, ...)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘ioctl’ function performs the generic I/O operation COMMAND on
     FILEDES.

     A third argument is usually present, either a single number or a
     pointer to a structure.  The meaning of this argument, the returned
     value, and any error codes depends upon the command used.  Often -1
     is returned for a failure.

   On some systems, IOCTLs used by different devices share the same
numbers.  Thus, although use of an inappropriate IOCTL _usually_ only
produces an error, you should not attempt to use device-specific IOCTLs
on an unknown device.

   Most IOCTLs are OS-specific and/or only used in special system
utilities, and are thus beyond the scope of this document.  For an
example of the use of an IOCTL, see *note Out-of-Band Data::.

   ---------- Footnotes ----------

   (1) Actually, the terminal-specific functions are implemented with
IOCTLs on many platforms.


File: libc.info,  Node: Other Low-Level I/O APIs,  Prev: IOCTLs,  Up: Low-Level I/O

13.21 Other low-level-I/O-related functions
===========================================

 -- Data Type: struct pollfd

 -- Data Type: struct epoll_event

 -- Function: int poll (struct pollfd *FDS, nfds_t NFDS, int TIMEOUT)

     This documentation is a stub.  For additional information on this
     function, consult the manual page poll(2) (Latest, online:
     <https://man7.org/linux/man-pages/man2/poll.2.html>) *Note Linux
     Kernel::.

 -- Function: int epoll_create (int SIZE)

     This documentation is a stub.  For additional information on this
     function, consult the manual page epoll_create(2) (Latest, online:
     <https://man7.org/linux/man-pages/man2/epoll_create.2.html>) *Note
     Linux Kernel::.

 -- Function: int epoll_wait (int EPFD, struct epoll_event *EVENTS, int
          MAXEVENTS, int TIMEOUT)

     This documentation is a stub.  For additional information on this
     function, consult the manual page epoll_wait(2) (Latest, online:
     <https://man7.org/linux/man-pages/man2/epoll_wait.2.html>) *Note
     Linux Kernel::.


File: libc.info,  Node: File System Interface,  Next: Pipes and FIFOs,  Prev: Low-Level I/O,  Up: Top

14 File System Interface
************************

This chapter describes the GNU C Library's functions for manipulating
files.  Unlike the input and output functions (*note I/O on Streams::;
*note Low-Level I/O::), these functions are concerned with operating on
the files themselves rather than on their contents.

   Among the facilities described in this chapter are functions for
examining or modifying directories, functions for renaming and deleting
files, and functions for examining and setting file attributes such as
access permissions and modification times.

* Menu:

* Working Directory::           This is used to resolve relative
				 file names.
* Descriptor-Relative Access::  Ways to control file name lookup.
* Accessing Directories::       Finding out what files a directory
				 contains.
* Working with Directory Trees:: Apply actions to all files or a selectable
                                 subset of a directory hierarchy.
* Hard Links::                  Adding alternate names to a file.
* Symbolic Links::              A file that "points to" a file name.
* Deleting Files::              How to delete a file, and what that means.
* Renaming Files::              Changing a file's name.
* Creating Directories::        A system call just for creating a directory.
* File Attributes::             Attributes of individual files.
* Making Special Files::        How to create special files.
* Temporary Files::             Naming and creating temporary files.


File: libc.info,  Node: Working Directory,  Next: Descriptor-Relative Access,  Up: File System Interface

14.1 Working Directory
======================

Each process has associated with it a directory, called its “current
working directory” or simply “working directory”, that is used in the
resolution of relative file names (*note File Name Resolution::).

   When you log in and begin a new session, your working directory is
initially set to the home directory associated with your login account
in the system user database.  You can find any user's home directory
using the ‘getpwuid’ or ‘getpwnam’ functions; see *note User Database::.

   Users can change the working directory using shell commands like
‘cd’.  The functions described in this section are the primitives used
by those commands and by other programs for examining and changing the
working directory.

   Prototypes for these functions are declared in the header file
‘unistd.h’.

 -- Function: char * getcwd (char *BUFFER, size_t SIZE)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note
     POSIX Safety Concepts::.

     The ‘getcwd’ function returns an absolute file name representing
     the current working directory, storing it in the character array
     BUFFER that you provide.  The SIZE argument is how you tell the
     system the allocation size of BUFFER.

     The GNU C Library version of this function also permits you to
     specify a null pointer for the BUFFER argument.  Then ‘getcwd’
     allocates a buffer automatically, as with ‘malloc’ (*note
     Unconstrained Allocation::).  If the SIZE is greater than zero,
     then the buffer is that large; otherwise, the buffer is as large as
     necessary to hold the result.

     The return value is BUFFER on success and a null pointer on
     failure.  The following ‘errno’ error conditions are defined for
     this function:

     ‘EINVAL’
          The SIZE argument is zero and BUFFER is not a null pointer.

     ‘ERANGE’
          The SIZE argument is less than the length of the working
          directory name.  You need to allocate a bigger array and try
          again.

     ‘EACCES’
          Permission to read or search a component of the file name was
          denied.

   You could implement the behavior of GNU's ‘getcwd (NULL, 0)’ using
only the standard behavior of ‘getcwd’:

     char *
     gnu_getcwd ()
     {
       size_t size = 100;

       while (1)
         {
           char *buffer = (char *) xmalloc (size);
           if (getcwd (buffer, size) == buffer)
             return buffer;
           free (buffer);
           if (errno != ERANGE)
             return 0;
           size *= 2;
         }
     }

*Note Malloc Examples::, for information about ‘xmalloc’, which is not a
library function but is a customary name used in most GNU software.

 -- Deprecated Function: char * getwd (char *BUFFER)

     Preliminary: | MT-Safe | AS-Unsafe heap i18n | AC-Unsafe mem fd |
     *Note POSIX Safety Concepts::.

     This is similar to ‘getcwd’, but has no way to specify the size of
     the buffer.  The GNU C Library provides ‘getwd’ only for backwards
     compatibility with BSD.

     The BUFFER argument should be a pointer to an array at least
     ‘PATH_MAX’ bytes long (*note Limits for Files::).  On GNU/Hurd
     systems there is no limit to the size of a file name, so this is
     not necessarily enough space to contain the directory name.  That
     is why this function is deprecated.

 -- Function: char * get_current_dir_name (void)

     Preliminary: | MT-Safe env | AS-Unsafe heap | AC-Unsafe mem fd |
     *Note POSIX Safety Concepts::.

     The ‘get_current_dir_name’ function is basically equivalent to
     ‘getcwd (NULL, 0)’, except the value of the ‘PWD’ environment
     variable is first examined, and if it does in fact correspond to
     the current directory, that value is returned.  This is a subtle
     difference which is visible if the path described by the value in
     ‘PWD’ is using one or more symbolic links, in which case the value
     returned by ‘getcwd’ would resolve the symbolic links and therefore
     yield a different result.

     This function is a GNU extension.

 -- Function: int chdir (const char *FILENAME)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is used to set the process's working directory to
     FILENAME.

     The normal, successful return value from ‘chdir’ is ‘0’.  A value
     of ‘-1’ is returned to indicate an error.  The ‘errno’ error
     conditions defined for this function are the usual file name syntax
     errors (*note File Name Errors::), plus ‘ENOTDIR’ if the file
     FILENAME is not a directory.

 -- Function: int fchdir (int FILEDES)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is used to set the process's working directory to
     directory associated with the file descriptor FILEDES.

     The normal, successful return value from ‘fchdir’ is ‘0’.  A value
     of ‘-1’ is returned to indicate an error.  The following ‘errno’
     error conditions are defined for this function:

     ‘EACCES’
          Read permission is denied for the directory named by
          ‘dirname’.

     ‘EBADF’
          The FILEDES argument is not a valid file descriptor.

     ‘ENOTDIR’
          The file descriptor FILEDES is not associated with a
          directory.

     ‘EINTR’
          The function call was interrupt by a signal.

     ‘EIO’
          An I/O error occurred.


File: libc.info,  Node: Descriptor-Relative Access,  Next: Accessing Directories,  Prev: Working Directory,  Up: File System Interface

14.2 Descriptor-Relative Access
===============================

Many functions that accept file names have ‘...at’ variants which accept
a file descriptor and a file name argument instead of just a file name
argument.  For example, ‘fstatat’ is the descriptor-based variant of the
‘fstat’ function.  Most such functions also accept an additional flags
argument which changes the behavior of the file name lookup based on the
passed ‘AT_...’ flags.

   There are several reasons to use descriptor-relative access:

   • The working directory is a process-wide resource, so individual
     threads cannot change it without affecting other threads in the
     process.  Explicitly specifying the directory against which
     relative paths are resolved can be a thread-safe alternative to
     changing the working directory.

   • If a program wishes to access a directory tree which is being
     modified concurrently, perhaps even by a different user on the
     system, the program must avoid looking up file names with multiple
     components, in order to detect symbolic links, using the
     ‘O_NOFOLLOW’ flag (*note Open-time Flags::) or the
     ‘AT_SYMLINK_FOLLOW’ flag (described below).  Without
     directory-relative access, it is necessary to use the ‘fchdir’
     function to change the working directory (*note Working
     Directory::), which is not thread-safe.

   • Listing directory contents using the ‘readdir’ or ‘readdir64’
     functions (*note Reading/Closing Directory::) does not provide full
     file name paths.  Using ‘...at’ functions, it is possible to use
     the file names directly, without having to construct such full
     paths.

   • Additional flags available with some of the ‘...at’ functions
     provide access to functionality which is not available otherwise.

   The file descriptor used by these ‘...at’ functions has the following
uses:

   • It can be a file descriptor referring to a directory.  Such a
     descriptor can be created explicitly using the ‘open’ function and
     the ‘O_RDONLY’ file access mode, with or without the ‘O_DIRECTORY’
     flag.  *Note Opening and Closing Files::.  Or it can be created
     implicitly by ‘opendir’ and retrieved using the ‘dirfd’ function.
     *Note Opening a Directory::.

     If a directory descriptor is used with one of the ‘...at’
     functions, a relative file name argument is resolved relative to
     directory referred to by the file descriptor, just as if that
     directory were the current working directory.  Absolute file name
     arguments (starting with ‘/’) are resolved against the file system
     root, and the descriptor argument is effectively ignored.

     This means that file name lookup is not constrained to the
     directory of the descriptor.  For example, it is possible to access
     a file ‘example’ in the descriptor's parent directory using a file
     name argument ‘"../example"’, or in the root directory using
     ‘"/example"’.

     If the file descriptor refers to a directory, the empty string ‘""’
     is not a valid file name argument.  It is possible to use ‘"."’ to
     refer to the directory itself.  Also see ‘AT_EMPTY_PATH’ below.

   • The special value ‘AT_FDCWD’.  This means that the current working
     directory is used for the lookup if the file name is a relative.
     For ‘...at’ functions with an ‘AT_...’ flags argument, this
     provides a shortcut to use those flags with regular (not
     descriptor-based) file name lookups.

     If ‘AT_FDCWD’ is used, the empty string ‘""’ is not a valid file
     name argument.

   • An arbitrary file descriptor, along with an empty string ‘""’ as
     the file name argument, and the ‘AT_EMPTY_PATH’ flag.  In this
     case, the operation uses the file descriptor directly, without
     further file name resolution.  On Linux, this allows operations on
     descriptors opened with the ‘O_PATH’ flag.  For regular descriptors
     (opened without ‘O_PATH’), the same functionality is also available
     through the plain descriptor-based functions (for example, ‘fstat’
     instead of ‘fstatat’).

     This is a GNU extension.

   The flags argument in ‘...at’ functions can be a combination of the
following flags, defined in ‘fcntl.h’.  Not all such functions support
all flags, and some (such as ‘openat’) do not accept a flags argument at
all.  Although the flags specific to each function have distinct values
from each other, some flags (relevant to different functions) might
share the same value and therefore are not guaranteed to have unique
values.

   A non-exhaustive list of common flags and their descriptions follows.
Flags specific to a function are described alongside the function
itself.  In these flag descriptions, the “effective final path
component” refers to the final component (basename) of the full path
constructed from the descriptor and file name arguments, using file name
lookup, as described above.

‘AT_EMPTY_PATH’
     This flag is used with an empty file name ‘""’ and a descriptor
     which does not necessarily refer to a directory.  It is most useful
     with ‘O_PATH’ descriptors, as described above.  This flag is a GNU
     extension.

‘AT_NO_AUTOMOUNT’
     If the effective final path component refers to a potential file
     system mount point controlled by an auto-mounting service, the
     operation does not trigger auto-mounting and refers to the
     unmounted mount point instead.  *Note Mount-Unmount-Remount::.  If
     a file system has already been mounted at the effective final path
     component, the operation applies to the file or directory in the
     mounted file system, not the underlying file system that was
     mounted over.  This flag is a GNU extension.

‘AT_SYMLINK_FOLLOW’
     If the effective final path component is a symbolic link, the
     operation follows the symbolic link and operates on its target.
     (For most functions, this is the default behavior.)

‘AT_SYMLINK_NOFOLLOW’
     If the effective final path component is a symbolic link, the
     operation operates on the symbolic link, without following it.  The
     difference in behavior enabled by this flag is similar to the
     difference between the ‘lstat’ and ‘stat’ functions, or the
     behavior activated by the ‘O_NOFOLLOW’ argument to the ‘open’
     function.  Even with the ‘AT_SYMLINK_NOFOLLOW’ flag present,
     symbolic links in a non-final component of the file name are still
     followed.

   *Note:* There is no relationship between these flags and the type
argument to the ‘getauxval’ function (with ‘AT_...’ constants defined in
‘elf.h’).  *Note Auxiliary Vector::.

   The ‘...at’ functions have some common error conditions due to the
nature of descriptor-relative access.  A list of common errors and their
descriptions follows.  Errors specific to a function are described
alongside the function itself.

‘EBADF’
     The file name argument is a relative path but the descriptor
     argument is neither ‘AT_FDCWD’ nor a valid file descriptor.

