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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 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.

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 .