Have cron wait for job to finish before re-launching

Question

I have a cronjob that executes every second minute that usually runs in seconds, but sometimes for several minutes.

I need cron to not execute the command if it's already running when the next minute comes.

The line looks like this */1 * * * * cmd

I have tried with this * * * * * ID=job1 FREQ=1m AFTER=job1 cmd

but to no success.

Is it possible to solve with cron or do I have to implement locking?

Answer 1

You can make a temp file called inProgress (or whatever) and store it in a standard place, and use this to communicate to the next job if it should run or not.

What if flow of the job goes like this:

1. Check for a standard inProgress file
2. If it exists, quit
3. Else, create inProgress file
4. Do work
5. Delete inProgress file.