How to install SSH server on Ubuntu

Ubuntu Desktop and its variants do not come with an SSH server installed by default, unlike Ubuntu Server which includes it pre-installed and enabled. This difference is due to the common use of SSH in server environments for secure remote management.

OpenSSH provides the SSH server functionality on Ubuntu and is available in the default repository of Ubuntu's package manager, apt. This makes the installation process straightforward and can be accomplished using simple terminal commands.

Enabling SSH on an Ubuntu system allows secure remote connections, crucial for administrative tasks, especially in environments where physical access to servers is limited. Once installed and running, the SSH server can be configured to meet specific security requirements and operational preferences, ensuring the server's accessibility and integrity.

1. Open terminal from the application launcher.
2. Update the package list.

   $ sudo apt update
   [sudo] password for user: 
   Get:1 http://security.ubuntu.com/ubuntu focal-security InRelease [107 kB]
   Get:2 http://security.ubuntu.com/ubuntu focal-security/main amd64 DEP-11 Metadata [21.2 kB]
   Get:3 http://security.ubuntu.com/ubuntu focal-security/universe amd64 DEP-11 Metadata [36.0 kB]
   Hit:4 http://jp.archive.ubuntu.com/ubuntu focal InRelease                      
   Get:5 http://jp.archive.ubuntu.com/ubuntu focal-updates InRelease [111 kB]
   Get:6 http://jp.archive.ubuntu.com/ubuntu focal-backports InRelease [98.3 kB]
   Get:7 http://jp.archive.ubuntu.com/ubuntu focal-updates/main amd64 DEP-11 Metadata [196 kB]
   Get:8 http://jp.archive.ubuntu.com/ubuntu focal-updates/universe amd64 DEP-11 Metadata [177 kB]
   Get:9 http://jp.archive.ubuntu.com/ubuntu focal-updates/multiverse amd64 DEP-11 Metadata [2,468 B]
   Get:10 http://jp.archive.ubuntu.com/ubuntu focal-backports/universe amd64 DEP-11 Metadata [1,976 B]
   Fetched 751 kB in 6s (130 kB/s)                                               
   Reading package lists... Done
   Building dependency tree       
   Reading state information... Done
   All packages are up to date.

3. Install the openssh-server package.

   $ sudo apt install --assume-yes openssh-server
   Reading package lists... Done
   Building dependency tree       
   Reading state information... Done
   The following additional packages will be installed:
     ncurses-term openssh-sftp-server ssh-import-id
   Suggested packages:
     molly-guard monkeysphere ssh-askpass
   The following NEW packages will be installed:
     ncurses-term openssh-server openssh-sftp-server ssh-import-id
   0 upgraded, 4 newly installed, 0 to remove and 0 not upgraded.
   Need to get 688 kB of archives.
   After this operation, 6,010 kB of additional disk space will be used.
   ##### snipped

4. Configure the firewall to allow SSH traffic (optional).

   $ sudo ufw allow ssh
   Rules updated
   Rules updated (v6)

   Ubuntu does not block ssh traffic by default so it's only required if you've configured your firewall to drop ssh traffic.

5. Check if the SSH service is running.

   $ sudo systemctl status ssh
   ● ssh.service - OpenBSD Secure Shell server
        Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: e>
        Active: active (running) since Fri 2020-08-07 16:24:58 +08; 55s ago
          Docs: man:sshd(8)
                man:sshd_config(5)
      Main PID: 3247 (sshd)
         Tasks: 1 (limit: 4624)
        Memory: 1.4M
        CGroup: /system.slice/ssh.service
                └─3247 sshd: /usr/sbin/sshd -D [listener] 0 of 10-100 startups
   
   Ogos 07 16:24:58 host systemd[1]: Starting OpenBSD Secure Shell server...
   Ogos 07 16:24:58 host sshd[3247]: Server listening on 0.0.0.0 port 22.
   Ogos 07 16:24:58 host sshd[3247]: Server listening on :: port 22.
   Ogos 07 16:24:58 host systemd[1]: Started OpenBSD Secure Shell server.

6. Start the SSH service if it is not running.

   $ sudo systemctl start ssh

7. Disable SSH from starting automatically during system boot if required.

   $ sudo systemctl disable ssh
   Synchronizing state of ssh.service with SysV service script with /lib/systemd/systemd-sysv-install.
   Executing: /lib/systemd/systemd-sysv-install disable ssh
   Removed /etc/systemd/system/multi-user.target.wants/ssh.service.
   Removed /etc/systemd/system/sshd.service.

8. Configure SSH to start automatically during system boot if preferred.

   $ sudo systemctl enable ssh
   Synchronizing state of ssh.service with SysV service script with /lib/systemd/systemd-sysv-install.
   Executing: /lib/systemd/systemd-sysv-install enable ssh
   Created symlink /etc/systemd/system/sshd.service → /lib/systemd/system/ssh.service.
   Created symlink /etc/systemd/system/multi-user.target.wants/ssh.service → /lib/systemd/system/ssh.service.

9. Edit the SSH server configuration file for any custom settings using your favorite editor.

   $ sudo vi /etc/ssh/sshd_config

   Related: Guide list for SSH

10. Restart the SSH service to apply changes.

    $ sudo systemctl restart ssh