SSH (Secure Shell) is the standard way to log into remote Linux servers over an encrypted connection. From your Ubuntu workstation or any client, run ssh username@server_ip, accept the host key on first connect, then authenticate with a password or—preferably—an SSH key pair.

This guide covers client usage, enabling OpenSSH on Ubuntu 24.04 LTS and 26.04 LTS, key-based login, sshd configuration, and common errors. For the full protocol picture, see SSH Essentials: Working with SSH Servers, Clients, and Keys.

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Version note: Commands below were validated on Ubuntu 22.04 LTS, 24.04 LTS (Noble Numbat), and 26.04 LTS (Resolute Raccoon). On current LTS releases the systemd unit is ssh.service (manage it with systemctl … ssh). OpenSSH on 24.04 and 26.04 reads drop-in files under /etc/ssh/sshd_config.d/ before values in the main sshd_config. Cloud images (including DigitalOcean Droplets) often ship with openssh-server already installed and your SSH public key injected at create time.

• Connect from any client with ssh user@host; use -p for a non-default port and -i to pick a specific private key.
• On Ubuntu, install the server with sudo apt install openssh-server, then sudo systemctl enable --now ssh.
• On 24.04 and 26.04, put custom sshd settings in /etc/ssh/sshd_config.d/ so they are not overwritten on package updates.
• Run sudo sshd -t before sudo systemctl reload ssh to catch config syntax errors and avoid locking yourself out.
• Prefer ssh-keygen -t ed25519 over RSA for new keys; copy the public key with ssh-copy-id.
• Allow SSH through UFW with sudo ufw allow OpenSSH when the firewall is active.
• After keys work, set PasswordAuthentication no and PermitRootLogin no for production servers.
• Use the Droplet web Console for emergency access if SSH misconfiguration blocks your session.

1. Open your terminal.

   • On Linux/macOS: use Terminal.
   • On Windows: PowerShell, WSL, or Git Bash.

2. Run the SSH command:

   ssh username@your_server_ip
   

3. Review and accept the host fingerprint when prompted on first connect.

4. Authenticate with your password or SSH key.

5. Disconnect with exit.

Successful SSH connection using Termius, showing Ubuntu welcome screen and shell prompt

Ubuntu Server cloud images usually include OpenSSH. Ubuntu Desktop often does not—you install it yourself. The steps are the same on 22.04, 24.04, and 26.04; differences are called out where they matter.

Install and start the OpenSSH server

On the machine you want to reach remotely:

sudo apt update
sudo apt install openssh-server
sudo systemctl enable --now ssh

Confirm the service is listening:

sudo systemctl status ssh
ss -tlnp | grep ':22'

Expected state: active (running) and port 22 in LISTEN.

Open the firewall (UFW)

On Ubuntu, UFW may be inactive on local installs but is commonly enabled on servers. If UFW is active, allow SSH before connecting from another host:

sudo ufw allow OpenSSH
sudo ufw status

The OpenSSH application profile maps to port 22. For a custom port, allow that port explicitly (see How To Set Up a Firewall with UFW on Ubuntu).

Ubuntu version differences at a glance

Official reference: OpenSSH server (Ubuntu Server documentation).

For first-time VPS hardening, follow Initial Server Setup with Ubuntu after SSH works.

To connect to a remote system, use the ssh command.

On Windows, install OpenSSH (built into current Windows 10/11), use WSL, or Git for Windows for a bash environment that includes ssh. See Microsoft’s OpenSSH documentation for PowerShell setup.

On macOS and Linux, ssh is available in the terminal by default.

Basic form:

ssh remote_host

Replace remote_host with an IP address or domain name. If your username on the remote system differs from your local username, specify it:

ssh remote_username@remote_host

After you connect, you may be prompted for a password unless key-based auth is configured. End the session with:

exit

SSH connects a client (ssh) to a server (sshd).

On most Ubuntu systems, sshd starts automatically once openssh-server is installed. If the service is stopped, start it with:

sudo systemctl start ssh

If you cannot reach the host over the network, use your provider’s out-of-band console. On DigitalOcean, open the Droplet Access tab and launch the web Console—useful when SSH keys or firewall rules block normal login.

Access your server through DigitalOcean’s browser-based Console, ideal for emergency access without an SSH client.

For encryption and handshake details, read Understanding the SSH Encryption and Connection Process.

Server settings live in /etc/ssh/sshd_config. On Ubuntu 24.04 and 26.04, the first line is typically:

Include /etc/ssh/sshd_config.d/*.conf

OpenSSH applies the first value it finds for most directives. Store custom changes in a drop-in such as /etc/ssh/sshd_config.d/99-custom.conf instead of editing the main file when possible.

Back up before editing:

sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.bak.$(date +%F)

Common directives to review:

Port 22

Leave at 22 unless you have a documented reason to change it. Nonstandard ports reduce noise from automated scans but are not a substitute for keys and firewall rules.

PermitRootLogin prohibit-password

On current Ubuntu LTS releases, direct root password login is usually disabled; root may still log in with a key. For production, set PermitRootLogin no after you have a sudo user with key access.

PubkeyAuthentication yes
PasswordAuthentication yes
KbdInteractiveAuthentication no

Older guides reference ChallengeResponseAuthentication; on OpenSSH 8.4+ use KbdInteractiveAuthentication instead.

LogLevel INFO

Raise to DEBUG temporarily when diagnosing auth failures (revert afterward).

