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FLOCK
Section: H. Peter Anvin (1)
Updated: 4 Feb 2006
Index
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NAME
flock - Manage locks from shell scripts
SYNOPSIS
flock [-sxon] [-w timeout] lockfile [-c] command...
flock [-sxon] [-w timeout] lockdir [-c] command...
flock [-sxun] [-w timeout] fd
DESCRIPTION
This utility manages
flock(2)
locks from within shell scripts or the command line.
The first and second forms wraps the lock around the executing a command, in a manner similar to
su(1)
or
newgrp(1).
It locks a specified file or directory, which is created (assuming appropriate
permissions), if it does not already exist.
The third form is convenient 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.
OPTIONS
- -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.
AUTHOR
Written by H. Peter Anvin <hpa@zytor.com>.
COPYRIGHT
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.
SEE ALSO
flock(2)
AVAILABILITY
The flock command is part of the util-linux-ng package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- AUTHOR
-
- COPYRIGHT
-
- SEE ALSO
-
- AVAILABILITY
-
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