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LOCKF(1)                FreeBSD General Commands Manual               LOCKF(1)

     lockf - execute a command while holding a file lock

     lockf [-ks] [-t seconds] file command [arguments]

     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.

     -t seconds  Specifies a timeout for waiting for the lock.  By default,
                 lockf waits indefinitely to acquire the lock.  If a timeout
                 is specified 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

     In no event will lockf break a lock that is held by another process.

     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

     EX_CANTCREAT  The lockf utility was unable to create the lock file, e.g.,
                   because of insufficient access privileges.

     EX_USAGE      There was an error on the lockf command line.

     EX_OSERR      A system call (e.g., fork) failed unexpectedly.

     EX_SOFTWARE   The command did not exit normally, but may have been
                   signaled or stopped.

     flock(2), sysexits(3)

     A lockf utility first appeared in FreeBSD 2.2.

     John Polstra <>.

FreeBSD 11.0-PRERELEASE          July 7, 1998          FreeBSD 11.0-PRERELEASE


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