cron-scheduler

# Cron Scheduler ## Overview Translate human scheduling intent into correct cron expressions, explain existing expressions in plain language, preview the next fire times, and avoid the subtle traps (DOM/DOW OR-logic, timezone/DST drift, overlapping long-running jobs, missed runs on downtime). Covers classic Vixie/POSIX cron, plus the dialects used by systemd timers, Quartz, AWS EventBridge, Kubernetes CronJobs, and GitHub Actions. **Keywords:** cron, crontab, cron expression, schedule, scheduler, scheduled job, `*/5`, `0 9 * * 1-5`, timezone, TZ, DST, daylight saving, day-of-week, day-of-month, systemd timer, OnCalendar, Quartz, EventBridge rate/cron, Kubernetes CronJob, GitHub Actions schedule, every N minutes, weekday, next run, overlap, concurrencyPolicy, flock. ## Workflow 1. **Identify the target system.** Cron dialects differ. Ask or infer: classic crontab (5 fields), systemd `OnCalendar`, Quartz/Spring (6-7 fields with seconds + `?`), AWS EventBridge (6 fields, year, requires `?`), Kubernetes CronJob (5 fields, UTC by default), or GitHub Actions (5 fields, UTC only). See `references/cron-syntax.md` for the field tables per dialect. 2. **Pin down the timezone.** Determine where the schedule should fire in wall-clock terms and which TZ the runner uses. Most engines run in UTC or the daemon's local TZ — not the user's. Decide and state explicitly. See `references/timezones-and-dst.md`. 3. **Build the expression** field by field using `references/cron-syntax.md`. Pref...