Cron Expression Examples for Schedulers

Cron syntax schedules recurring jobs: backups, report emails, cache clears. A five-field cron line (minute hour day-of-month month day-of-week) is standard on Linux crontab; some platforms add seconds or use slightly different field order — always read the host docs. systemd timers on Linux offer an alternative to cron with clearer logging; many teams still paste five-field lines into Kubernetes CronJob manifests and vendor schedulers.

Field order reminder

Classic cron: minute (0–59), hour (0–23), day of month (1–31), month (1–12), day of week (0–7, Sunday = 0 or 7). An asterisk means every. Commas list values; hyphens ranges; slashes step values. Example: 0 2 * * * — daily at 02:00. 30 9 * * 1 — Mondays at 09:30.

Common patterns

Every 15 minutes: */15 * * * *. Weekdays at 8 AM: 0 8 * * 1-5. First day of month midnight: 0 0 1 * *. Every Sunday: 0 0 * * 0. Spring cron in Java uses six fields with seconds first — copying Linux crontab lines without reading docs schedules the wrong minute. Combine day-of-month and day-of-week carefully — on some systems they are OR, on others AND, depending on implementation.

GitHub Actions and cloud variants

GitHub Actions uses five fields in schedule with UTC time: on: schedule: - cron: '0 6 * * *'. AWS EventBridge and Kubernetes CronJob may use one extra seconds field or require question marks in specific positions. Never assume local timezone — convert to UTC or use platform timezone settings explicitly. Random sleep 0–300 before heavy jobs spreads load when thousands of hosts share midnight UTC.

Build and validate expressions

Open /tool/cron-expression-builder to pick schedule parts and copy the string. Document whether daylight saving shifts local schedules; UTC cron avoids ambiguous local hours. Paste the expression into staging before production — daylight saving shifts can surprise you if the scheduler uses local time.

Safety habits

Idempotent jobs survive duplicate runs. Log start and end. Avoid thundering herds — stagger tenants with random minutes. Document owner and runbook link in the crontab comment.

Document schedules for on-call

Paste the cron line, timezone, and owner into the runbook beside what the job does and how to re-run it manually. When daylight saving shifts local schedules, note whether the server uses UTC — on-call engineers should not guess why a report arrived an hour early. Use /tool/cron-expression-builder when someone asks for plain English; store the resulting string in infrastructure-as-code so drift between environments is visible in diff review.

Avoid scheduling heavy database vacuum jobs at the same minute as backup snapshots unless I/O capacity is proven. Use flock or pidfiles in wrapper scripts so a slow run does not overlap the next cron fire. For multi-tenant SaaS, tenant-specific schedules belong in data with a worker queue, not one crontab line per customer. Test cron changes in staging with accelerated clocks or manual trigger before production. Document dependency order: ETL after ingest, reports after ETL. When migrating servers, export crontab with crontab -l and diff timezones on the new host.

CI systems often use cron syntax in workflow schedules — copy UTC times from the builder into YAML comments so reviewers see local intent. For daylight saving, prefer UTC cron on servers and convert for human docs only. Avoid 0 0 * * * on shared hosts if maintenance windows already saturate disk I/O at midnight.

CI systems often use cron syntax in workflow schedules — copy UTC times from the builder into YAML comments so reviewers see local intent. For daylight saving, prefer UTC cron on servers and convert for human docs only. Avoid 0 0 * * * on shared hosts if maintenance windows already saturate disk I/O at midnight.

FAQ

Can I run every second? Classic cron is minute granularity; sub-minute needs other schedulers.

What is @daily? Some implementations support macros (@hourly, @daily); not portable everywhere.

Why did my job skip? Check timezone, field OR logic, and machine downtime during the minute slot.

Does the builder know AWS rules? Use it for standard five-field lines; cloud consoles often show examples inline too.