Every Monday cron: what 0 9 * * 1 means for a start-of-week job

Reading 0 9 * * 1

The first two fields pin the time to 09:00, the date fields are wildcards, and the day-of-week field is 1, which is Monday in standard cron (0 and 7 are Sunday). MON is accepted in place of 1 by the common implementations and by this page's parser.

The parser reads it as: At 09:00, on Monday. The next run times in the panel above are computed in your browser, in your own timezone, so they are not printed in this text.

What Monday jobs are for

Start-of-week jobs typically summarise the previous seven days: dependency update reports, cost reports, stale-branch cleanups, on-call handover notes. 0 9 * * 1 /opt/finops/bin/weekly-cost-report --window 7d is a representative line. Compute the reporting window from explicit dates, not from now minus seven days, so a delayed or retried run still reports the same week.

A weekly job fails silently more easily than a frequent one: if it breaks, nobody notices for a week. Send its exit status somewhere, or use a dead-man's-switch check that alerts when the Monday ping does not arrive.

Pitfalls: first Monday and timezones

Adding a day of month does not narrow it down. 0 9 1-7 * 1 runs on the 1st to the 7th of every month and on every Monday, because cron combines a restricted day of month and day of week with OR. For the first Monday only, keep 0 9 * * 1 and let the command exit unless the date is 7 or lower.

The weekday is evaluated in the cron daemon's zone. A job at 09:00 Monday in Sydney is 22:00 or 23:00 on Sunday in UTC, so converting the hour for a UTC server, or for GitHub Actions, can move the job to a different day as well.

systemd, Kubernetes and GitHub Actions

systemd: OnCalendar=Mon *-*-* 09:00:00; note that systemd's own weekly shorthand also means Monday, but at 00:00. Kubernetes accepts schedule: "0 9 * * 1" with an optional timeZone. GitHub Actions runs it at 09:00 UTC on Monday. Related: every weekday for Monday to Friday, every Sunday for the end of the week.