SSH connection basics in Linux CLI - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does SSH stand for and what is its main purpose?

SSH stands for Secure Shell. It is used to securely connect to a remote computer over a network, allowing you to control it as if you were sitting in front of it.

beginner

What is the basic command syntax to connect to a remote server using SSH?

The basic command is ssh username@hostname. Here, username is your user on the remote machine, and hostname is the server's address or IP.

beginner

Why is SSH considered secure compared to older methods like Telnet?

SSH encrypts all data sent between your computer and the remote server, protecting passwords and commands from being seen by others on the network.

intermediate

What is the purpose of SSH keys in connection?

SSH keys are pairs of cryptographic keys used to authenticate without typing a password. The private key stays on your computer, and the public key is placed on the server.

beginner

How can you specify a different port number when connecting with SSH?

Use the -p option followed by the port number, like ssh -p 2222 username@hostname if the server uses a port other than the default 22.

What default port does SSH use to connect to a server?

A 22

B 80

C 443

D 21

SSH uses port 22 by default for secure connections.

Which command would you use to connect to user 'alice' on server 'example.com'?

A ssh example.com@alice

B ssh [e-mail]

C ssh connect alice example.com

D ssh -u alice example.com

The correct syntax is ssh username@hostname, so ssh [e-mail] is correct.

What does SSH encrypt during a connection?

A Nothing, it is not encrypted

B Only the commands

C Only the password

D All data including commands and passwords

SSH encrypts all data sent between client and server, including commands and passwords.

How do SSH keys improve security?

A By allowing anonymous login

B By making the connection faster

C By replacing passwords with cryptographic keys

D By disabling encryption

SSH keys replace passwords with cryptographic keys, making authentication more secure.

Which option lets you connect to a non-default SSH port?

A -p

B -d

C -P

D -port

The -p option specifies the port number for SSH connections.

Explain how you would connect to a remote server using SSH and what information you need.

Think about the command format and what identifies the remote machine and user.

Describe why SSH is a secure way to connect to remote computers compared to older methods.

Focus on what SSH protects during the connection.

Practice

1. What does the command ssh user@hostname do?

easy

A. Lists files on the remote computer.

B. Copies files from the remote computer to local.

C. Starts a secure connection to the remote computer as 'user'.

D. Deletes the user account on the remote computer.

Solution

1. Step 1: Understand the ssh command purpose

   The ssh command is used to securely connect to another computer over a network.

2. Step 2: Analyze the syntax ssh user@hostname

   This syntax means connect as 'user' to the computer identified by 'hostname'.

3. Final Answer:

   Starts a secure connection to the remote computer as 'user'. -> Option C

4. Quick Check:

   ssh user@hostname = Secure connection [OK]

Hint: ssh user@host means connect securely as user [OK]

Common Mistakes:

• Thinking ssh copies files instead of connecting
• Confusing ssh with file listing commands
• Assuming ssh deletes accounts

2. Which of these is the correct syntax to connect to a remote server with ssh?

easy

A. ssh user@hostname

B. ssh -connect user hostname

C. ssh connect user@hostname

D. ssh user hostname

Solution

1. Step 1: Recall ssh command syntax

   The correct syntax is ssh user@hostname without extra words or flags for basic connection.

2. Step 2: Check each option

   Options A, B, and D have incorrect syntax or missing '@' sign.

3. Final Answer:

   ssh user@hostname -> Option A

4. Quick Check:

   Correct ssh syntax = ssh user@hostname [OK]

Hint: ssh always uses user@hostname format [OK]

Common Mistakes:

• Adding extra words like 'connect' in command
• Omitting '@' between user and hostname
• Using flags incorrectly for basic ssh

3. What will happen if you run ssh alice@192.168.1.10 and the password is correct?

medium

A. You will see a list of files on your local computer.

B. The remote computer will shut down.

C. Your local files will be deleted.

D. You will be logged into the remote computer as user alice.

Solution

1. Step 1: Understand ssh login process

   Running ssh with user and IP tries to connect and log in to that remote machine.

2. Step 2: Check what happens on correct password

   If password is correct, you get a command prompt on the remote machine as that user.

3. Final Answer:

   You will be logged into the remote computer as user alice. -> Option D

4. Quick Check:

   ssh + correct password = remote login [OK]

Hint: Correct password means remote login success [OK]

Common Mistakes:

• Thinking ssh shuts down remote machine
• Confusing ssh with file deletion
• Assuming ssh lists local files

4. You try to connect with ssh [e-mail] but get the error: Permission denied (publickey). What is the likely problem?

medium

A. You typed the wrong hostname.

B. Your SSH key is missing or not accepted by the server.

C. The server is turned off.

D. You forgot to install ssh on your computer.

Solution

1. Step 1: Understand the error message

   "Permission denied (publickey)" means the server expects an SSH key for authentication but did not accept yours.

2. Step 2: Identify cause of error

   This usually means your SSH key is missing, not loaded, or not authorized on the server.

3. Final Answer:

   Your SSH key is missing or not accepted by the server. -> Option B

4. Quick Check:

   Permission denied (publickey) = SSH key issue [OK]

Hint: Permission denied (publickey) means SSH key problem [OK]

Common Mistakes:

• Assuming hostname typo causes this error
• Thinking server power state causes this error
• Believing ssh must be installed locally to connect

5. You want to connect to a remote server at example.com as user admin but the server uses a non-standard port 2222. Which command will connect correctly?

hard

A. ssh -p 2222 [e-mail]

B. ssh [e-mail]:2222

C. ssh [e-mail] -port 2222

D. ssh [e-mail]

Solution

1. Step 1: Recall how to specify a port in ssh

   The correct flag to specify a port is -p followed by the port number.

2. Step 2: Analyze each option

   ssh -p 2222 [e-mail] uses -p 2222 correctly. Options A, C, and D use incorrect syntax or wrong placement.

3. Final Answer:

   ssh -p 2222 [e-mail] -> Option A

4. Quick Check:

   Use -p to specify port in ssh [OK]

Hint: Use ssh -p port user@host for custom ports [OK]

Common Mistakes:

• Putting port after hostname with colon
• Using -port instead of -p
• Changing hostname to include port number