dotlockfile

[Bill Campbell]

On Tue, Jul 24, 2007, Michael Hipp wrote:
>Lonni J Friedman wrote:
>> On 7/24/07, Michael Hipp <Michael at hipp.com> wrote:
>>> Jay Nugent wrote:
>>>> Greetings,
>>>>
>>>> On Tue, 24 Jul 2007, Michael Hipp wrote:
>>>>
>>>>> Does anyone have a bash script that does essentially the same thing as
>>>>> the 'dotlockfile' utility?
>>>>>
>>>>> I have a system without dotlockfile but I need that functionality to
>>>>> keep a script from clobbering itself.
>>>>    I just ran into this problem earlier today.  So I'll be implementing
>>>> this lockfile code into my scripts tonight.
>>>>
>>>>
>>>> #
>>>> #==================================================================
>>>> # Test to see if we have a LOCK file (i.e. a copy is still running)
>>>> #
>>>> LCKFYLE="/home/wwnet/LCK-wwnet-dialusage"
>>>> #
>>>> if [ -f $LCKFYLE ]; then
>>>>         /bin/mail -s "$LCKFYLE exists" jjn at nuge.com
>>>>         exit 0
>>>> else
>>>>         touch $LCKFYLE
>>>> #
>>>> #==================================================================
>>>> # We wrap the rest of the code from here on...
>>>> #
>>>>
>>>>    [ place the rest of your script in here ]
>>>>
>>>> #
>>>> #==================================================================
>>>> #
>>>> # ... the end of the LCKFYLE test wrapper
>>>> #
>>>> rm $LCKFYLE
>>>> #
>>>> fi
>>>> #
>>>> #----------
>>>> #
>>>> # - end -
>>>> #
>>> Thanks. Unfortunately this doesn't handle the "stale lock file" syndrome
>>> (where the script crashes in the middle part and the lock file stays
>>> around even tho the job is dead).
>> 
>> So add a grep ps output for the process name of whatever it is you're
>> running (or more than one instance (pipe it to 'wc -l', if the concern
>> is running multiples concurrently).
>> 
>> I guess i don't understand the obstacle.  Is it that you aren't sure
>> how to implement this, or something else?
>
>I just believe in the concept of not reinventing the wheel. Figured 
>someone else had already done it and could share a few stanzas of script 
>code. That's kinda what we're about here, isn't it?
>
>Oddly enough, I've found a plethora of bash scripting websites that talk 
>about lock files but none of them handle the "what ifs" very well. Odd.

There's the perl LockFile::Simple module, and probably a python
equivalent.

The code for shlock is available in the inn news distribution,
and easy enough to compile outside of it.

Bill
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