Cron Syntax Explained, With Examples

A standard cron expression has five space-separated fields: minute, hour, day of month, month and day of week. A job runs whenever the current time matches all of them, with one exception: when both day fields are restricted, a match on either one is enough. For example, 30 2 * * 1-5 means 02:30 on Monday to Friday, in the time zone of the machine running the cron daemon.

The five fields

┌───────────── minute        (0–59)
    │ ┌─────────── hour          (0–23)
    │ │ ┌───────── day of month  (1–31)
    │ │ │ ┌─────── month         (1–12 or JAN–DEC)
    │ │ │ │ ┌───── day of week   (0–7 or SUN–SAT; 0 and 7 are both Sunday)
    │ │ │ │ │
    30 2 * * 1-5  /path/to/command

Names are the first three letters of the English month or day, and case does not matter. The reference for Linux is the crontab(5) manual page; most Linux distributions ship cronie or a Vixie cron derivative, and the rules below follow those.

Operators: * , - and /

Steps count from the start of the range and restart at each boundary, so they are not a true interval. */7 in the minute field matches minutes 0, 7, 14 … 56 and then 0 again, leaving a four-minute gap across each hour. Similarly 0 */5 * * * runs at 00:00, 05:00, 10:00, 15:00 and 20:00, then again four hours later at midnight. For an even spread, choose a step that divides 60 (minutes) or 24 (hours).

Lists and steps combine with ranges: */15 9-17 * * 1-5 means every 15 minutes from 09:00 to 17:45 on weekdays. Some crontab(5) pages say that ranges and lists of names are not allowed, so 1-5 is more portable than MON-FRI.

The day-of-month and day-of-week rule

This is the part of cron that surprises people most. The crontab(5) page states that if both day fields are restricted, the job runs when either matches. So:

0 8 1-7 * 1    # 08:00 on each of days 1–7 AND on every Monday
                   # (not "the first Monday of the month")

If either day field is *, only the other one matters. Classic cron has no way to say "first Monday"; the usual workaround is to schedule 0 8 1-7 * * and test the weekday inside the command. When writing that test in a crontab line, remember that an unescaped % in the command is turned into a newline, so date +%u must be written as date +\%u.

One subtlety: Vixie-derived implementations, including cronie, decide whether a day field is restricted by whether it begins with an asterisk. A field such as */2 therefore counts as unrestricted there, and 0 0 */2 * 1 runs only on Mondays that fall on odd-numbered dates. The Cron Expression Parser on this site follows the same rule. Other schedulers may not, so expressions that mix a stepped day field with a day-of-week value are best avoided.

Special strings: @daily, @reboot and friends

@reboot runs when the daemon starts, which is usually but not necessarily at boot.

Common schedules

Every row below was checked with the parsing code used by the Cron Expression Parser, including the next run times it produces.

A frequent mistake is * 2 * * * when "daily at 2am" was meant: it runs every minute from 02:00 to 02:59. Set the minute too, as in 0 2 * * *.

Time zones and daylight saving

Classic cron evaluates schedules in the local time zone of the system or daemon, not of the user who wrote the crontab. cronie also supports a CRON_TZ variable in the crontab to run its entries in a different zone; not every implementation does, so check your manual page before relying on it.

Daylight saving changes mean that a local time such as 02:30 can be skipped or occur twice. Vixie-derived daemons document special handling for clock changes of less than three hours, but behaviour differs between implementations, so the simplest options are to keep servers on UTC or to avoid scheduling important jobs between 01:00 and 03:00 local time. To convert a run time between zones or into a Unix timestamp, use the Unix Timestamp Converter.

Cron in other systems

Many schedulers borrow cron syntax but change the details:

Check each system's own documentation before copying an expression between them, particularly the day-of-week numbering.

What the Cron Expression Parser accepts

The Cron Expression Parser describes an expression in plain English and lists its next five run times as you type. Based on its code:

• It needs exactly five fields; six- or seven-field Quartz or AWS expressions are rejected with a message giving the number of fields found.
• It accepts *, lists, ranges and steps, month and day names in any case (including in ranges and lists, such as MON-FRI), 7 for Sunday, and ?, which it treats like *.
• It accepts @yearly, @annually, @monthly, @weekly, @daily, @midnight and @hourly. @reboot is reported as an unknown macro, because it has no run times to show.
• It rejects L, W and #, out-of-range values (such as minute 60) and ranges that run backwards (such as FRI-MON).
• It also accepts a start and step without a range, such as 5/15 (minutes 5, 20, 35 and 50). Not every cron implementation accepts this form; 5-59/15 is the portable way to write it.
• Next run times are shown in your browser's local time zone, which may differ from your server's. It looks up to about eight years ahead, so 0 0 29 2 * lists only the leap days in that window, and 0 0 31 2 * shows "Never — this date does not occur".

Frequently asked questions

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