Run a Cron Job Every 8 Hours
To run a job every 8 hours, use 0 */8 * * *. The */8 step in the hour field fires three times a day — at 00:00, 08:00, and 16:00, on the hour.
The expression
0 */8 * * * runs at minute 0 of every eighth hour: 00:00, 08:00, and 16:00. That is three runs per day.
Why not four runs?
The step counts from 0 across a 24-hour day: 0, 8, 16. The next multiple (24) is the following midnight, so you get three runs, not four. This trips people up who expect an even 24 / 8 = 3 — which is correct, but note it is not every 8 hours starting from when you save the crontab.
Custom start hours
To run at 02:00, 10:00, 18:00 instead, list them explicitly: 0 2,10,18 * * *. A plain */8 always aligns to midnight.
FAQ
What is the cron expression for every 8 hours?
0 */8 * * * runs on the hour every 8 hours: 00:00, 08:00, 16:00 — three times a day.
Why does */8 only run 3 times a day?
The step counts 0, 8, 16 within the 24-hour day; 24 is the next midnight. Three runs is correct for every-8-hours aligned to midnight.
How do I choose different 8-hour start times?
List the hours explicitly, e.g. 0 2,10,18 * * * runs at 02:00, 10:00, and 18:00.