Separate identity from host trustYour key proves who you are; the host key proves which server answered. Identify whether the error is publickey or host key related.
Remote access
SSH Keys and Known Hosts for Makers
Learn how SSH identity, authorized keys, host keys, and file modes fit together before deleting warnings.
Ladder steps
Each step should prove one idea before the project asks for the next one.
Check local key filesPrivate keys need restrictive permissions. ls -l ~/.ssh shows file modes.
Check remote authorized_keysThe server must have the right public key for the right user. authorized_keys contains public keys, not private keys.
Verify host changes out of bandA changed host key can be normal or a security warning. Confirm fingerprint before editing known_hosts.
Examples to inspect
Use examples to read signals, not as blind recipes.
Inspect SSH auth flow
ssh -vvv user@example.comExpected signal: Debug lines naming keys attempted and server response
Caution: Do not paste full debug output publicly without reviewing it.
Find a host in known_hosts
ssh-keygen -F example.comExpected signal: Known host lines for that host
Check local SSH file modes
ls -l ~/.sshExpected signal: Private keys should not be world-readable
Common traps
- Posting private keys.
- Deleting known_hosts blindly.
- Debugging the wrong remote user.
Practice task
Describe how you would tell apart a publickey failure from a changed host key warning.
Next steps
- Use LinuxOneLiners SSH publickey path.
- Learn permissions.
- Learn server log search.
Practice ladder
- Near-Copy Rebuild: Recreate one example, decision path, or worked explanation from SSH Keys and Known Hosts for Makers. Keep most givens the same, then apply, explain, and check while naming each cue you used. Use the lesson's example block when it helps.
- One-Change Transfer: Change exactly one condition, number, input, symptom, material, or constraint from the near-copy case. Then apply, explain, and check again and explain what changed.
- Mixed Review Set: Interleave this topic with one prerequisite or adjacent idea. Write three short prompts: one recall, one application, and one comparison.
- Find And Fix The Error: Invent a plausible wrong answer, unsafe step, invalid assumption, or bad classification. Mark the first point where it goes wrong, then correct it using the lesson's check.
Flashcard preview
What is the difference between your SSH key and a host key?
Your key authenticates you; the host key helps verify the server you reached.
What does the 'Separate identity from host trust' step prove?
Your key proves who you are; the host key proves which server answered. Check: Identify whether the error is publickey or host key related.
What does the 'Check local key files' step prove?
Private keys need restrictive permissions. Check: ls -l ~/.ssh shows file modes.
What does the 'Check remote authorized_keys' step prove?
The server must have the right public key for the right user. Check: authorized_keys contains public keys, not private keys.
What does the 'Verify host changes out of band' step prove?
A changed host key can be normal or a security warning. Check: Confirm fingerprint before editing known_hosts.
When would you use `ssh -vvv user@example.com`?
Use it to inspect ssh auth flow. Expected signal: Debug lines naming keys attempted and server response
Downloadable study pack
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Related paths
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Study assets
Project context
- Deploy a Static Site on a VPS
- Browse Software and Linux
- Next ladder clue: Use LinuxOneLiners SSH publickey path.
Related references
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