Text and logs · Lesson 11 of 38 · 7 minutes

Kernel log basics

Inspect simulated kernel messages for mount and network clues.

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Your objectives

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1
Read start
Run head -n 2 /var/log/kern.log.
Hint & worked example
Show the beginning of an input; -n sets how many lines to include.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
head -n 2 /var/log/kern.log
```
Remember: A small sample may omit the failure. Choose the time window you actually need.
2
Search mount
Run grep mount /var/log/kern.log.
Hint & worked example
Select input lines that match a pattern; -i ignores case, -n adds line numbers, and -v inverts selection.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
grep mount /var/log/kern.log
```
Remember: No matches is exit status 1, which is different from a malformed invocation.
3
Read end
Run tail -n 2 /var/log/kern.log.
Hint & worked example
Show the end of an input; -n selects the number of lines.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
tail -n 2 /var/log/kern.log
```
Remember: This browser lab snapshots output; it does not keep a live tail -f stream.

Understand the pattern

Kernel messages can explain storage and network symptoms.

head: Show the beginning of an input; -n sets how many lines to include.
A small sample may omit the failure. Choose the time window you actually need.
grep: Select input lines that match a pattern; -i ignores case, -n adds line numbers, and -v inverts selection.
No matches is exit status 1, which is different from a malformed invocation.
tail: Show the end of an input; -n selects the number of lines.
This browser lab snapshots output; it does not keep a live tail -f stream.

Worked example and expected result

$ head -n 2 /var/log/kern.log

May 26 08:12:00 clairos-learn kernel: fake root filesystem mounted read/write
May 26 08:13:01 clairos-learn kernel: eth0 link up

Exit status: 0. The command completed successfully in the training fixture.

$ grep mount /var/log/kern.log

May 26 08:12:00 clairos-learn kernel: fake root filesystem mounted read/write

Exit status: 0. The command completed successfully in the training fixture.

$ tail -n 2 /var/log/kern.log

May 26 08:13:01 clairos-learn kernel: eth0 link up
May 26 08:16:44 clairos-learn kernel: training memory pressure normal

Exit status: 0. The command completed successfully in the training fixture.

Try a variation

Repeat this workflow in the sandbox with a different scratch filename. Keep the system fixtures unchanged and compare the observed output with your expectation before moving on.

Explain it

In “Kernel log basics”, which interpretation is safe?No matches is exit status 1, which is different from a malformed invocation.A command appearing in history proves it completed successfully.A successful first check guarantees that every dependent service is healthy.

Apply it elsewhere

Before adapting the grep workflow from “Kernel log basics” to another server, what should you do?Paste the training paths unchanged into production.Skip output inspection whenever the command is familiar.Confirm the current directory, target identity, permissions, and the installed command behavior first.

Keep the momentum.

Complete the lab, then explain and apply the pattern.

Next: Package log basics Try an incident drill

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