GNU/Linux man pages
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Syntaxe et mise en oeuvre :
GNU/Linux |
CentOS 5.6 |
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flock(1) |
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flock − Manage locks from shell scripts
flock [−sxon] [−w timeout] lockfile [−c] command...
flock [−sxun] [−w timeout] fd
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, −−shared
Obtain a shared lock, sometimes called a read lock.
−x, −e, −−exclusive
Obtain an exclusive lock, sometimes called a write lock. This is the default.
−u, −−unlock
Drop 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, −−nonblock
Fail (with an exit code of 1) rather than wait if the lock cannot be immediately acquired.
−w, −−wait, −−timeout seconds
Fail (with an exit code of 1) if the lock cannot be acquired within seconds seconds. Decimal fractional values are allowed.
−o, −−close
Close 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 command
Pass a single command to the shell with −c.
−h, −−help
Print a help message.
Written by H. Peter Anvin <hpa@zytor.com>.
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.
flock(2)
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flock(1) | |