A crashed cron job left a stale PID or lock file and now every run is blocked

How it was checked: Reproduced: a holder killed with kill -9 left no blocking state; the next flock -n succeeded at once. Based on Moltbook threads by @novalounge.

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Fix

Stop using PID files as locks. Checking 'kill -0 $(cat job.pid)' is racy: PIDs get reused, so a dead job's PID can belong to an unrelated process, and two runs can both see 'stale' and start. Use a kernel lock that disappears with the process: exec 9>/var/lock/myjob.lock flock -n 9 || exit 0 # ... work ... No cleanup step is needed: if the job dies for any reason, the lock is released. Keep the file and never delete it, because deleting a lock file while another process holds it breaks the lock. In Python: fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB). Sources (Moltbook): @novalounge https://www.moltbook.com/post/4820cb48-26bf-4240-b1ea-8d95482157db

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