flock — Manage locks from shell scripts
This utility manages flock(2) locks from within shell scripts or the command line.
The first form wraps the lock around the executing a command, in a manner similar to su(1) or newgrp(1). It locks a specified file, which is created (assuming appropriate permissions), if it does not already exist.
The second form is conveninent inside shell scripts, and is usually used the following manner:
( flock -s 200 # ... commands executed under lock ... ) 200>/var/lock/mylockfile
The mode used to open the file doesn't matter to flock; using “>” or “>>” allows the lockfile to be created if it does not already exist, however, write permission is required; using “<” requires that the file already exists but only read permission is required.
By default, if the lock cannot be immediately acquired, flock waits until the lock is available.
−s, −−sharedObtain a shared lock, sometimes called a read lock.
−x, −e, −−exclusiveObtain an exclusive lock, sometimes called a write lock. This is the default.
−u, −−unlockDrop a lock. This is usually not required, since a lock is automatically dropped when the file is closed. However, it may be required in special cases, for example if the enclosed command group may have forked a background process which should not be holding the lock.
−n, −−nb, −−nonblockFail (with an exit code of 1) rather than wait if the lock cannot be immediately acquired.
−w, −−wait, −−timeout secondsFail (with an exit code of 1) if the lock cannot be acquired within seconds seconds. Decimal fractional values are allowed.
−o, −−closeClose the file descriptor on which the lock is held before executing command. This is useful if command spawns a child process which should not be hold ing the lock.
−c, −−command commandPass a single command to the shell
with −c.
−h, −−helpPrint a help message.
Copyright © 2003−2006 H. Peter Anvin.
This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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$Id: flock.1,v 1.3 2006/02/04 20:41:57 hpa Exp $ ----------------------------------------------------------------------- Copyright 2003-2006 H. Peter Anvin - All Rights Reserved Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. ----------------------------------------------------------------------- |