‘EINVAL’
     If the function accepts a FLAGS argument, the flag combination
     passed is not valid for the function.

‘ENOTDIR’
     The file name argument is a relative file name but the descriptor
     argument is associated with a file that is not a directory.


File: libc.info,  Node: Accessing Directories,  Next: Working with Directory Trees,  Prev: Descriptor-Relative Access,  Up: File System Interface

14.3 Accessing Directories
==========================

The facilities described in this section let you read the contents of a
directory file.  This is useful if you want your program to list all the
files in a directory, perhaps as part of a menu.

   The ‘opendir’ function opens a “directory stream” whose elements are
directory entries.  Alternatively ‘fdopendir’ can be used which can have
advantages if the program needs to have more control over the way the
directory is opened for reading.  This allows, for instance, to pass the
‘O_NOATIME’ flag to ‘open’.

   You use the ‘readdir’ function on the directory stream to retrieve
these entries, represented as ‘struct dirent’ objects.  The name of the
file for each entry is stored in the ‘d_name’ member of this structure.
There are obvious parallels here to the stream facilities for ordinary
files, described in *note I/O on Streams::.

* Menu:

* Directory Entries::           Format of one directory entry.
* Opening a Directory::         How to open a directory stream.
* Reading/Closing Directory::   How to read directory entries from the stream.
* Simple Directory Lister::     A very simple directory listing program.
* Random Access Directory::     Rereading part of the directory
                                 already read with the same stream.
* Scanning Directory Content::  Get entries for user selected subset of
                                 contents in given directory.
* Simple Directory Lister Mark II::  Revised version of the program.
* Low-level Directory Access::  AS-Safe functions for directory access.


File: libc.info,  Node: Directory Entries,  Next: Opening a Directory,  Up: Accessing Directories

14.3.1 Format of a Directory Entry
----------------------------------

This section describes what you find in a single directory entry, as you
might obtain it from a directory stream.  All the symbols are declared
in the header file ‘dirent.h’.

 -- Data Type: struct dirent

     This is a structure type used to return information about directory
     entries.  It contains the following fields:

     ‘char d_name[]’
          This is the null-terminated file name component.  This is the
          only field you can count on in all POSIX systems.

          While this field is defined with a specified length, functions
          such as ‘readdir’ may return a pointer to a ‘struct dirent’
          where the ‘d_name’ extends beyond the end of the struct.

     ‘ino_t d_fileno’
          This is the file serial number.  For BSD compatibility, you
          can also refer to this member as ‘d_ino’.  On GNU/Linux and
          GNU/Hurd systems and most POSIX systems, for most files this
          the same as the ‘st_ino’ member that ‘stat’ will return for
          the file.  *Note File Attributes::.

     ‘off_t d_off’
          This value contains the offset of the next directory entry
          (after this entry) in the directory stream.  The value may not
          be compatible with ‘lseek’ or ‘seekdir’, especially if the
          width of ‘d_off’ is less than 64 bits.  Directory entries are
          not ordered by offset, and the ‘d_off’ and ‘d_reclen’ values
          are unrelated.  Seeking on directory streams is not
          recommended.  The symbol ‘_DIRENT_HAVE_D_OFF’ is defined if
          the ‘d_ino’ member is available.

     ‘unsigned char d_namlen’
          This is the length of the file name, not including the
          terminating null character.  Its type is ‘unsigned char’
          because that is the integer type of the appropriate size.
          This member is a BSD extension.  The symbol
          ‘_DIRENT_HAVE_D_NAMLEN’ is defined if this member is
          available.  (It is not available on Linux.)

     ‘unsigned short int d_reclen’
          This is the length of the entire directory record.  When
          iterating through a buffer filled by ‘getdents64’ (*note
          Low-level Directory Access::), this value needs to be added to
          the offset of the current directory entry to obtain the offset
          of the next entry.  When using ‘readdir’ and related
          functions, the value of ‘d_reclen’ is undefined and should not
          be accessed.  The symbol ‘_DIRENT_HAVE_D_RECLEN’ is defined if
          this member is available.

     ‘unsigned char d_type’
          This is the type of the file, possibly unknown.  The following
          constants are defined for its value:

          ‘DT_UNKNOWN’
               The type is unknown.  Only some filesystems have full
               support to return the type of the file, others might
               always return this value.

          ‘DT_REG’
               A regular file.

          ‘DT_DIR’
               A directory.

          ‘DT_FIFO’
               A named pipe, or FIFO. *Note FIFO Special Files::.

          ‘DT_SOCK’
               A local-domain socket.

          ‘DT_CHR’
               A character device.

          ‘DT_BLK’
               A block device.

          ‘DT_LNK’
               A symbolic link.

          This member is a BSD extension.  The symbol
          ‘_DIRENT_HAVE_D_TYPE’ is defined if this member is available.
          On systems where it is used, it corresponds to the file type
          bits in the ‘st_mode’ member of ‘struct stat’.  If the value
          cannot be determined the member value is ‘DT_UNKNOWN’.  These
          two macros convert between ‘d_type’ values and ‘st_mode’
          values:

           -- Function: int IFTODT (mode_t MODE)

               Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX
               Safety Concepts::.

               This returns the ‘d_type’ value corresponding to MODE.

           -- Function: mode_t DTTOIF (int DTYPE)

               Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX
               Safety Concepts::.

               This returns the ‘st_mode’ value corresponding to DTYPE.

     This structure may contain additional members in the future.  Their
     availability is always announced in the compilation environment by
     a macro named ‘_DIRENT_HAVE_D_XXX’ where XXX is replaced by the
     name of the new member.  For instance, the member ‘d_reclen’
     available on some systems is announced through the macro
     ‘_DIRENT_HAVE_D_RECLEN’.

     When a file has multiple names, each name has its own directory
     entry.  The only way you can tell that the directory entries belong
     to a single file is that they have the same value for the
     ‘d_fileno’ field.

     File attributes such as size, modification times etc., are part of
     the file itself, not of any particular directory entry.  *Note File
     Attributes::.


File: libc.info,  Node: Opening a Directory,  Next: Reading/Closing Directory,  Prev: Directory Entries,  Up: Accessing Directories

14.3.2 Opening a Directory Stream
---------------------------------

This section describes how to open a directory stream.  All the symbols
are declared in the header file ‘dirent.h’.

 -- Data Type: DIR

     The ‘DIR’ data type represents a directory stream.

   You shouldn't ever allocate objects of the ‘struct dirent’ or ‘DIR’
data types, since the directory access functions do that for you.
Instead, you refer to these objects using the pointers returned by the
following functions.

   Directory streams are a high-level interface.  On Linux, alternative
interfaces for accessing directories using file descriptors are
available.  *Note Low-level Directory Access::.

 -- Function: DIR * opendir (const char *DIRNAME)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note
     POSIX Safety Concepts::.

     The ‘opendir’ function opens and returns a directory stream for
     reading the directory whose file name is DIRNAME.  The stream has
     type ‘DIR *’.

     If unsuccessful, ‘opendir’ returns a null pointer.  In addition to
     the usual file name errors (*note File Name Errors::), the
     following ‘errno’ error conditions are defined for this function:

     ‘EACCES’
          Read permission is denied for the directory named by
          ‘dirname’.

     ‘EMFILE’
          The process has too many files open.

     ‘ENFILE’
          The entire system, or perhaps the file system which contains
          the directory, cannot support any additional open files at the
          moment.  (This problem cannot happen on GNU/Hurd systems.)

     ‘ENOMEM’
          Not enough memory available.

     The ‘DIR’ type is typically implemented using a file descriptor,
     and the ‘opendir’ function in terms of the ‘open’ function.  *Note
     Low-Level I/O::.  Directory streams and the underlying file
     descriptors are closed on ‘exec’ (*note Executing a File::).

   The directory which is opened for reading by ‘opendir’ is identified
by the name.  In some situations this is not sufficient.  Or the way
‘opendir’ implicitly creates a file descriptor for the directory is not
the way a program might want it.  In these cases an alternative
interface can be used.

 -- Function: DIR * fdopendir (int FD)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note
     POSIX Safety Concepts::.

     The ‘fdopendir’ function works just like ‘opendir’ but instead of
     taking a file name and opening a file descriptor for the directory
     the caller is required to provide a file descriptor.  This file
     descriptor is then used in subsequent uses of the returned
     directory stream object.

     The caller must make sure the file descriptor is associated with a
     directory and it allows reading.

     If the ‘fdopendir’ call returns successfully the file descriptor is
     now under the control of the system.  It can be used in the same
     way the descriptor implicitly created by ‘opendir’ can be used but
     the program must not close the descriptor.

     In case the function is unsuccessful it returns a null pointer and
     the file descriptor remains to be usable by the program.  The
     following ‘errno’ error conditions are defined for this function:

     ‘EBADF’
          The file descriptor is not valid.

     ‘ENOTDIR’
          The file descriptor is not associated with a directory.

     ‘EINVAL’
          The descriptor does not allow reading the directory content.

     ‘ENOMEM’
          Not enough memory available.

   In some situations it can be desirable to get hold of the file
descriptor which is created by the ‘opendir’ call.  For instance, to
switch the current working directory to the directory just read the
‘fchdir’ function could be used.  Historically the ‘DIR’ type was
exposed and programs could access the fields.  This does not happen in
the GNU C Library.  Instead a separate function is provided to allow
access.

 -- Function: int dirfd (DIR *DIRSTREAM)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The function ‘dirfd’ returns the file descriptor associated with
     the directory stream DIRSTREAM.  This descriptor can be used until
     the directory is closed with ‘closedir’.  If the directory stream
     implementation is not using file descriptors the return value is
     ‘-1’.


File: libc.info,  Node: Reading/Closing Directory,  Next: Simple Directory Lister,  Prev: Opening a Directory,  Up: Accessing Directories

14.3.3 Reading and Closing a Directory Stream
---------------------------------------------

This section describes how to read directory entries from a directory
stream, and how to close the stream when you are done with it.  All the
symbols are declared in the header file ‘dirent.h’.

 -- Function: struct dirent * readdir (DIR *DIRSTREAM)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     This function reads the next entry from the directory.  It normally
     returns a pointer to a structure containing information about the
     file.  This structure is associated with the DIRSTREAM handle and
     can be rewritten by a subsequent call.

     *Portability Note:* On some systems ‘readdir’ may not return
     entries for ‘.’ and ‘..’, even though these are always valid file
     names in any directory.  *Note File Name Resolution::.

     If a directory is modified between a call to ‘readdir’ and after
     the directory stream was created or ‘rewinddir’ was last called on
     it, it is unspecified according to POSIX whether newly created or
     removed entries appear among the entries returned by repeated
     ‘readdir’ calls before the end of the directory is reached.
     However, due to practical implementation constraints, it is
     possible that entries (including unrelated, unmodified entries)
     appear multiple times or do not appear at all if the directory is
     modified while listing it.  If the application intends to create
     files in the directory, it may be necessary to complete the
     iteration first and create a copy of the information obtained
     before creating any new files.  (See below for instructions
     regarding copying of ‘d_name’.)  The iteration can be restarted
     using ‘rewinddir’.  *Note Random Access Directory::.

     If there are no more entries in the directory or an error is
     detected, ‘readdir’ returns a null pointer.  The following ‘errno’
     error conditions are defined for this function:

     ‘EBADF’
          The DIRSTREAM argument is not valid.

     To distinguish between an end-of-directory condition or an error,
     you must set ‘errno’ to zero before calling ‘readdir’.  To avoid
     entering an infinite loop, you should stop reading from the
     directory after the first error.

     *Caution:* The pointer returned by ‘readdir’ points to a buffer
     within the ‘DIR’ object.  The data in that buffer will be
     overwritten by the next call to ‘readdir’.  You must take care, for
     instance, to copy the ‘d_name’ string if you need it later.

     Because of this, it is not safe to share a ‘DIR’ object among
     multiple threads, unless you use your own locking to ensure that no
     thread calls ‘readdir’ while another thread is still using the data
     from the previous call.  In the GNU C Library, it is safe to call
     ‘readdir’ from multiple threads as long as each thread uses its own
     ‘DIR’ object.  POSIX.1-2008 does not require this to be safe, but
     we are not aware of any operating systems where it does not work.

     ‘readdir_r’ allows you to provide your own buffer for the ‘struct
     dirent’, but it is less portable than ‘readdir’, and has problems
     with very long filenames (see below).  We recommend you use
     ‘readdir’, but do not share ‘DIR’ objects.

 -- Function: int readdir_r (DIR *DIRSTREAM, struct dirent *ENTRY,
          struct dirent **RESULT)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     This function is a version of ‘readdir’ which performs internal
     locking.  Like ‘readdir’ it returns the next entry from the
     directory.  To prevent conflicts between simultaneously running
     threads the result is stored inside the ENTRY object.

     *Portability Note:* ‘readdir_r’ is deprecated.  It is recommended
     to use ‘readdir’ instead of ‘readdir_r’ for the following reasons:

        • On systems which do not define ‘NAME_MAX’, it may not be
          possible to use ‘readdir_r’ safely because the caller does not
          specify the length of the buffer for the directory entry.

        • On some systems, ‘readdir_r’ cannot read directory entries
          with very long names.  If such a name is encountered, the GNU
          C Library implementation of ‘readdir_r’ returns with an error
          code of ‘ENAMETOOLONG’ after the final directory entry has
          been read.  On other systems, ‘readdir_r’ may return
          successfully, but the ‘d_name’ member may not be
          NUL-terminated or may be truncated.

        • POSIX-1.2008 does not guarantee that ‘readdir’ is thread-safe,
          even when access to the same DIRSTREAM is serialized.  But in
          current implementations (including the GNU C Library), it is
          safe to call ‘readdir’ concurrently on different DIRSTREAMs,
          so there is no need to use ‘readdir_r’ in most multi-threaded
          programs.  In the rare case that multiple threads need to read
          from the same DIRSTREAM, it is still better to use ‘readdir’
          and external synchronization.

