What is the cron expression for every 12 hours?

The cron expression for every 12 hours is "0 */12 * * *". Runs twice a day, at midnight and noon.

What should I watch out for when running a cron job every 12 hours?

Midnight and noon are both popular slots — you inherit two daily congestion spikes. 0 4,16 * * * is the same promise without the queue. A mirror sync that occasionally takes 13 hours will overlap itself. flock turns that into a skipped run — almost always the better failure.

Cron expression for Every 12 hours

0 */12 * * *

Runs twice a day, at midnight and noon.

Next 5 runs (your local time)

These are shown in your browser’s timezone. The job itself runs in the scheduler’s timezone — often UTC — so the real run time can differ.

What people actually schedule with `0 /12 * *`

Dependency and container-image vulnerability scans
Refreshing OAuth tokens that expire daily (12h gives you one retry window)
Mirror syncs of package repos or static datasets

Use `0 /12 * *` on your platform

It’s the same 5-field expression everywhere — what changes is where you put it and which timezone it runs in.

Linux / crontab

0 */12 * * * /path/to/your-command

Runs in the server’s local timezone — check it with timedatectl. Full field reference: crontab(5) man page.

GitHub Actions

on:
  schedule:
    - cron: "0 */12 * * *"

GitHub Actions always runs scheduled jobs in UTC — there is no timezone setting, and runs can be delayed under load (official docs).

Kubernetes CronJob

spec:
  schedule: "0 */12 * * *"

Defaults to UTC. Set spec.timeZone (Kubernetes 1.27+) for a specific zone — see the CronJob docs.

Quartz / Spring `@Scheduled`

Quartz uses 6 fields (seconds first): 0 0 */12 * * *. Watch out: Quartz day-of-week is 1=SUN … 7=SAT (not 0–6), and day-of-month / day-of-week use ? — double-check if your schedule touches those fields (Quartz cron reference).

Gotchas with every 12 hours schedules

Midnight and noon are both popular slots — you inherit two daily congestion spikes. 0 4,16 * * * is the same promise without the queue.
A mirror sync that occasionally takes 13 hours will overlap itself. flock turns that into a skipped run — almost always the better failure.
0 */12 and 0 0,12 * * * are identical; the second tells the next engineer exactly when it fires without mental math.

Will you know if this job silently fails?

Cron jobs fail quietly — a server reboots, a path changes, or an error code is ignored — and nobody notices until the data is missing. A cron monitor (a dead-man’s-switch) alerts you when a scheduled job does not check in on time.

Monitor your cron jobs with UptimeRobot →

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Is `0 /12 * *` the right schedule?

If once a day is honestly enough, daily at midnight (or better, 3am). Tighter freshness goes to every 6 hours.

Or use the interactive cron generator & explainer, read the complete cron syntax guide, or pick another common schedule: