Run job for a period of time

Shell Programming and Scripting
1

I have a job that runs for an unspecified amount of time. I want to run this as a cron job for a specified amount of time, say 2 hours. Once the time is up, the program should be killed in the middle of execution. How can I do this?

Thanks.

2

If your process is written in C and you have access to the code, you can use the alarm(2) function which will generate a SIGALARM signal after a specified number of seconds. You can capture the signal for a graceful exit or let it abort the program.

You can do the same with a script by sending a HUP signal to your script via at(1). At the beginning of your script, run the following command:

echo "/bin/kill -HUP $$" | at now + 120 minutes

With a trap, the HUP signal could be intercepted for a graceful termination or, as in the alarm(2) example, let it abort the script. Also, the at-job number could be saved used to remove it from the queue if your script completes early.

A third option would be to create a pid-file from within your process (giving it a shell wrapper if necessary). Then you could cron another job to check for the existence of the pid file after a specified period of time and send a signal to it if the PID is still active.

Here's kind of a not-too-useful example:

#!/bin/ksh

    trap 'echo terminated counts: $I : $J : $K ; exit 3' HUP

    echo "kill -HUP $$" | at now + 1 minute

    I=0

    while [ $I -lt 1000 ]
    do
        J=0

        while [ $J -lt 1000 ]
        do
            K=0

            while [ $K -lt $J ]
            do
                (( K = K + 1 ))
            done

            (( J = J + 1 ))
        done

        (( I = I + 1 ))
    done

     echo final counts $I : $J : $K
    exit 0
3

Wow, that's just what I needed. I appreciate you going through with the effort with this.
I have some questions though:

  • why do I get the following message each time when I run the above script in succession:
    Job 2 will be executed using /bin/sh
    Job 3 will be executed using /bin/sh
    ...

  • in general, is there a preference of using SIGHUP over SIGINT in these situations?

4

this is one more way of implementing;

./yourscript.ksh & sleep 7200; kill $!

run your script as a background process; then sleep for specified number of seconds later send a signal to the process put in background using the last background identifier from ksh builtin variables

5

That's cool, too. Thanks!

6

By default, the at command uses the Bourne shell. What you're seeing with "Job 2 will be executed using /bin/sh" message is a warning. You can call at with a -k option to tell it to use the Korn shell.

As far as SIGHUP vs SIGINT, it depends on the process you're trying to interrupt. Many processes handle SIGHUPs gracefully -- for example syslogd will reread its configuration file. Other process, if not coded specifically for processing SIGHUP will terminate. SIGINTs, on the other hand, are almost universally "process-terminating". Experiment.

I'm glad I could be of help.