flock(1) [netbsd man page]
FLOCK(1) BSD General Commands Manual FLOCK(1) NAME
flock -- Provide locking API for shell scripts SYNOPSIS
flock [-dnosvx] [-w timeout] lockfile|lockdir [-c command] | [command ...] flock [-dnsuvx] [-w timeout] lockfd DESCRIPTION
The flock utility provides flock(2) access to the command line or scripts. The first form locks a file or directory while the command pro- vided is executed. If the file or directory does not exist, then a file is created. The second form can use an arbitrary file descriptor that is provided from a shell script for example: ( flock -s 100 # commands to be executed under the lock ) 100> /path/to/lockfile The following options are available: -c command Pass a command to a the shell. -d, --debug Provide debugging output. -n, --nb, --nonblock Don't block and fail immediately if the lock could not be obtained. -o, --close Close the file before executing the command. This is useful if the child forks and should not be holding the lock. -s, --shared Obtain a shared lock. -u, --unlock Unlock an existing lock. This is available only for a file descriptor. -v, --verbose On error print an explanation of the failure. -w, --wait, --timeout seconds Fail if the lock could not be obtained after seconds. -x, --exclusive Obtain an exclusive lock. EXIT STATUS
The flock utility exits 0 on success, and >0 if an error occurs. SEE ALSO
shlock(1), flock(2) HISTORY
An flock utility appeared in NetBSD 6.1. BSD
November 2, 2012 BSD
Check Out this Related Man Page
FLOCK(1) H. Peter Anvin FLOCK(1) 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, how- ever, 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 hold- ing 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 (C) 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 PARTICU- LAR 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/. flock utility 4 Feb 2006 FLOCK(1)