linux - Run cron job only if it isn't already running

Question

I'm trying to set up a cron job as a sort of watchdog for a daemon that I've created. If the daemon errors out and fails, I want the cron job to periodically restart it... I'm not sure how possible this is, but I read through a couple of cron tutorials and couldn't find anything that would do what I'm looking for...

My daemon gets started from a shell script, so I'm really just looking for a way to run a cron job ONLY if the previous run of that job isn't still running.

I found this post, which did provide a solution for what I'm trying to do using lock files, not I'm not sure if there is a better way to do it...

Answer 1

Use flock. It's new. It's better.

Now you don't have to write the code yourself. Check out more reasons here: https://serverfault.com/a/82863

/usr/bin/flock -n /tmp/my.lockfile /usr/local/bin/my_script