Signal Processing

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# 1  
Old 10-04-2001
Question Signal Processing

Can any body give example of using Unix Signals. What I want to do is
I am running a sql query in a shell script
I want, if sql query exceed the defined no. of seconds limit, then I would like to kill the process.

I know this can be done thru Unix Signal Handling but I do not know how ?

# 2  
Old 10-04-2001

I have the following example in one unix book but some how it is not working as supposed to. I do not see the echo message
echo "Got SIGALRM, cmd took too long." which AlarmHandler should display when timeout. ALthough I have noticed that it is killing the process (sleep 60 &) after the timeout.

Can anybody explain me what step, I am doing wrong ?


#! /bin/ksh

AlarmHandler() {
echo "Got SIGALRM, cmd took too long."
# exit 14

KillSubProcs() {
kill ${CHPROCIDS:-$!}
if [ $? -eq 0 ] ; then echo "Sub-processes killed." ; fi

SetTimer() {
if [ $DEF_TOUT -ne 0 ] ; then
sleep $DEF_TOUT && kill -s ALRM $$ &

UnsetTimer() {

# main()

trap AlarmHandler ALRM
SetTimer 4
# Command to run
# For Testing
sleep 60 &
wait $!
echo $?
echo "All Done."
#exit 0
# 3  
Old 10-04-2001
I have never been able to get ksh to work right with SIGARLM. I suspect that ksh uses it internally somehow. Change all occurences of ARLM to USR1 in your script and I think it will work. But also try this:
#! /usr/bin/ksh
(sleep 10 ; kill -TERM -$mypid) &
sleep 60  ## this takes too long
kill -TERM %1 
exit 0

# 4  
Old 10-04-2001
Thank you very much. You are genius.
I do not whether ALRM signal is not working in ksh or the trap command. In my original post, I can see that ALRM is working but only the echo message are not working.
I replaced ALRM with USR1 and it is now displaying message as well.

Any Idea why trap command not working properly in K shell in case of ALRM signal. I have tried INT Signal and it is working fine.


trap "echo hello" ALRM
kill -s ALRM $$
# 5  
Old 10-05-2001
Hello Perderabo,

#! /usr/bin/ksh
(sleep 120 ; kill -TERM -$mypid) & ## This will send signal when
## 120 seconds will pass.
sleep 10 ## this is the command which I want to run.
## which will take 10 seconds.
kill -TERM %1
exit 0

When this is executed, you will still see that one background process against sleep still be running even after completion of the shell job and that process will be sleep and that sleep command will be active for 120 seconds. Is there any way, we can terminate/kill this job after finishing the sleep 10 job.
In short, I would like to kill the sleep process, if the command which I want to run (in our example it is sleep 10) is taking < 120 seconds.

Do you understand what I want to say.

Thank for your help.

# 6  
Old 10-05-2001
I have never figured out why I can't get ARLM to work with ksh. I just use another signal.

I know that my method leaves a sleep process running if the timed command completes in time. I think that's harmless. It will be reaped by init when it exits. That's the only real cost of a very easily coded solution. Capturing and killing that last pid will drive script back up in complexity.
# 7  
Old 10-05-2001
Yes, if Perderabo continues to razzle and dazzle the board with his deep technical contributions; I'm considering changing his forum title to 'Forum Genius'....... great work and thanks for the excellent contributions Perderabo!!!

Also, while we are on the subject, thanks all the forum members, new and old, who take the time to be patient and help others is so many ways, each and every day. All of you make the combined 'Genius' of the forum better and better each day.

BTW, I could go on and on about the Genius in the forums... including praises to PxT, LivinFree, Optimus_P, mib, 98_1LE, rwb1959... for other major contributors and forum-gurus, visit:

Thanks again. -Neo
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