Provided by: manpages-posix-dev_2013a-1_all 
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 .