Text and logs · Lesson 5 of 38 · 8 minutes

Paging logs

Use less, head, and tail to read logs in chunks.

Open the lab Course map

Mastery 0/3Run itExplain itApply it

learner@clairos:~ $

↑ history · Tab complete · Ctrl+C cancel · Esc, Tab to leaveExit 0

Your objectives

Hints are always available. Wrong turns never cost XP.

1
Page auth log
Run less /var/log/auth.log.
Hint & worked example
Inspect text without changing the file. This simulator displays a bounded snapshot rather than an interactive pager.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
less /var/log/auth.log
```
Remember: The real less pager has navigation controls that are outside this lab subset.
2
Read first lines
Run head -n 2 /var/log/auth.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/auth.log
```
Remember: A small sample may omit the failure. Choose the time window you actually need.
3
Read last lines
Run tail -n 2 /var/log/auth.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/auth.log
```
Remember: This browser lab snapshots output; it does not keep a live tail -f stream.

Understand the pattern

Operators often need a quick view without opening an editor.

less: Inspect text without changing the file. This simulator displays a bounded snapshot rather than an interactive pager.
The real less pager has navigation controls that are outside this lab subset.
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.
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

$ less /var/log/auth.log

May 26 08:14:02 clairos-learn sshd[104]: accepted publickey for learner
May 26 08:18:33 clairos-learn sshd[118]: denied password for root
May 26 08:19:10 clairos-learn sudo[126]: learner : command=list services
May 26 08:21:44 clairos-learn sshd[141]: denied password for admin

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

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

May 26 08:14:02 clairos-learn sshd[104]: accepted publickey for learner
May 26 08:18:33 clairos-learn sshd[118]: denied password for root

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

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

May 26 08:19:10 clairos-learn sudo[126]: learner : command=list services
May 26 08:21:44 clairos-learn sshd[141]: denied password for admin

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 “Paging logs”, which interpretation is safe?A small sample may omit the failure. Choose the time window you actually need.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 head workflow from “Paging 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: Case-insensitive search Try an incident drill

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