Cron Job Every 12 Hours

Cron expression for every 12 hours

0 */12 * * *

On the hour, every 12 hours. It runs twice a day, 730 times a year.

Runs twice a day, at midnight and noon. 0 0,12 * * * is equivalent and easier to read at a glance. If you need 6 AM and 6 PM instead, use 0 6,18 * * *.

Field by field

Examples

crontab

Run crontab -e and add:

0 */12 * * * /usr/local/bin/job.sh >> /var/log/job.log 2>&1

Kubernetes CronJob

apiVersion: batch/v1
kind: CronJob
metadata:
  name: my-job
spec:
  schedule: "0 */12 * * *"
  timeZone: "Etc/UTC"          # Kubernetes 1.27+
  concurrencyPolicy: Forbid    # skip a run if the last one is still going
  jobTemplate:
    spec:
      template:
        spec:
          containers:
            - name: job
              image: ghcr.io/acme/job:1.0
          restartPolicy: OnFailure

GitHub Actions

on:
  schedule:
    - cron: '0 */12 * * *'   # UTC

GitHub evaluates schedules in UTC, and runs can start several minutes late at busy times.

systemd timer

# /etc/systemd/system/job.timer
[Unit]
Description=Run job.service every 12 hours

[Timer]
OnCalendar=*-*-* 00,12:00:00
Persistent=true

[Install]
WantedBy=timers.target

Enable it with systemctl enable --now job.timer, and check the next runs with systemd-analyze calendar "*-*-* 00,12:00:00". Persistent=true runs a missed job after downtime, which cron can’t do.

AWS EventBridge

cron(0 0,12 * * ? *)

EventBridge cron has six fields (the last is the year), uses ? in either the day-of-month or the day-of-week field, and numbers weekdays from 1 (Sunday) to 7. Rules run in UTC; EventBridge Scheduler also accepts a time zone.

Similar schedules: hourly

• Every hour: 0 * * * *
• Every hour at half past: 30 * * * *
• Every 2 hours: 0 */2 * * *
• Every 3 hours: 0 */3 * * *
• Every 4 hours: 0 */4 * * *
• Every 6 hours: 0 */6 * * *
• Every 8 hours: 0 */8 * * *
• Every hour during business hours: 0 9-17 * * 1-5

Have a different schedule? Paste any expression into the Cron Expression Generator, or browse all cron examples.

Sources

• POSIX: crontab
• crontab(5) manual page
• Kubernetes docs: CronJob
• GitHub Actions docs: schedule event
• systemd.time(7): calendar events
• AWS docs: EventBridge Scheduler cron expressions

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Frequently asked questions