killing processes

[Bill Campbell]

On Thu, Dec 04, 2008, David A. Bandel wrote:
>On Thu, Dec 4, 2008 at 2:19 AM, Machiel Richards
><MachielR at agilitytech.co.za> wrote:
>> Hi Guys
>>
>>        Here is the details from the administrator of that system:
>>
>> Processes were spawned by the Oracle backup cron (rman).
>>
>> "Any chance the cron could run a second time while the first is running?"
>>
>> This is what happened yes.  The 2nd cron started while the previous one was still running (took longer than 24 hrs).  I then killed the first one, but it left processes behind with parent id 1 (kill -9 doesn't work on them).
>
>OK, you're going to have to write an actual script to run this, write
>a pid file when the process starts, but one line above check for the
>pid file to see if one already exists and exit if it does.  Don't
>forget to remove your pid file when you're done.

Simply checking for the existence of a pid file doesn't take into
account the original process dying or exiting without removing
the pid file.  At least check with a ``kill -0'' on the PID in
the file as I showed in a previous example.

pidfile=/var/run/`basename $0`.pid
[ -s $pidfile ] && {
	kill -0 `cat $pidfile` 2>/dev/null && {
		echo 'some error message still running' 2>&1
		exit 1
	}
	rm -f $pidfile
}
# create new pid file with my process id
echo $$ > $pidfile
# more processing here
rm -f $pidfile

Bill
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