Question 1

How can I write a Crontab that will run my script every 2 hours?

Accepted Answer

Use `0 */2 * * * /home/username/script.sh`. The minute is `0` (top of the hour) and the hour step `*/2` selects every even hour (00:00, 02:00, …, 22:00). For odd hours, use `0 1-23/2 * * *`. Cron is schedule-driven, not interval-driven — missed runs are not retried automatically.

Question 2

How can I run command every six hours every day?

Accepted Answer

Use `0 */6 * * * command`. It fires four times a day at 00:00, 06:00, 12:00 and 18:00. The minute is `0` (top of the hour) and the hour step `*/6` selects every sixth hour. To shift the start, use a range: `0 3-23/6 * * *` fires at 03/09/15/21.

Question 3

I am trying to add a crontab entry to execute a script every 30 minutes, on the hour and 30 minutes past the hour or something similar. How can I do this?

Accepted Answer

Use `30 * * * * command` to run at half past every hour, or `0,30 * * * * command` (equivalently `*/30 * * * *`) to run on the hour and at 30 past. Cron matches a schedule, not an interval — the actual time between runs depends on which clock minutes match the expression.

Question 4

How can I set up a cron job to run every night at 2:30? I am familiar with configuring it to run at 2:00, but not 2:30.

Accepted Answer

Use `30 2 * * * command`. The minute field comes first in cron, then the hour — so 2:30 AM is `30 2`, not `2 30`. Cron uses 24-hour time (no AM/PM), so 2:30 PM is `30 14`. The expression runs in the scheduler's timezone, which may not match your local time.

How can I write a Crontab that will run my script every 2 hours?

Calendar

April 2026

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