What happens to cron jobs when system in shutdown? [closed]

Question

From man page of crontab.

      string         meaning
      ------         -------
      @daily         Run once a day, "0 0 * * *".
      @midnight      (same as @daily)

So a job @daily will never be executed if the system is always shutdown at midnight? What is the proper way to specify that I want to run this job once daily but I don't care when exactly it is executed in a day?

Answer 1

The job may run, but probably won't complete. cron is implemented via a daemon, so it's always running. Depending on your system's shutdown order, cron may actually be sent the shutdown signal fairly late in the shutdown process, so jobs scheduled for the moment the shutdown started may still run.

e.g. If the shutdown starts at 00:00:00 exactly, but doesn't get to sending cron a kill signal until 00:00:05 (5 seconds after midnight(, then a short running 2-second job may still have time to complete.

However, if any services that job depends on have already been shutdown or are in the process of shutting down, then it's unlikely to be able to finish. e.g.... the script pings a mysql server for one little piece of data... but mysql shut down at 00:00:01 and your script didn't get to the mysql portion until 00:00:02.

tl;dr: it's a race condition and your job MAY execute, but probably won't.