Text and logs · Lesson 26 of 38 · 8 minutes

Evidence bundle

Capture a focused evidence bundle into lab notes.

Open the lab Course map

Mastery 0/3Run itExplain itApply it

learner@clairos:~ $

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Your objectives

Hints are always available. Wrong turns never cost XP.

1
Capture auth evidence
Run grep denied /var/log/auth.log | tee lab/auth-evidence.txt.
Hint & worked example
Select input lines that match a pattern; -i ignores case, -n adds line numbers, and -v inverts selection. 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.
```
grep denied /var/log/auth.log | tee lab/auth-evidence.txt
```
Remember: No matches is exit status 1, which is different from a malformed invocation. tee can overwrite a file even though the output is also visible on screen.
2
Capture nginx evidence
Run tail -n 2 /var/log/nginx-error.log | tee lab/nginx-evidence.txt.
Hint & worked example
Show the end of an input; -n selects the number of lines. 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.
```
tail -n 2 /var/log/nginx-error.log | tee lab/nginx-evidence.txt
```
Remember: This browser lab snapshots output; it does not keep a live tail -f stream. tee can overwrite a file even though the output is also visible on screen.
3
Read auth evidence
Run cat lab/auth-evidence.txt.
Hint & worked example
Read one or more files to standard output without editing their contents.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
cat lab/auth-evidence.txt
```
Remember: Reading a source file should precede changing it; avoid printing real secrets.

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.
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.
tail: Show the end of an input; -n selects the number of lines.
This browser lab snapshots output; it does not keep a live tail -f stream.
cat: Read one or more files to standard output without editing their contents.
Reading a source file should precede changing it; avoid printing real secrets.

Worked example and expected result

$ grep denied /var/log/auth.log | tee lab/auth-evidence.txt

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.

$ tail -n 2 /var/log/nginx-error.log | tee lab/nginx-evidence.txt

May 26 08:10:01 [notice] nginx: using fake static configuration
May 26 08:20:05 [warn] nginx: /api/test returned 404 by design

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

$ cat lab/auth-evidence.txt

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.

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 “Evidence bundle”, which interpretation is safe?A successful first check guarantees that every dependent service is healthy.This browser lab snapshots output; it does not keep a live tail -f stream.A command appearing in history proves it completed successfully.

Apply it elsewhere

Before adapting the tail workflow from “Evidence bundle” 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.

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