Enabling SSH on Ubuntu

SSH (Secure Shell) allows secure remote access to a system over a network. It is commonly used to manage servers, execute remote commands and transfer files securely. Ubuntu supports SSH through the OpenSSH server package, which can be installed and configured directly from the terminal.

• Securely connect to remote systems over a network
• Manage servers and execute administrative commands remotely
• Configure authentication and access settings
• Allow SSH traffic through the firewall when required

Method 1: Using OpenSSH Server Package

Step 1: Update Repository

Command:

sudo apt update

Output:

Note: While updating the repository it will ask your password enter the password to complete the process

Step 2: Check OpenSSH Server Status

After updating use the following command to verify OpenSSH status

Command:

sudo apt list openssh-server

Output:

• If SSH is already installed in your system then output will look similar to

Output:

• If it's not installed then you can install using the following command:

Command:

sudo apt install openssh-server

Output:

Note: Once the installation process ends the SSH service will start automatically.

Step 3: Start and Enable SSH Service

Although the SSH service starts automatically after installation. But if the SSH server is not started then by using the following command you can start the SSH server.

Command:

sudo service ssh start

Output:

• To ensure it starts on boot, enable the service using following command

Command:

sudo systemctl enable ssh

Output:

Step 4: Check SSH Status

After enable the SSH server now check the SSH server status to ensure the SSH service are running.

Command:

sudo service ssh status

Output:

• SSH is now enabled on your Ubuntu system.

Note: Press Q to return to the command prompt.

Method 2: Configure SSH via Config File

Step 1: Open SSH Configuration File

Open the SSH configuration file using a text editor.

Command:

sudo nano /etc/ssh/sshd_config

Output:

Step 2: Modify Root Login (If Required)

Locate the line #PermitRootLogin prohibit-password and uncomment it by removing the # at the beginning then save and exit.

Note: Incorrect SSH configuration can lock you out of the server. Keep an active session open and ensure you have alternative access before making changes.

Uncomment:

#PermitRootLogin prohibit-password

Output:

• Restart the SSH service to apply the changes.

Command:

sudo service ssh restart

Output:

Method 3: Configure Firewall Using UFW

Step 1: Allow SSH Through UFW (Uncomplicated Firewall)

If we have a firewall turned on, we can allow SSH traffic. If we are using UFW, we can allow SSH by executing the following command:

Command:

sudo ufw allow ssh

Output:

Step 2: Enable UFW (Uncomplicated Firewall)

Enable UFW to start at boot.

Command:

sudo ufw enable

Output:

Step 3: Verify Firewall Status

Now Verify the status of UFW to confirm that SSH is allowed.

Command:

sudo ufw status

Output:

Now, as you can see the SSH is enabled and UFW is configured to allow SSH traffic.

Step 4: Access SSH

Now this is final steps to check the Access of SSH whether it is Enabled or not. We can also access our Ubuntu machine via SSH using its IP address or hostname.

• Use the following command from another system:

Command:

ssh username@your_ubuntu_ip

Output:

Troubleshooting SSH

1. Check SSH Service

Run the following command to restart or check the status:

Command:

sudo systemctl status ssh
sudo systemctl restart ssh

2. Allow SSH in Firewall

If your Firewall is blocking, run the following command:

Command:

sudo ufw allow ssh

3. Fix Permission Denied Issue

If SSH key is properly not set, ensure to allow the permission by using the following command:

Command:

chmod 600 ~/.ssh/authorized_keys

4. Connection Timeout

This might occur due to network issues or a misconfigured firewall. Try fixing any blockage between client and the server.

Also Check

• How to use SSH to connect to a remote server in Linux
• Difference between SSH and SSL