How To Use The SSH Login Command

The SSH login command lets you open an encrypted shell session on a remote machine over any network. It replaced older, insecure protocols like Telnet and rlogin and has been the standard for remote server access for over two decades. This guide covers the exact syntax, platform-specific steps, key-based authentication, and the flags you’ll actually use day to day.

SSH Login Command Syntax

The base syntax is straightforward. You pass a username and a host — either a domain name or an IP address — separated by @:

ssh username@hostname_or_ip

SSH defaults to TCP port 22. If the remote server runs on a different port, add the -p flag. For the full list of accepted flags, the full ssh command reference on commandlinux.com covers every option in detail.

Once connected, your terminal prompt changes to reflect the remote machine. Everything you type after that runs on the server, not your local system.

What You Need Before Connecting

Before the ssh login command works, a few things have to be in place:

The remote side runs sshd, the OpenSSH daemon. For its configuration options and behavior, the sshd daemon documentation explains every directive in /etc/ssh/sshd_config.

How to Use the SSH Login Command on Linux

Linux ships with an SSH client. Open a terminal and run:

ssh [email protected]

The first time you connect to a host, SSH displays the server’s fingerprint and asks you to confirm. Type yes. The fingerprint gets saved to ~/.ssh/known_hosts and future connections skip this step.

After that, enter your password when prompted. There’s no visual feedback — the cursor won’t move — but keystrokes are being captured. Press Enter when done.

To end the session, type exit or press Ctrl+D.

How to Use the SSH Login Command on Windows

Windows 10 and later include OpenSSH by default. Open Command Prompt or PowerShell and run the same command:

ssh username@server_ip

If the client isn’t available, go to Settings → Apps → Optional Features and install “OpenSSH Client.” Alternatively, PuTTY provides a GUI-based option for older Windows versions.

Windows Subsystem for Linux (WSL2) also gives you a native Linux environment, which brings OpenSSH along with it.

SSH Key-Based Authentication

Passwords work, but SSH keys are faster and more secure. The approach uses a key pair — a private key that stays on your machine and a public key that gets placed on the server.

Generating SSH Keys

Run ssh-keygen to create a key pair. Ed25519 is the current recommendation:

ssh-keygen -t ed25519 -C "[email protected]"

The command asks where to save the keys (default: ~/.ssh/id_ed25519) and lets you set an optional passphrase. The ssh-keygen man page documents all key types and generation options.

Copying the Public Key to the Server

Use ssh-copy-id to install the public key on the remote host:

ssh-copy-id username@server_ip

This appends your public key to the server’s ~/.ssh/authorized_keys file. After that, the ssh login command authenticates via key automatically. The complete behavior of this utility is documented in the ssh-copy-id manual.

Common SSH Login Command Options

Connecting on a Custom Port

If the server runs SSH on port 2222 instead of the default:

ssh -p 2222 username@server_ip

Using a Specific Identity File

When you have multiple keys, specify which one to use with -i:

ssh -i ~/.ssh/id_project username@server_ip

You can also load keys into ssh-agent so you don’t have to type the passphrase on every connection. The ssh-add reference explains how to manage identities in the agent.

Running a Remote Command Without Opening a Shell

Append a command to run it on the server and return output to your local terminal:

ssh username@server_ip 'df -h'

The session closes as soon as the command finishes. This is useful for one-off tasks or scripts.

SSH Tunneling with Port Forwarding

Local port forwarding lets you route traffic from your machine through the SSH connection to a remote service:

ssh -L 8080:localhost:3306 username@server_ip

This forwards local port 8080 to port 3306 on the server — handy for accessing a remote database without exposing it publicly.

Troubleshooting SSH Login Issues

If the connection fails, run with -v for verbose output. It shows each handshake step and usually pinpoints the problem — wrong port, key not found, or a permission error on ~/.ssh.

Permission errors are common. SSH refuses to use keys if file permissions are too open. Set them correctly:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/id_ed25519
chmod 644 ~/.ssh/id_ed25519.pub

If root login fails, check whether PermitRootLogin is set to no in /etc/ssh/sshd_config on the server. Most distributions disable it by default as a security measure.

Connection timeouts often come from a firewall blocking port 22. Confirm the port is open on the server side with ss -tlnp | grep 22, then check any cloud firewall or security group rules that might be filtering the traffic.

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