Field by field
0 */12 * * * reads: At 00:00 and 12:00. That is 2 runs a day.
| Field | Value | Selects |
|---|---|---|
| Minute | 0 | 0 |
| Hour | */12 | every 12 hours: 00:00 and 12:00 |
| Day of month | * | any day of the month |
| Month | * | every month |
| Day of week | * | any day of the week |
Worth knowing
- Two runs a day, at 00:00 and 12:00.
- For two runs that avoid midnight, list the hours:
0 9,21 * * *.
Variations
0 9,21 * * *Twice a day, at 09:00 and 21:00Explain it0 6-18/12 * * *Twice a day, at 06:00 and 18:00Explain it
The same schedule elsewhere
crontab
0 */12 * * * /path/to/job.sh
Runs in the machine's local timezone. crontab -e to edit.
GitHub Actions
on:
schedule:
- cron: "0 */12 * * *"Always UTC. Nothing more often than every 5 minutes, and runs can start late when GitHub is busy.
Kubernetes CronJob
spec: schedule: "0 */12 * * *" timeZone: "Asia/Kolkata"
timeZone needs Kubernetes 1.27 or later; without it the controller's zone applies, usually UTC.
Spring @Scheduled
@Scheduled(cron = "0 0 */12 * * *")
Six fields: seconds come first. Days are written as names, which Spring and cron read alike.
Quartz
0 0 0/12 * * ?
One of day-of-month and day-of-week must be ?. Quartz counts days 1-7 from Sunday, so names are safer than numbers.
AWS EventBridge
cron(0 0/12 * * ? *)
Six fields, the last one the year. UTC unless the schedule sets a timezone. Days count from Sunday, as in Quartz.
systemd timer
[Timer] OnCalendar=*-*-* 00/12:00:00 Persistent=true
Persistent=true runs a job that was missed while the machine was off, once it is back.