Security administration · Lesson 16 of 35 · 8 minutes

SSH key fingerprint

Read a simulated key fingerprint.

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Mastery 0/3Run itExplain itApply it

learner@clairos:~ $

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Your objectives

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1
Fingerprint key
Run ssh-keygen -lf ~/.ssh/authorized_keys.
Hint & worked example
Review or create a simulated SSH-key artifact. It is not a usable cryptographic credential.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
ssh-keygen -lf ~/.ssh/authorized_keys
```
Remember: Do not confuse public keys, private keys, and host fingerprints.
2
Inspect key file
Run stat ~/.ssh/authorized_keys.
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/authorized_keys
```
Remember: Metadata and file contents answer different questions.
3
Confirm key file
Run test -f ~/.ssh/authorized_keys.
Hint & worked example
Evaluate a file or string condition through its exit status rather than printed output.
The command outcome must match the task, including successful access or the explicitly requested failure.
```
test -f ~/.ssh/authorized_keys
```
Remember: A successful test usually prints nothing; inspect $? or chain a command.

Understand the pattern

Junior operators build confidence by gathering evidence before changing systems.

ssh-keygen: Review or create a simulated SSH-key artifact. It is not a usable cryptographic credential.
Do not confuse public keys, private keys, and host fingerprints.
stat: Inspect a file or directory metadata record, including ownership, permissions, and size.
Metadata and file contents answer different questions.
test: Evaluate a file or string condition through its exit status rather than printed output.
A successful test usually prints nothing; inspect $? or chain a command.

Worked example and expected result

$ ssh-keygen -lf ~/.ssh/authorized_keys

256 SHA256:36a69dc636a69dc636a69dc636a69dc6 /home/learner/.ssh/authorized_keys (ED25519)

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

$ stat ~/.ssh/authorized_keys

Path: /home/learner/.ssh/authorized_keys
Type: file
Mode: -rw-------
Owner: learner
Group: learners
Size: 40 bytes

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

$ test -f ~/.ssh/authorized_keys

(no output; exit 0)

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 key fingerprint”, which interpretation is safe?A command appearing in history proves it completed successfully.A successful first check guarantees that every dependent service is healthy.Metadata and file contents answer different questions.

Apply it elsewhere

Before adapting the stat workflow from “SSH key fingerprint” 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: SCP dry run Try an incident drill

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