Textbook of Linux

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cron

The classic Unix time-based job scheduler.

cron is the classic Unix time-based job scheduler. Each user maintains a crontab — a list of time specifications and commands to run when the time matches — that the cron daemon reads and dispatches. Time specifications cover minute, hour, day-of-month, month, and day-of-week, with wildcards and lists that allow flexible scheduling expressions.

The first cron shipped with Version 7 Unix in 1979. Vixie cron (by Paul Vixie, 1987) is the version that most modern Linux distributions actually ship; cronie is a fork that has become the default on Red Hat-derived distributions, with several small enhancements over Vixie cron's original code.

systemd timers are the modern alternative on systemd-based systems, with better integration into the rest of systemd's service management and accurate handling of missed jobs. Many distributions still install a cron daemon by default for backward compatibility, but modern packages increasingly ship systemd timer units instead of /etc/cron.d entries.

Already installed as cronie or vixie-cron on most distros.
To install explicitly:
  Debian/Ubuntu: sudo apt install cron
  Fedora/RHEL:   sudo dnf install cronie
  Arch:          sudo pacman -S cronie