website/content/en/docs/tasks/debug-application-cluster/determine-reason-pod-failure.md

---
title: Determine the Reason for Pod Failure
content_template: templates/task
---

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This page shows how to write and read a Container
termination message.

Termination messages provide a way for containers to write
information about fatal events to a location where it can
be easily retrieved and surfaced by tools like dashboards
and monitoring software. In most cases, information that you
put in a termination message should also be written to
the general
[Kubernetes logs](/docs/concepts/cluster-administration/logging/).

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## Writing and reading a termination message

In this exercise, you create a Pod that runs one container.
The configuration file specifies a command that runs when
the container starts.

{{< codenew file="debug/termination.yaml" >}}

1. Create a Pod based on the YAML configuration file:

        kubectl create -f https://k8s.io/examples/debug/termination.yaml

    In the YAML file, in the `cmd` and `args` fields, you can see that the
    container sleeps for 10 seconds and then writes "Sleep expired" to
    the `/dev/termination-log` file. After the container writes
    the "Sleep expired" message, it terminates.

1. Display information about the Pod:

        kubectl get pod termination-demo

    Repeat the preceding command until the Pod is no longer running.

1. Display detailed information about the Pod:

        kubectl get pod --output=yaml

    The output includes the "Sleep expired" message:

        apiVersion: v1
        kind: Pod
        ...
            lastState:
              terminated:
                containerID: ...
                exitCode: 0
                finishedAt: ...
                message: |
                  Sleep expired
                ...

1. Use a Go template to filter the output so that it includes
only the termination message:

        kubectl get pod termination-demo -o go-template="{{range .status.containerStatuses}}{{.lastState.terminated.message}}{{end}}"

## Customizing the termination message

Kubernetes retrieves termination messages from the termination message file
specified in the `terminationMessagePath` field of a Container, which as a default
value of `/dev/termination-log`. By customizing this field, you can tell Kubernetes
to use a different file. Kubernetes use the contents from the specified file to
populate the Container's status message on both success and failure.

In the following example, the container writes termination messages to
`/tmp/my-log` for Kubernetes to retrieve:

```yaml
apiVersion: v1
kind: Pod
metadata:
  name: msg-path-demo
spec:
  containers:
  - name: msg-path-demo-container
    image: debian
    terminationMessagePath: "/tmp/my-log"
```

Moreover, users can set the `terminationMessagePolicy` field of a Container for
further customization. This field defaults to "`File`" which means the termination
messages are retrieved only from the termination message file. By setting the
`terminationMessagePolicy` to "`FallbackToLogsOnError`", you can tell Kubernetes
to use the last chunk of container log output if the termination message file
is empty and the container exited with an error. The log output is limited to
2048 bytes or 80 lines, whichever is smaller.

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* See the `terminationMessagePath` field in
  [Container](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#container-v1-core).
* Learn about [retrieving logs](/docs/concepts/cluster-administration/logging/).
* Learn about [Go templates](https://golang.org/pkg/text/template/).

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