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Interview question · Systems, OS & Memory Safety

How would you secure SSH access to a fleet of Linux servers: keys, SSH certificates, bastions and revocation?

Turning off passwords is the easy half. The interview is about the other half: how keys are issued, how long they live, how a host proves itself, and how you cut someone off at 5pm on a Friday.

mediumNewPreparation tags: Google, Amazon, CloudflareUpdated Nov 2026

Turning off passwords is the easy half. The interview is about the other half: how keys are issued, how long they live, how a host proves itself, and how you cut someone off at 5pm on a Friday.

Make your first attempt

What would you say before reading the answer?

  1. 01 State the assumptions your answer depends on.
  2. 02 Explain the mechanism and choose a control.
  3. 03 Name a condition that would change your decision.

The worked answer includes an approach, scoring criteria and follow-up questions. Compare the reasoning with your own.

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What if · the follow-ups in this answer

The answer works through 5 follow-ups like an interviewer would

A company has 400 Linux servers. Engineers log in with personal keys in authorized_keys, some servers still allow passwords, and SSH is open to the internet. An engineer left last week and nobody is sure where their key is.

  1. What do you change first, today?
  2. How do you find and remove the leaver's access?
  3. What replaces authorized_keys?
  4. What if an attacker sits between an engineer and a new server?
  5. What does the finished design look like?

Each rung has a nudge, a model answer, the principle that carries over and the weak answer to avoid. Premium opens every answer and ladder.

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