LZH-YS1998
61 lines
1.3 KiB
Markdown
61 lines
1.3 KiB
Markdown
---
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name: cron
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description: Schedule reminders, recurring tasks, and one-time jobs using system crontab.
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---
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# Cron
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Schedule tasks using the system crontab via `shell_exec`.
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## List current cron jobs
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```bash
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crontab -l
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```
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## Add a recurring job
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```bash
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(crontab -l 2>/dev/null; echo "*/20 * * * * echo 'Time to take a break!' >> /tmp/opc-reminders.log") | crontab -
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```
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## Common schedules
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| Schedule | Cron expression |
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|----------|----------------|
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| Every 20 minutes | `*/20 * * * *` |
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| Every hour | `0 * * * *` |
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| Every day at 8am | `0 8 * * *` |
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| Weekdays at 5pm | `0 17 * * 1-5` |
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| Every Monday at 9am | `0 9 * * 1` |
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## One-time scheduled task
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Use `at` for one-time jobs:
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```bash
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echo "echo 'Meeting reminder' >> /tmp/opc-reminders.log" | at 14:30
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```
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Or schedule with a specific date:
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```bash
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echo "echo 'Deadline reminder' >> /tmp/opc-reminders.log" | at 10:00 2026-03-20
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```
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## Remove a job
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Edit the crontab directly:
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```bash
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crontab -e
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```
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Or filter out a specific job:
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```bash
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crontab -l | grep -v 'pattern-to-remove' | crontab -
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```
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## Notes
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- Use full paths in cron commands (cron has a minimal `$PATH`).
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- Redirect output to a log file or `/dev/null` to avoid mail noise.
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- Check `at` availability: `which at` (install with `apt install at` if missing).
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