Security administration · Lesson 2 of 35 · 9 minutes

SSH hardening

Read training SSH settings and confirm safer defaults without connecting anywhere.

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learner@clairos:~ $

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Your objectives

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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
Read SSH journal
Run journalctl -u ssh.
Hint & worked example
Read the training journal by unit or a bounded line window.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
journalctl -u ssh
```
Remember: A relevant unit and time range are more useful than an unfiltered wall of logs.

Understand the pattern

SSH is a common administrative entry point and deserves careful review.

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.
journalctl: Read the training journal by unit or a bounded line window.
A relevant unit and time range are more useful than an unfiltered wall of logs.

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.

$ journalctl -u ssh

May 26 08:14:02 clairos-learn sshd[104]: publickey accepted for learner
May 26 08:18:33 clairos-learn sshd[118]: password authentication refused
May 26 08:21:44 clairos-learn sshd[141]: root login refused by policy

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 hardening”, 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 hardening” 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: Firewall and incident review Try an incident drill

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