Field-by-field breakdown
| Field | Value | Meaning |
|---|---|---|
| Minute | 0 | 0 |
| Hour | */3 | Every 3 (0, 3, 6 … 21) |
| Day of month | * | Every day of the month |
| Month | * | Every month |
| Day of week | * | Every day of the week |
Copy-paste examples
Linux crontab
# crontab -e
0 */3 * * * /usr/local/bin/my-job.sh >> /var/log/my-job.log 2>&1Kubernetes CronJob
apiVersion: batch/v1
kind: CronJob
metadata:
name: my-job
spec:
schedule: "0 */3 * * *"
concurrencyPolicy: Forbid
jobTemplate:
spec:
template:
spec:
restartPolicy: OnFailure
containers:
- name: my-job
image: busybox:1.36
command: ["sh", "-c", "date; echo Hello from cron"]GitHub Actions
on:
schedule:
- cron: '0 */3 * * *' # always UTCGitHub Actions evaluates schedules in UTC, does not accept macros such as @daily, and will not run workflows more often than every 5 minutes; runs can also be delayed during periods of high load.
Common variations
Click an expression to load it into the tool above.
| Cron expression | Schedule |
|---|---|
| At 0 minutes past the hour, every 3 hours, between 1:00 AM and 11:59 PM. | |
| At 30 minutes past the hour, every 3 hours. | |
| At 0 minutes past the hour, every 3 hours, Monday through Friday. | |
| At 0 minutes past the hour, every 3 hours, between 9:00 AM and 6:59 PM. |
Frequently asked questions
What does 0 */3 * * * mean in cron?
At 0 minutes past the hour, every 3 hours. The five fields are minute 0, hour */3, day of month *, month * and day of week *.
How do I run a cron job every 3 hours in Linux?
Run crontab -e, add the line 0 */3 * * * /path/to/command, then save and exit. Use absolute paths, redirect output to a log file, and confirm it runs with grep CRON /var/log/syslog.
When will 0 */3 * * * run next?
It depends on the current time and the time zone of the machine running cron. The calculator on this page shows the next 5 run times in your local time zone; on a server, cron uses the system time zone, which is often UTC.