        • It is expected that future versions of POSIX will obsolete
          ‘readdir_r’ and mandate the level of thread safety for
          ‘readdir’ which is provided by the GNU C Library and other
          implementations today.

     Normally ‘readdir_r’ returns zero and sets ‘*RESULT’ to ENTRY.  If
     there are no more entries in the directory or an error is detected,
     ‘readdir_r’ sets ‘*RESULT’ to a null pointer and returns a nonzero
     error code, also stored in ‘errno’, as described for ‘readdir’.

     It is also important to look at the definition of the ‘struct
     dirent’ type.  Simply passing a pointer to an object of this type
     for the second parameter of ‘readdir_r’ might not be enough.  Some
     systems don't define the ‘d_name’ element sufficiently long.  In
     this case the user has to provide additional space.  There must be
     room for at least ‘NAME_MAX + 1’ characters in the ‘d_name’ array.
     Code to call ‘readdir_r’ could look like this:

            union
            {
              struct dirent d;
              char b[offsetof (struct dirent, d_name) + NAME_MAX + 1];
            } u;

            if (readdir_r (dir, &u.d, &res) == 0)
              ...

   To support large filesystems on 32-bit machines there are LFS
variants of the last two functions.

 -- Function: struct dirent64 * readdir64 (DIR *DIRSTREAM)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     The ‘readdir64’ function is just like the ‘readdir’ function except
     that it returns a pointer to a record of type ‘struct dirent64’.
     Some of the members of this data type (notably ‘d_ino’) might have
     a different size to allow large filesystems.

     In all other aspects this function is equivalent to ‘readdir’.

 -- Function: int readdir64_r (DIR *DIRSTREAM, struct dirent64 *ENTRY,
          struct dirent64 **RESULT)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     The deprecated ‘readdir64_r’ function is equivalent to the
     ‘readdir_r’ function except that it takes parameters of base type
     ‘struct dirent64’ instead of ‘struct dirent’ in the second and
     third position.  The same precautions mentioned in the
     documentation of ‘readdir_r’ also apply here.

 -- Function: int closedir (DIR *DIRSTREAM)

     Preliminary: | MT-Safe | AS-Unsafe heap lock/hurd | AC-Unsafe mem
     fd lock/hurd | *Note POSIX Safety Concepts::.

     This function closes the directory stream DIRSTREAM.  It returns
     ‘0’ on success and ‘-1’ on failure.

     The following ‘errno’ error conditions are defined for this
     function:

     ‘EBADF’
          The DIRSTREAM argument is not valid.


File: libc.info,  Node: Simple Directory Lister,  Next: Random Access Directory,  Prev: Reading/Closing Directory,  Up: Accessing Directories

14.3.4 Simple Program to List a Directory
-----------------------------------------

Here's a simple program that prints the names of the files in the
current working directory:


     #include <stdio.h>
     #include <sys/types.h>
     #include <dirent.h>

     int
     main (void)
     {
       DIR *dp;
       struct dirent *ep;

       dp = opendir ("./");
       if (dp != NULL)
         {
           while (ep = readdir (dp))
             puts (ep->d_name);
           (void) closedir (dp);
         }
       else
         perror ("Couldn't open the directory");

       return 0;
     }

   The order in which files appear in a directory tends to be fairly
random.  A more useful program would sort the entries (perhaps by
alphabetizing them) before printing them; see *note Scanning Directory
Content::, and *note Array Sort Function::.


File: libc.info,  Node: Random Access Directory,  Next: Scanning Directory Content,  Prev: Simple Directory Lister,  Up: Accessing Directories

14.3.5 Random Access in a Directory Stream
------------------------------------------

This section describes how to reread parts of a directory that you have
already read from an open directory stream.  All the symbols are
declared in the header file ‘dirent.h’.

 -- Function: void rewinddir (DIR *DIRSTREAM)

     Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note
     POSIX Safety Concepts::.

     The ‘rewinddir’ function is used to reinitialize the directory
     stream DIRSTREAM, so that if you call ‘readdir’ it returns
     information about the first entry in the directory again.  This
     function also notices if files have been added or removed to the
     directory since it was opened with ‘opendir’.  (Entries for these
     files might or might not be returned by ‘readdir’ if they were
     added or removed since you last called ‘opendir’ or ‘rewinddir’.)

     For example, it is recommended to call ‘rewinddir’ followed by
     ‘readdir’ to check if a directory is empty after listing it with
     ‘readdir’ and deleting all encountered files from it.

 -- Function: long int telldir (DIR *DIRSTREAM)

     Preliminary: | MT-Safe | AS-Unsafe heap/bsd lock/bsd | AC-Unsafe
     mem/bsd lock/bsd | *Note POSIX Safety Concepts::.

     The ‘telldir’ function returns the file position of the directory
     stream DIRSTREAM.  You can use this value with ‘seekdir’ to restore
     the directory stream to that position.

     Using the the ‘telldir’ function is not recommended.

     The value returned by ‘telldir’ may not be compatible with the
     ‘d_off’ field in ‘struct dirent’, and cannot be used with the
     ‘lseek’ function.  The returned value may not unambiguously
     identify the position in the directory stream.

 -- Function: void seekdir (DIR *DIRSTREAM, long int POS)

     Preliminary: | MT-Safe | AS-Unsafe heap/bsd lock/bsd | AC-Unsafe
     mem/bsd lock/bsd | *Note POSIX Safety Concepts::.

     The ‘seekdir’ function sets the file position of the directory
     stream DIRSTREAM to POS.  The value POS must be the result of a
     previous call to ‘telldir’ on this particular stream; closing and
     reopening the directory can invalidate values returned by
     ‘telldir’.

     Using the the ‘seekdir’ function is not recommended.  To seek to
     the beginning of the directory stream, use ‘rewinddir’.


File: libc.info,  Node: Scanning Directory Content,  Next: Simple Directory Lister Mark II,  Prev: Random Access Directory,  Up: Accessing Directories

14.3.6 Scanning the Content of a Directory
------------------------------------------

A higher-level interface to the directory handling functions is the
‘scandir’ function.  With its help one can select a subset of the
entries in a directory, possibly sort them and get a list of names as
the result.

 -- Function: int scandir (const char *DIR, struct dirent ***NAMELIST,
          int (*SELECTOR) (const struct dirent *), int (*CMP) (const
          struct dirent **, const struct dirent **))

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note
     POSIX Safety Concepts::.

     The ‘scandir’ function scans the contents of the directory selected
     by DIR.  The result in *NAMELIST is an array of pointers to
     structures of type ‘struct dirent’ which describe all selected
     directory entries and which is allocated using ‘malloc’.  Instead
     of always getting all directory entries returned, the user supplied
     function SELECTOR can be used to decide which entries are in the
     result.  Only the entries for which SELECTOR returns a non-zero
     value are selected.

     Finally the entries in *NAMELIST are sorted using the user-supplied
     function CMP.  The arguments passed to the CMP function are of type
     ‘struct dirent **’, therefore one cannot directly use the ‘strcmp’
     or ‘strcoll’ functions; instead see the functions ‘alphasort’ and
     ‘versionsort’ below.

     The return value of the function is the number of entries placed in
     *NAMELIST.  If it is ‘-1’ an error occurred (either the directory
     could not be opened for reading or memory allocation failed) and
     the global variable ‘errno’ contains more information on the error.

   As described above, the fourth argument to the ‘scandir’ function
must be a pointer to a sorting function.  For the convenience of the
programmer the GNU C Library contains implementations of functions which
are very helpful for this purpose.

 -- Function: int alphasort (const struct dirent **A, const struct
          dirent **B)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     The ‘alphasort’ function behaves like the ‘strcoll’ function (*note
     String/Array Comparison::).  The difference is that the arguments
     are not string pointers but instead they are of type ‘struct dirent
     **’.

     The return value of ‘alphasort’ is less than, equal to, or greater
     than zero depending on the order of the two entries A and B.

 -- Function: int versionsort (const struct dirent **A, const struct
          dirent **B)

     Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | *Note POSIX
     Safety Concepts::.

     The ‘versionsort’ function is like ‘alphasort’ except that it uses
     the ‘strverscmp’ function internally.

   If the filesystem supports large files we cannot use the ‘scandir’
anymore since the ‘dirent’ structure might not able to contain all the
information.  The LFS provides the new type ‘struct dirent64’.  To use
this we need a new function.

 -- Function: int scandir64 (const char *DIR, struct dirent64
          ***NAMELIST, int (*SELECTOR) (const struct dirent64 *), int
          (*CMP) (const struct dirent64 **, const struct dirent64 **))

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note
     POSIX Safety Concepts::.

     The ‘scandir64’ function works like the ‘scandir’ function except
     that the directory entries it returns are described by elements of
     type ‘struct dirent64’.  The function pointed to by SELECTOR is
     again used to select the desired entries, except that SELECTOR now
     must point to a function which takes a ‘struct dirent64 *’
     parameter.

     Similarly the CMP function should expect its two arguments to be of
     type ‘struct dirent64 **’.

   As CMP is now a function of a different type, the functions
‘alphasort’ and ‘versionsort’ cannot be supplied for that argument.
Instead we provide the two replacement functions below.

 -- Function: int alphasort64 (const struct dirent64 **A, const struct
          dirent **B)

     Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem |
     *Note POSIX Safety Concepts::.

     The ‘alphasort64’ function behaves like the ‘strcoll’ function
     (*note String/Array Comparison::).  The difference is that the
     arguments are not string pointers but instead they are of type
     ‘struct dirent64 **’.

     Return value of ‘alphasort64’ is less than, equal to, or greater
     than zero depending on the order of the two entries A and B.

 -- Function: int versionsort64 (const struct dirent64 **A, const struct
          dirent64 **B)

     Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | *Note POSIX
     Safety Concepts::.

     The ‘versionsort64’ function is like ‘alphasort64’, excepted that
     it uses the ‘strverscmp’ function internally.

   It is important not to mix the use of ‘scandir’ and the 64-bit
comparison functions or vice versa.  There are systems on which this
works but on others it will fail miserably.


File: libc.info,  Node: Simple Directory Lister Mark II,  Next: Low-level Directory Access,  Prev: Scanning Directory Content,  Up: Accessing Directories

14.3.7 Simple Program to List a Directory, Mark II
--------------------------------------------------

Here is a revised version of the directory lister found above (*note
Simple Directory Lister::).  Using the ‘scandir’ function we can avoid
the functions which work directly with the directory contents.  After
the call the returned entries are available for direct use.


     #include <stdio.h>
     #include <dirent.h>

     static int
     one (const struct dirent *unused)
     {
       return 1;
     }

     int
     main (void)
     {
       struct dirent **eps;
       int n;

       n = scandir ("./", &eps, one, alphasort);
       if (n >= 0)
         {
           int cnt;
           for (cnt = 0; cnt < n; ++cnt)
             puts (eps[cnt]->d_name);
         }
       else
         perror ("Couldn't open the directory");

       return 0;
     }

   Note the simple selector function in this example.  Since we want to
see all directory entries we always return ‘1’.


File: libc.info,  Node: Low-level Directory Access,  Prev: Simple Directory Lister Mark II,  Up: Accessing Directories

14.3.8 Low-level Directory Access
---------------------------------

The stream-based directory functions are not AS-Safe and cannot be used
after ‘vfork’.  *Note POSIX Safety Concepts::.  The functions below
provide an alternative that can be used in these contexts.

   Directory data is obtained from a file descriptor, as created by the
‘open’ function, with or without the ‘O_DIRECTORY’ flag.  *Note Opening
and Closing Files::.

 -- Function: ssize_t getdents64 (int FD, void *BUFFER, size_t LENGTH)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘getdents64’ function reads at most LENGTH bytes of directory
     entry data from the file descriptor FD and stores it into the byte
     array starting at BUFFER.

     On success, the function returns the number of bytes written to the
     buffer.  This number is zero if FD is already at the end of the
     directory stream.  On error, the function returns ‘-1’ and sets
     ‘errno’ to the appropriate error code.

     The data is stored as a sequence of ‘struct dirent64’ records,
     which can be traversed using the ‘d_reclen’ member.  The buffer
     should be large enough to hold the largest possible directory
     entry.  Note that some file systems support file names longer than
     ‘NAME_MAX’ bytes (e.g., because they support up to 255 Unicode
     characters), so a buffer size of at least 1024 is recommended.

     If the directory has been modified since the first call to
     ‘getdents64’ on the directory (opening the descriptor or seeking to
     offset zero), it is possible that the buffer contains entries that
     have been encountered before.  Likewise, it is possible that files
     that are still present are not reported before the end of the
     directory is encountered (and ‘getdents64’ returns zero).

     This function is specific to Linux.

   Systems that support ‘getdents64’ support seeking on directory
streams.  *Note File Position Primitive::.  However, the only offset
that works reliably is offset zero, indicating that reading the
directory should start from the beginning.


File: libc.info,  Node: Working with Directory Trees,  Next: Hard Links,  Prev: Accessing Directories,  Up: File System Interface

14.4 Working with Directory Trees
=================================

The functions described so far for handling the files in a directory
have allowed you to either retrieve the information bit by bit, or to
process all the files as a group (see ‘scandir’).  Sometimes it is
useful to process whole hierarchies of directories and their contained
files.  The X/Open specification defines two functions to do this.  The
simpler form is derived from an early definition in System V systems and
therefore this function is available on SVID-derived systems.  The
prototypes and required definitions can be found in the ‘ftw.h’ header.

   There are four functions in this family: ‘ftw’, ‘nftw’ and their
64-bit counterparts ‘ftw64’ and ‘nftw64’.  These functions take as one
of their arguments a pointer to a callback function of the appropriate
type.

 -- Data Type: __ftw_func_t

          int (*) (const char *, const struct stat *, int)

     The type of callback functions given to the ‘ftw’ function.  The
     first parameter points to the file name, the second parameter to an
     object of type ‘struct stat’ which is filled in for the file named
     in the first parameter.

