lockf man page on FreeBSD

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LOCKF(1)		  BSD General Commands Manual		      LOCKF(1)

NAME
     lockf — execute a command while holding a file lock

SYNOPSIS
     lockf [-ks] [-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 com‐
		 mand 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
		 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 pro‐
     duced 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_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 sig‐
		   naled 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
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