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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

rpc.lockd(8)						      System Manager's Manual						      rpc.lockd(8)

NAME
rpc.lockd, lockd - Network lock daemon SYNOPSIS
/usr/sbin/rpc.lockd [-b hostname] [-c] [-d debug] [-g graceperiod] [-h hashsize] [-s] [-t timeout] OPTIONS
The default behavior will create and bind a socket for each protocol per interface on the system. When the -b switch is specified, one socket per protocol will be created and bind to the passed IP address. Available only on TruCluster Server systems. This option starts the clusterwide lock daemon, which helps provide highly available NFS service. Do not use -c directly. Highly available NFS service is config- ured by default and typically does not require intervention. If you do need to start the clusterwide lock daemon, use the CAA command, caa_start cluster_lockd. For more information, see the TruCluster Server Administration manual. Internal Use Only. Use this option only under the direction of technical support personnel. Causes the rpc.lockd daemon to use the variable graceperiod (in seconds) as the grace period dura- tion instead of the default value of 15 seconds. Internal Use Only. Causes the rpc.lockd daemon to use the variable timeout (in seconds) as the interval instead of the default value of 5 seconds to retransmit a lock request to the remote server. DESCRIPTION
The rpc.lockd daemon processes lock requests that are either sent locally by the kernel or remotely by another lock daemon. The NFS locking service makes this advisory locking support possible by using the fcntl system call and the lockf subroutine. The rpc.lockd daemon forwards lock requests for remote data to the server site's lock daemon. The rpc.lockd daemon then requests the status monitor daemon, rpc.statd, for monitor service. The reply to the lock request is not sent to the kernel until the status daemon and the server site's lock daemon have replied. If either the status monitor or server site's lock daemon is unavailable, the reply to a lock request for remote data is delayed until all daemons become available. When a server recovers, it waits for a grace period for all client site lock daemons to submit reclaim requests. Client site lock daemons are notified by rpc.statd of the server recovery and promptly resubmit previously granted lock requests. If a client site's lock daemon fails to secure previously granted locks at the server site, it sends the signal SIGLOST to all the processes that were previously holding locks and cannot reclaim them. SEE ALSO
Commands: rpc.statd(8) Functions: fcntl(2), signal(2), lockf(3) rpc.lockd(8)
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