fcntl.h(3)                 POSIX Programmer's Manual                fcntl.h(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       fcntl.h -- file control options

SYNOPSIS
       #include <fcntl.h>

DESCRIPTION
       The <fcntl.h> header shall define the following symbolic constants for
       the cmd argument used by fcntl().  The values shall be unique and shall
       be suitable for use in #if preprocessing directives.

       F_DUPFD     Duplicate file descriptor.

       F_DUPFD_CLOEXEC
                   Duplicate file descriptor with the close-on-exec flag
                   FD_CLOEXEC set.

       F_GETFD     Get file descriptor flags.

       F_SETFD     Set file descriptor flags.

       F_GETFL     Get file status flags and file access modes.

       F_SETFL     Set file status flags.

       F_GETLK     Get record locking information.

       F_SETLK     Set record locking information.

       F_SETLKW    Set record locking information; wait if blocked.

       F_GETOWN    Get process or process group ID to receive SIGURG signals.

       F_SETOWN    Set process or process group ID to receive SIGURG signals.

       The <fcntl.h> header shall define the following symbolic constant used
       for the fcntl() file descriptor flags, which shall be suitable for use
       in #if preprocessing directives.

       FD_CLOEXEC  Close the file descriptor upon execution of an exec family
                   function.

       The <fcntl.h> header shall also define the following symbolic constants
       for the _l__type argument used for record locking with fcntl().  The
       values shall be unique and shall be suitable for use in #if
       preprocessing directives.

       F_RDLCK     Shared or read lock.

       F_UNLCK     Unlock.

       F_WRLCK     Exclusive or write lock.

       The <fcntl.h> header shall define the values used for _l__whence,
       SEEK_SET, SEEK_CUR, and SEEK_END as described in <stdio.h>.

       The <fcntl.h> header shall define the following symbolic constants as
       file creation flags for use in the oflag value to open() and openat().
       The values shall be bitwise-distinct and shall be suitable for use in
       #if preprocessing directives.

       O_CLOEXEC   The FD_CLOEXEC flag associated with the new descriptor
                   shall be set to close the file descriptor upon execution of
                   an exec family function.

       O_CREAT     Create file if it does not exist.

       O_DIRECTORY Fail if file is a non-directory file.

       O_EXCL      Exclusive use flag.

       O_NOCTTY    Do not assign controlling terminal.

       O_NOFOLLOW  Do not follow symbolic links.

       O_TRUNC     Truncate flag.

       O_TTY_INIT  Set the termios structure terminal parameters to a state
                   that provides conforming behavior; see Section 11.2,
                   Parameters that Can be Set.

       The O_TTY_INIT flag can have the value zero and in this case it need
       not be bitwise-distinct from the other flags.

       The <fcntl.h> header shall define the following symbolic constants for
       use as file status flags for open(), openat(), and fcntl().  The values
       shall be suitable for use in #if preprocessing directives.

       O_APPEND    Set append mode.

       O_DSYNC     Write according to synchronized I/O data integrity
                   completion.

       O_NONBLOCK  Non-blocking mode.

       O_RSYNC     Synchronized read I/O operations.

       O_SYNC      Write according to synchronized I/O file integrity
                   completion.

       The <fcntl.h> header shall define the following symbolic constant for
       use as the mask for file access modes. The value shall be suitable for
       use in #if preprocessing directives.

       O_ACCMODE   Mask for file access modes.

       The <fcntl.h> header shall define the following symbolic constants for
       use as the file access modes for open(), openat(), and fcntl().  The
       values shall be unique, except that O_EXEC and O_SEARCH may have equal
       values. The values shall be suitable for use in #if preprocessing
       directives.

       O_EXEC      Open for execute only (non-directory files). The result is
                   unspecified if this flag is applied to a directory.

       O_RDONLY    Open for reading only.

       O_RDWR      Open for reading and writing.

       O_SEARCH    Open directory for search only. The result is unspecified
                   if this flag is applied to a non-directory file.

       O_WRONLY    Open for writing only.

