lockfile-progs - command-line programs to safely lock and unlock files and mailboxes (via liblockfile).
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 users mailbox mail-unlock - unlock the current users mailbox mail-touchlock - touch the lock on the current users 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, --quietSuppress any output. Success or failure will only be indicated by the exit status.
-v, --verboseEnable diagnostic output.
-l, --lock-nameDo not append .lock to the filename. This option applies to lockfile-create, lockfile-remove, lockfile-touch, or lockfile-check.
-p, --use-pidWrite the parent process id (PPID) to the lockfile whenever a lockfile is created, and use that pid when checking a locks 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, --oneshotTouch 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-countTry 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-touch /some/file &
# Save the PID of the lockfile-touch process
0For lockfile-check this indicates that a valid lock exists, otherwise it just indicates successful program execution.
Not 0For 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 <email@example.com>