Reference

Cron expressions, explained field by field

A cron expression is five small patterns that together decide one schedule. These entries explain what each field accepts, how the fields combine, and where implementations disagree — the places schedules silently fire at the wrong time.

One line, five fields

A traditional crontab line is minute hour day-of-month month day-of-week command. Each of the first five fields is a set of allowed values; a job runs when the current time is in all five sets. There is no seconds field, so the finest resolution is one minute.

The fields are not interchangeable. Moving a value one position to the right changes the schedule entirely, and a * means “every value”, which is why an expression with several stars fires far more often than most people expect.

Dialects are not one standard

Vixie cron and its descendants (cronie on Fedora/RHEL, Debian's cron) define the common five-field behaviour plus @daily-style macros. Quartz, Spring's scheduler, AWS EventBridge and Jenkins reuse the idea with different field counts and day-of-week numbering.

Every entry here states which dialect a rule belongs to. When a schedule matters, verify it on the machine that will run it rather than assuming a syntax you saw in another product.

All entries

Cron field orderA five-field cron expression runs minute, hour, day-of-month, month and day-of-week, in that order. Cron step valuesA slash adds a step to a range: */5 means every fifth value starting at the range's lower bound. Cron ranges and listsCommas combine values and hyphens define inclusive ranges; both can be mixed and both may use month or weekday names. Month and weekday namesCron accepts JAN–DEC and SUN–SAT, case-insensitively, but the numbering of Sunday differs between dialects. Day-of-month and day-of-week togetherWhen both day fields are restricted, Vixie-style cron runs the job if either field matches. Cron special stringsMacros such as @daily and @reboot replace common five-field schedules in Vixie-style cron. Cron and time zonesCron schedules run in the system's local time zone unless the implementation offers CRON_TZ or TZ support. Cron vs systemd timersCron is one line per job; systemd timers separate a unit from its schedule and can catch up on missed runs. Six-field cron dialectsQuartz, Spring, AWS EventBridge and Jenkins extend cron with seconds or other fields, and they do not agree on order. Common cron schedulesThe expressions people ask for most: every five minutes, hourly, daily, weekdays at 09:00 and first of the month.

Use these with

Cron Expression Explainer

Turn a five-field cron expression into plain English and the next five run times.

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Unix Timestamp Converter

Epoch seconds or milliseconds to ISO, UTC, local time and back.

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