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PROLOG

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

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 not a directory.

       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.1‐2008, 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,  2013  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013  by  the
       Institute  of  Electrical  and  Electronics  Engineers,  Inc and The Open Group.  (This is
       POSIX.1-2008 with the  2013  Technical  Corrigendum  1  applied.)  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.unix.org/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 .