SSH connection basics in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this SSH command?

You run the command ssh -v user@192.168.1.10 to connect to a server. Which of the following lines will you see in the verbose output indicating a successful key exchange?

Linux CLI

ssh -v user@192.168.1.10

A Permission denied (password).

B debug1: Authentication succeeded (publickey).

C ssh: Could not resolve hostname 192.168.1.10: Name or service not known

D Connection timed out during banner exchange

💡 Hint

Look for messages that confirm authentication success in verbose SSH output.

The line 'debug1: Authentication succeeded (publickey).' shows that the SSH client successfully authenticated using a public key. Other options indicate errors or failures.

🧠 Conceptual

intermediate

Which SSH option disables strict host key checking?

You want to connect to a new SSH server without being prompted to confirm the server's fingerprint. Which SSH option disables this prompt?

A -o PasswordAuthentication=no

B -o UserKnownHostsFile=/dev/null

C -o StrictHostKeyChecking=no

D -o ConnectTimeout=5

💡 Hint

This option controls whether SSH asks to confirm the server's fingerprint.

The option '-o StrictHostKeyChecking=no' disables the prompt asking to confirm the server's fingerprint, allowing automatic connection.

🔧 Debug

advanced

Why does this SSH command fail with 'Permission denied'?

You run ssh user@host but get Permission denied (publickey,password). error. Which of the following is the most likely cause?

A The SSH server does not allow password authentication and your public key is not set up.

B The SSH client is using the wrong port number.

C The SSH server is down and unreachable.

D The username is misspelled in the command.

💡 Hint

Consider what authentication methods the server accepts and what keys you have.

The error means the server rejected both public key and password authentication. Usually, this happens if the server requires a public key but the client has none configured.

🚀 Application

advanced

How to copy a file securely using SSH?

You want to copy a file named report.txt from your local machine to the remote server server.example.com under the directory /home/user/docs. Which command correctly does this?

A scp report.txt [e-mail]:/home/user/docs/

B ssh [e-mail] cp report.txt /home/user/docs/

C ssh-copy-id report.txt [e-mail]:/home/user/docs/

D rsync report.txt [e-mail]:/home/user/docs/

💡 Hint

Think about which command is designed to copy files over SSH.

The scp command securely copies files over SSH. Option A tries to run a copy command on the remote server but does not transfer the file. Option A copies SSH keys, not files. Option A can copy files but requires rsync installed and configured.

💻 Command Output

expert

What is the output of this SSH command with a custom port?

You run ssh -p 2222 user@host but get the error message. Which option shows the exact error you will see if port 2222 is closed on the server?

Linux CLI

ssh -p 2222 user@host

A Connection timed out during banner exchange

B ssh: Could not resolve hostname host: Name or service not known

C Permission denied (publickey).

D ssh: connect to host host port 2222: Connection refused

💡 Hint

Think about what happens when the port is closed but the host is reachable.

If the port is closed, SSH cannot connect and shows 'Connection refused'. Other errors indicate DNS issues, authentication failure, or timeout.