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Add docs section for info on logs #4727

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Jul 8, 2024
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Add docs section for info on logs #4727

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20 changes: 20 additions & 0 deletions docs/logs.md
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# Logs

k0s runs most of the Kubernetes and other system components as plain Linux child processes. As it acts as a watchdog for the child processes it also combines the logs for all such processes into its own log stream.

k0s adds a "selector" to each components log stream so it is easier to distinguish logs from various components. For example the log stream from kubelet is enhanced with a selector `component=kubelet`:

```text
Jul 08 08:46:25 worker-kppzr-lls2q k0s[1766]: time="2024-07-08 08:46:25" level=info msg="I0708 08:46:25.876821 1814 operation_generator.go:721] \"MountVolume.SetUp succeeded for volume \\\"kube-api-access-7tfxw\\\" (UniqueName: \\\"kubernetes.io/projected/ca514728-a1de-4408-9be5-8b36ee896752-kube-api-access-7tfxw\\\") pod \\\"node-shell-a16894ee-eb67-4865-8964-44ca5c87e18d\\\" (UID: \\\"ca514728-a1de-4408-9be5-8b36ee896752\\\") \" pod=\"kube-system/node-shell-a16894ee-eb67-4865-8964-44ca5c87e18d\"" component=kubelet stream=stderr
Jul 08 08:46:26 worker-kppzr-lls2q k0s[1766]: time="2024-07-08 08:46:26" level=info msg="I0708 08:46:26.112550 1814 kuberuntime_container_linux.go:167] \"No swap cgroup controller present\" swapBehavior=\"\" pod=\"kube-system/node-shell-a16894ee-eb67-4865-8964-44ca5c87e18d\" containerName=\"shell\"" component=kubelet stream=stderr
```

## Where are the logs?

### systemd based setups

SystemD uses journal log system for all logs. This means that you can access k0s and all the sub-component logs using `journalctl`. For example if you are interested in kubelet logs, you can run something like `journalctl -u k0sworker | grep component=kubelet`.

### openRC based setups

openRC stores logs of services in `/var/log/k0sworker.log`. Again, if you're interested in specific component logs you cat run something like `grep component=kubelet /var/log/k0s.log`.
1 change: 1 addition & 0 deletions mkdocs.yml
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Expand Up @@ -66,6 +66,7 @@ nav:
- OpenEBS storage: examples/openebs.md
- Troubleshooting:
- FAQ: FAQ.md
- Logs: logs.md
- Common Pitfalls: troubleshooting.md
- Support Insights: support-dump.md
- Reference:
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