lockf(1) [freebsd man page]
LOCKF(1) BSD General Commands Manual LOCKF(1) NAME
lockf -- execute a command while holding a file lock SYNOPSIS
lockf [-kns] [-t seconds] file command [arguments] DESCRIPTION
The lockf utility acquires an exclusive lock on a file, creating it if necessary, and removing the file on exit unless explicitly told not to. While holding the lock, it executes a command with optional arguments. After the command completes, lockf releases the lock, and removes the file unless the -k option is specified. BSD-style locking is used, as described in flock(2); the mere existence of the file is not considered to constitute a lock. If the lockf utility is being used to facilitate concurrency between a number of processes, it is recommended that the -k option be used. This will guarantee lock ordering, as well as implement a performance enhanced algorithm which minimizes CPU load associated with concurrent unlink, drop and re-acquire activity. It should be noted that if the -k option is not used, then no guarantees around lock ordering can be made. The following options are supported: -k Causes the lock file to be kept (not removed) after the command completes. -s Causes lockf to operate silently. Failure to acquire the lock is indicated only in the exit status. -n Causes lockf to fail if the specified lock file does not exist. If -n is not specified, lockf will create file if necessary. -t seconds Specifies a timeout for waiting for the lock. By default, lockf waits indefinitely to acquire the lock. If a timeout is speci- fied with this option, lockf will wait at most the given number of seconds before giving up. A timeout of 0 may be given, in which case lockf will fail unless it can acquire the lock immediately. When a lock times out, command is not executed. In no event will lockf break a lock that is held by another process. EXIT STATUS
If lockf successfully acquires the lock, it returns the exit status produced by command. Otherwise, it returns one of the exit codes defined in sysexits(3), as follows: EX_TEMPFAIL The specified lock file was already locked by another process. EX_CANTCREAT The lockf utility was unable to create the lock file, e.g., because of insufficient access privileges. EX_UNAVAILABLE The -n option is specified and the specified lock file does not exist. EX_USAGE There was an error on the lockf command line. EX_OSERR A system call (e.g., fork(2)) failed unexpectedly. EX_SOFTWARE The command did not exit normally, but may have been signaled or stopped. SEE ALSO
flock(2), sysexits(3) HISTORY
A lockf utility first appeared in FreeBSD 2.2. AUTHORS
John Polstra <jdp@polstra.com> BSD
July 7, 1998 BSD
Check Out this Related Man Page
LOCKF(3) Linux Programmer's Manual LOCKF(3) NAME
lockf - apply, test or remove a POSIX lock on an open file SYNOPSIS
#include <unistd.h> int lockf(int fd, int cmd, off_t len); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): lockf(): _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED DESCRIPTION
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 pos..pos+len-1 if len is positive, and pos-len..pos-1 if 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 end-of-file. On Linux, lockf() is just an interface on top of fcntl(2) locking. Many other systems implement lockf() in this way, but note that POSIX.1-2001 leaves the relationship between lockf() and fcntl(2) locks unspecified. A portable application should probably avoid mixing calls to these interfaces. Valid operations are given below: F_LOCK 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_TLOCK Same as F_LOCK but the call never blocks and returns an error instead if the file is already locked. F_ULOCK Unlock the indicated section of the file. This may cause a locked section to be split into two locked sections. F_TEST Test the lock: return 0 if the specified section is unlocked or locked by this process; return -1, set errno to EAGAIN (EACCES on some other systems), if another process holds a lock. RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately. ERRORS
EACCES or EAGAIN The file is locked and F_TLOCK or F_TEST was specified, or the operation is prohibited because the file has been memory-mapped by another process. EBADF fd is not an open file descriptor; or cmd is F_LOCK or F_TLOCK and fd is not a writable file descriptor. EDEADLK The command was F_LOCK and this lock operation would cause a deadlock. EINVAL An invalid operation was specified in fd. ENOLCK Too many segment locks open, lock table is full. CONFORMING TO
SVr4, POSIX.1-2001. SEE ALSO
fcntl(2), flock(2) locks.txt and mandatory-locking.txt in the Linux kernel source directory Documentation/filesystems (on older kernels, these files are directly under the Documentation directory, and mandatory-locking.txt is called mandatory.txt) COLOPHON
This page is part of release 3.44 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. GNU
2012-07-07 LOCKF(3)