What Is SSH? Understanding Secure Shell Protocol

Learn how SSH secures remote logins, file transfers, and tunneling, and how to use it from the command line.

SSH Overview and Use Cases

Secure Shell (SSH) is a cryptographic protocol for securely administering remote systems over an untrusted network. It replaces older, insecure protocols like Telnet and rlogin by encrypting credentials and all session data.

Admins use SSH to log into servers, run commands, copy files, and set up encrypted tunnels for other traffic. Developers rely on it for Git operations over SSH and secure access to build infrastructure.

Basic SSH Commands on Desktop Systems

Most Unix-like systems, including macOS and Linux, ship with the ssh client preinstalled. On Windows 10 and 11, OpenSSH is available in recent versions of PowerShell and the command prompt, or via third‑party tools like PuTTY.

Common operations include connecting to a server, copying files with scp, and using key-based authentication instead of passwords.

Command examples
Windows — SSH from Windows

Use Command Prompt, PowerShell, or Windows Terminal. 

ssh user@example.com
ssh -p 2222 user@example.com        # Nonstandard port
scp file.txt user@example.com:/tmp  # Copy file to server
macOS — SSH from macOS or Linux

Run these in Terminal. 

ssh user@example.com
ssh -i ~/.ssh/id_ed25519 user@example.com
scp ~/Documents/report.pdf user@example.com:~/