Cron Expressions for Kubernetes and Linux — A Practical Guide

Schedules in Kubernetes CronJob manifests and Linux crontab files use the same five-field cron syntax. A small typo (* in the wrong column) can run a backup job every minute instead of once a day — or not at all.

This post explains the format, gives copy-paste patterns for Kubernetes, and links to our free Cron Parser on skybin.io.

The five fields

┌──────────── minute (0–59)
│ ┌────────── hour (0–23)
│ │ ┌──────── day of month (1–31)
│ │ │ ┌────── month (1–12)
│ │ │ │ ┌──── day of week (0–7, 0 and 7 = Sunday)
│ │ │ │ │
* * * * *

Special characters:

Char	Meaning
`*`	Any value
`,`	List (`1,15` = 1st and 15th)
`-`	Range (`9-17` = 9am–5pm)
`/`	Step (`*/15` = every 15 units)

Kubernetes uses the standard 5-field form in spec.schedule. Quartz-style 6-field cron (with seconds) is not the same — do not paste Quartz expressions into a K8s manifest without converting.

Patterns we use in production

Schedule	Expression	Use case
Every minute	`* * * * *`	Debugging only — rarely in prod
Every 15 minutes	`/15 * * *`	Health pings, queue drain
Hourly	`0 * * * *`	Top of each hour
Daily midnight UTC	`0 0 * * *`	Reports, cleanup
Weekdays 9am	`0 9 * * 1-5`	Business-hours jobs
Monday 9am	`0 9 * * 1`	Weekly digest
First of month	`0 0 1 * *`	Billing, archives

Example Kubernetes CronJob:

apiVersion: batch/v1
kind: CronJob
metadata:
  name: nightly-report
spec:
  schedule: "0 2 * * *"   # 02:00 every day
  jobTemplate:
    spec:
      template:
        spec:
          containers:
            - name: report
              image: your-registry/report-runner:latest
          restartPolicy: OnFailure

Timezones matter

crontab on a server uses the machine timezone. Kubernetes CronJob schedules are interpreted in the controller manager timezone (often UTC on managed clusters). Document whether 0 9 * * * means UTC or local — and use Timezone Converter when coordinating across regions.

For Unix timestamps in logs, pair cron debugging with the Epoch tool.

Validate before you deploy

Before merging a manifest:

Paste the expression into the Cron Parser.
Read the plain-English description.
Confirm the next 5–10 run times match intent.
Use presets in the tool for common K8s/Linux patterns.

The parser runs in your browser — no cluster access required.

Cron vs other schedulers

Kubernetes CronJob — native, good for cluster-internal batch work.
systemd timers — modern Linux VMs.
Cloud scheduler (EventBridge, Cloud Scheduler) — cross-service, outside the cluster.

Cron expressions are still the lingua franca; getting them right once saves pages of on-call notes.