Copyright (C) 1998 John D. Polstra. All rights reserved.
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$FreeBSD: releng/10.2/usr.bin/lockf/lockf.1 250462 2013-05-10 17:30:29Z eadler $
.Dd July 7, 1998 .Dt LOCKF 1 .Os .Sh NAME .Nm lockf .Nd execute a command while holding a file lock .Sh SYNOPSIS .Nm .Op Fl kns .Op Fl t Ar seconds .Ar file .Ar command .Op Ar arguments .Sh DESCRIPTION The .Nm utility acquires an exclusive lock on a .Ar file , creating it if necessary, f Em and removing the file on exit unless explicitly told not to. .Ef While holding the lock, it executes a .Ar command with optional .Ar arguments . After the .Ar command completes, .Nm releases the lock, and removes the .Ar file unless the .Fl k option is specified. x Ns -style locking is used, as described in .Xr flock 2 ; the mere existence of the .Ar file is not considered to constitute a lock.
p If the .Nm utility is being used to facilitate concurrency between a number of processes, it is recommended that the .Fl 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 .Fl k option is not used, then no guarantees around lock ordering can be made.
p The following options are supported: l -tag -width ".Fl t Ar seconds" t Fl k Causes the lock file to be kept (not removed) after the command completes. t Fl s Causes .Nm to operate silently. Failure to acquire the lock is indicated only in the exit status. t Fl n Causes .Nm to fail if the specified lock .Ar file does not exist. If .Fl n is not specified, .Nm will create .Ar file if necessary. t Fl t Ar seconds Specifies a timeout for waiting for the lock. By default, .Nm waits indefinitely to acquire the lock. If a timeout is specified with this option, .Nm will wait at most the given number of .Ar seconds before giving up. A timeout of 0 may be given, in which case .Nm will fail unless it can acquire the lock immediately. When a lock times out, .Ar command is .Em not executed. .El
p In no event will .Nm break a lock that is held by another process. .Sh EXIT STATUS If .Nm successfully acquires the lock, it returns the exit status produced by .Ar command . Otherwise, it returns one of the exit codes defined in .Xr sysexits 3 , as follows: l -tag -width ".Dv EX_CANTCREAT" t Dv EX_TEMPFAIL The specified lock file was already locked by another process. t Dv EX_CANTCREAT The .Nm utility was unable to create the lock file, e.g., because of insufficient access privileges. t Dv EX_UNAVAILABLE The .Fl n option is specified and the specified lock file does not exist. t Dv EX_USAGE There was an error on the .Nm command line. t Dv EX_OSERR A system call (e.g., .Xr fork 2 ) failed unexpectedly. t Dv EX_SOFTWARE The .Ar command did not exit normally, but may have been signaled or stopped. .El .Sh SEE ALSO .Xr flock 2 , .Xr sysexits 3 .Sh HISTORY A .Nm utility first appeared in .Fx 2.2 . .Sh AUTHORS .An John Polstra Aq jdp@polstra.com