OpenSSH Server lets you connect to an Ubuntu Linux system securely from another computer, making it essential for remote administration, file transfers, server maintenance, and headless systems. On Ubuntu, the standard way to install it is through the apt package tools, which pull the OpenSSH packages from the configured repositories.
This guide covers installing SSH on Ubuntu with apt-get, updating package indexes first, starting and enabling the SSH service, checking that it is running, opening firewall access with UFW, and confirming that remote login works from another machine.
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Prerequisites and When You Need SSH on Ubuntu
Before installing OpenSSH Server on Ubuntu, make sure you are working on the Ubuntu machine that should accept incoming SSH connections. This is usually a server, virtual machine, cloud instance, lab system, or desktop that you want to manage remotely. The package you will install is openssh-server; it is different from the SSH client, which is often already installed and lets you connect out to other systems.
You need a user account with administrative privileges because installing packages, enabling services, and changing firewall rules require sudo. You also need a working network connection so Ubuntu can download packages from the configured apt repositories. If this is a fresh installation, confirm that the system can reach the internet or an internal Ubuntu mirror before continuing.
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Basic prerequisites
- Ubuntu system: A supported Ubuntu release such as Ubuntu 20.04 LTS, 22.04 LTS, or 24.04 LTS.
- Sudo access: A user that can run administrative commands with
sudo. - Network access: Connectivity to Ubuntu package repositories and to the network clients that will connect by SSH.
- Terminal access: Local console access, a hypervisor console, or an existing shell session on the machine.
- Firewall awareness: Knowledge of whether UFW, cloud firewall rules, or network security groups control inbound traffic.
SSH is useful when you need secure command-line access without sitting in front of the computer. After OpenSSH Server is running, you can administer Ubuntu from another Linux, macOS, or Windows machine using an SSH client. Common tasks include installing software, editing configuration files, checking logs, restarting services, copying files with scp or sftp, and managing remote workloads.
| Scenario | When SSH helps |
|---|---|
| Cloud server administration | Connect to a VPS or cloud instance from your workstation to configure services and deploy applications. |
| Home lab or office server | Manage a headless Ubuntu machine without attaching a monitor and keyboard. |
| Remote troubleshooting | Inspect logs, restart failed services, and run diagnostics from another location. |
| File transfer | Use encrypted transfers with scp, sftp, or tools that run over SSH. |
If the machine is exposed to the internet, plan the access model before enabling inbound SSH. Use strong passwords or, preferably, SSH keys; keep the system updated; and allow port 22/tcp only from trusted networks where possible. On cloud platforms, remember that Ubuntu’s local firewall is only one layer: provider-level security groups or firewall policies must also allow SSH traffic before remote connections can succeed.
Update apt Package Indexes
Before installing OpenSSH Server, refresh Ubuntu’s local package index so apt-get knows which package versions are currently available from the configured software repositories. This does not upgrade installed software by itself; it only downloads updated metadata such as package names, versions, dependencies, and repository locations. Running this step first helps avoid installation failures caused by stale package information.
Open a terminal on the Ubuntu system where you want to install the SSH server, then run:
sudo apt-get update
The sudo command runs the update with administrative privileges, which are required because Ubuntu stores package metadata in system directories under /var/lib/apt/. If prompted, enter your user password. You should see output showing Ubuntu contacting repositories such as archive.ubuntu.com, security.ubuntu.com, or your configured mirror. Lines beginning with Hit, Get, and Fetched are normal.
If the command completes without errors, continue to the OpenSSH Server installation step. If you see repository or network errors, resolve them before installing packages. Common causes include no internet connection, incorrect DNS settings, expired repository entries, or a disabled Ubuntu mirror. You can quickly confirm basic connectivity with:
ping -c 4 archive.ubuntu.com
On minimal servers or freshly created cloud instances, it is also common to update the package index immediately after first login because the image may have been built days or weeks earlier. For systems behind a proxy, make sure the proxy settings are configured for apt-get before retrying the update.
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After refreshing package indexes, you can check whether Ubuntu can locate the OpenSSH Server package:
apt-cache policy openssh-server
This command displays the candidate version that apt-get would install and the repository it would come from. A typical result shows an available candidate from the main Ubuntu repository or from the Ubuntu security updates repository. If the candidate value is shown as (none), your enabled repositories may be incomplete, and you should review your /etc/apt/sources.list file or the repository configuration under /etc/apt/sources.list.d/.
Once sudo apt-get update has completed successfully and openssh-server is available, the system is ready for installation using apt-get.
Install OpenSSH Server Using apt-get
After refreshing the package indexes, install the Ubuntu SSH server package with apt-get. The package you need is openssh-server, which provides the sshd daemon that listens for incoming SSH connections. On a local Ubuntu terminal, run:
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sudo apt-get install openssh-server
Enter your user password when prompted, then review the package list that apt-get displays. Ubuntu may install supporting packages such as openssh-client, openssh-sftp-server, or related libraries if they are not already present. Confirm the installation by typing Y and pressing Enter. When the command finishes, the OpenSSH Server files and default configuration are installed under standard system locations, including /etc/ssh/sshd_config for server settings.
