Lockfile-progs provides a set a programs that can be used to lock and
unlock mailboxes and files safely (via liblockfile):
mail-lock - lock the current user's mailbox
mail-unlock - unlock the current user's mailbox
mail-touchlock - touch the lock on the current user's mailbox
lockfile-create - lock a given file
lockfile-remove - remove the lock on a given file
lockfile-touch - touch the lock on a given file
lockfile-check - check the lock on a given file
By default, the filename argument refers to the name of the file
to be locked, and the name of the lockfile will be
filename .lock. However, if the --lock-name argument is
specified, then filename will be taken as the name of the
Each of the mail locking commands attempts to lock
/var/spool/mail/<user>, where <user> is the name associated with the
effective user ID, as determined by via geteuid(2).
Once a file is locked, the lock must be touched at least once every
five minutes or the lock will be considered stale, and subsequent lock
attempts will succeed. Also see the --use-pid option and the
The lockfile-check command tests whether or not a valid lock
Suppress any output. Success or failure will only be indicated by the
Enable diagnostic output.
Do not append .lock to the filename. This option applies to
lockfile-create, lockfile-remove, lockfile-touch,
Write the current process id (PID) to the lockfile whenever a lockfile
is created, and use that pid when checking a lock's validity. See the
lockfile_create(3) manpage for more information. This option
applies to lockfile-create, lockfile-remove,
lockfile-touch, and lockfile-check.
Touch the lock and exit immediately. This option applies to
lockfile-touch and mail-touchlock. When not provided,
these commands will run forever, touching the lock once every minute
Try to lock filenameretry-count times before giving up.
Each attempt will be delayed a bit longer than the last (in 5 second
increments) until reaching a maximum delay of one minute between
retries. If retry-count is unspecified, the default is 9 which
will give up after 180 seconds (3 minutes) if all 9 lock attempts
Locking a file during a lengthy process:
lockfile-touch /some/file &
# Save the PID of the lockfile-touch process
For lockfile-check this indicates that a valid lock exists,
otherwise it just indicates successful program execution.
For lockfile-check a non-zero exit status indicates that the
specified lock does not exist or is not valid. For other programs it
indicates that some problem was encountered.