Definition
cron is a traditional Unix/Linux scheduler that executes commands at configured dates and times.
How it works
A user crontab entry commonly has five scheduling fields followed by a command: minute, hour, day of month, month and day of week. How day-of-month and weekday fields interact can vary by implementation. Jobs run with a limited environment.
Real-world example
For example, a 02:00 backup may fail because PATH is different from an interactive shell or because the working directory is not what the script expects. Absolute paths and redirected logs make failures easier to diagnose.
Limits and best practices
Prevent overlapping runs with a lock, define timezone behavior, monitor exit status and handle secrets securely. Consider systemd timers when dependency handling, missed-run recovery or tighter service integration matters.