Introduction
When establishing a remote connection between a client and a server, the primary concern is ensuring security. For Linux users, the best practice of accessing and managing a server remotely is through the cryptographic protocol known as Secure Shell (SSH).
SSH encrypts all data transferred from one machine to another, making sure that no sensitive information is compromised during the process. As a desktop client, you can safely run a command line, transfer files, secure network services, and much more.
By following the steps below, you will learn how to enable SSH on Ubuntu.
Prerequisites
- A user with sudo privileges.
- Permissions to access the remote computer.
- Access to a terminal/command line.
- The
apt-gettool, pre-loaded in Ubuntu.
Note: The guide is tested on Ubuntu 18.04, 20.04 and 22.04.
Enable SSH on Ubuntu
The SSH server is not installed by default on all Ubuntu versions. To install and enable SSH on Ubuntu follow the steps below:
1. Open the terminal either by using the CTRL+ALT+T keyboard shortcut or by running a search in Ubuntu Dash and selecting the Terminal Icon.
2. Before starting the installation process, check if an SSH server has already been installed on your computer with the following ssh command:
ssh localhost
If you see the SSH “Connection Refused” message, you will have to go through the SSH installation process.
3. To install SSH, first update the package repository cache with:
sudo apt-get update4. Now install the OpenSSH software package by entering:
sudo apt-get install openssh-server
If prompted, type in your password and press y (yes) to permit the installation.
5. To verify the installation was successful and SSH is running use the command:
sudo service ssh status
The confirmation message that you are looking for is: Active: active (running).
This means you have installed and enabled SSH on your remote machine, which can now accept commands from your SSH client.
6. To return to the command line prompt enter q.
Log Into Remote Server With SSH
Once you have gone through the process of enabling SSH on Ubuntu, you are ready to log into your remote machine.
1. Open the terminal (CTRL+ALT+T) and type the following command:
ssh username@public_IP -p22
Change the username and IP address to the username and IP address of the Ubuntu computer on which you have installed SSH.
2. If you do not know the IP address, you can quickly identify it through the terminal by typing the command:
ip a
This displays the public IP address of the machine where SSH was installed.
Once you have identified and typed in all the information, you are officially logged into the server. You are free to manage it from the comfort of your workstation safely.
Note: Read more about secure remote access to implement and enforce the best practices for employees.
SSH Configuration Options
The default SSH configuration options can be adjusted. You can change the default port (generally a good idea, as a precautionary security measure), disable the root user, or make other configuration adjustments.
Edit Configuration File
After successfully installing OpenSSH on Ubuntu, you can edit its configuration file.
1. Open the SSH configuration file with the command:
sudo nano /etc/ssh/sshd_config2. Now that you have opened the file using nano (or with any Linux text editor) find and make any necessary changes.
For example, to change the port number to listen on TCP port 2222 instead of the default TCP port 22, find the line in which Port 22 is specified by default, uncomment the line, and change it to Port 2222.
Note: Changing the default port number is an SSH security best practice. Everyone is aware of the default port number so changing it is a recommended security precaution.
Disable Root
Another critical security precaution is to disable remote root access. That way, the root user cannot be invoked remotely, and security will be significantly improved.
1. In the configuration file, find the line that reads PermitRootLogin_yes and change it to PermitRootLogin_no.
2. For the changes to take effect, restart the SSH service with the following command:
sudo systemctl restart sshd.serviceConfigure Firewall
If you have decided to change the default port number, you must configure your firewall to allow traffic via the specified port.
Let’s use the example of Port 2222.
The default firewall configurations tool in Ubuntu is UFW, configure it with the command:
sudo ufw allow from any to any port 2222 proto tcpSome firewalls may require allowing traffic to the public IP address of the machine running SSH.
Note: The port 2222 is the port number we have defined in the Configure SSH section. If you used the default port 22, then it is not necessary to put the port number.
How to Disable SSH on Ubuntu
To temporarily disable SSH on Ubuntu, run:
sudo service ssh stopStart the SSH service with:
sudo service ssh startTo completely disable SSH after reboot:
sudo systemctl disable sshEnable SSH on Ubuntu after reboot with:
sudo systemctl enable sshNote: Learn more about how to change SSH port.
Conclusion
By following the simple steps above, you now know how to enable SSH on Ubuntu. Now you can establish a reliable and secure protocol between you and a remote device.
Get started by logging to your machine to perform sysadmin tasks with the command prompt.
Next, we suggest learning about SSH config files that can help you easily configure the default values for these connections and enables efficient streamlining of SSH connections.
