On November 21, 2014 7:57:22 AM CET, Pete Vickers <peter.vick...@gmail.com>
wrote:
>Hi,
>
>I suspect this may be the wrong list for this question. However
>although strictly it's a Bourne shell script query, it only seem to act
>up under OpenBSD (for me).
>
>Essentially I have a job which needs to be run periodically. So I have
>a shell script to do the necessary commands, and this is scheduled via
>(root's) crontab.
>It is however very important that multiple instances of the job are not
>run concurrently (e.g. if an previous invocation hung), and so the
>script should detect this upon invocation before proceeding.
>
>I don't want a single long running job (which could e.g. sleep between
>loops) for various reasons. And I also don't like PID files and other
>fragile locking hacks.
>
>
>So down to business, below is the gist of my script. Most of the time
>it appears to run fine. However occasionally (once every couple of
>days?) it reports via email that a duplicate process is detected, but
>the included ps listing shows no other instance. I don't believe that
>this is just due to an old instance exiting in the small time window
>between the pgrep, and the ps invocations. So basically I guess there
>is an error in my script or it's logic, or something else I'm not
>seeing.
>
>Any hit with the clue bat gratefully received.
>
>
>
>#!/bin/sh
>#
>#
>SHOUT="/usr/bin/logger -i -t MYPERIODICJOB"
>#
>#
># Ensure another instance of this is not running
>#
>MYNAME=`basename $0`
>MYPID=$$
>#
>/usr/bin/pgrep -fu root $MYNAME | /usr/bin/grep -v $MYPID && \
> {
> $SHOUT "HELP - duplicate process detected $?" ; \
>ps -axjwww | mail -s "HELP MYPERIODICJOB $MYPID $MYNAME $PPID"
>m...@example.com ; \
> exit 1 ;
> }
>
>#
>#
># starting doing useful stuff here..
>#
>
>
>Disclaimer: I know my scripting is far from optimal...
>
>
>/Pete
# pkg_add flock
Far less hackish than what you're trying to achieve.
/Alexander
