locking mechanism

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LEARN ABOUT NETBSD

flock

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

Shell Programming and Scripting