Manual browser: flock(1)

FLOCK(1) General Commands Manual FLOCK(1)


flockProvide locking API for shell scripts


flock [-dnosvx] [-w timeout] lockfile|lockdir [-c command] | [command ...]

flock [-dnsuvx] [-w timeout] lockfd


The flock utility provides flock(2) access to the command line or scripts. The first form locks a file or directory while the command provided 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. This is the default.


The flock utility exits 0 on success, and >0 if an error occurs.


shlock(1), flock(2)


An flock utility appeared in NetBSD 6.1.
August 18, 2014 NetBSD 7.0