Networking · Lesson 23 of 26 · 8 minutes

Network incident logs

Search kernel and access logs for network clues.

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Your objectives

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1
Find link event
Run grep eth0 /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 eth0 /var/log/kern.log
```
Remember: No matches is exit status 1, which is different from a malformed invocation.
2
Find web requests
Run grep GET /var/log/nginx-access.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 GET /var/log/nginx-access.log
```
Remember: No matches is exit status 1, which is different from a malformed invocation.
3
Read rotated access
Run tail -n 2 /var/log/nginx-access.log.1.
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/nginx-access.log.1
```
Remember: This browser lab snapshots output; it does not keep a live tail -f stream.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

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

$ grep eth0 /var/log/kern.log

May 26 08:13:01 clairos-learn kernel: eth0 link up

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

$ grep GET /var/log/nginx-access.log

127.0.0.1 GET / 200
127.0.0.1 GET /assets/learn-terminal.js 200
127.0.0.1 GET /api/test 404

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

$ tail -n 2 /var/log/nginx-access.log.1

127.0.0.1 GET /unix/courses/ 200
127.0.0.1 GET /missing 404

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 “Network incident logs”, 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 “Network incident logs” 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: Local name resolution Try an incident drill

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