Install without interactive prompts
If you are installing SSH as part of a script or cloud-init setup, add the -y option so apt-get automatically confirms package installation:
sudo apt-get -y install openssh-server
This is useful for repeatable server builds, but on a manually administered system it is often better to run the command without -y so you can see exactly which packages will be installed or upgraded. For a minimal server, the download is usually small and installation should complete quickly.
Confirm the package is installed
You can verify that Ubuntu recognizes the OpenSSH Server package as installed with dpkg:
dpkg -l openssh-server
A successful installation shows a line beginning with ii, followed by the package name and version. You can also check that the SSH daemon binary is available:
which sshd
On a typical Ubuntu system, this returns /usr/sbin/sshd. At this point, the server package is installed, but you should still verify that the service is running and enabled to start at boot in the next step.
Optional: inspect the default SSH server configuration
The main SSH server configuration file is:
/etc/ssh/sshd_config
The default Ubuntu configuration is suitable for basic username-and-password SSH access in many environments. You do not need to edit it just to start using SSH, but it is helpful to know where settings such as Port, PermitRootLogin, PasswordAuthentication, and PubkeyAuthentication are defined. If you later make changes, reload or restart the SSH service so they take effect.
Start, Enable, and Check the SSH Service
After installing the OpenSSH server package, Ubuntu usually starts the SSH daemon automatically. Still, you should confirm that the service is running and configured to start after a reboot. On Ubuntu, the OpenSSH server service is managed by systemd and is commonly named ssh. The daemon process behind it is sshd, but the service unit you normally control is ssh.service.
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Start the SSH service with systemctl if it is not already running:
sudo systemctl start ssh
To make SSH start automatically whenever the server boots, enable the service:
sudo systemctl enable ssh
You can also start it and enable it in one command:
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sudo systemctl enable --now ssh
Next, check the current service status:
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A healthy SSH service should show active (running) in the output. You may also see the loaded unit file path, whether the service is enabled, the main process ID, and recent log lines. If the service is listed as inactive, start it again. If it is failed, inspect the status output carefully because it often points to a configuration error, missing host key, or port binding problem.
Useful service management commands
sudo systemctl restart sshrestarts the SSH service after configuration changes.sudo systemctl reload sshreloads supported configuration changes without a full restart.sudo systemctl stop sshstops the SSH service and prevents new SSH logins until it is started again.systemctl is-enabled sshprints whether SSH is enabled at boot.systemctl is-active sshprints a short status such asactiveorinactive.
Before changing SSH settings in /etc/ssh/sshd_config, keep an existing terminal or console session open when possible. A syntax mistake or restrictive setting can block remote logins. After editing the configuration, test it before restarting the service:
sudo sshd -t
If the command returns no output, the syntax check passed. You can then restart SSH safely with sudo systemctl restart ssh. If the command prints an error, fix the referenced line in the configuration file before restarting.
To confirm that Ubuntu is listening for SSH connections, check for a listening socket on port 22, which is the default SSH port:
ss -tlnp | grep ':22'
Typical output shows LISTEN on 0.0.0.0:22, [::]:22, or a specific server IP address. If you changed the SSH port in sshd_config, replace 22 with your configured port. Once the service is active and listening, continue by allowing SSH through the Ubuntu firewall so remote clients can reach it.
Allow SSH Through the Ubuntu Firewall
After installing and starting OpenSSH Server, make sure the Ubuntu firewall allows incoming SSH connections. Ubuntu commonly uses UFW, short for Uncomplicated Firewall, as a front end for managing firewall rules. If UFW is active and no SSH rule exists, remote clients may see connection timeouts even though the ssh service is running correctly.
First, check the current firewall status and rules:
sudo ufw status verbose
If the output says Status: inactive, UFW is not currently filtering connections. You can still add the SSH rule now so it is ready when UFW is enabled later. If the output says Status: active, review the listed rules to see whether SSH is already allowed.
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sudo ufw allow OpenSSH
This profile usually allows TCP traffic on port 22, which is the default SSH port. You can confirm the application profile with:
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sudo ufw app info OpenSSH
The output should show that the OpenSSH profile permits 22/tcp. If you prefer to allow the port directly instead of using the profile, use:
sudo ufw allow 22/tcp
If you changed the SSH server to listen on a custom port, allow that port instead. For example, if SSH listens on TCP port 2222, run:
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When enabling UFW on a remote server, add the SSH rule before turning the firewall on. This prevents accidentally blocking your own administrative session. After the SSH rule is in place, enable UFW if you want the firewall active:
sudo ufw enable
Then verify the rules again:
sudo ufw status numbered
| Command | Use |
|---|---|
sudo ufw status verbose |
Shows whether UFW is active and lists current firewall rules. |
sudo ufw allow OpenSSH |
Allows SSH using Ubuntu’s OpenSSH application profile. |
sudo ufw allow 22/tcp |
Allows SSH on the default TCP port directly. |
sudo ufw status numbered |
Displays firewall rules with numbers for easier review and removal. |
For tighter access control, restrict SSH to a trusted source IP address instead of opening it to every network. Replace 203.0.113.10 with your admin workstation’s public IP address:
sudo ufw allow from 203.0.113.10 to any port 22 proto tcp
If you added a broad SSH rule earlier and want to remove it, list numbered rules and delete the matching entry:
sudo ufw status numbered
sudo ufw delete 1
Once the firewall permits the correct SSH port, the server should accept remote login attempts as long as the SSH daemon is running, the network path is reachable, and your cloud provider or router also allows inbound traffic to that port.
