Capstone labs · Lesson 13 of 18 · 8 minutes

Capstone suspicious login

Review auth evidence, SSH policy, firewall state, and notes.

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learner@clairos:~ $

Exit 0

Your objectives

Hints are always available. Wrong turns never cost XP.

1
Find denied logins
Run grep denied /var/log/auth.log.
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.
```
grep denied /var/log/auth.log
```
Remember: No matches is exit status 1, which is different from a malformed invocation.
2
Read SSH journal
Run journalctl -u ssh -n 2.
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 -n 2
```
Remember: A relevant unit and time range are more useful than an unfiltered wall of logs.
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 review
Run printf suspicious-login-reviewed | tee lab/login-review.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 suspicious-login-reviewed | tee lab/login-review.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.
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.
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.
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

$ grep denied /var/log/auth.log

May 26 08:18:33 clairos-learn sshd[118]: denied password for root
May 26 08:21:44 clairos-learn sshd[141]: denied password for admin

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

$ journalctl -u ssh -n 2

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.

$ 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.

$ printf suspicious-login-reviewed | tee lab/login-review.txt

suspicious-login-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 “Capstone suspicious login”, 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 relevant unit and time range are more useful than an unfiltered wall of logs.

Apply it elsewhere

Before adapting the journalctl workflow from “Capstone suspicious login” 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: Capstone bad deploy Try an incident drill

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