Security administration · Lesson 6 of 35 · 7 minutes

SSH config review

Verify key SSH hardening settings.

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
Check password auth
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.
2
Check root login
Run sudo grep PermitRootLogin /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 PermitRootLogin /etc/ssh/sshd_config
```
Remember: No matches is exit status 1, which is different from a malformed invocation.
3
Check pubkey
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

SSH is one of the most important admin entry points.

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

$ sudo grep PasswordAuthentication /etc/ssh/sshd_config

PasswordAuthentication no

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

$ sudo grep PermitRootLogin /etc/ssh/sshd_config

PermitRootLogin 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 config review”, which interpretation is safe?A successful first check guarantees that every dependent service is healthy.No matches is exit status 1, which is different from a malformed invocation.A command appearing in history proves it completed successfully.

Apply it elsewhere

Before adapting the grep workflow from “SSH config 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: Least privilege review 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