Re: how to run scripts uniquely

[Jeff D <fixedored@gmail.com>]

cs wrote:
> I thought I'd worked out how to ensure only 1 instance of a shell script
> was running (using grep and wc) but I now see that sometimes the script
> name appears twice in the list of processes - any ideas?
>
> eg (apols for wrapping) when running /home/michael/bin/backup-rsync-VERI
> we get the below where it appears twice in the list of processes...
>
> ++ mktemp /tmp/chk_procs_XXX
> + TEMPFILE=/tmp/chk_procs_220
> + trap 'date|mail -s "$0 error" michael.bane@manchester.ac.uk;echo Error
> - aborting; exit' ERR
> + ps -elf
> + grep /home/michael/bin/backup-rsync-VERI
> + grep -v grep
> + tee /tmp/chk_procs_220
> 4 R michael  20219 20218  0  83   0 -  1020 -      18:18 ?
> 00:00:00 /bin/bash -x /home/michael/bin/backup-rsync-VERI
> 1 R michael  20223 20219  0  83   0 -  1020 -      18:18 ?
> 00:00:00 /bin/bash -x /home/michael/bin/backup-rsync-VERI
> ++ cat /tmp/chk_procs_220
> ++ wc -l
> + [[ 2 -gt 1 ]]
> + date
> ++ hostname -s
> + mail -s 'ratty /home/michael/bin/backup-rsync-VERI - already running'
> michael.bane@manchester.ac.uk
> + rm /tmp/chk_procs_220
> + exit -1


This is what I do in situations like this:
#!/bin/sh
#get pid
PID=$$

#check to see if a previous process is running
if [ -e  /var/run/sync.check ] ; then
        if ps -p `cat /var/run/sync.check` >> /dev/null 2>&1 ; then
                echo "Sync process already running, exiting"
                exit 1
        fi
fi
#write out pid
echo $PID > /var/run/sync.check

#do stuff

#end of script, remove pid file
rm -f /var/run/sync.check