     The last parameter is a flag giving more information about the
     current file.  It can have the following values:

     ‘FTW_F’
          The item is either a normal file or a file which does not fit
          into one of the following categories.  This could be special
          files, sockets etc.
     ‘FTW_D’
          The item is a directory.
     ‘FTW_NS’
          The ‘stat’ call failed and so the information pointed to by
          the second parameter is invalid.
     ‘FTW_DNR’
          The item is a directory which cannot be read.
     ‘FTW_SL’
          The item is a symbolic link.  Since symbolic links are
          normally followed seeing this value in a ‘ftw’ callback
          function means the referenced file does not exist.  The
          situation for ‘nftw’ is different.

          This value is only available if the program is compiled with
          ‘_XOPEN_EXTENDED’ defined before including the first header.
          The original SVID systems do not have symbolic links.

     If the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     type is in fact ‘__ftw64_func_t’ since this mode changes ‘struct
     stat’ to be ‘struct stat64’.

   For the LFS interface and for use in the function ‘ftw64’, the header
‘ftw.h’ defines another function type.

 -- Data Type: __ftw64_func_t

          int (*) (const char *, const struct stat64 *, int)

     This type is used just like ‘__ftw_func_t’ for the callback
     function, but this time is called from ‘ftw64’.  The second
     parameter to the function is a pointer to a variable of type
     ‘struct stat64’ which is able to represent the larger values.

 -- Data Type: __nftw_func_t

          int (*) (const char *, const struct stat *, int, struct FTW *)

     The first three arguments are the same as for the ‘__ftw_func_t’
     type.  However for the third argument some additional values are
     defined to allow finer differentiation:
     ‘FTW_DP’
          The current item is a directory and all subdirectories have
          already been visited and reported.  This flag is returned
          instead of ‘FTW_D’ if the ‘FTW_DEPTH’ flag is passed to ‘nftw’
          (see below).
     ‘FTW_SLN’
          The current item is a stale symbolic link.  The file it points
          to does not exist.

     The last parameter of the callback function is a pointer to a
     structure with some extra information as described below.

     If the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     type is in fact ‘__nftw64_func_t’ since this mode changes ‘struct
     stat’ to be ‘struct stat64’.

   For the LFS interface there is also a variant of this data type
available which has to be used with the ‘nftw64’ function.

 -- Data Type: __nftw64_func_t

          int (*) (const char *, const struct stat64 *, int, struct FTW *)

     This type is used just like ‘__nftw_func_t’ for the callback
     function, but this time is called from ‘nftw64’.  The second
     parameter to the function is this time a pointer to a variable of
     type ‘struct stat64’ which is able to represent the larger values.

 -- Data Type: struct FTW

     The information contained in this structure helps in interpreting
     the name parameter and gives some information about the current
     state of the traversal of the directory hierarchy.

     ‘int base’
          The value is the offset into the string passed in the first
          parameter to the callback function of the beginning of the
          file name.  The rest of the string is the path of the file.
          This information is especially important if the ‘FTW_CHDIR’
          flag was set in calling ‘nftw’ since then the current
          directory is the one the current item is found in.
     ‘int level’
          Whilst processing, the code tracks how many directories down
          it has gone to find the current file.  This nesting level
          starts at 0 for files in the initial directory (or is zero for
          the initial file if a file was passed).

 -- Function: int ftw (const char *FILENAME, __ftw_func_t FUNC, int
          DESCRIPTORS)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note
     POSIX Safety Concepts::.

     The ‘ftw’ function calls the callback function given in the
     parameter FUNC for every item which is found in the directory
     specified by FILENAME and all directories below.  The function
     follows symbolic links if necessary but does not process an item
     twice.  If FILENAME is not a directory then it itself is the only
     object returned to the callback function.

     The file name passed to the callback function is constructed by
     taking the FILENAME parameter and appending the names of all passed
     directories and then the local file name.  So the callback function
     can use this parameter to access the file.  ‘ftw’ also calls ‘stat’
     for the file and passes that information on to the callback
     function.  If this ‘stat’ call is not successful the failure is
     indicated by setting the third argument of the callback function to
     ‘FTW_NS’.  Otherwise it is set according to the description given
     in the account of ‘__ftw_func_t’ above.

     The callback function is expected to return 0 to indicate that no
     error occurred and that processing should continue.  If an error
     occurred in the callback function or it wants ‘ftw’ to return
     immediately, the callback function can return a value other than 0.
     This is the only correct way to stop the function.  The program
     must not use ‘setjmp’ or similar techniques to continue from
     another place.  This would leave resources allocated by the ‘ftw’
     function unfreed.

     The DESCRIPTORS parameter to ‘ftw’ specifies how many file
     descriptors it is allowed to consume.  The function runs faster the
     more descriptors it can use.  For each level in the directory
     hierarchy at most one descriptor is used, but for very deep ones
     any limit on open file descriptors for the process or the system
     may be exceeded.  Moreover, file descriptor limits in a
     multi-threaded program apply to all the threads as a group, and
     therefore it is a good idea to supply a reasonable limit to the
     number of open descriptors.

     The return value of the ‘ftw’ function is 0 if all callback
     function calls returned 0 and all actions performed by the ‘ftw’
     succeeded.  If a function call failed (other than calling ‘stat’ on
     an item) the function returns -1.  If a callback function returns a
     value other than 0 this value is returned as the return value of
     ‘ftw’.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a
     32-bit system this function is in fact ‘ftw64’, i.e., the LFS
     interface transparently replaces the old interface.

 -- Function: int ftw64 (const char *FILENAME, __ftw64_func_t FUNC, int
          DESCRIPTORS)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note
     POSIX Safety Concepts::.

     This function is similar to ‘ftw’ but it can work on filesystems
     with large files.  File information is reported using a variable of
     type ‘struct stat64’ which is passed by reference to the callback
     function.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a
     32-bit system this function is available under the name ‘ftw’ and
     transparently replaces the old implementation.

 -- Function: int nftw (const char *FILENAME, __nftw_func_t FUNC, int
          DESCRIPTORS, int FLAG)

     Preliminary: | MT-Safe cwd | AS-Unsafe heap | AC-Unsafe mem fd cwd
     | *Note POSIX Safety Concepts::.

     The ‘nftw’ function works like the ‘ftw’ functions.  They call the
     callback function FUNC for all items found in the directory
     FILENAME and below.  At most DESCRIPTORS file descriptors are
     consumed during the ‘nftw’ call.

     One difference is that the callback function is of a different
     type.  It is of type ‘struct FTW *’ and provides the callback
     function with the extra information described above.

     A second difference is that ‘nftw’ takes a fourth argument, which
     is 0 or a bitwise-OR combination of any of the following values.

     ‘FTW_PHYS’
          While traversing the directory symbolic links are not
          followed.  Instead symbolic links are reported using the
          ‘FTW_SL’ value for the type parameter to the callback
          function.  If the file referenced by a symbolic link does not
          exist ‘FTW_SLN’ is returned instead.
     ‘FTW_MOUNT’
          The callback function is only called for items which are on
          the same mounted filesystem as the directory given by the
          FILENAME parameter to ‘nftw’.
     ‘FTW_CHDIR’
          If this flag is given the current working directory is changed
          to the directory of the reported object before the callback
          function is called.  When ‘ntfw’ finally returns the current
          directory is restored to its original value.
     ‘FTW_DEPTH’
          If this option is specified then all subdirectories and files
          within them are processed before processing the top directory
          itself (depth-first processing).  This also means the type
          flag given to the callback function is ‘FTW_DP’ and not
          ‘FTW_D’.
     ‘FTW_ACTIONRETVAL’
          If this option is specified then return values from callbacks
          are handled differently.  If the callback returns
          ‘FTW_CONTINUE’, walking continues normally.  ‘FTW_STOP’ means
          walking stops and ‘FTW_STOP’ is returned to the caller.  If
          ‘FTW_SKIP_SUBTREE’ is returned by the callback with ‘FTW_D’
          argument, the subtree is skipped and walking continues with
          next sibling of the directory.  If ‘FTW_SKIP_SIBLINGS’ is
          returned by the callback, all siblings of the current entry
          are skipped and walking continues in its parent.  No other
          return values should be returned from the callbacks if this
          option is set.  This option is a GNU extension.

     The return value is computed in the same way as for ‘ftw’.  ‘nftw’
     returns 0 if no failures occurred and all callback functions
     returned 0.  In case of internal errors, such as memory problems,
     the return value is -1 and ‘errno’ is set accordingly.  If the
     return value of a callback invocation was non-zero then that value
     is returned.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a
     32-bit system this function is in fact ‘nftw64’, i.e., the LFS
     interface transparently replaces the old interface.

 -- Function: int nftw64 (const char *FILENAME, __nftw64_func_t FUNC,
          int DESCRIPTORS, int FLAG)

     Preliminary: | MT-Safe cwd | AS-Unsafe heap | AC-Unsafe mem fd cwd
     | *Note POSIX Safety Concepts::.

     This function is similar to ‘nftw’ but it can work on filesystems
     with large files.  File information is reported using a variable of
     type ‘struct stat64’ which is passed by reference to the callback
     function.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a
     32-bit system this function is available under the name ‘nftw’ and
     transparently replaces the old implementation.


File: libc.info,  Node: Hard Links,  Next: Symbolic Links,  Prev: Working with Directory Trees,  Up: File System Interface

14.5 Hard Links
===============

In POSIX systems, one file can have many names at the same time.  All of
the names are equally real, and no one of them is preferred to the
others.

   To add a name to a file, use the ‘link’ function.  (The new name is
also called a “hard link” to the file.)  Creating a new link to a file
does not copy the contents of the file; it simply makes a new name by
which the file can be known, in addition to the file's existing name or
names.

   One file can have names in several directories, so the organization
of the file system is not a strict hierarchy or tree.

   In most implementations, it is not possible to have hard links to the
same file in multiple file systems.  ‘link’ reports an error if you try
to make a hard link to the file from another file system when this
cannot be done.

   The prototype for the ‘link’ function is declared in the header file
‘unistd.h’.

 -- Function: int link (const char *OLDNAME, const char *NEWNAME)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘link’ function makes a new link to the existing file named by
     OLDNAME, under the new name NEWNAME.

     This function returns a value of ‘0’ if it is successful and ‘-1’
     on failure.  In addition to the usual file name errors (*note File
     Name Errors::) for both OLDNAME and NEWNAME, the following ‘errno’
     error conditions are defined for this function:

     ‘EACCES’
          You are not allowed to write to the directory in which the new
          link is to be written.

     ‘EEXIST’
          There is already a file named NEWNAME.  If you want to replace
          this link with a new link, you must remove the old link
          explicitly first.

     ‘EMLINK’
          There are already too many links to the file named by OLDNAME.
          (The maximum number of links to a file is ‘LINK_MAX’; see
          *note Limits for Files::.)

     ‘ENOENT’
          The file named by OLDNAME doesn't exist.  You can't make a
          link to a file that doesn't exist.

     ‘ENOSPC’
          The directory or file system that would contain the new link
          is full and cannot be extended.

     ‘EPERM’
          On GNU/Linux and GNU/Hurd systems and some others, you cannot
          make links to directories.  Many systems allow only privileged
          users to do so.  This error is used to report the problem.

     ‘EROFS’
          The directory containing the new link can't be modified
          because it's on a read-only file system.

     ‘EXDEV’
          The directory specified in NEWNAME is on a different file
          system than the existing file.

     ‘EIO’
          A hardware error occurred while trying to read or write the to
          filesystem.

 -- Function: int linkat (int oldfd, const char *OLDNAME, int newfd,
          const char *NEWNAME, int flags)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘linkat’ function is analogous to the ‘link’ function, except
     that it identifies its source and target using a combination of a
     file descriptor (referring to a directory) and a file name.  *Note
     Descriptor-Relative Access::.  For ‘linkat’, if a file name is not
     absolute, it is resolved relative to the corresponding file
     descriptor.  As usual, the special value ‘AT_FDCWD’ denotes the
     current directory.

     The FLAGS argument is a combination of the following flags:

     ‘AT_SYMLINK_FOLLOW’
          If the source path identified by OLDFD and OLDNAME is a
          symbolic link, ‘linkat’ follows the symbolic link and creates
          a link to its target.  If the flag is not set, a link for the
          symbolic link itself is created; this is not supported by all
          file systems and ‘linkat’ can fail in this case.

     ‘AT_EMPTY_PATH’
          If this flag is specified, OLDNAME can be an empty string.  In
          this case, a new link to the file denoted by the descriptor
          OLDFD is created, which may have been opened with ‘O_PATH’ or
          ‘O_TMPFILE’.  This flag is a GNU extension.


File: libc.info,  Node: Symbolic Links,  Next: Deleting Files,  Prev: Hard Links,  Up: File System Interface

14.6 Symbolic Links
===================

GNU systems support “soft links” or “symbolic links”.  This is a kind of
"file" that is essentially a pointer to another file name.  Unlike hard
links, symbolic links can be made to directories or across file systems
with no restrictions.  You can also make a symbolic link to a name which
is not the name of any file.  (Opening this link will fail until a file
by that name is created.)  Likewise, if the symbolic link points to an
existing file which is later deleted, the symbolic link continues to
point to the same file name even though the name no longer names any
file.

   The reason symbolic links work the way they do is that special things
happen when you try to open the link.  The ‘open’ function realizes you
have specified the name of a link, reads the file name contained in the
link, and opens that file name instead.  The ‘stat’ function likewise
operates on the file that the symbolic link points to, instead of on the
link itself.

   By contrast, other operations such as deleting or renaming the file
operate on the link itself.  The functions ‘readlink’ and ‘lstat’ also
refrain from following symbolic links, because their purpose is to
obtain information about the link.  ‘link’, the function that makes a
hard link, does too.  It makes a hard link to the symbolic link, which
one rarely wants.

   Some systems have, for some functions operating on files, a limit on
how many symbolic links are followed when resolving a path name.  The
limit if it exists is published in the ‘sys/param.h’ header file.

