What Is Cron? — The Complete Guide

Cron is a time-based job scheduler built into virtually every Unix and Linux system. It runs in the background as a daemon and executes commands or scripts at dates and times you specify using cron expressions — compact strings like 0 9 * * * that mean "every day at 9 AM."

Cron was introduced in Version 7 Unix (1979) and has been a cornerstone of system administration ever since. Every major operating system now supports cron or a cron-compatible scheduler: Linux distributions ship crond, macOS uses launchd with crontab compatibility, and cloud platforms like AWS, Vercel, and GitHub Actions accept cron expressions to schedule serverless functions and CI/CD pipelines.

Common uses include running backups, sending scheduled emails, rotating logs, syncing data between systems, clearing caches, and triggering builds. If something needs to happen on a recurring schedule, cron is usually the first tool to reach for. Tools like SimpleCronTab make it easy to build and test cron expressions visually before deploying them.