cron
also: cron daemon, crond
A system daemon that automatically executes scheduled tasks (called cron jobs) at specified times or intervals. It runs continuously in the background and uses configuration files called crontabs to determine what commands to execute and when.
cron is the Linux task scheduler—a background process that wakes up every minute and checks if any scheduled jobs need to run. Each user can have their own crontab file (cron table) defining tasks, and the system has its own crontabs for administrative jobs.
Cron jobs are defined using a special six-field syntax: minute, hour, day-of-month, month, day-of-week, and the command to execute. For example, 0 2 * * * /usr/local/bin/backup.sh runs backup.sh every day at 2:00 AM.
Common use cases include system maintenance tasks (log rotation, backups), periodic reports, cache clearing, and automated updates. You manage your crontab with the crontab -e command, which opens your personal job list in an editor.