After edits, test and reload:

sudo sshd -t
sudo systemctl reload ssh

Keep a second terminal session open while testing so you can revert if something breaks.

Create or edit ~/.ssh/config on your local machine:

Host dev-server
    HostName 192.168.1.10
    User devuser
    Port 2222
    IdentityFile ~/.ssh/dev_key

Connect with:

ssh dev-server

This helps when you manage several keys, users, or ports. See How to Configure SSH Key-Based Authentication on a Linux Server for a full walkthrough.

Password login works for testing; key-based authentication is faster and resists brute-force attacks.

How key-based authentication works

You generate a private key (stays on your computer) and a public key (copied to the server). The server challenges the client to prove it holds the private key matching the public key in ~/.ssh/authorized_keys.

Create SSH keys on Ubuntu 24.04 / 26.04

Generate keys on the machine you connect from (your laptop or workstation):

ssh-keygen -t ed25519

Press Enter to accept the default path (~/.ssh/id_ed25519). Optionally set a passphrase for the private key.

For legacy systems that do not support Ed25519, use RSA:

ssh-keygen -t rsa -b 4096

Check permissions:

ls -l ~/.ssh/

Private keys should be mode 600; authorized_keys on the server should be 600 and the .ssh directory 700.

Copy your public key to the server

If password login still works:

ssh-copy-id username@remote_host

On DigitalOcean, you can also add keys at Droplet creation or in the control panel—see How to Add SSH Keys to Droplets.

Useful flags when connecting:

Non-default port (must match Port in sshd_config):

ssh -p port_number remote_username@remote_host

Changing the SSH port adds obscurity, not strong security. Pair key-based auth, PermitRootLogin no, and firewall rules for meaningful protection.

Run one remote command:

ssh remote_host "command_to_run"

X11 forwarding (if enabled in sshd_config on both sides):

ssh -X remote_host

Verbose debugging:

ssh -vvv remote_username@remote_host

Advanced issues

On the server, watch live logs:

sudo journalctl -fu ssh

After key login works, disable password-only auth.

Confirm your public key is in ~/.ssh/authorized_keys before disabling passwords. Keep the web Console available until you verify key login.

Create or edit a drop-in on Ubuntu 24.04 / 26.04:

sudo nano /etc/ssh/sshd_config.d/99-disable-password.conf

Add:

PasswordAuthentication no
KbdInteractiveAuthentication no
PubkeyAuthentication yes

Validate and reload:

sudo sshd -t
sudo systemctl reload ssh

Test from a new terminal before closing your existing session.

• Use Ed25519 or 4096-bit RSA keys; avoid password-only login on public servers.
• Set PermitRootLogin no after creating a sudo user.
• Keep openssh-server updated (sudo apt upgrade openssh-server).
• Restrict SSH with UFW or cloud firewalls to known IPs when possible.
• Consider fail2ban for additional brute-force protection.
• Use SFTP/SCP over SSH for file transfer—see How to Use SFTP.

Windows: PowerShell, WSL, or Git Bash—all support ssh user@server_ip and ssh-keygen.

macOS / Linux: Use the built-in terminal; same commands apply.

Generate keys:

ssh-keygen -t ed25519

1. How do you use SSH in the Ubuntu terminal?

Open Terminal and run:

ssh username@server_ip

Replace username with your account on the remote host and server_ip with its public IP or hostname. The first time you connect, type yes to trust the host key, then enter your password or use an SSH key if configured.

2. How do you set up SSH on Ubuntu Linux?

On the server, install and enable OpenSSH:

sudo apt update
sudo apt install openssh-server
sudo systemctl enable --now ssh

If UFW is active, run sudo ufw allow OpenSSH. On your client, generate a key with ssh-keygen -t ed25519 and run ssh-copy-id user@server_ip to install the public key.

3. How do you enable OpenSSH on Ubuntu?

The server package is openssh-server; the client tools are in openssh-client (often preinstalled). Install the server with apt, start ssh.service, and confirm with sudo systemctl status ssh. On Ubuntu Desktop 24.04 or 26.04, this step is required before remote login works.

4. How do you check if SSH is enabled on Ubuntu?

sudo systemctl status ssh

Look for active (running). Also verify the port:

ss -tlnp | grep ':22'

From another machine, test with ssh -v user@host or nc -zv host 22.

5. Why is SSH not working on Ubuntu?

Common causes:

1. openssh-server not installed (especially on Desktop)—install it with apt.
2. sshd not running—sudo systemctl start ssh.
3. Firewall blocking port 22—sudo ufw allow OpenSSH or open the port in your cloud firewall.
4. Wrong IP, username, or key—use ssh -vvv for details.
5. Bad sshd_config—run sudo sshd -t; fix errors before reload.

Use the provider console (DigitalOcean Console tab) if SSH is down but the VM is still running.

SSH remains the default for remote Linux administration because it is encrypted, lightweight, and works across clouds and local networks. On Ubuntu 24.04 and 26.04, install openssh-server, use sshd_config.d for custom settings, prefer Ed25519 keys, and test with sshd -t before reloading the service.

Go deeper with:

• SSH Essentials: Working with SSH Servers, Clients, and Keys
• Understanding the SSH Encryption and Connection Process
• How to Configure SSH Key-Based Authentication on a Linux Server
• How to Use SFTP to Securely Transfer Files

Add SSH keys to new Droplets in one step—see How to Add SSH Keys to Droplets.