Security administration · Lesson 19 of 35 · 8 minutes

Auth config checkpoint

Review SSH, identity, firewall, and notes.

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
Resolve SSH config
Run ssh -G lab.
Hint & worked example
Inspect a fixed SSH training scenario; no real remote connection is made.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
ssh -G lab
```
Remember: Verify host identity and choose credentials deliberately on real systems.
2
Fingerprint key
Run ssh-keygen -lf ~/.ssh/authorized_keys.
Hint & worked example
Review or create a simulated SSH-key artifact. It is not a usable cryptographic credential.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
ssh-keygen -lf ~/.ssh/authorized_keys
```
Remember: Do not confuse public keys, private keys, and host fingerprints.
3
Review firewall
Run ufw status verbose.
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 verbose
```
Remember: Firewall rules should be scoped and reviewed; simulator access is not a production change approval.
4
Write auth note
Run echo auth-reviewed > lab/auth-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 auth-reviewed > lab/auth-review.txt
```
Remember: Redirection can overwrite an existing file before the command runs.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

ssh: Inspect a fixed SSH training scenario; no real remote connection is made.
Verify host identity and choose credentials deliberately on real systems.
ssh-keygen: Review or create a simulated SSH-key artifact. It is not a usable cryptographic credential.
Do not confuse public keys, private keys, and host fingerprints.
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

$ ssh -G lab

host lab
user learner
hostname clairos-learn-lab
identityfile ~/.ssh/training_key
pubkeyauthentication yes
passwordauthentication no

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

$ ssh-keygen -lf ~/.ssh/authorized_keys

256 SHA256:36a69dc636a69dc636a69dc636a69dc6 /home/learner/.ssh/authorized_keys (ED25519)

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

$ ufw status verbose

Status: active
Logging: on (simulated)
Default: deny incoming, allow outgoing
- allow 22/tcp
- allow 80/tcp
- allow 443/tcp
- deny 23/tcp

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

$ echo auth-reviewed > lab/auth-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 “Auth config checkpoint”, which interpretation is safe?A command appearing in history proves it completed successfully.A successful first check guarantees that every dependent service is healthy.Do not confuse public keys, private keys, and host fingerprints.

Apply it elsewhere

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

Keep the momentum.

Complete the lab, then explain and apply the pattern.

Next: Hardening summary Try an incident drill

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