Shell Programming and Scripting

Is there a way to trap kill -9 pid? or is there any other way to detect kill -9 so that some files can be deleted before the process ends?

The trap command can catch signals being sent but I don't think you can trap a SIGKILL signal. Can you trap another signal instead and use that for graceful shutdown?
Simple ksh93 script to illustrate, run it:

Code:

$ cat efs
#!/usr/dt/bin/dtksh

trap 'print TERM received;exit 1' 15

while :
do
  sleep 5
done

exit 0
$

Then open another terminal window and send a 15 to the process above:

Code:

kill -15 <PID>

You will see in the first window:

Code:

$ efs
TERM received
$

No. You cannot trap "kill -9".

The "kill -9" is an absolute last resort and IMHO should never appear in a script unless preceded by reasonable attempts to remove the bad process according to the Signals specified for the software. This is paramount for database software where it is important to learn the correct signals and to use database tools rather than unix "kill".

The best fix for "kill -9" is to never issue the command except where you can prove that that killing the process will not cause data corruption.


@gary_w
(Just read your amended post). There is no problem trapping "kill -15" (HANGUP) and I rely on this for many a cleanup. Some O/S can take 2 hours to realise that a connection has disappeared and then record a HANGUP. The issue is with "kill -9" which should never be issued by anybody other than an expert. I have shut down databases rather than issue "kill -9" to database clients in the full knowledge that the database engine can deal with the situation much better than someone working at a unix command prompt.
However you do occasionally come across looping client processes with no database connection and no parent process (except "init" PID 1) which need a "kill -9" to get rid of them.

Btw. I've never had a problem with "trap '<cleanup>' 1 2 3 15"

I totally agree with avoiding kill -9. That is always a last resort in my opinion. I was just suggesting to the original poster that maybe he could construct his script to use a different signal to allow him to do some cleanup upon receipt of that signal, and to show an example in case he was not sure how to set that up.