SSH automation in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is SSH automation?

SSH automation means using scripts to connect and run commands on remote computers without typing passwords every time.

beginner

How does SSH key-based authentication help in automation?

It uses a pair of keys (private and public) so you don't need to enter a password each time you connect, making scripts run smoothly.

beginner

What command generates an SSH key pair?

The command is ssh-keygen. It creates a private key and a public key for secure login.

beginner

How do you copy your public SSH key to a remote server?

Use ssh-copy-id user@remote_host. It adds your public key to the server's authorized keys for passwordless login.

beginner

What is a simple bash script example to run a command on a remote server using SSH?

Example:
ssh user@remote_host 'ls -l /home/user'
This runs the ls -l command on the remote server.

Which command creates an SSH key pair for automation?

A ssh-add

B ssh-copy-id

C ssh-keygen

D scp

ssh-keygen creates the key pair needed for passwordless SSH login.

What does ssh-copy-id do?

A Copies files between computers

B Starts an SSH session

C Generates SSH keys

D Copies your public SSH key to a remote server

ssh-copy-id adds your public key to the remote server's authorized keys.

Why use SSH keys for automation instead of passwords?

A Keys allow passwordless login for scripts

B Keys are easier to remember

C Passwords are more secure

D Keys slow down connection

SSH keys let scripts connect without typing passwords, making automation smooth.

Which command runs uptime on a remote server via SSH?

A ssh user@host uptime

B ssh user@host 'uptime'

C ssh user@host; uptime

D ssh uptime user@host

Use quotes to run commands remotely: ssh user@host 'command'.

What file on the remote server stores authorized public keys?

A ~/.ssh/authorized_keys

B ~/.ssh/config

C ~/.ssh/id_rsa

D ~/.ssh/known_hosts

The authorized_keys file lists public keys allowed to connect.

Explain how to set up SSH automation from scratch.

Think about creating keys, sharing keys, and running commands without passwords.

Describe why SSH automation is useful in scripting and give an example use case.

Consider repetitive tasks on remote machines.

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