Linux Basic — Scheduling with Cron Practice

Practice Exercises — Scheduling with Cron

Work through these to gain fluency with crontab editing, expressions, and logging.

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Warm-up

1. Write a crontab entry to run /opt/hello.sh every minute.
2. Write an entry for daily at 3:30 AM.
3. Write an entry for every Monday at 9 AM.
4. Use @daily shortcut for /opt/backup.sh.

Expressions

1. Every 15 minutes.
2. Every 2 hours, but only between 9 AM and 5 PM.
3. Weekdays only (Mon–Fri) at 8 AM.
4. First and fifteenth of every month at midnight.
5. Every Sunday at noon.

Environment & Debugging

1. Add a cron job that runs env > /tmp/cronenv.txt to see the cron environment.
2. Set PATH=/usr/local/bin:/usr/bin:/bin in your crontab.
3. Set MAILTO=you@example.com and confirm cron emails you on job output.
4. Disable email with MAILTO="".

Logging

1. Redirect a job’s output to /var/log/myjob.log (append mode, stderr too).
2. Use logger -t myjob to send output to syslog.
3. Add a job that logs “hello at $(date)” every minute for 5 minutes, then remove it.

Real Scenarios

1. Schedule /opt/backup.sh to run daily at 2 AM, logging to /var/log/backup.log.
2. Schedule /opt/cleanup.sh to run weekly on Sundays at 3 AM.
3. Use @reboot to run /opt/startup.sh once at boot.
4. Combine: run a job every 10 minutes during work hours (9–5, Mon–Fri), log to a file, and email on failure.

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Verification Checklist

• All jobs use absolute paths for scripts and commands
• PATH is set explicitly in crontab if needed
• Logs use >> to append, not > to overwrite
• Test each job manually before scheduling
• Verify jobs run by checking logs or temporary outputs

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Next chapter → Clean & Readable Code