Crontab Generator

The five fields

A crontab line is `minute hour day-of-month month day-of-week` (crontab(5)). Examples:

• `0 9 * * 1-5` — 9:00 on weekdays
• `*/15 * * * *` — every 15 minutes
• `0 0 1 * *` — midnight on the 1st of each month

The trap everyone hits once

When both day-of-month and day-of-week are set, they combine with OR, not AND: `0 0 13 * 5` runs on the 13th *and* every Friday — not only Friday the 13th.

Operational pitfalls

• Cron runs in the server's timezone — a 9am job on a UTC server fires at 6pm KST. Check `TZ` before anything else.
• Cron's environment is minimal: `PATH` is not your shell's. Use absolute paths for commands and files.
• Jobs that overlap (a run starting before the last finished) need a lock (`flock`) — a classic source of duplicated work.
• There is no built-in logging: redirect output (`>> /var/log/job.log 2>&1`) or you'll debug blind.