Question 1

What is a cron expression?

Accepted Answer

A cron expression is a string of 5 (or 6) fields that tells the cron scheduler when to run a job. The five standard fields are: minute, hour, day of month, month, and day of week. For example, in "*/5 * * * *" the job runs every 5 minutes. The first (minute) field says "every 5 minutes", while the remaining fields are "*" meaning every hour, every day, every month, and any weekday.

Question 2

What do the 5 fields in a cron expression mean?

Accepted Answer

The 5 fields are: 1) minute (0-59), 2) hour (0-23), 3) day of month (1-31), 4) month (1-12), 5) day of week (0-7, where 0 and 7 are Sunday). Asterisk (*) means "every", a slash (/) sets an interval like */15 for every 15 units, a hyphen (-) defines a range, a comma (,) lists multiple values, and L means "last" (for example "L" in the day-of-month field is the last day of the month).

Question 3

What is the difference between * and */1 in cron?

Accepted Answer

They behave the same for most schedulers — both mean every single unit. "*/1" is the explicit interval syntax for "every 1", while "*" is shorthand for "every". The cron generator uses "*" for every-field values and "*/n" only when an interval greater than 1 is needed.

Question 4

How do I schedule a cron job every 5 minutes?

Accepted Answer

Use the expression "*/5 * * * *". The minute field is */5, so the job fires at minute 0, 5, 10, 15, 20, and so on. Every other field is "*" (every hour, every day, every month, any weekday). Paste it into crontab with: */5 * * * * your_command

Question 5

Why won't my cron job run? Common cron mistakes

Accepted Answer

The most common mistakes are: 1) the cron daemon (cron) is not running or the container exits (add "cron -f" in Docker), 2) the script path is not absolute (use /usr/bin/python3 instead of python), 3) missing execute permissions (chmod +x), 4) the script runs before environment variables like PATH are set — export them inside the script, and 5) using "@every 5m" syntax which only works in Kubernetes and some tools, not in standard crontab.

Question 6

What is the difference between cron on Linux, Kubernetes, and Vercel?

Accepted Answer

Standard Linux crontab uses the classic 5-field syntax. Kubernetes CronJobs use the same 5-field syntax but support special macros like @hourly, @daily, and @every 5m. Vercel Cron Jobs also use standard 5-field cron syntax defined in vercel.json. The expressions from this generator work in all three — only the surrounding syntax differs.

Question 7

Does cron run in the server's local timezone?

Accepted Answer

Yes — classic crontab evaluates expressions in the server's local timezone. On Ubuntu/Debian you can set it with "timedatectl set-timezone UTC" and check with "date". Managed schedulers like Vercel, AWS EventBridge, and GitHub Actions use UTC by default, so convert your desired local time to UTC when scheduling there.

Question 8

Can I use seconds in a cron expression?

Accepted Answer

Standard 5-field crontab cannot express seconds. Some systems support a 6-field Vixie syntax where the first field is seconds, e.g. "*/30 * * * * *" runs every 30 seconds. In standard crontab the fastest reliable interval is every minute: "* * * * *".

Cron Job on the last day of the month

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