System security audit

Audit and improve the security of a Debian/Ubuntu Linux machine. Work through the checklist below interactively. Inspection is read-only and runs freely; every change is explained first, including how it could lock you out, and waits for confirmation.

Security checklist

1. User and access control

• Review user accounts: who should have access?
• Check for unused accounts.
• Verify sudo permissions.
• Review SSH keys.
• Check password policies.
• Disable root login over SSH.

2. SSH hardening