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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  com-
       mand,  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 -n 9
	 # ... commands	executed under lock ...
       ) 9>/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 com-
	      mand 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 can-
	      not 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  exe-
	      cuting  command.	 This  is  useful  if  command	spawns a child
	      process which should not be holding 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 PARTICULAR
       PURPOSE.

SEE ALSO
       flock(2)

AVAILABILITY
       The flock command is part of the	util-linux package  and	 is  available
       from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.

flock utility			  4 Feb	2006			      FLOCK(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | AUTHOR | COPYRIGHT | SEE ALSO | AVAILABILITY

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