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, however, write permission is required; using < requires that the file already exists but only read permis-
       sion 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.   How-
              ever,  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 <hpaATzytor.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 FIT-
       NESS 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/.



flock utility                                              4 Feb 2006                                                   FLOCK(1)