Security administration · Lesson 3 of 35 · 10 minutes

Firewall and incident review

Inspect firewall state, add a simulated rule, and write a short incident note.

Open the lab Course map

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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
Inspect firewall
Run ufw status.
Hint & worked example
Inspect or adjust the training firewall rule list. No real firewall changes occur.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
ufw status
```
Remember: Firewall rules should be scoped and reviewed; simulator access is not a production change approval.
2
Add deny rule
Run ufw deny 23/tcp.
Hint & worked example
Inspect or adjust the training firewall rule list. No real firewall changes occur.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
ufw deny 23/tcp
```
Remember: Firewall rules should be scoped and reviewed; simulator access is not a production change approval.
3
Write an incident note
Run echo reviewed-denied-logins > incident-review.txt.
Hint & worked example
Write simple text to standard output. Prefer printf when exact formatting matters.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
echo reviewed-denied-logins > incident-review.txt
```
Remember: Redirection can overwrite an existing file before the command runs.

Understand the pattern

Security changes need evidence and notes, even in a toy lab.

ufw: Inspect or adjust the training firewall rule list. No real firewall changes occur.
Firewall rules should be scoped and reviewed; simulator access is not a production change approval.
echo: Write simple text to standard output. Prefer printf when exact formatting matters.
Redirection can overwrite an existing file before the command runs.

Worked example and expected result

$ ufw status

Status: active
- allow 22/tcp
- allow 80/tcp
- allow 443/tcp
- deny 23/tcp

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

$ ufw deny 23/tcp

simulated firewall rule added: deny 23/tcp

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

$ echo reviewed-denied-logins > incident-review.txt

(no output; exit 0)

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 “Firewall and incident review”, which interpretation is safe?A successful first check guarantees that every dependent service is healthy.Firewall rules should be scoped and reviewed; simulator access is not a production change approval.A command appearing in history proves it completed successfully.

Apply it elsewhere

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

Keep the momentum.

Complete the lab, then explain and apply the pattern.

Next: Auth log review Try an incident drill

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