Section (3) lockf
lockf — apply, test or remove a POSIX lock on an open file
Apply, test or remove a POSIX lock on a section of an open
file. The file is specified by
fd, a file descriptor open for
writing, the action by
cmd, and the section consists
of byte positions
len is positive, and
len is negative, where
pos is the current
file position, and if
len is zero, the section
extends from the current file position to infinity,
encompassing the present and future end-of-file positions. In
all cases, the section may extend past current
lockf() is just an
interface on top of fcntl(2) locking. Many
other systems implement
in this way, but note that POSIX.1 leaves the relationship
lockf() and fcntl(2) locks unspecified.
A portable application should probably avoid mixing calls to
Valid operations are given below:
Set an exclusive lock on the specified section of the file. If (part of) this section is already locked, the call blocks until the previous lock is released. If this section overlaps an earlier locked section, both are merged. File locks are released as soon as the process holding the locks closes some file descriptor for the file. A child process does not inherit these locks.
F_LOCKbut the call never blocks and returns an error instead if the file is already locked.
Unlock the indicated section of the file. This may cause a locked section to be split into two locked sections.
Test the lock: return 0 if the specified section is unlocked or locked by this process; return −1, set
errnoto EAGAIN (EACCES on some other systems), if another process holds a lock.
On success, zero is returned. On error, −1 is
errno is set
- EACCES or EAGAIN
The file is locked and
F_TESTwas specified, or the operation is prohibited because the file has been memory-mapped by another process.
fdis not an open file descriptor; or
fdis not a writable file descriptor.
The command was
F_LOCKand this lock operation would cause a deadlock.
While waiting to acquire a lock, the call was interrupted by delivery of a signal caught by a handler; see signal(7).
An invalid operation was specified in
Too many segment locks open, lock table is full.
For an explanation of the terms used in this section, see attributes(7).
mandatory-locking.txt in the
Linux kernel source directory
Documentation/filesystems (on older
kernels, these files are directly under the
Documentation directory, and
This page is part of release 5.04 of the Linux
man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
Copyright 1997 Nicolás Lichtmaier <nickdebian.org>
Created Thu Aug 7 00:44:00 ART 1997
This is free documentation; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of
the License, or (at your option) any later version.
The GNU General Public License_zsingle_quotesz_s references to object code
and executables are to be interpreted as the output of any
document formatting or typesetting system, including
intermediate and printed output.
This manual is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public
License along with this manual; if not, see
Added section stuff, aeb, 2002-04-22.
Corrected include file, drepper, 2003-06-15.