Setup an SSH Server with VirtualBox

Server Setup Steps

To enable SSH access to your VirtualBox virtual machine, follow these steps:

Step 1: Configure Network Settings

• Open VirtualBox and go to the Network Settings of your virtual machine.
• Select an available network adapter or replace an existing one.
• Set the Network Adapter mode to Bridged and choose your Primary Network Adapter as the Bridge.
• Under Advanced, make sure that Promiscuous Mode is set to Allow All.

Step 2: Set Up UFW Rules (If applicable)

Check if UFW (Uncomplicated Firewall) is active or disabled on your virtual machine by running the following command:

sudo ufw status

If UFW is inactive or disabled, you can skip this step. Otherwise, follow the instructions Setting Up UFW Rules on the Firewall.

Step 3: Install OpenSSH Server

Install the OpenSSH server on your virtual machine using the appropriate package manager:

For Ubuntu/Debian-based systems:

sudo apt update
sudo apt-get install openssh-server

For CentOS/RHEL-based systems:

sudo yum install openssh-server

Step 4: Enable SSH Server at Startup

To configure the SSH server to start automatically during boot, run the following command:

sudo systemctl enable ssh

If you ever want to remove the SSH server from startup, you can use the following command:

sudo systemctl disable ssh

Step 5: Start the SSH Server

Start the SSH server on your virtual machine with the following command:

sudo systemctl start ssh

Setting Up Public Key Authentication

Public key authentication is preferred as it eliminates the need for password input each time a connection is established. Follow these steps to set up public key authentication:

Step 1: Create the SSH Directory

If you don’t already have an ~/.ssh directory on your virtual machine, create it using the following command:

mkdir -p ~/.ssh

Step 2: Set Directory Permissions

Set the proper permissions for the ~/.ssh directory to allow the owner to read, write, and execute files within it:

chmod 700 ~/.ssh

Step 3: Generate an SSH Key Pair

To generate an SSH key pair on your virtual machine, run the following command:

ssh-keygen -t rsa -b 2048 -f ~/.ssh/id_rsa -C "" -N ""

If you want to set a password for your private key, remove the -N "" option.

Once the key pair is generated, copy the private key (id_rsa) to your host machine, preferably to your current user’s ~/.ssh/ directory or %USERPROFILE%/.ssh/ for Windows.

You can use one of the following methods to copy the private key:

Method 1: Manual Copy/Paste

On your virtual machine, display the contents of the private key and public key files:

cat ~/.ssh/id_rsa
cat ~/.ssh/id_rsa.pub

Save the contents in the same location on your host machine:

~/.ssh/<vm-shortname>.id_rsa
~/.ssh/<vm-shortname>.id_rsa.pub

For Windows users:

%USERPROFILE%/.ssh/<vm-shortname>.id_rsa
%USERPROFILE%/.ssh/<vm-shortname>.id_rsa.pub

Method 2: Use SCP Command

Copy the private key from your virtual machine to your host machine using the SCP command:

scp <username>@<ip-addr>:~/.ssh/id_rsa ~/.ssh/id_rsa

For Windows users:

scp <username>@<ip-addr>:~/.ssh/id_rsa %USERPROFILE%/.ssh/id_rsa

Step 4: Transfer the Public Key to the Virtual Machine

Copy the public key from your host machine to your virtual machine:

scp ~/.ssh/id_rsa.pub <username>@<ip-addr>:~/.ssh/id_rsa.pub

For Windows users:

scp %USERPROFILE%/.ssh/id_rsa.pub <username>@<ip-addr>:~/.ssh/id_rsa.pub

If you encounter any issues during the transfer, ensure that the ~/.ssh directory on your virtual machine has the correct permissions:

chmod 700 ~/.ssh

Step 5: Add Public Key to authorized_keys File

On your virtual machine, append the contents of the public key file (id_rsa.pub) to the ~/.ssh/authorized_keys file:

cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys

Ensure that the authorized_keys file has the correct permissions so that it is properly read during the connection:

chmod 600 ~/.ssh/authorized_keys

Step 6: Verify SSH Key Setup

From your host machine, establish an SSH connection to your virtual machine, specifying your private key:

ssh -i ~/.ssh/id_rsa <username>@<ip-addr>

For Windows users:

ssh -i %USERPROFILE%/.ssh/id_rsa <username>@<ip-addr>

If you are prompted to provide a password while using the above command, it means your key pair is not working correctly.

Possible reasons for this issue include:

• The private key path provided in the command is invalid or doesn’t exist on the host machine.
• The private key (id_rsa) on the host machine is not a valid pair for the public key on the virtual machine.
• The ~/.ssh directory on the virtual machine does not have the correct 700 permissions.
• The ~/.ssh/authorized_keys file on the virtual machine does not have the correct 600 permissions.
• The SSH configuration on the virtual machine has the PubkeyAuthentication variable set to “no” instead of its default “yes” (this can be fixed by following the steps below).

Step 7: Update SSH Server Configuration

Edit the SSH server configuration file using a text editor:

sudo vi /etc/sshd_config

Locate the PubkeyAuthentication line, remove the leading # if applicable, and set it to “yes”:

PubkeyAuthentication yes

Scroll down and find the PasswordAuthentication line, change the value from “yes” to “no”:

PasswordAuthentication no

Save the changes and exit the text editor.

Step 8: Restart the SSH Server

To apply the changes made to the SSH server configuration, restart the SSH server:

sudo systemctl restart ssh

Setting Up UFW Rules on the Firewall

If UFW is active on your virtual machine, follow these steps to set up the necessary firewall rules:

Step 1: Check UFW Status

Verify the status of UFW by running the following command:

sudo ufw status

Step 2: Allow SSH Access

To allow SSH access through the firewall, add a rule to allow port 22:

sudo ufw allow 22

You can also allow SSH access using TCP or UDP specifically:

sudo ufw allow 22/tcp
sudo ufw allow 22/udp

Alternatively, you can allow SSH access by specifying the service name:

sudo ufw allow ssh

This method utilizes the default port for SSH as specified in the /etc/services file.

Another option is to use UFW’s built-in application profiles. List the available profiles using:

sudo ufw app list

Locate the profile specific to your SSH service and allow it:

sudo ufw allow OpenSSH

Finally, you can verify the added rules:

sudo ufw show added

These steps should help you set up an SSH server with VirtualBox and configure it for public key authentication.