 -- Macro: int MAXSYMLINKS

     The macro ‘MAXSYMLINKS’ specifies how many symlinks some function
     will follow before returning ‘ELOOP’.  Not all functions behave the
     same and this value is not the same as that returned for
     ‘_SC_SYMLOOP’ by ‘sysconf’.  In fact, the ‘sysconf’ result can
     indicate that there is no fixed limit although ‘MAXSYMLINKS’ exists
     and has a finite value.

   Prototypes for most of the functions listed in this section are in
‘unistd.h’.

 -- Function: int symlink (const char *OLDNAME, const char *NEWNAME)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘symlink’ function makes a symbolic link to OLDNAME named
     NEWNAME.

     The normal return value from ‘symlink’ is ‘0’.  A return value of
     ‘-1’ indicates an error.  In addition to the usual file name syntax
     errors (*note File Name Errors::), the following ‘errno’ error
     conditions are defined for this function:

     ‘EEXIST’
          There is already an existing file named NEWNAME.

     ‘EROFS’
          The file NEWNAME would exist on a read-only file system.

     ‘ENOSPC’
          The directory or file system cannot be extended to make the
          new link.

     ‘EIO’
          A hardware error occurred while reading or writing data on the
          disk.

 -- Function: ssize_t readlink (const char *FILENAME, char *BUFFER,
          size_t SIZE)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘readlink’ function gets the value of the symbolic link
     FILENAME.  The file name that the link points to is copied into
     BUFFER.  This file name string is _not_ null-terminated; ‘readlink’
     normally returns the number of characters copied.  The SIZE
     argument specifies the maximum number of characters to copy,
     usually the allocation size of BUFFER.

     If the return value equals SIZE, you cannot tell whether or not
     there was room to return the entire name.  So make a bigger buffer
     and call ‘readlink’ again.  Here is an example:

          char *
          readlink_malloc (const char *filename)
          {
            size_t size = 50;
            char *buffer = NULL;

            while (1)
              {
                buffer = xreallocarray (buffer, size, 2);
                size *= 2;
                ssize_t nchars = readlink (filename, buffer, size);
                if (nchars < 0)
                  {
                    free (buffer);
                    return NULL;
                  }
                if (nchars < size)
                  return buffer;
              }
          }

     A value of ‘-1’ is returned in case of error.  In addition to the
     usual file name errors (*note File Name Errors::), the following
     ‘errno’ error conditions are defined for this function:

     ‘EINVAL’
          The named file is not a symbolic link.

     ‘EIO’
          A hardware error occurred while reading or writing data on the
          disk.

   In some situations it is desirable to resolve all the symbolic links
to get the real name of a file where no prefix names a symbolic link
which is followed and no filename in the path is ‘.’ or ‘..’.  This is
for instance desirable if files have to be compared in which case
different names can refer to the same inode.

 -- Function: char * canonicalize_file_name (const char *NAME)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note
     POSIX Safety Concepts::.

     The ‘canonicalize_file_name’ function returns the absolute name of
     the file named by NAME which contains no ‘.’, ‘..’ components nor
     any repeated path separators (‘/’) or symlinks.  The result is
     passed back as the return value of the function in a block of
     memory allocated with ‘malloc’.  If the result is not used anymore
     the memory should be freed with a call to ‘free’.

     If any of the path components are missing the function returns a
     NULL pointer.  This is also what is returned if the length of the
     path reaches or exceeds ‘PATH_MAX’ characters.  In any case ‘errno’
     is set accordingly.

     ‘ENAMETOOLONG’
          The resulting path is too long.  This error only occurs on
          systems which have a limit on the file name length.

     ‘EACCES’
          At least one of the path components is not readable.

     ‘ENOENT’
          The input file name is empty.

     ‘ENOENT’
          At least one of the path components does not exist.

     ‘ELOOP’
          More than ‘MAXSYMLINKS’ many symlinks have been followed.

     This function is a GNU extension and is declared in ‘stdlib.h’.

   The Unix standard includes a similar function which differs from
‘canonicalize_file_name’ in that the user has to provide the buffer
where the result is placed in.

 -- Function: char * realpath (const char *restrict NAME, char *restrict
          RESOLVED)

     Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note
     POSIX Safety Concepts::.

     A call to ‘realpath’ where the RESOLVED parameter is ‘NULL’ behaves
     exactly like ‘canonicalize_file_name’.  The function allocates a
     buffer for the file name and returns a pointer to it.  If RESOLVED
     is not ‘NULL’ it points to a buffer into which the result is
     copied.  It is the callers responsibility to allocate a buffer
     which is large enough.  On systems which define ‘PATH_MAX’ this
     means the buffer must be large enough for a pathname of this size.
     For systems without limitations on the pathname length the
     requirement cannot be met and programs should not call ‘realpath’
     with anything but ‘NULL’ for the second parameter.

     One other difference is that the buffer RESOLVED (if nonzero) will
     contain the part of the path component which does not exist or is
     not readable if the function returns ‘NULL’ and ‘errno’ is set to
     ‘EACCES’ or ‘ENOENT’.

     This function is declared in ‘stdlib.h’.

   The advantage of using this function is that it is more widely
available.  The drawback is that it reports failures for long paths on
systems which have no limits on the file name length.


File: libc.info,  Node: Deleting Files,  Next: Renaming Files,  Prev: Symbolic Links,  Up: File System Interface

14.7 Deleting Files
===================

You can delete a file with ‘unlink’ or ‘remove’.

   Deletion actually deletes a file name.  If this is the file's only
name, then the file is deleted as well.  If the file has other remaining
names (*note Hard Links::), it remains accessible under those names.

 -- Function: int unlink (const char *FILENAME)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘unlink’ function deletes the file name FILENAME.  If this is a
     file's sole name, the file itself is also deleted.  (Actually, if
     any process has the file open when this happens, deletion is
     postponed until all processes have closed the file.)

     The function ‘unlink’ is declared in the header file ‘unistd.h’.

     This function returns ‘0’ on successful completion, and ‘-1’ on
     error.  In addition to the usual file name errors (*note File Name
     Errors::), the following ‘errno’ error conditions are defined for
     this function:

     ‘EACCES’
          Write permission is denied for the directory from which the
          file is to be removed, or the directory has the sticky bit set
          and you do not own the file.

     ‘EBUSY’
          This error indicates that the file is being used by the system
          in such a way that it can't be unlinked.  For example, you
          might see this error if the file name specifies the root
          directory or a mount point for a file system.

     ‘ENOENT’
          The file name to be deleted doesn't exist.

     ‘EPERM’
          On some systems ‘unlink’ cannot be used to delete the name of
          a directory, or at least can only be used this way by a
          privileged user.  To avoid such problems, use ‘rmdir’ to
          delete directories.  (On GNU/Linux and GNU/Hurd systems
          ‘unlink’ can never delete the name of a directory.)

     ‘EROFS’
          The directory containing the file name to be deleted is on a
          read-only file system and can't be modified.

 -- Function: int unlinkat (int FILEDES, const char *FILENAME, int
          FLAGS)

     | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt | *Note POSIX
     Safety Concepts::.

     This function is a descriptor-relative version of the ‘unlink’
     function above.  *Note Descriptor-Relative Access::.  The FLAGS
     argument may either be ‘0’ or contain the flag ‘AT_REMOVEDIR’:

     ‘AT_REMOVEDIR’
          This flag causes ‘unlinkat’ to perform an ‘rmdir’ operation on
          ‘filename’ instead of performing the equivalent of ‘unlink’.

     Compared to ‘unlink’, some additional error conditions can occur
     due to descriptor-relative access.  *Note Descriptor-Relative
     Access::.  In addition to this, the following other errors can also
     occur:

     ‘EISDIR’
          The effective final path derived from FILENAME and FILEDES is
          a directory but ‘AT_REMOVEDIR’ was not passed in ‘flags’.

 -- Function: int rmdir (const char *FILENAME)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘rmdir’ function deletes a directory.  The directory must be
     empty before it can be removed; in other words, it can only contain
     entries for ‘.’ and ‘..’.

     In most other respects, ‘rmdir’ behaves like ‘unlink’.  There are
     two additional ‘errno’ error conditions defined for ‘rmdir’:

     ‘ENOTEMPTY’
     ‘EEXIST’
          The directory to be deleted is not empty.

     These two error codes are synonymous; some systems use one, and
     some use the other.  GNU/Linux and GNU/Hurd systems always use
     ‘ENOTEMPTY’.

     The prototype for this function is declared in the header file
     ‘unistd.h’.

 -- Function: int remove (const char *FILENAME)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This is the ISO C function to remove a file.  It works like
     ‘unlink’ for files and like ‘rmdir’ for directories.  ‘remove’ is
     declared in ‘stdio.h’.


File: libc.info,  Node: Renaming Files,  Next: Creating Directories,  Prev: Deleting Files,  Up: File System Interface

14.8 Renaming Files
===================

The ‘rename’ function is used to change a file's name.

 -- Function: int rename (const char *OLDNAME, const char *NEWNAME)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘rename’ function renames the file OLDNAME to NEWNAME.  The
     file formerly accessible under the name OLDNAME is afterwards
     accessible as NEWNAME instead.  (If the file had any other names
     aside from OLDNAME, it continues to have those names.)

     The directory containing the name NEWNAME must be on the same file
     system as the directory containing the name OLDNAME.

     One special case for ‘rename’ is when OLDNAME and NEWNAME are two
     names for the same file.  The consistent way to handle this case is
     to delete OLDNAME.  However, in this case POSIX requires that
     ‘rename’ do nothing and report success--which is inconsistent.  We
     don't know what your operating system will do.

     If OLDNAME is not a directory, then any existing file named NEWNAME
     is removed during the renaming operation.  However, if NEWNAME is
     the name of a directory, ‘rename’ fails in this case.

     If OLDNAME is a directory, then either NEWNAME must not exist or it
     must name a directory that is empty.  In the latter case, the
     existing directory named NEWNAME is deleted first.  The name
     NEWNAME must not specify a subdirectory of the directory ‘oldname’
     which is being renamed.

     One useful feature of ‘rename’ is that the meaning of NEWNAME
     changes "atomically" from any previously existing file by that name
     to its new meaning (i.e., the file that was called OLDNAME).  There
     is no instant at which NEWNAME is non-existent "in between" the old
     meaning and the new meaning.  If there is a system crash during the
     operation, it is possible for both names to still exist; but
     NEWNAME will always be intact if it exists at all.

     If ‘rename’ fails, it returns ‘-1’.  In addition to the usual file
     name errors (*note File Name Errors::), the following ‘errno’ error
     conditions are defined for this function:

     ‘EACCES’
          One of the directories containing NEWNAME or OLDNAME refuses
          write permission; or NEWNAME and OLDNAME are directories and
          write permission is refused for one of them.

     ‘EBUSY’
          A directory named by OLDNAME or NEWNAME is being used by the
          system in a way that prevents the renaming from working.  This
          includes directories that are mount points for filesystems,
          and directories that are the current working directories of
          processes.

     ‘ENOTEMPTY’
     ‘EEXIST’
          The directory NEWNAME isn't empty.  GNU/Linux and GNU/Hurd
          systems always return ‘ENOTEMPTY’ for this, but some other
          systems return ‘EEXIST’.

     ‘EINVAL’
          OLDNAME is a directory that contains NEWNAME.

     ‘EISDIR’
          NEWNAME is a directory but the OLDNAME isn't.

     ‘EMLINK’
          The parent directory of NEWNAME would have too many links
          (entries).

     ‘ENOENT’
          The file OLDNAME doesn't exist.

     ‘ENOSPC’
          The directory that would contain NEWNAME has no room for
          another entry, and there is no space left in the file system
          to expand it.

     ‘EROFS’
          The operation would involve writing to a directory on a
          read-only file system.

     ‘EXDEV’
          The two file names NEWNAME and OLDNAME are on different file
          systems.

 -- Function: int renameat (int OLDFILEDES, const char *OLDNAME, int
          NEWFILEDES, const char *NEWNAME)

     | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt | *Note POSIX
     Safety Concepts::.

     This function is a descriptor-relative version of the ‘rename’
     function above.  *Note Descriptor-Relative Access::.  If OLDNAME or
     NEWNAME is a relative path, it is interpreted relative to the
     directory associated with OLDFILEDES or NEWFILEDES, respectively.
     Absolute paths are interpreted in the usual way.

     Compared to ‘rename’, some additional error conditions can occur.
     *Note Descriptor-Relative Access::.


File: libc.info,  Node: Creating Directories,  Next: File Attributes,  Prev: Renaming Files,  Up: File System Interface

14.9 Creating Directories
=========================

Directories are created with the ‘mkdir’ function.  (There is also a
shell command ‘mkdir’ which does the same thing.)

 -- Function: int mkdir (const char *FILENAME, mode_t MODE)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘mkdir’ function creates a new, empty directory with name
     FILENAME.

     The argument MODE specifies the file permissions for the new
     directory file.  *Note Permission Bits::, for more information
     about this.

     A return value of ‘0’ indicates successful completion, and ‘-1’
     indicates failure.  In addition to the usual file name syntax
     errors (*note File Name Errors::), the following ‘errno’ error
     conditions are defined for this function:

     ‘EACCES’
          Write permission is denied for the parent directory in which
          the new directory is to be added.

     ‘EEXIST’
          A file named FILENAME already exists.

     ‘EMLINK’
          The parent directory has too many links (entries).

          Well-designed file systems never report this error, because
          they permit more links than your disk could possibly hold.
          However, you must still take account of the possibility of
          this error, as it could result from network access to a file
          system on another machine.

     ‘ENOSPC’
          The file system doesn't have enough room to create the new
          directory.

     ‘EROFS’
          The parent directory of the directory being created is on a
          read-only file system and cannot be modified.

     To use this function, your program should include the header file
     ‘sys/stat.h’.

 -- Function: int mkdirat (int FILEDES, const char *FILENAME, mode_t
          MODE)

     | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt | *Note POSIX
     Safety Concepts::.

