A developer is unable to access a Linux server via SSH.

The reason the developer cannot log in is because their account is locked. This is indicated by the "!!" in the /etc/shadow file:

developer:!!::0:99999:7:::

The "!!" in the password field means the account is locked, and the user cannot authenticate using a password.

To unlock the account, the administrator must reset the password:

passwd developer

OR, if SSH key authentication is used, the administrator can remove the lock without setting a password:

usermod -U developer

Why the other options are incorrect?

A. The developer’s private key has been deleted from the server. → Incorrect, because the login attempt is failing before key authentication even starts.

C. The developer's public key is in the wrong location. → Incorrect, because the SSH configuration (PubkeyAuthentication yes) allows key-based authentication, but the user is still unable to log in. The issue is with the account lock.

D. SSH has been disabled for user log-in. → Incorrect, because PasswordAuthentication yes confirms SSH is enabled for users (except root).