ssh
also: Secure Shell, SSH protocol, sshd (daemon)
SSH (Secure Shell) is a cryptographic network protocol that allows secure remote login and command execution on distant computers over an insecure network.
SSH replaces older, insecure protocols like Telnet by encrypting all data transmitted between client and server, including passwords and commands. It uses public-key cryptography to authenticate hosts and users, preventing eavesdropping and man-in-the-middle attacks.
The most common use is remote login. For example, ssh [email protected] opens an encrypted shell session on a remote machine, where you can execute commands as if sitting at that computer's terminal.
SSH also enables secure file transfer via scp (Secure Copy) and sftp (SSH File Transfer Protocol), port forwarding for tunneling other services, and automated authentication using key pairs instead of passwords.
Modern Linux systems run an SSH server daemon (sshd) by default, making remote administration and DevOps workflows possible without exposing credentials.