     This function is a descriptor-relative version of the ‘mkdir’
     function above.  *Note Descriptor-Relative Access::.

     Compared to ‘mkdir’, some additional error conditions can occur.
     *Note Descriptor-Relative Access::.


File: libc.info,  Node: File Attributes,  Next: Making Special Files,  Prev: Creating Directories,  Up: File System Interface

14.10 File Attributes
=====================

When you issue an ‘ls -l’ shell command on a file, it gives you
information about the size of the file, who owns it, when it was last
modified, etc.  These are called the “file attributes”, and are
associated with the file itself and not a particular one of its names.

   This section contains information about how you can inquire about and
modify the attributes of a file.

* Menu:

* Attribute Meanings::          The names of the file attributes,
                                 and what their values mean.
* Reading Attributes::          How to read the attributes of a file.
* Testing File Type::           Distinguishing ordinary files,
                                 directories, links...
* File Owner::                  How ownership for new files is determined,
			         and how to change it.
* Permission Bits::             How information about a file's access
                                 mode is stored.
* Access Permission::           How the system decides who can access a file.
* Setting Permissions::         How permissions for new files are assigned,
			         and how to change them.
* Testing File Access::         How to find out if your process can
                                 access a file.
* File Times::                  About the time attributes of a file.
* File Size::			Manually changing the size of a file.
* Storage Allocation::          Allocate backing storage for files.


File: libc.info,  Node: Attribute Meanings,  Next: Reading Attributes,  Up: File Attributes

14.10.1 The meaning of the File Attributes
------------------------------------------

When you read the attributes of a file, they come back in a structure
called ‘struct stat’.  This section describes the names of the
attributes, their data types, and what they mean.  For the functions to
read the attributes of a file, see *note Reading Attributes::.

   The header file ‘sys/stat.h’ declares all the symbols defined in this
section.

 -- Data Type: struct stat

     The ‘stat’ structure type is used to return information about the
     attributes of a file.  It contains at least the following members:

     ‘mode_t st_mode’
          Specifies the mode of the file.  This includes file type
          information (*note Testing File Type::) and the file
          permission bits (*note Permission Bits::).

     ‘ino_t st_ino’
          The file serial number, which distinguishes this file from all
          other files on the same device.

     ‘dev_t st_dev’
          Identifies the device containing the file.  The ‘st_ino’ and
          ‘st_dev’, taken together, uniquely identify the file.  The
          ‘st_dev’ value is not necessarily consistent across reboots or
          system crashes, however.

     ‘nlink_t st_nlink’
          The number of hard links to the file.  This count keeps track
          of how many directories have entries for this file.  If the
          count is ever decremented to zero, then the file itself is
          discarded as soon as no process still holds it open.  Symbolic
          links are not counted in the total.

     ‘uid_t st_uid’
          The user ID of the file's owner.  *Note File Owner::.

     ‘gid_t st_gid’
          The group ID of the file.  *Note File Owner::.

     ‘off_t st_size’
          This specifies the size of a regular file in bytes.  For files
          that are really devices this field isn't usually meaningful.
          For symbolic links this specifies the length of the file name
          the link refers to.

     ‘time_t st_atime’
          This is the last access time for the file.  *Note File
          Times::.

     ‘unsigned long int st_atime_usec’
          This is the fractional part of the last access time for the
          file.  *Note File Times::.

     ‘time_t st_mtime’
          This is the time of the last modification to the contents of
          the file.  *Note File Times::.

     ‘unsigned long int st_mtime_usec’
          This is the fractional part of the time of the last
          modification to the contents of the file.  *Note File Times::.

     ‘time_t st_ctime’
          This is the time of the last modification to the attributes of
          the file.  *Note File Times::.

     ‘unsigned long int st_ctime_usec’
          This is the fractional part of the time of the last
          modification to the attributes of the file.  *Note File
          Times::.

     ‘blkcnt_t st_blocks’
          This is the amount of disk space that the file occupies,
          measured in units of 512-byte blocks.

          The number of disk blocks is not strictly proportional to the
          size of the file, for two reasons: the file system may use
          some blocks for internal record keeping; and the file may be
          sparse--it may have "holes" which contain zeros but do not
          actually take up space on the disk.

          You can tell (approximately) whether a file is sparse by
          comparing this value with ‘st_size’, like this:

               (st.st_blocks * 512 < st.st_size)

          This test is not perfect because a file that is just slightly
          sparse might not be detected as sparse at all.  For practical
          applications, this is not a problem.

     ‘unsigned int st_blksize’
          The optimal block size for reading or writing this file, in
          bytes.  You might use this size for allocating the buffer
          space for reading or writing the file.  (This is unrelated to
          ‘st_blocks’.)

   The extensions for the Large File Support (LFS) require, even on
32-bit machines, types which can handle file sizes up to 2^63.
Therefore a new definition of ‘struct stat’ is necessary.

 -- Data Type: struct stat64

     The members of this type are the same and have the same names as
     those in ‘struct stat’.  The only difference is that the members
     ‘st_ino’, ‘st_size’, and ‘st_blocks’ have a different type to
     support larger values.

     ‘mode_t st_mode’
          Specifies the mode of the file.  This includes file type
          information (*note Testing File Type::) and the file
          permission bits (*note Permission Bits::).

     ‘ino64_t st_ino’
          The file serial number, which distinguishes this file from all
          other files on the same device.

     ‘dev_t st_dev’
          Identifies the device containing the file.  The ‘st_ino’ and
          ‘st_dev’, taken together, uniquely identify the file.  The
          ‘st_dev’ value is not necessarily consistent across reboots or
          system crashes, however.

     ‘nlink_t st_nlink’
          The number of hard links to the file.  This count keeps track
          of how many directories have entries for this file.  If the
          count is ever decremented to zero, then the file itself is
          discarded as soon as no process still holds it open.  Symbolic
          links are not counted in the total.

     ‘uid_t st_uid’
          The user ID of the file's owner.  *Note File Owner::.

     ‘gid_t st_gid’
          The group ID of the file.  *Note File Owner::.

     ‘off64_t st_size’
          This specifies the size of a regular file in bytes.  For files
          that are really devices this field isn't usually meaningful.
          For symbolic links this specifies the length of the file name
          the link refers to.

     ‘time_t st_atime’
          This is the last access time for the file.  *Note File
          Times::.

     ‘unsigned long int st_atime_usec’
          This is the fractional part of the last access time for the
          file.  *Note File Times::.

     ‘time_t st_mtime’
          This is the time of the last modification to the contents of
          the file.  *Note File Times::.

     ‘unsigned long int st_mtime_usec’
          This is the fractional part of the time of the last
          modification to the contents of the file.  *Note File Times::.

     ‘time_t st_ctime’
          This is the time of the last modification to the attributes of
          the file.  *Note File Times::.

     ‘unsigned long int st_ctime_usec’
          This is the fractional part of the time of the last
          modification to the attributes of the file.  *Note File
          Times::.

     ‘blkcnt64_t st_blocks’
          This is the amount of disk space that the file occupies,
          measured in units of 512-byte blocks.

     ‘unsigned int st_blksize’
          The optimal block size for reading of writing this file, in
          bytes.  You might use this size for allocating the buffer
          space for reading of writing the file.  (This is unrelated to
          ‘st_blocks’.)

   Some of the file attributes have special data type names which exist
specifically for those attributes.  (They are all aliases for well-known
integer types that you know and love.)  These typedef names are defined
in the header file ‘sys/types.h’ as well as in ‘sys/stat.h’.  Here is a
list of them.

 -- Data Type: mode_t

     This is an integer data type used to represent file modes.  In the
     GNU C Library, this is an unsigned type no narrower than ‘unsigned
     int’.

 -- Data Type: ino_t

     This is an unsigned integer type used to represent file serial
     numbers.  (In Unix jargon, these are sometimes called “inode
     numbers”.)  In the GNU C Library, this type is no narrower than
     ‘unsigned int’.

     If the source is compiled with ‘_FILE_OFFSET_BITS == 64’ this type
     is transparently replaced by ‘ino64_t’.

 -- Data Type: ino64_t

     This is an unsigned integer type used to represent file serial
     numbers for the use in LFS. In the GNU C Library, this type is no
     narrower than ‘unsigned int’.

     When compiling with ‘_FILE_OFFSET_BITS == 64’ this type is
     available under the name ‘ino_t’.

 -- Data Type: dev_t

     This is an arithmetic data type used to represent file device
     numbers.  In the GNU C Library, this is an integer type no narrower
     than ‘int’.

 -- Data Type: nlink_t

     This is an integer type used to represent file link counts.

 -- Data Type: blkcnt_t

     This is a signed integer type used to represent block counts.  In
     the GNU C Library, this type is no narrower than ‘int’.

     If the source is compiled with ‘_FILE_OFFSET_BITS == 64’ this type
     is transparently replaced by ‘blkcnt64_t’.

 -- Data Type: blkcnt64_t

     This is a signed integer type used to represent block counts for
     the use in LFS. In the GNU C Library, this type is no narrower than
     ‘int’.

     When compiling with ‘_FILE_OFFSET_BITS == 64’ this type is
     available under the name ‘blkcnt_t’.


File: libc.info,  Node: Reading Attributes,  Next: Testing File Type,  Prev: Attribute Meanings,  Up: File Attributes

14.10.2 Reading the Attributes of a File
----------------------------------------

To examine the attributes of files, use the functions ‘stat’, ‘fstat’
and ‘lstat’.  They return the attribute information in a ‘struct stat’
object.  All three functions are declared in the header file
‘sys/stat.h’.

 -- Function: int stat (const char *FILENAME, struct stat *BUF)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘stat’ function returns information about the attributes of the
     file named by FILENAME in the structure pointed to by BUF.

     If FILENAME is the name of a symbolic link, the attributes you get
     describe the file that the link points to.  If the link points to a
     nonexistent file name, then ‘stat’ fails reporting a nonexistent
     file.

     The return value is ‘0’ if the operation is successful, or ‘-1’ on
     failure.  In addition to the usual file name errors (*note File
     Name Errors::, the following ‘errno’ error conditions are defined
     for this function:

     ‘ENOENT’
          The file named by FILENAME doesn't exist.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     function is in fact ‘stat64’ since the LFS interface transparently
     replaces the normal implementation.

 -- Function: int stat64 (const char *FILENAME, struct stat64 *BUF)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is similar to ‘stat’ but it is also able to work on
     files larger than 2^31 bytes on 32-bit systems.  To be able to do
     this the result is stored in a variable of type ‘struct stat64’ to
     which BUF must point.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     function is available under the name ‘stat’ and so transparently
     replaces the interface for small files on 32-bit machines.

 -- Function: int fstat (int FILEDES, struct stat *BUF)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘fstat’ function is like ‘stat’, except that it takes an open
     file descriptor as an argument instead of a file name.  *Note
     Low-Level I/O::.

     Like ‘stat’, ‘fstat’ returns ‘0’ on success and ‘-1’ on failure.
     The following ‘errno’ error conditions are defined for ‘fstat’:

     ‘EBADF’
          The FILEDES argument is not a valid file descriptor.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     function is in fact ‘fstat64’ since the LFS interface transparently
     replaces the normal implementation.

 -- Function: int fstat64 (int FILEDES, struct stat64 *BUF)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is similar to ‘fstat’ but is able to work on large
     files on 32-bit platforms.  For large files the file descriptor
     FILEDES should be obtained by ‘open64’ or ‘creat64’.  The BUF
     pointer points to a variable of type ‘struct stat64’ which is able
     to represent the larger values.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     function is available under the name ‘fstat’ and so transparently
     replaces the interface for small files on 32-bit machines.

 -- Function: int fstatat (int FILEDES, const char *FILENAME, struct
          stat *BUF, int FLAGS)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is a descriptor-relative version of the ‘fstat’
     function above.  *Note Descriptor-Relative Access::.  The FLAGS
     argument can contain a combination of the flags ‘AT_EMPTY_PATH’,
     ‘AT_NO_AUTOMOUNT’, ‘AT_SYMLINK_NOFOLLOW’.

     Compared to ‘fstat’, the following additional error conditions can
     occur:

     ‘EBADF’
          The FILEDES argument is not a valid file descriptor.

     ‘EINVAL’
          The FLAGS argument is not valid for this function.

     ‘ENOTDIR’
          The descriptor FILEDES is not associated with a directory, and
          FILENAME is a relative file name.

     ‘ENOENT’
          The file named by FILENAME does not exist, it's a dangling
          symbolic link and FLAGS does not contain
          ‘AT_SYMLINK_NOFOLLOW’, or FILENAME is an empty string and
          FLAGS does not contain ‘AT_EMPTY_PATH’.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     function is in fact ‘fstatat64’ since the LFS interface
     transparently replaces the normal implementation.

 -- Function: int fstatat64 (int FILEDES, const char *FILENAME, struct
          stat64 *BUF, int FLAGS)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is the large-file variant of ‘fstatat’, similar to
     how ‘fstat64’ is the variant of ‘fstat’.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     function is available under the name ‘fstatat’ and so transparently
     replaces the interface for small files on 32-bit machines.

 -- Function: int lstat (const char *FILENAME, struct stat *BUF)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘lstat’ function is like ‘stat’, except that it does not follow
     symbolic links.  If FILENAME is the name of a symbolic link,
     ‘lstat’ returns information about the link itself; otherwise
     ‘lstat’ works like ‘stat’.  *Note Symbolic Links::.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     function is in fact ‘lstat64’ since the LFS interface transparently
     replaces the normal implementation.

 -- Function: int lstat64 (const char *FILENAME, struct stat64 *BUF)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is similar to ‘lstat’ but it is also able to work on
     files larger than 2^31 bytes on 32-bit systems.  To be able to do
     this the result is stored in a variable of type ‘struct stat64’ to
     which BUF must point.

     When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this
     function is available under the name ‘lstat’ and so transparently
     replaces the interface for small files on 32-bit machines.


