Linux – Minutely cron, ensuring only a single instance

cronlinux

Is there a way to run a script every minute (or 2, or 5, etc), but only if it isn't already running?

We have a set of scripts that need to run every minute. Sometimes they might start and finish in a second, other times they might go on for 5 minutes.

Our current way of avoiding simultaneous executions is by setting a is_running flag in each script, and exiting if it's still enabled. But this is a little unreliable (i.e., fatal errors would cause the flag to remain enabled even after the script halted).

We could write our own little manager, but I'm wondering if there is a more fashionable solution that already exists.

Best Answer

a better way is to use flock instead of a pidfile. check the manpage: flock(1). The advantage is that no matter how a process finishes/dies, the lock is gone with it.

Related Solutions

Cron – How to Prevent Duplicate Cron Jobs Running

There are a couple of programs that automate this feature, take away the annoyance and potential bugs from doing this yourself, and avoid the stale lock problem by using flock behind the scenes, too (which is a risk if you're just using touch). I've used lockrun and lckdo in the past, but now there's flock(1) (in newish versions of util-linux) which is great. It's really easy to use:

* * * * * /usr/bin/flock -n /tmp/fcj.lockfile /usr/local/bin/frequent_cron_job

Crond – Schedule with Five Minute Offset

You can run scripts whenever you want using cron. If you want to run script 1 every 5 minutes, you might start like this:

*/5 * * * * /path/to/script1

But this is really just shorthand for:

0,5,10,15,20,25,30,35,40,45,50,55 * * * * /path/to/script1

If you want to run script 2 one minute after script 1, you can do this:

1,6,11,16,21,26,31,36,41,46,51,56 * * * * /path/to/script2

You could also do this:

*/5 * * * * /path/to/script1
*/5 * * * * /path/to/script2

And then at the start of script 2, sleep for one minute:

sleep 60

Best Answer

Related Solutions

Cron – How to Prevent Duplicate Cron Jobs Running

Crond – Schedule with Five Minute Offset

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