lockfile-progs

mail-lock [--use-pid] [--retry retry-count]
mail-unlock
mail-touchlock [--oneshot]

lockfile-create [--use-pid] [--retry retry-count] [--lock-name] filename
lockfile-remove [--lock-name] filename
lockfile-touch [--oneshot] [--lock-name] filename
lockfile-check [--use-pid] [--lock-name] filename

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 lockfile itself.

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 lockfile_create(3) manpage.

The lockfile-check command tests whether or not a valid lock already exists.

-q, --quiet

Suppress any output. Success or failure will only be indicated by the exit status.

-v, --verbose

Enable diagnostic output.

-l, --lock-name

Do not append .lock to the filename. This option applies to lockfile-create, lockfile-remove, lockfile-touch, or lockfile-check.

-p, --use-pid

Write the parent process id (PPID) 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 and lockfile-check. NOTE: this option will not work correctly between machines sharing a filesystem.

-o, --oneshot

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 until killed.

-r retry-count, --retry retry-count

Try to lock filename retry-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 fail.

Locking a file during a lengthy process:

lockfile-create /some/file
lockfile-touch /some/file &
# Save the PID of the lockfile-touch process
BADGER="$!"
do-something-important-with /some/file
kill "${BADGER}"
lockfile-remove /some/file

0

For lockfile-check this indicates that a valid lock exists, otherwise it just indicates successful program execution.

Not 0

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.

maillock(3) touchlock(3) mailunlock(3) lockfile_create(3) lockfile_remove(3) lockfile_touch(3) lockfile_check(3)

Written by Rob Browning <rlb@defaultvalue.org>