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‎content/ja/docs/tasks/job/automated-tasks-with-cron-jobs.md

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---
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title: Running Automated Tasks with a CronJob
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min-kubernetes-server-version: v1.21
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reviewers:
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- chenopis
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content_type: task
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weight: 10
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---
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<!-- overview -->
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CronJobs was promoted to general availability in Kubernetes v1.21. If you are using an older version of
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Kubernetes, please refer to the documentation for the version of Kubernetes that you are using,
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so that you see accurate information. Older Kubernetes versions do not support the `batch/v1` CronJob API.
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You can use a {{< glossary_tooltip text="CronJob" term_id="cronjob" >}} to run {{< glossary_tooltip text="Jobs" term_id="job" >}} on a time-based schedule.
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These automated jobs run like [Cron](https://en.wikipedia.org/wiki/Cron) tasks on a Linux or UNIX system.
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Cron jobs are useful for creating periodic and recurring tasks, like running backups or sending emails.
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Cron jobs can also schedule individual tasks for a specific time, such as if you want to schedule a job for a low activity period.
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Cron jobs have limitations and idiosyncrasies.
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For example, in certain circumstances, a single cron job can create multiple jobs.
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Therefore, jobs should be idempotent.
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For more limitations, see [CronJobs](/docs/concepts/workloads/controllers/cron-jobs).
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## {{% heading "prerequisites" %}}
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* {{< include "task-tutorial-prereqs.md" >}}
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<!-- steps -->
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## Creating a Cron Job
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Cron jobs require a config file.
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This example cron job config `.spec` file prints the current time and a hello message every minute:
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{{< codenew file="application/job/cronjob.yaml" >}}
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Run the example CronJob by using this command:
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```shell
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kubectl create -f https://k8s.io/examples/application/job/cronjob.yaml
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```
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The output is similar to this:
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```
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cronjob.batch/hello created
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```
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After creating the cron job, get its status using this command:
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```shell
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kubectl get cronjob hello
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```
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The output is similar to this:
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```
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NAME SCHEDULE SUSPEND ACTIVE LAST SCHEDULE AGE
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hello */1 * * * * False 0 <none> 10s
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```
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As you can see from the results of the command, the cron job has not scheduled or run any jobs yet.
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Watch for the job to be created in around one minute:
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```shell
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kubectl get jobs --watch
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```
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The output is similar to this:
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```
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NAME COMPLETIONS DURATION AGE
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hello-4111706356 0/1 0s
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hello-4111706356 0/1 0s 0s
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hello-4111706356 1/1 5s 5s
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```
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Now you've seen one running job scheduled by the "hello" cron job.
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You can stop watching the job and view the cron job again to see that it scheduled the job:
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```shell
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kubectl get cronjob hello
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```
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The output is similar to this:
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```
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NAME SCHEDULE SUSPEND ACTIVE LAST SCHEDULE AGE
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hello */1 * * * * False 0 50s 75s
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```
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You should see that the cron job `hello` successfully scheduled a job at the time specified in `LAST SCHEDULE`. There are currently 0 active jobs, meaning that the job has completed or failed.
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Now, find the pods that the last scheduled job created and view the standard output of one of the pods.
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{{< note >}}
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The job name and pod name are different.
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{{< /note >}}
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```shell
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# Replace "hello-4111706356" with the job name in your system
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pods=$(kubectl get pods --selector=job-name=hello-4111706356 --output=jsonpath={.items[*].metadata.name})
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```
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Show pod log:
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```shell
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kubectl logs $pods
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```
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The output is similar to this:
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```
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Fri Feb 22 11:02:09 UTC 2019
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Hello from the Kubernetes cluster
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```
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## Deleting a Cron Job
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When you don't need a cron job any more, delete it with `kubectl delete cronjob <cronjob name>`:
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```shell
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kubectl delete cronjob hello
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```
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Deleting the cron job removes all the jobs and pods it created and stops it from creating additional jobs.
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You can read more about removing jobs in [garbage collection](/docs/concepts/workloads/controllers/garbage-collection/).
