cron

# Cron Schedule tasks using the system crontab via `shell_exec`. ## List current cron jobs ```bash crontab -l ``` ## Add a recurring job ```bash (crontab -l 2>/dev/null; echo "*/20 * * * * echo 'Time to take a break!' >> /tmp/opc-reminders.log") | crontab - ``` ## Common schedules | Schedule | Cron expression | |----------|----------------| | Every 20 minutes | `*/20 * * * *` | | Every hour | `0 * * * *` | | Every day at 8am | `0 8 * * *` | | Weekdays at 5pm | `0 17 * * 1-5` | | Every Monday at 9am | `0 9 * * 1` | ## One-time scheduled task Use `at` for one-time jobs: ```bash echo "echo 'Meeting reminder' >> /tmp/opc-reminders.log" | at 14:30 ``` Or schedule with a specific date: ```bash echo "echo 'Deadline reminder' >> /tmp/opc-reminders.log" | at 10:00 2026-03-20 ``` ## Remove a job Edit the crontab directly: ```bash crontab -e ``` Or filter out a specific job: ```bash crontab -l | grep -v 'pattern-to-remove' | crontab - ``` ## Notes - Use full paths in cron commands (cron has a minimal `$PATH`). - Redirect output to a log file or `/dev/null` to avoid mail noise. - Check `at` availability: `which at` (install with `apt install at` if missing).