Security administration · Lesson 31 of 35 · 8 minutes

SSH client and server policy

Compare resolved client settings with server authentication policy.

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 the client configuration
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
Read password policy
Run sudo grep PasswordAuthentication /etc/ssh/sshd_config.
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.
```
sudo grep PasswordAuthentication /etc/ssh/sshd_config
```
Remember: No matches is exit status 1, which is different from a malformed invocation.
3
Read key policy
Run sudo grep PubkeyAuthentication /etc/ssh/sshd_config.
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.
```
sudo grep PubkeyAuthentication /etc/ssh/sshd_config
```
Remember: No matches is exit status 1, which is different from a malformed invocation.

Understand the pattern

Separating SSH client configuration from server policy helps operators explain what they know before they change anything.

ssh: Inspect a fixed SSH training scenario; no real remote connection is made.
Verify host identity and choose credentials deliberately on real 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.

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.

$ sudo grep PasswordAuthentication /etc/ssh/sshd_config

PasswordAuthentication no

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

$ sudo grep PubkeyAuthentication /etc/ssh/sshd_config

PubkeyAuthentication yes

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 “SSH client and server policy”, 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 “SSH client and server policy” 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: Known-hosts hygiene Try an incident drill

Anonymous lesson and mastery progress lasts for this session. Sign in to keep synced lesson XP between sessions; mastery stays device-local. No speed bonus, lost lives, or hint penalties.

Keep learning

GNU Coreutils manual · GNU Bash manual