File: libc.info,  Node: Testing File Type,  Next: File Owner,  Prev: Reading Attributes,  Up: File Attributes

14.10.3 Testing the Type of a File
----------------------------------

The “file mode”, stored in the ‘st_mode’ field of the file attributes,
contains two kinds of information: the file type code, and the access
permission bits.  This section discusses only the type code, which you
can use to tell whether the file is a directory, socket, symbolic link,
and so on.  For details about access permissions see *note Permission
Bits::.

   There are two ways you can access the file type information in a file
mode.  Firstly, for each file type there is a “predicate macro” which
examines a given file mode and returns whether it is of that type or
not.  Secondly, you can mask out the rest of the file mode to leave just
the file type code, and compare this against constants for each of the
supported file types.

   All of the symbols listed in this section are defined in the header
file ‘sys/stat.h’.

   The following predicate macros test the type of a file, given the
value M which is the ‘st_mode’ field returned by ‘stat’ on that file:

 -- Macro: int S_ISDIR (mode_t M)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This macro returns non-zero if the file is a directory.

 -- Macro: int S_ISCHR (mode_t M)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This macro returns non-zero if the file is a character special file
     (a device like a terminal).

 -- Macro: int S_ISBLK (mode_t M)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This macro returns non-zero if the file is a block special file (a
     device like a disk).

 -- Macro: int S_ISREG (mode_t M)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This macro returns non-zero if the file is a regular file.

 -- Macro: int S_ISFIFO (mode_t M)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This macro returns non-zero if the file is a FIFO special file, or
     a pipe.  *Note Pipes and FIFOs::.

 -- Macro: int S_ISLNK (mode_t M)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This macro returns non-zero if the file is a symbolic link.  *Note
     Symbolic Links::.

 -- Macro: int S_ISSOCK (mode_t M)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This macro returns non-zero if the file is a socket.  *Note
     Sockets::.

   An alternate non-POSIX method of testing the file type is supported
for compatibility with BSD. The mode can be bitwise AND-ed with ‘S_IFMT’
to extract the file type code, and compared to the appropriate constant.
For example,

     S_ISCHR (MODE)

is equivalent to:

     ((MODE & S_IFMT) == S_IFCHR)

 -- Macro: int S_IFMT

     This is a bit mask used to extract the file type code from a mode
     value.

   These are the symbolic names for the different file type codes:

‘S_IFDIR’

     This is the file type constant of a directory file.

‘S_IFCHR’

     This is the file type constant of a character-oriented device file.

‘S_IFBLK’

     This is the file type constant of a block-oriented device file.

‘S_IFREG’

     This is the file type constant of a regular file.

‘S_IFLNK’

     This is the file type constant of a symbolic link.

‘S_IFSOCK’

     This is the file type constant of a socket.

‘S_IFIFO’

     This is the file type constant of a FIFO or pipe.

   The POSIX.1b standard introduced a few more objects which possibly
can be implemented as objects in the filesystem.  These are message
queues, semaphores, and shared memory objects.  To allow differentiating
these objects from other files the POSIX standard introduced three new
test macros.  But unlike the other macros they do not take the value of
the ‘st_mode’ field as the parameter.  Instead they expect a pointer to
the whole ‘struct stat’ structure.

 -- Macro: int S_TYPEISMQ (struct stat *S)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     If the system implements POSIX message queues as distinct objects
     and the file is a message queue object, this macro returns a
     non-zero value.  In all other cases the result is zero.

 -- Macro: int S_TYPEISSEM (struct stat *S)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     If the system implements POSIX semaphores as distinct objects and
     the file is a semaphore object, this macro returns a non-zero
     value.  In all other cases the result is zero.

 -- Macro: int S_TYPEISSHM (struct stat *S)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     If the system implements POSIX shared memory objects as distinct
     objects and the file is a shared memory object, this macro returns
     a non-zero value.  In all other cases the result is zero.


File: libc.info,  Node: File Owner,  Next: Permission Bits,  Prev: Testing File Type,  Up: File Attributes

14.10.4 File Owner
------------------

Every file has an “owner” which is one of the registered user names
defined on the system.  Each file also has a “group” which is one of the
defined groups.  The file owner can often be useful for showing you who
edited the file (especially when you edit with GNU Emacs), but its main
purpose is for access control.

   The file owner and group play a role in determining access because
the file has one set of access permission bits for the owner, another
set that applies to users who belong to the file's group, and a third
set of bits that applies to everyone else.  *Note Access Permission::,
for the details of how access is decided based on this data.

   When a file is created, its owner is set to the effective user ID of
the process that creates it (*note Process Persona::).  The file's group
ID may be set to either the effective group ID of the process, or the
group ID of the directory that contains the file, depending on the
system where the file is stored.  When you access a remote file system,
it behaves according to its own rules, not according to the system your
program is running on.  Thus, your program must be prepared to encounter
either kind of behavior no matter what kind of system you run it on.

   You can change the owner and/or group owner of an existing file using
the ‘chown’ function.  This is the primitive for the ‘chown’ and ‘chgrp’
shell commands.

   The prototype for this function is declared in ‘unistd.h’.

 -- Function: int chown (const char *FILENAME, uid_t OWNER, gid_t GROUP)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘chown’ function changes the owner of the file FILENAME to
     OWNER, and its group owner to GROUP.

     Changing the owner of the file on certain systems clears the
     set-user-ID and set-group-ID permission bits.  (This is because
     those bits may not be appropriate for the new owner.)  Other file
     permission bits are not changed.

     The return value is ‘0’ on success and ‘-1’ on failure.  In
     addition to the usual file name errors (*note File Name Errors::),
     the following ‘errno’ error conditions are defined for this
     function:

     ‘EPERM’
          This process lacks permission to make the requested change.

          Only privileged users or the file's owner can change the
          file's group.  On most file systems, only privileged users can
          change the file owner; some file systems allow you to change
          the owner if you are currently the owner.  When you access a
          remote file system, the behavior you encounter is determined
          by the system that actually holds the file, not by the system
          your program is running on.

          *Note Options for Files::, for information about the
          ‘_POSIX_CHOWN_RESTRICTED’ macro.

     ‘EROFS’
          The file is on a read-only file system.

 -- Function: int fchown (int FILEDES, uid_t OWNER, gid_t GROUP)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This is like ‘chown’, except that it changes the owner of the open
     file with descriptor FILEDES.

     The return value from ‘fchown’ is ‘0’ on success and ‘-1’ on
     failure.  The following ‘errno’ error codes are defined for this
     function:

     ‘EBADF’
          The FILEDES argument is not a valid file descriptor.

     ‘EINVAL’
          The FILEDES argument corresponds to a pipe or socket, not an
          ordinary file.

     ‘EPERM’
          This process lacks permission to make the requested change.
          For details see ‘chmod’ above.

     ‘EROFS’
          The file resides on a read-only file system.


File: libc.info,  Node: Permission Bits,  Next: Access Permission,  Prev: File Owner,  Up: File Attributes

14.10.5 The Mode Bits for Access Permission
-------------------------------------------

The “file mode”, stored in the ‘st_mode’ field of the file attributes,
contains two kinds of information: the file type code, and the access
permission bits.  This section discusses only the access permission
bits, which control who can read or write the file.  *Note Testing File
Type::, for information about the file type code.

   All of the symbols listed in this section are defined in the header
file ‘sys/stat.h’.

   These symbolic constants are defined for the file mode bits that
control access permission for the file:

‘S_IRUSR’
‘S_IREAD’

     Read permission bit for the owner of the file.  On many systems
     this bit is 0400.  ‘S_IREAD’ is an obsolete synonym provided for
     BSD compatibility.

‘S_IWUSR’
‘S_IWRITE’

     Write permission bit for the owner of the file.  Usually 0200.
     ‘S_IWRITE’ is an obsolete synonym provided for BSD compatibility.

‘S_IXUSR’
‘S_IEXEC’

     Execute (for ordinary files) or search (for directories) permission
     bit for the owner of the file.  Usually 0100.  ‘S_IEXEC’ is an
     obsolete synonym provided for BSD compatibility.

‘S_IRWXU’

     This is equivalent to ‘(S_IRUSR | S_IWUSR | S_IXUSR)’.

‘S_IRGRP’

     Read permission bit for the group owner of the file.  Usually 040.

‘S_IWGRP’

     Write permission bit for the group owner of the file.  Usually 020.

‘S_IXGRP’

     Execute or search permission bit for the group owner of the file.
     Usually 010.

‘S_IRWXG’

     This is equivalent to ‘(S_IRGRP | S_IWGRP | S_IXGRP)’.

‘S_IROTH’

     Read permission bit for other users.  Usually 04.

‘S_IWOTH’

     Write permission bit for other users.  Usually 02.

‘S_IXOTH’

     Execute or search permission bit for other users.  Usually 01.

‘S_IRWXO’

     This is equivalent to ‘(S_IROTH | S_IWOTH | S_IXOTH)’.

‘S_ISUID’

     This is the set-user-ID on execute bit, usually 04000.  *Note How
     Change Persona::.

‘S_ISGID’

     This is the set-group-ID on execute bit, usually 02000.  *Note How
     Change Persona::.

‘S_ISVTX’

     This is the “sticky” bit, usually 01000.

     For a directory it gives permission to delete a file in that
     directory only if you own that file.  Ordinarily, a user can either
     delete all the files in a directory or cannot delete any of them
     (based on whether the user has write permission for the directory).
     The same restriction applies--you must have both write permission
     for the directory and own the file you want to delete.  The one
     exception is that the owner of the directory can delete any file in
     the directory, no matter who owns it (provided the owner has given
     himself write permission for the directory).  This is commonly used
     for the ‘/tmp’ directory, where anyone may create files but not
     delete files created by other users.

     Originally the sticky bit on an executable file modified the
     swapping policies of the system.  Normally, when a program
     terminated, its pages in core were immediately freed and reused.
     If the sticky bit was set on the executable file, the system kept
     the pages in core for a while as if the program were still running.
     This was advantageous for a program likely to be run many times in
     succession.  This usage is obsolete in modern systems.  When a
     program terminates, its pages always remain in core as long as
     there is no shortage of memory in the system.  When the program is
     next run, its pages will still be in core if no shortage arose
     since the last run.

     On some modern systems where the sticky bit has no useful meaning
     for an executable file, you cannot set the bit at all for a
     non-directory.  If you try, ‘chmod’ fails with ‘EFTYPE’; *note
     Setting Permissions::.

     Some systems (particularly SunOS) have yet another use for the
     sticky bit.  If the sticky bit is set on a file that is _not_
     executable, it means the opposite: never cache the pages of this
     file at all.  The main use of this is for the files on an NFS
     server machine which are used as the swap area of diskless client
     machines.  The idea is that the pages of the file will be cached in
     the client's memory, so it is a waste of the server's memory to
     cache them a second time.  With this usage the sticky bit also
     implies that the filesystem may fail to record the file's
     modification time onto disk reliably (the idea being that no-one
     cares for a swap file).

     This bit is only available on BSD systems (and those derived from
     them).  Therefore one has to use the ‘_GNU_SOURCE’ feature select
     macro, or not define any feature test macros, to get the definition
     (*note Feature Test Macros::).

   The actual bit values of the symbols are listed in the table above so
you can decode file mode values when debugging your programs.  These bit
values are correct for most systems, but they are not guaranteed.

   *Warning:* Writing explicit numbers for file permissions is bad
practice.  Not only is it not portable, it also requires everyone who
reads your program to remember what the bits mean.  To make your program
clean use the symbolic names.


File: libc.info,  Node: Access Permission,  Next: Setting Permissions,  Prev: Permission Bits,  Up: File Attributes

14.10.6 How Your Access to a File is Decided
--------------------------------------------

Recall that the operating system normally decides access permission for
a file based on the effective user and group IDs of the process and its
supplementary group IDs, together with the file's owner, group and
permission bits.  These concepts are discussed in detail in *note
Process Persona::.

   If the effective user ID of the process matches the owner user ID of
the file, then permissions for read, write, and execute/search are
controlled by the corresponding "user" (or "owner") bits.  Likewise, if
any of the effective group ID or supplementary group IDs of the process
matches the group owner ID of the file, then permissions are controlled
by the "group" bits.  Otherwise, permissions are controlled by the
"other" bits.

   Privileged users, like ‘root’, can access any file regardless of its
permission bits.  As a special case, for a file to be executable even by
a privileged user, at least one of its execute bits must be set.


File: libc.info,  Node: Setting Permissions,  Next: Testing File Access,  Prev: Access Permission,  Up: File Attributes

14.10.7 Assigning File Permissions
----------------------------------

The primitive functions for creating files (for example, ‘open’ or
‘mkdir’) take a MODE argument, which specifies the file permissions to
give the newly created file.  This mode is modified by the process's
“file creation mask”, or “umask”, before it is used.

   The bits that are set in the file creation mask identify permissions
that are always to be disabled for newly created files.  For example, if
you set all the "other" access bits in the mask, then newly created
files are not accessible at all to processes in the "other" category,
even if the MODE argument passed to the create function would permit
such access.  In other words, the file creation mask is the complement
of the ordinary access permissions you want to grant.

   Programs that create files typically specify a MODE argument that
includes all the permissions that make sense for the particular file.
For an ordinary file, this is typically read and write permission for
all classes of users.  These permissions are then restricted as
specified by the individual user's own file creation mask.

   To change the permission of an existing file given its name, call
‘chmod’.  This function uses the specified permission bits and ignores
the file creation mask.

   In normal use, the file creation mask is initialized by the user's
login shell (using the ‘umask’ shell command), and inherited by all
subprocesses.  Application programs normally don't need to worry about
the file creation mask.  It will automatically do what it is supposed to
do.

   When your program needs to create a file and bypass the umask for its
access permissions, the easiest way to do this is to use ‘fchmod’ after
opening the file, rather than changing the umask.  In fact, changing the
umask is usually done only by shells.  They use the ‘umask’ function.

