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cron

Schedule recurring jobs on Unix-like systems.

Crontab basics​

  • Edit your crontab
crontab -e
  • List crontab
crontab -l
  • Crontab time fields
minute hour day-of-month month day-of-week command

Special strings​

  • @reboot, @yearly, @monthly, @weekly, @daily, @hourly
@daily /usr/local/bin/backup

Examples​

  • Every 5 minutes
*/5 * * * * /path/script.sh
  • At 2:30am daily
30 2 * * * /path/cleanup.sh
  • Weekdays at 9:00
0 9 * * 1-5 /path/report.sh
  • First day of month at 01:15
15 1 1 * * /path/monthly.sh

Environment & logging​

  • Set PATH and SHELL at top of crontab
SHELL=/bin/bash
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
  • Redirect output to log
0 * * * * /path/job.sh >> /var/log/job.log 2>&1

Common gotchas​

  • Use absolute paths for commands and files.
  • Cron has a minimal environment; source env if needed.
0 * * * * . $HOME/.profile && /path/job.sh

System cron locations​

  • User crontab: crontab -e
  • System-wide: /etc/crontab, /etc/cron.d/*, /etc/cron.{hourly,daily,weekly,monthly}