FLOCK(1) General Commands Manual FLOCK(1)

flockProvide locking API for shell scripts

flock [-dnosvx] [-w timeout] file|directory command [args ...]

flock [-dnosvx] [-w timeout] file|directory -c command

flock [-dnsuvx] [-w timeout] number

The flock utility provides flock(2) access to the command line or scripts. The first two forms lock the specified file or directory while the provided command is executed. If the path does not exist, then a file of that name is created with mode 0600.

The third form can use an arbitrary file descriptor number 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:

command
Pass a command to a the shell.
, --debug
Provide debugging output.
, --nb, --nonblock
Don't block and fail immediately if the lock could not be obtained.
, --close
Close the file before executing the command. This is useful if the child forks and should not be holding the lock.
, --shared
Obtain a shared lock.
, --unlock
Unlock an existing lock. This is available only for a file descriptor.
, --verbose
On error print an explanation of the failure.
, --wait, --timeout seconds
Fail if the lock could not be obtained after seconds.
, --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.

October 4, 2019 NetBSD 10.99