   The functions in this section are declared in ‘sys/stat.h’.

 -- Function: mode_t umask (mode_t MASK)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘umask’ function sets the file creation mask of the current
     process to MASK, and returns the previous value of the file
     creation mask.

     Here is an example showing how to read the mask with ‘umask’
     without changing it permanently:

          mode_t
          read_umask (void)
          {
            mode_t mask = umask (0);
            umask (mask);
            return mask;
          }

     However, on GNU/Hurd systems it is better to use ‘getumask’ if you
     just want to read the mask value, because it is reentrant.

 -- Function: mode_t getumask (void)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     Return the current value of the file creation mask for the current
     process.  This function is a GNU extension and is only available on
     GNU/Hurd systems.

 -- Function: int chmod (const char *FILENAME, mode_t MODE)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘chmod’ function sets the access permission bits for the file
     named by FILENAME to MODE.

     If FILENAME is a symbolic link, ‘chmod’ changes the permissions of
     the file pointed to by the link, not those of the link itself.

     This function returns ‘0’ if successful and ‘-1’ if not.  In
     addition to the usual file name errors (*note File Name Errors::),
     the following ‘errno’ error conditions are defined for this
     function:

     ‘ENOENT’
          The named file doesn't exist.

     ‘EPERM’
          This process does not have permission to change the access
          permissions of this file.  Only the file's owner (as judged by
          the effective user ID of the process) or a privileged user can
          change them.

     ‘EROFS’
          The file resides on a read-only file system.

     ‘EFTYPE’
          MODE has the ‘S_ISVTX’ bit (the "sticky bit") set, and the
          named file is not a directory.  Some systems do not allow
          setting the sticky bit on non-directory files, and some do
          (and only some of those assign a useful meaning to the bit for
          non-directory files).

          You only get ‘EFTYPE’ on systems where the sticky bit has no
          useful meaning for non-directory files, so it is always safe
          to just clear the bit in MODE and call ‘chmod’ again.  *Note
          Permission Bits::, for full details on the sticky bit.

 -- Function: int fchmod (int FILEDES, mode_t MODE)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This is like ‘chmod’, except that it changes the permissions of the
     currently open file given by FILEDES.

     The return value from ‘fchmod’ is ‘0’ on success and ‘-1’ on
     failure.  The following ‘errno’ error codes are defined for this
     function:

     ‘EBADF’
          The FILEDES argument is not a valid file descriptor.

     ‘EINVAL’
          The FILEDES argument corresponds to a pipe or socket, or
          something else that doesn't really have access permissions.

     ‘EPERM’
          This process does not have permission to change the access
          permissions of this file.  Only the file's owner (as judged by
          the effective user ID of the process) or a privileged user can
          change them.

     ‘EROFS’
          The file resides on a read-only file system.


File: libc.info,  Node: Testing File Access,  Next: File Times,  Prev: Setting Permissions,  Up: File Attributes

14.10.8 Testing Permission to Access a File
-------------------------------------------

In some situations it is desirable to allow programs to access files or
devices even if this is not possible with the permissions granted to the
user.  One possible solution is to set the setuid-bit of the program
file.  If such a program is started the _effective_ user ID of the
process is changed to that of the owner of the program file.  So to
allow write access to files like ‘/etc/passwd’, which normally can be
written only by the super-user, the modifying program will have to be
owned by ‘root’ and the setuid-bit must be set.

   But besides the files the program is intended to change the user
should not be allowed to access any file to which s/he would not have
access anyway.  The program therefore must explicitly check whether _the
user_ would have the necessary access to a file, before it reads or
writes the file.

   To do this, use the function ‘access’, which checks for access
permission based on the process's _real_ user ID rather than the
effective user ID. (The setuid feature does not alter the real user ID,
so it reflects the user who actually ran the program.)

   There is another way you could check this access, which is easy to
describe, but very hard to use.  This is to examine the file mode bits
and mimic the system's own access computation.  This method is
undesirable because many systems have additional access control
features; your program cannot portably mimic them, and you would not
want to try to keep track of the diverse features that different systems
have.  Using ‘access’ is simple and automatically does whatever is
appropriate for the system you are using.

   ‘access’ is _only_ appropriate to use in setuid programs.  A
non-setuid program will always use the effective ID rather than the real
ID.

   The symbols in this section are declared in ‘unistd.h’.

 -- Function: int access (const char *FILENAME, int HOW)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     The ‘access’ function checks to see whether the file named by
     FILENAME can be accessed in the way specified by the HOW argument.
     The HOW argument either can be the bitwise OR of the flags ‘R_OK’,
     ‘W_OK’, ‘X_OK’, or the existence test ‘F_OK’.

     This function uses the _real_ user and group IDs of the calling
     process, rather than the _effective_ IDs, to check for access
     permission.  As a result, if you use the function from a ‘setuid’
     or ‘setgid’ program (*note How Change Persona::), it gives
     information relative to the user who actually ran the program.

     The return value is ‘0’ if the access is permitted, and ‘-1’
     otherwise.  (In other words, treated as a predicate function,
     ‘access’ returns true if the requested access is _denied_.)

     In addition to the usual file name errors (*note File Name
     Errors::), the following ‘errno’ error conditions are defined for
     this function:

     ‘EACCES’
          The access specified by HOW is denied.

     ‘ENOENT’
          The file doesn't exist.

     ‘EROFS’
          Write permission was requested for a file on a read-only file
          system.

   These macros are defined in the header file ‘unistd.h’ for use as the
HOW argument to the ‘access’ function.  The values are integer
constants.

 -- Macro: int R_OK

     Flag meaning test for read permission.

 -- Macro: int W_OK

     Flag meaning test for write permission.

 -- Macro: int X_OK

     Flag meaning test for execute/search permission.

 -- Macro: int F_OK

     Flag meaning test for existence of the file.

 -- Function: int faccessat (int FILEDES, const char *FILENAME, int HOW,
          int FLAGS)

     | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt | *Note POSIX
     Safety Concepts::.

     This function is a descriptor-relative version of the ‘access’
     function above.  *Note Descriptor-Relative Access::.  The FLAGS
     argument can contain a combination of the flags ‘AT_EACCESS’
     described below, ‘AT_EMPTY_PATH’, and ‘AT_SYMLINK_NOFOLLOW’.

     ‘AT_EACCESS’
          This flag when passed to the ‘faccessat’ function causes it to
          perform access checks using effective user and group IDs
          instead of real IDs, which is the default and matches the
          ‘access’ function.

     Compared to ‘access’, some additional error conditions can occur.
     *Note Descriptor-Relative Access::.

     This function may not work correctly on older kernels missing the
     ‘faccessat2’ system call.


File: libc.info,  Node: File Times,  Next: File Size,  Prev: Testing File Access,  Up: File Attributes

14.10.9 File Times
------------------

Each file has three time stamps associated with it: its access time, its
modification time, and its attribute modification time.  These
correspond to the ‘st_atime’, ‘st_mtime’, and ‘st_ctime’ members of the
‘stat’ structure; see *note File Attributes::.

   All of these times are represented in calendar time format, as
‘time_t’ objects.  This data type is defined in ‘time.h’.  For more
information about representation and manipulation of time values, see
*note Calendar Time::.

   Reading from a file updates its access time attribute, and writing
updates its modification time.  When a file is created, all three time
stamps for that file are set to the current time.  In addition, the
attribute change time and modification time fields of the directory that
contains the new entry are updated.

   Adding a new name for a file with the ‘link’ function updates the
attribute change time field of the file being linked, and both the
attribute change time and modification time fields of the directory
containing the new name.  These same fields are affected if a file name
is deleted with ‘unlink’, ‘remove’ or ‘rmdir’.  Renaming a file with
‘rename’ affects only the attribute change time and modification time
fields of the two parent directories involved, and not the times for the
file being renamed.

   Changing the attributes of a file (for example, with ‘chmod’) updates
its attribute change time field.

   You can also change some of the time stamps of a file explicitly
using the ‘utime’ function--all except the attribute change time.  You
need to include the header file ‘utime.h’ to use this facility.

 -- Data Type: struct utimbuf

     The ‘utimbuf’ structure is used with the ‘utime’ function to
     specify new access and modification times for a file.  It contains
     the following members:

     ‘time_t actime’
          This is the access time for the file.

     ‘time_t modtime’
          This is the modification time for the file.

 -- Function: int utime (const char *FILENAME, const struct utimbuf
          *TIMES)

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is used to modify the file times associated with the
     file named FILENAME.

     If TIMES is a null pointer, then the access and modification times
     of the file are set to the current time.  Otherwise, they are set
     to the values from the ‘actime’ and ‘modtime’ members
     (respectively) of the ‘utimbuf’ structure pointed to by TIMES.

     The attribute modification time for the file is set to the current
     time in either case (since changing the time stamps is itself a
     modification of the file attributes).

     The ‘utime’ function returns ‘0’ if successful and ‘-1’ on failure.
     In addition to the usual file name errors (*note File Name
     Errors::), the following ‘errno’ error conditions are defined for
     this function:

     ‘EACCES’
          There is a permission problem in the case where a null pointer
          was passed as the TIMES argument.  In order to update the time
          stamp on the file, you must either be the owner of the file,
          have write permission for the file, or be a privileged user.

     ‘ENOENT’
          The file doesn't exist.

     ‘EPERM’
          If the TIMES argument is not a null pointer, you must either
          be the owner of the file or be a privileged user.

     ‘EROFS’
          The file lives on a read-only file system.

   Each of the three time stamps has a corresponding microsecond part,
which extends its resolution.  These fields are called ‘st_atime_usec’,
‘st_mtime_usec’, and ‘st_ctime_usec’; each has a value between 0 and
999,999, which indicates the time in microseconds.  They correspond to
the ‘tv_usec’ field of a ‘timeval’ structure; see *note Time Types::.

   The ‘utimes’ function is like ‘utime’, but also lets you specify the
fractional part of the file times.  The prototype for this function is
in the header file ‘sys/time.h’.

 -- Function: int utimes (const char *FILENAME, const struct timeval
          TVP[2])

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function sets the file access and modification times of the
     file FILENAME.  The new file access time is specified by ‘TVP[0]’,
     and the new modification time by ‘TVP[1]’.  Similar to ‘utime’, if
     TVP is a null pointer then the access and modification times of the
     file are set to the current time.  This function comes from BSD.

     The return values and error conditions are the same as for the
     ‘utime’ function.

 -- Function: int lutimes (const char *FILENAME, const struct timeval
          TVP[2])

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is like ‘utimes’, except that it does not follow
     symbolic links.  If FILENAME is the name of a symbolic link,
     ‘lutimes’ sets the file access and modification times of the
     symbolic link special file itself (as seen by ‘lstat’; *note
     Symbolic Links::) while ‘utimes’ sets the file access and
     modification times of the file the symbolic link refers to.  This
     function comes from FreeBSD, and is not available on all platforms
     (if not available, it will fail with ‘ENOSYS’).

     The return values and error conditions are the same as for the
     ‘utime’ function.

 -- Function: int futimes (int FD, const struct timeval TVP[2])

     Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety
     Concepts::.

     This function is like ‘utimes’, except that it takes an open file
     descriptor as an argument instead of a file name.  *Note Low-Level
     I/O::.  This function comes from FreeBSD, and is not available on
     all platforms (if not available, it will fail with ‘ENOSYS’).

     Like ‘utimes’, ‘futimes’ returns ‘0’ on success and ‘-1’ on
     failure.  The following ‘errno’ error conditions are defined for
     ‘futimes’:

     ‘EACCES’
          There is a permission problem in the case where a null pointer
          was passed as the TIMES argument.  In order to update the time
          stamp on the file, you must either be the owner of the file,
          have write permission for the file, or be a privileged user.

     ‘EBADF’
          The FILEDES argument is not a valid file descriptor.

     ‘EINVAL’
          At least one of the fields in the ‘tvp’ array passed has an
          invalid value.

     ‘EPERM’
          If the TIMES argument is not a null pointer, you must either
          be the owner of the file or be a privileged user.

     ‘EROFS’
          The file lives on a read-only file system.

 -- Function: int futimens (int FILEDES, const struct timespec TSP[2])

     | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt | *Note POSIX
     Safety Concepts::.

     This function is like ‘futimes’, except that it sets the file
     access and modification timestamps with nanosecond precision.  The
     argument ‘tsp’ is used similarly to ‘futimes’' ‘tvp’, but has a
     ‘const struct timespec’ type that can express calendar time with
     nanosecond precision.  *Note Time Types::.

 -- Function: int utimensat (int FILEDES, const char *FILENAME, const
          struct timespec TSP[2], int FLAGS)

     | MT-Safe | AS-Unsafe corrupt | AC-Unsafe corrupt | *Note POSIX
     Safety Concepts::.

     This function is a descriptor-relative version of the ‘futimens’
     function above.  *Note Descriptor-Relative Access::.  The FLAGS
     argument can contain a combination of the flags ‘AT_EMPTY_PATH’,
     and ‘AT_SYMLINK_NOFOLLOW’.  The call:

          futimens (FILEDES, TSP)

     is equivalent to:

          utimensat (FILEDES, NULL, TSP, 0)

     Compared to ‘futimens’, some additional error conditions can occur
     due to descriptor-relative access.  *Note Descriptor-Relative
     Access::.  In addition to this, the following other errors can also
     occur:

     ‘EINVAL’
          The FILENAME argument is NULL, FILEDES is not ‘AT_FDCWD’, and
          FLAGS is not ‘0’.

     ‘ELOOP’
          There are too many levels of indirection.  This can be the
          result of circular symbolic links to directories.

     ‘ENAMETOOLONG’
          The resulting path is too long.  This error only occurs on
          systems which have a limit on the file name length.

     ‘ENOENT’
          The FILENAME argument is an empty string and FLAGS does not
          contain ‘AT_EMPTY_PATH’, or FILENAME does not refer to an
          existing file.

     ‘ESRCH’
          Search permission was denied for one of the prefix components
          of the the FILENAME argument.