SSH automation in Bash Scripting - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of SSH command with remote script

What is the output of this bash script that uses SSH to run a remote command?

Bash Scripting

ssh user@remotehost 'echo Hello from $(hostname)'

A Hello from $(hostname)

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

C Hello from localmachine

D Hello from remotehost

💡 Hint

The command runs on the remote host, so hostname is evaluated there.

The $(hostname) runs on the remote machine, so the output shows the remote hostname.

📝 Syntax

intermediate

Correct SSH key usage in bash script

Which option correctly uses an SSH private key file to connect to a remote server in a bash script?

A ssh --key ~/.ssh/id_rsa user@host

B ssh -i ~/.ssh/id_rsa user@host

C ssh -keyfile ~/.ssh/id_rsa user@host

D ssh -k ~/.ssh/id_rsa user@host

💡 Hint

The correct option uses the -i flag for identity file.

The -i option specifies the private key file for SSH authentication.

🔧 Debug

advanced

Why does this SSH command fail?

This bash script tries to copy a file to a remote server using SSH and SCP but fails. Why? scp /local/path/file.txt user@remotehost:/remote/path/ Options:

A The remote path does not exist or user has no write permission

B The local file path is incorrect

C The SSH server is not running on remotehost

D The scp command syntax is invalid

💡 Hint

Check permissions and existence of remote directory.

If the remote directory does not exist or user lacks write permission, scp fails.

🚀 Application

advanced

Automate running multiple commands over SSH

You want to run these two commands on a remote server via SSH in one connection: 1. cd /var/log 2. ls -l Which option correctly does this in a bash script?

A ssh user@host 'cd /var/log && ls -l'

B ssh user@host 'cd /var/log ls -l'

C ssh user@host 'cd /var/log; ls -l'

D ssh user@host 'cd /var/log | ls -l'

💡 Hint

Separate commands with semicolon or && to run sequentially.

Using semicolon or && runs commands sequentially; pipe (|) sends output of first as input to second.

🧠 Conceptual

expert

Understanding SSH agent forwarding security

What is the main security risk of enabling SSH agent forwarding when automating remote commands?

A A compromised remote server can use your SSH keys to access other servers without your passphrase

B Your private key file is copied to the remote server

C Your SSH password is sent in plain text over the network

D Agent forwarding disables encryption of SSH traffic

💡 Hint

Agent forwarding allows remote servers to use your keys temporarily.

Agent forwarding lets the remote server use your SSH keys to connect elsewhere, so if compromised, it can misuse your keys.

Practice

1. What is the main benefit of using SSH keys for automation instead of passwords?

easy

A. It allows passwordless login for automated scripts.

B. It makes the connection slower but more secure.

C. It requires manual password entry every time.

D. It disables encryption for faster transfers.

Solution

1. Step 1: Understand SSH key usage

   SSH keys allow scripts to connect without typing passwords manually.

2. Step 2: Compare with password login

   Password login needs manual input, which breaks automation.

3. Final Answer:

   It allows passwordless login for automated scripts. -> Option A

4. Quick Check:

   SSH keys enable passwordless login = B [OK]

Hint: SSH keys = no password prompts for scripts [OK]

Common Mistakes:

• Thinking SSH keys slow down connection
• Assuming passwords work without manual input
• Believing SSH keys disable encryption

2. Which of the following is the correct syntax to copy a local file file.txt to a remote server using SSH automation?

easy

A. ssh file.txt user@remote:/path/

B. scp file.txt user@remote:/path/

C. ssh-copy file.txt user@remote:/path/

D. copy file.txt user@remote:/path/

Solution

1. Step 1: Identify the command for secure copy

   scp is used to copy files over SSH securely.

2. Step 2: Check other options

   ssh runs commands, ssh-copy is not a valid command, and copy is not for SSH.

3. Final Answer:

   scp file.txt user@remote:/path/ -> Option B

4. Quick Check:

   Use scp to copy files over SSH = A [OK]

Hint: Use scp to copy files remotely [OK]

Common Mistakes:

• Using ssh instead of scp for file copy
• Typing ssh-copy which is invalid
• Using copy command which is local only

3. What will be the output of this command if the remote server is reachable and the user has SSH key access?
ssh user@remote 'echo Hello from remote'

medium

A. Connection timed out.

B. Permission denied (publickey).

C. Hello from remote

D. ssh: Could not resolve hostname remote: Name or service not known

Solution

1. Step 1: Understand the command

   The command runs echo Hello from remote on the remote server via SSH.

2. Step 2: Check conditions

   If the server is reachable and SSH keys are set, the command outputs the echoed text.

3. Final Answer:

   Hello from remote -> Option C

4. Quick Check:

   SSH runs remote echo command = Hello from remote [OK]

Hint: SSH runs remote commands and shows output [OK]

Common Mistakes:

• Assuming permission denied without checking keys
• Confusing hostname errors with command output
• Thinking SSH command outputs nothing

4. You wrote this script to automate a remote command:

ssh user@remote 'uptime'

But it fails with "Permission denied (publickey)". What is the most likely fix?

medium

A. Generate SSH keys and add the public key to remote's authorized_keys.

B. Change the command to ssh user@remote uptime without quotes.

C. Use scp instead of ssh to run commands.

D. Restart the remote server to reset SSH.

Solution

1. Step 1: Understand the error

   "Permission denied (publickey)" means SSH keys are missing or not accepted.

2. Step 2: Fix SSH key setup

   Generate SSH keys locally and add the public key to ~/.ssh/authorized_keys on remote.

3. Final Answer:

   Generate SSH keys and add the public key to remote's authorized_keys. -> Option A

4. Quick Check:

   Permission denied means missing keys = A [OK]

Hint: Add your public key to remote authorized_keys [OK]

Common Mistakes:

• Removing quotes does not fix permission errors
• Using scp instead of ssh for commands
• Restarting server won't fix key issues

5. You want to automate running multiple commands on a remote server via SSH in one script. Which is the best way to do this?

hard

A. Use a single SSH command with multiple commands separated by semicolons inside quotes.

B. Run separate SSH commands for each remote command in the script.

C. Use scp to send commands instead of SSH.

D. Copy a script file to remote and run it with one SSH command.

Solution

1. Step 1: Consider multiple commands execution

   Running many commands inline can be complex and error-prone.

2. Step 2: Use script file for clarity and reuse

   Copying a script file to remote and running it via SSH is cleaner and easier to maintain.

3. Final Answer:

   Copy a script file to remote and run it with one SSH command. -> Option D

4. Quick Check:

   Script file on remote is best for multiple commands = C [OK]

Hint: Send script file and run remotely for many commands [OK]

Common Mistakes:

• Running many commands inline can cause quoting errors
• Running separate SSH commands is slower and complex
• Using scp to send commands is incorrect