Permissions and users · Lesson 22 of 33 · 8 minutes

Known hosts review

Inspect known_hosts as sensitive SSH context.

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learner@clairos:~ $

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Your objectives

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1
Read known hosts
Run cat ~/.ssh/known_hosts.
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 ~/.ssh/known_hosts
```
Remember: Reading a source file should precede changing it; avoid printing real secrets.
2
Inspect mode
Run stat ~/.ssh/known_hosts.
Hint & worked example
Inspect a file or directory metadata record, including ownership, permissions, and size.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
stat ~/.ssh/known_hosts
```
Remember: Metadata and file contents answer different questions.
3
Find lab host
Run grep clairos ~/.ssh/known_hosts.
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 clairos ~/.ssh/known_hosts
```
Remember: No matches is exit status 1, which is different from a malformed invocation.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

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.
stat: Inspect a file or directory metadata record, including ownership, permissions, and size.
Metadata and file contents answer different questions.
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

$ cat ~/.ssh/known_hosts

clairos-learn-lab ssh-ed25519 AAAAFAKEHOSTKEY
10.20.30.40 ssh-ed25519 AAAAFAKEHOSTIP

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

$ stat ~/.ssh/known_hosts

Path: /home/learner/.ssh/known_hosts
Type: file
Mode: -rw-------
Owner: learner
Group: learners
Size: 84 bytes

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

$ grep clairos ~/.ssh/known_hosts

clairos-learn-lab ssh-ed25519 AAAAFAKEHOSTKEY

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 “Known hosts review”, which interpretation is safe?Metadata and file contents answer different questions.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 stat workflow from “Known hosts review” 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: Service user ownership Try an incident drill

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