Task scheduling (cron & at)

Per-user crontabs, system cron files, one-shot at jobs, and the five-field cron expression syntax with shortcuts like @daily.

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Task scheduling (cron & at)

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Domain 8 · Automation & ScriptingEX200 V10 (RHEL 10)

Task scheduling (cron & at)

Per-user crontabs, system cron files, one-shot at jobs, and the five-field cron expression syntax with shortcuts like @daily.

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Task scheduling (cron & at) — CertForged

◆Concept — Task scheduling — cron, at, and system cron files

Linux has several complementary ways to run a command at a specific time or on a recurring schedule: cron (recurring jobs managed per-user via crontab or system-wide via drop-in files under /etc/cron.d/, /etc/cron.daily/, etc.), at (one-shot jobs — "run this once at 3am tomorrow"), and anacron (catch-up runs for daily/weekly/monthly jobs when the machine wasn't powered on). A separate, more modern option is systemd timers — covered in the Services domain. On the RHCSA you'll almost certainly be asked to create a user crontab entry or schedule a one-off at job.

✨Mental Model

Think of cron as a wall calendar: every minute the cron daemon glances at it, and if "today/this hour/this minute" matches an entry, it runs the command. at is a sticky-note on the fridge — "at 3am tomorrow, do this once" — which the atd daemon pulls down after executing. anacron is for laptops: if your machine was asleep when the daily job was due, it catches up on next boot.