write a background process to check process is still active

Question

In UNIX, I have a utility, say 'Test_Ex', a binary file. How can I write a job or a shell script(as a cron job) running always in the background which keeps checking if 'Test_Ex' is still running every 5 seconds(and probably hide this job). If it is running, do nothing. If not, delete a directory at the specified path.

Answer 1

Try this script:

pgrep Test_Ex > /dev/null || rm -r dir

If you don't have pgrep, use

ps -e -ocomm | grep Test_Ex || ...

instead.

Answer 2

Utilities like upstart, originally part of the Ubuntu linux distribution I believe, are good for monitoring running tasks.

Answer 3

The best way to do this is to not do it. If you want to know if Test_Ex is still running, then start it from a script that looks something like:

#!/bin/sh
Test_Ex
logger "Test_Ex died"
rm /p/a/t/h

or

#!/bin/sh
while ! Test_ex
do
  logger "Test_Ex terminated unsuccesfully, restarting in 5 seconds"
  sleep 5
done

Querying ps regularly is a bad idea, and trying to monitor it from cron is a horrible, horrible idea. There seems to be some comfort in the idea that crond will always be running, but you can no more rely on that than you can rely on the wrapper script staying alive; either one can be killed at any time. Waking up every 10 seconds to query ps is just a waste of resources.