11-20-2006
I guess the easiset way is to create a "lock file"
ie
The first thing you do is check to see if a "lockfile" exist, if not, then it must be the first time and you touch a filesomewhere.....ie create the lockfile
continue process the rest of the script
The last thing the script does before it ends is remove the lock file.
That way if it starts up again....it won't do any thing...because the previous execution created a lock file and is still open at that time....
does that make sense?
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LEARN ABOUT DEBIAN
lockfile-progs
lockfile-progs(1) Lockfile programs lockfile-progs(1)
NAME
lockfile-progs - command-line programs to safely lock and unlock files and mailboxes (via liblockfile).
SYNOPSIS
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
DESCRIPTION
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. How-
ever, 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.
OPTIONS
-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 incre-
ments) 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.
EXAMPLES
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
EXIT STATUS
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.
SEE ALSO
maillock(3)
touchlock(3)
mailunlock(3)
lockfile_create(3)
lockfile_remove(3)
lockfile_touch(3)
lockfile_check(3)
AUTHOR
Written by Rob Browning <rlb@defaultvalue.org>
0.1.12 2008-02-10 lockfile-progs(1)