Explainer1 min readUpdated July 1, 2026

What is a cron job?

Short answer

A cron job is a command scheduled to run automatically at fixed times or intervals, defined by a five-field cron expression (minute, hour, day of month, month, day of week). Cron is the time-based job scheduler on Unix-like systems.

What cron does

Cron is a scheduler on Unix-like systems that runs commands at specified times without anyone triggering them. Each scheduled command is a cron job, and the timing is written as a five-field expression. For the field-by-field syntax, see cron syntax explained.

The five fields

* * * * *  command
| | | | |
| | | | +-- day of week (0-6, Sun=0)
| | | +---- month (1-12)
| | +------ day of month (1-31)
| +-------- hour (0-23)
+---------- minute (0-59)

Minute, hour, day of month, month, day of week

Common examples

0 * * * * — at the top of every hour
*/15 * * * * — every 15 minutes
0 9 * * 1-5 — 9:00 on weekdays
0 0 1 * * — midnight on the first of each month

Try it: Cron Expression BuilderBuild and read cron expressions with a plain-English preview.Open tool

Cron uses the server's time zoneA cron schedule runs in the server's local time by default. Around daylight-saving changes, jobs can run twice or be skipped — schedule critical jobs in UTC where possible.

References

Questions

What does cron stand for?

The name comes from Chronos, the Greek word for time. Cron is the time-based job scheduler; a scheduled task is called a cron job.

What is a crontab?

A crontab (cron table) is the file that lists a user's cron jobs, one schedule and command per line. You edit it to add, change, or remove scheduled tasks.

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