Security administration · Lesson 20 of 35 · 8 minutes

Hardening summary

Summarize posture from logs, config, and service exposure.

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 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.
2
Check listeners
Run ss -tulpn.
Hint & worked example
Inspect simulated listening sockets and connection information.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
ss -tulpn
```
Remember: A listening socket is not proof of correct application responses or external reachability.
3
Write hardening marker
Run printf hardening-reviewed | tee lab/hardening.txt.
Hint & worked example
Format data deliberately, including separators and final newlines. Copy a stream both to a file and standard output; -a appends.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
printf hardening-reviewed | tee lab/hardening.txt
```
Remember: A format string controls output; a newline is data, not an automatic guarantee. tee can overwrite a file even though the output is also visible on screen.

Understand the pattern

Junior operators build confidence by gathering evidence before changing 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.
ss: Inspect simulated listening sockets and connection information.
A listening socket is not proof of correct application responses or external reachability.
printf: Format data deliberately, including separators and final newlines.
A format string controls output; a newline is data, not an automatic guarantee.
tee: Copy a stream both to a file and standard output; -a appends.
tee can overwrite a file even though the output is also visible on screen.

Worked example and expected result

$ sudo grep PermitRootLogin /etc/ssh/sshd_config

PermitRootLogin no

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

$ ss -tulpn

Netid State  Local Address:Port  Process
udp   UNCONN 0.0.0.0:68          lab-dhcp
tcp   LISTEN 0.0.0.0:22          sshd
tcp   LISTEN 0.0.0.0:80          nginx
tcp   LISTEN 0.0.0.0:443         nginx

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

$ printf hardening-reviewed | tee lab/hardening.txt

hardening-reviewed

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 “Hardening summary”, which interpretation is safe?A command appearing in history proves it completed successfully.A successful first check guarantees that every dependent service is healthy.A listening socket is not proof of correct application responses or external reachability.

Apply it elsewhere

Before adapting the ss workflow from “Hardening summary” 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: SSH hardening deep 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