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Test SSH Access from a Remote Machine
After installing OpenSSH Server, starting the service, and allowing SSH through the firewall, test the connection from another computer on the same network or from a permitted external network. Use the Ubuntu server’s IP address or DNS name and a valid local user account on that Ubuntu system. If you are testing on a home or office LAN, the server address will often look like 192.168.x.x, 10.x.x.x, or 172.16.x.x.
On the Ubuntu machine running the SSH server, you can confirm its IP address with:
hostname -I
From the remote machine, connect with the ssh command. Replace username with an account that exists on the Ubuntu server and replace server_ip with the server’s address:
ssh username@server_ip
For example, if the Ubuntu server user is alex and the server IP address is 192.168.1.50, run:
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Test from Linux, macOS, or Windows
Most Linux distributions and macOS include an SSH client by default. Recent versions of Windows also include OpenSSH Client, so the same command works from PowerShell or Windows Terminal:
ssh username@server_ip
If SSH is listening on a custom port instead of the default port 22, include the -p option. For example, to connect on port 2222:
ssh -p 2222 username@server_ip
Confirm the Login Worked
After a successful login, the shell prompt should change to the Ubuntu server’s prompt. You can verify that you are on the remote system by running:
whoami
hostname
ip addr
To close the SSH session, run:
exit
Troubleshoot Common SSH Connection Errors
- Connection timed out: The remote machine cannot reach the Ubuntu server. Check the IP address, network route, cloud security group, router port forwarding if connecting over the internet, and firewall rules.
- Connection refused: The server is reachable, but SSH is not accepting connections on that port. Check the SSH service with systemctl status ssh and confirm the port in /etc/ssh/sshd_config.
- Permission denied: The SSH server is reachable, but authentication failed. Confirm the username, password, SSH key, and any restrictions such as AllowUsers in the SSH configuration.
- Host key verification failed: The client has a saved host key that no longer matches the server. This can happen after reinstalling the server, but it can also indicate a security issue. Verify the server identity before removing the old key from known_hosts.
If the test succeeds, OpenSSH Server is installed correctly, the service is running, the firewall permits access, and the Ubuntu system is ready for remote administration. For internet-facing servers, consider tightening access further with SSH keys, disabling password login, limiting users, and allowing connections only from trusted IP addresses.
Frequently Asked Questions
What is the exact apt-get command to install SSH server on Ubuntu?
Run sudo apt-get update first, then install the OpenSSH server package with sudo apt-get install openssh-server. After installation, check that it is running with sudo systemctl status ssh. On Ubuntu, the service name is usually ssh, not sshd.
How do I make SSH start automatically after reboot?
Enable the SSH service with sudo systemctl enable ssh. If it is not already running, start it with sudo systemctl start ssh. You can confirm both the current status and whether it is enabled using systemctl status ssh and systemctl is-enabled ssh.
Do I need to open the firewall before connecting with SSH?
If Ubuntu Firewall is enabled, you need to allow SSH traffic with sudo ufw allow ssh. If you changed SSH to a custom port, allow that port instead, such as sudo ufw allow 2222/tcp. Check the firewall rules with sudo ufw status before testing from another machine.
How do I test SSH access from another computer?
From the remote computer, run ssh username@server_ip_address, replacing the username and IP address with the Ubuntu server’s details. You can find the server IP with ip addr or hostname -I on the Ubuntu machine. On the first connection, confirm the host fingerprint prompt, then enter the user’s password unless key-based authentication is configured.
What should I check if SSH connection is refused or times out?
If the connection is refused, verify that OpenSSH Server is installed and running with sudo systemctl status ssh. If the connection times out, check the server IP address, network route, cloud security group rules, and ufw firewall settings. Also confirm SSH is listening on the expected port with sudo ss -tlnp | grep ssh.
Bottom Line
Installing SSH on Ubuntu with apt-get is straightforward: update your package indexes, install openssh-server, confirm the service is running, and allow SSH through the firewall if UFW is enabled. After that, test access from another machine using the server’s username and IP address.
Your next step is to connect with ssh user@server-ip and, if this server is exposed to the internet, harden access by using SSH keys, disabling root login, and limiting who can connect.
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