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## Writing a Cron Job Spec
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As with all other Kubernetes configs, a cron job needs `apiVersion`, `kind`, and `metadata` fields. For general
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information about working with config files, see [deploying applications](/docs/tasks/run-application/run-stateless-application-deployment/),
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and [using kubectl to manage resources](/docs/concepts/overview/working-with-objects/object-management/) documents.
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A cron job config also needs a [`.spec` section](https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status).
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{{< note >}}
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All modifications to a cron job, especially its `.spec`, are applied only to the following runs.
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{{< /note >}}
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### Schedule
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The `.spec.schedule` is a required field of the `.spec`.
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It takes a [Cron](https://en.wikipedia.org/wiki/Cron) format string, such as `0 * * * *` or `@hourly`, as schedule time of its jobs to be created and executed.
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The format also includes extended `vixie cron` step values. As explained in the
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[FreeBSD manual](https://www.freebsd.org/cgi/man.cgi?crontab%285%29):
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> Step values can be used in conjunction with ranges. Following a range
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> with `/<number>` specifies skips of the number's value through the
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> range. For example, `0-23/2` can be used in the hours field to specify
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> command execution every other hour (the alternative in the V7 standard is
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> `0,2,4,6,8,10,12,14,16,18,20,22`). Steps are also permitted after an
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> asterisk, so if you want to say "every two hours", just use `*/2`.
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{{< note >}}
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A question mark (`?`) in the schedule has the same meaning as an asterisk `*`, that is, it stands for any of available value for a given field.
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{{< /note >}}
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### Job Template
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The `.spec.jobTemplate` is the template for the job, and it is required.
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It has exactly the same schema as a [Job](/docs/concepts/workloads/controllers/job/), except that it is nested and does not have an `apiVersion` or `kind`.
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For information about writing a job `.spec`, see [Writing a Job Spec](/docs/concepts/workloads/controllers/job/#writing-a-job-spec).
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### Starting Deadline
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The `.spec.startingDeadlineSeconds` field is optional.
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It stands for the deadline in seconds for starting the job if it misses its scheduled time for any reason.
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After the deadline, the cron job does not start the job.
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Jobs that do not meet their deadline in this way count as failed jobs.
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If this field is not specified, the jobs have no deadline.
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If the `.spec.startingDeadlineSeconds` field is set (not null), the CronJob
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controller measures the time between when a job is expected to be created and
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now. If the difference is higher than that limit, it will skip this execution.
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For example, if it is set to `200`, it allows a job to be created for up to 200
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seconds after the actual schedule.
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### Concurrency Policy
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The `.spec.concurrencyPolicy` field is also optional.
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It specifies how to treat concurrent executions of a job that is created by this cron job.
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The spec may specify only one of the following concurrency policies:
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* `Allow` (default): The cron job allows concurrently running jobs
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* `Forbid`: The cron job does not allow concurrent runs; if it is time for a new job run and the previous job run hasn't finished yet, the cron job skips the new job run
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* `Replace`: If it is time for a new job run and the previous job run hasn't finished yet, the cron job replaces the currently running job run with a new job run
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Note that concurrency policy only applies to the jobs created by the same cron job.
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If there are multiple cron jobs, their respective jobs are always allowed to run concurrently.
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### Suspend
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The `.spec.suspend` field is also optional.
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If it is set to `true`, all subsequent executions are suspended.
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This setting does not apply to already started executions.
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Defaults to false.
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{{< caution >}}
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Executions that are suspended during their scheduled time count as missed jobs.
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When `.spec.suspend` changes from `true` to `false` on an existing cron job without a [starting deadline](#starting-deadline), the missed jobs are scheduled immediately.
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{{< /caution >}}
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### Jobs History Limits
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The `.spec.successfulJobsHistoryLimit` and `.spec.failedJobsHistoryLimit` fields are optional.
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These fields specify how many completed and failed jobs should be kept.
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By default, they are set to 3 and 1 respectively. Setting a limit to `0` corresponds to keeping none of the corresponding kind of jobs after they finish.
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