Understand quoi un cron expression actually exécute
Paste un cron expression, see le exact schedule champs et le suivant fire times, et apprendre le notations ce la plupart souvent surprise people.
- 1 Analyseur d'expressions Cron →
Paste expressions like */15 * * * * or 0 9 * * 1-5. The tool breaks the expression into minute / hour / day-of-month / month / day-of-week fields and explains each in plain language.
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Notation reminders: * means every value in the field; */5 means every 5th value starting from the field minimum; ranges (1-5) and lists (1,15) combine freely. The classic surprise: in standard cron, if both day-of-month and day-of-week are restricted (not *), a day matches when EITHER one matches — not both.
- 3 Générateur d'expressions Cron →
Going the other way: describe a schedule and get the expression, useful for 6-field systems that add a seconds field.
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Two portability warnings: some systems expect 6 or 7 fields (seconds, year) — verify your scheduler's dialect; cron fires in the server's local timezone, so a 9:00 expression runs at different UTC times on different hosts, and DST transitions can skip or duplicate runs.
Questions fréquentes
- Does cron handle daylight saving time?
- Cron evaluates wall-clock time, so runs can be skipped or duplicated around DST transitions. For interval-critical work, consider scheduling in UTC or using a monotonic timer.
- What is the difference between * and */5 in the minute field?
- * matches every minute. */5 matches minutes 0, 5, 10, ... 55 — every fifth minute starting at the field's minimum.
- Why doesn't my expression run on the expected day?
- If both day-of-month and day-of-week are restricted, standard cron ORs them. Use * in one of the two fields if you need AND semantics via a wrapper check.