Code-Memo

Cron jobs and scheduling

Cron basics

Cron runs commands on a schedule using entries called crontabs.

Edit user crontab:

crontab -e
crontab -l

Schedule format

Five fields: min hour day month weekday command

Examples:

# Every day at 02:30
30 2 * * * /usr/local/bin/backup.sh

# Every 5 minutes
*/5 * * * * /usr/local/bin/healthcheck.sh

# Every Monday at 09:00
0 9 * * 1 /usr/local/bin/report.sh

Common pitfalls

• PATH is minimal: use full paths or set PATH=...
• No interactive shell: don’t rely on .bashrc
• Output handling: redirect stdout/stderr
  • ... >>/var/log/job.log 2>&1

Logging / email

Cron may email output to the local mailbox depending on configuration.

Alternatives

• systemd timers: better logging, dependencies, and calendar syntax
• at: one-time scheduled jobs (at now + 1 hour)

Related

• systemd and systemctl
• Debugging and optimization