NAME
fcntl — file control options
SYNOPSIS
#include <sys/types.h>
#include <fcntl.h>
DESCRIPTION
The
fcntl()
function provides for control over open files.
The
<fcntl.h>
include file describes
requests
and
arguments
to
fcntl()
and
open().
See
fcntl(2)
and
open(2).
The access modes set by
open()
and accessed by
fcntl()
are:
The mask for file access modes is:
The file status flags set by
open()
or
fcntl()
and accessed by
fcntl()
are:
- O_NDELAY
Nonblocking I/O.
- O_NONBLOCK
POSIX-style nonblocking I/O.
- O_APPEND
Append (writes guaranteed at the end).
- O_DSYNC
Write through cache for data.
- O_SYNC
Write through cache for data and attributes.
- O_RSYNC|O_DSYNC
Write through cache for data on reads and writes.
- O_RSYNC|O_SYNC
Write through cache for data and attributes on reads and writes.
- O_LARGEFILE
When the filesystem is mounted as large files enabled, the
O_LARGEFILE
option allows the file to grow over 2 GB.
The flag
O_SYNCIO
is a synonym for
O_SYNC
and is defined for backward
compatibility in
<fcntl.h>.
The flag values accessible only to
open()
are:
- O_CREAT
Open with file create (uses third open arg).
- O_TRUNC
Open with truncation.
- O_EXCL
Exclusive open.
- O_NOCTTY
Do not assign a controlling terminal.
- O_NOFOLLOW
Do not traverse a symbolic link if it is the last component in the path.
The requests for
fcntl()
are:
- F_DUPFD
Duplicate file descriptor.
- F_GETFD
Get file descriptor flags.
- F_SETFD
Set file descriptor flags.
- F_GETFL
Get file flags.
- F_SETFL
Set file flags.
- F_GETLK
Get blocking file lock.
- F_SETLK
Set or clear file locks and fail on busy.
- F_SETLKW
Set or clear file locks and wait on busy.
- F_ADVISE
Fadvise service request (see
fadvise(2)).
The file descriptor flag for
F_GETFD,
F_SETFD
is:
The file segment locking control structure
struct flock,
includes the following members:
short l_type; /* F_RDLCK, F_WRLCK or F_UNLCK */
short l_whence; /* Flag - see lseek(2) */
off_t l_start; /* Relative offset in bytes */
off_t l_len; /* Size; if 0 then until EOF */
pid_t l_pid; /* By F_GETLK - process holding lock */
The file segment locking types are:
F_RDLCK Read lock.
F_WRLCK Write lock.
F_UNLCK Remove locks.
STANDARDS CONFORMANCE
<fcntl.h>: AES, SVID3, XPG2, XPG3, XPG4, FIPS 151-2, POSIX.1
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