Cron to systemd: Convert Crontab to Timers and CronJobs
A cron-to-systemd converter turns a 5-field crontab line into a systemd timer plus service unit, and into Kubernetes CronJob YAML. Paste the expression into the FindUtils Cron to systemd tool, set a unit name and command, then copy the files. Conversion runs in your browser. The tool does not run the job.
Six-field cron (with seconds) is rejected. Review ExecStart and the container command before you install anything.
Why Convert Cron
systemd timers use OnCalendar, not crontab syntax. Kubernetes CronJob keeps the 5-field cron string. One converter that emits both saves a manual rewrite.
Convert cron when:
- You are moving a crontab onto a host that uses systemd. You need a
.timerand a.service. - You are moving a schedule into a cluster. You need a CronJob object.
- You want to see
OnCalendarnext to the original line. The mapping is easy to get wrong by hand. - Both day-of-month and day-of-week are set. cron treats that as OR. systemd
OnCalendartreats it as AND. The page warns on that case.
The honest limit: the YAML is a starting CronJob. Review image, name, and schedule before kubectl apply.
How to Convert a Cron Expression
Use 5 fields: minute, hour, day-of-month, month, day-of-week.
Step 1: Paste a 5-field expression
Open the FindUtils Cron to systemd tool. Examples: */5 * * * * or 0 9 * * 1-5. Presets cover every 5 minutes, weekdays at 09:00, hourly, and daily midnight.
Step 2: Set a unit name and command
The unit name becomes the timer, service, and CronJob name. The command becomes ExecStart and the container command. Default command is /usr/local/bin/your-command if you leave it blank.
Step 3: Copy systemd units
Copy the timer plus service pair. Install them on a host that uses systemd. Enable the timer after you review the command.
Step 4: Copy CronJob YAML
Copy the YAML. Set a real image. Apply only after you read the schedule.
If you still need to build a cron line, use the Cron Expression Generator first, then convert it.
Cron vs systemd OnCalendar vs Kubernetes CronJob
The same English schedule is not the same syntax in each system.
| Aspect | Crontab (5-field) | systemd timer | Kubernetes CronJob |
|---|---|---|---|
| Schedule field | m h dom mon dow | OnCalendar= | schedule: 5-field cron |
| Seconds | Not in 5-field form | Yes, in OnCalendar | Not in standard CronJob |
| DOM + DOW both set | OR | AND | cron OR semantics |
| This converter | Input | Emits .timer + .service | Emits YAML |
| Runs the job | cron daemon | systemd | kube-controller |
Worked mappings from this converter:
*/5 * * * *becomesOnCalendar *-*-* *:00/5:00and a CronJob schedule of that same cron string.0 9 * * 1-5becomesOnCalendar Mon..Fri *-*-* 09:00:00and CronJob0 9 * * 1-5.
Practical Examples
Example 1: Every 5 minutes on a VM
Paste */5 * * * *. Set unit name backup and command /usr/local/bin/backup.sh. Copy the units. Enable the timer on the host.
Example 2: Weekday morning report in a cluster
Paste 0 9 * * 1-5. Copy CronJob YAML. Replace the image and command. Apply in the target namespace.
Example 3: Catch the DOM + DOW warning
Paste 0 0 1 * 1. Both day-of-month and day-of-week are set. cron fires on the 1st or on Monday. systemd OnCalendar needs both. Read the warning before you ship the timer.
Common Mistakes
Mistake 1: Pasting Quartz 6-field cron
A leading seconds field is rejected. Use 5 fields only.
Mistake 2: Installing units without reading ExecStart
The command you type is copied into the service. A placeholder path will fail at runtime.
Mistake 3: Assuming DOM + DOW match cron on systemd
That combination is OR in cron and AND in OnCalendar. Check the warning.
Mistake 4: Applying YAML with the sample image still in place
The YAML is a starting point. Set image, name, and schedule first.
Limits You Should Plan For
The converter accepts the 5-field form only. A sixth seconds field is an error, not a silent drop.
OnCalendar is a best-effort mapping of the fields you typed. Review the timer after you copy it, especially when the expression uses lists, ranges, or both day fields.
Kubernetes CronJob YAML from this page is a starting object. It does not set resource limits, a real container image, or a namespace. Fill those in before apply.
Conversion does not talk to systemd or to a cluster. Nothing is installed until you copy the files to a host you control.
Tools Used in This Guide
- Cron to systemd — Convert 5-field cron to systemd units and CronJob YAML
- Cron Expression Generator — Build and validate cron expressions
- JSON Formatter — Pretty-print JSON when you inspect related configs
- Regex Tester — Test field patterns while you edit expressions
FAQ
Q1: Is cron to systemd free? A: Yes. FindUtils Cron to systemd is free, with no signup. Conversion runs in your browser.
Q2: Is this 5-field cron? A: Yes. Six-field expressions with seconds are rejected.
Q3: Does it run the job? A: No. It emits unit files and YAML.
Q4: Can I use Quartz 6-field cron? A: No. This converter is 5-field only.
Q5: Is the YAML valid? A: It is a starting CronJob. Review image, name, and schedule before apply.
Q6: What about 0 9 * * 1-5?
A: OnCalendar is Mon..Fri *-*-* 09:00:00. The CronJob uses schedule 0 9 * * 1-5.
Q7: Do I need an account? A: No. Paste the expression and copy the files.
Next Steps
- Build the cron line first with the Cron Expression Generator
- Read the cron expression generator guide
- Validate YAML-shaped config with the YAML Validator
- Browse the complete guide to online developer tools