       The <fcntl.h> header shall define the symbolic constants for file modes
       for use as values of mode_t as described in <sys/stat.h>.

       The <fcntl.h> header shall define the following symbolic constant as a
       special value used in place of a file descriptor for the *at()
       functions which take a directory file descriptor as a parameter:

       AT_FDCWD    Use the current working directory to determine the target
                   of relative file paths.

       The <fcntl.h> header shall define the following symbolic constant as a
       value for the flag used by faccessat():

       AT_EACCESS  Check access using effective user and group ID.

       The <fcntl.h> header shall define the following symbolic constant as a
       value for the flag used by fstatat(), fchmodat(), fchownat(), and
       utimensat():

       AT_SYMLINK_NOFOLLOW
                   Do not follow symbolic links.

       The <fcntl.h> header shall define the following symbolic constant as a
       value for the flag used by linkat():

       AT_SYMLINK_FOLLOW
                   Follow symbolic link.

       The <fcntl.h> header shall define the following symbolic constant as a
       value for the flag used by unlinkat():

       AT_REMOVEDIR
                   Remove directory instead of file.

       The <fcntl.h> header shall define the following symbolic constants for
       the advice argument used by posix__fadvise():

       POSIX_FADV_DONTNEED
             The application expects that it will not access the specified
             data in the near future.

       POSIX_FADV_NOREUSE
             The application expects to access the specified data once and
             then not reuse it thereafter.

       POSIX_FADV_NORMAL
             The application has no advice to give on its behavior with
             respect to the specified data. It is the default characteristic
             if no advice is given for an open file.

       POSIX_FADV_RANDOM
             The application expects to access the specified data in a random
             order.

       POSIX_FADV_SEQUENTIAL
             The application expects to access the specified data sequentially
             from lower offsets to higher offsets.

       POSIX_FADV_WILLNEED
             The application expects to access the specified data in the near
             future.

       The <fcntl.h> header shall define the flock structure describing a file
       lock. It shall include the following members:


           short  l_type   Type of lock; F_RDLCK, F_WRLCK, F_UNLCK.
           short  l_whence Flag for starting offset.
           off_t  l_start  Relative offset in bytes.
           off_t  l_len    Size; if 0 then until EOF.
           pid_t  l_pid    Process ID of the process holding the lock; returned with F_GETLK.

       The <fcntl.h> header shall define the mode_t, off_t, and pid_t types as
       described in <sys/types.h>.

       The following shall be declared as functions and may also be defined as
       macros. Function prototypes shall be provided.


           int  creat(const char *, mode_t);
           int  fcntl(int, int, ...);
           int  open(const char *, int, ...);
           int  openat(int, const char *, int, ...);
           int  posix_fadvise(int, off_t, off_t, int);
           int  posix_fallocate(int, off_t, off_t);

       Inclusion of the <fcntl.h> header may also make visible all symbols
       from <sys/stat.h> and <unistd.h>.

       The following sections are informative.

APPLICATION USAGE
       Although no existing implementation defines AT_SYMLINK_FOLLOW and
       AT_SYMLINK_NOFOLLOW as the same numeric value, POSIX.1-2008 does not
       prohibit that as the two constants are not used with the same
       interfaces.

RATIONALE
       While many of the symbolic constants introduced in the <fcntl.h> header
       do not strictly need to be used in #if preprocessor directives,
       widespread historic practice has defined them as macros that are usable
       in such constructs, and examination of existing applications has shown
       that they are occasionally used in such a way. Therefore it was decided
       to retain this requirement on an implementation in POSIX.1-2008.

FUTURE DIRECTIONS
       None.

SEE ALSO
       <stdio.h>, <sys_stat.h>, <sys_types.h>, <unistd.h>

       The System Interfaces volume of POSIX.1-2017, creat(), exec, fcntl(),
       futimens(), open(), posix__fadvise(), posix__fallocate(), posix__madvise()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  In the event of any discrepancy between this version and the
       original IEEE and The Open Group Standard, the original IEEE and The
       Open Group Standard is the referee document. The original Standard can
       be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                           fcntl.h(3)
