SSH

SSH (Secure Shell) is a network protocol that provides secure, encrypted access to a remote server through the command line. It replaced older, insecure tools such as Telnet, which sent data — including passwords — in plain text. Today SSH is the primary way to administer VPS, dedicated and cloud servers.

How SSH works

SSH creates an encrypted channel between the client (the administrator's computer) and the server. When establishing the connection, both sides negotiate encryption keys, so all communication — commands, results and transferred data — is protected from eavesdropping and tampering. The user can authenticate in two ways:

• by password — simpler, but vulnerable to brute-force attacks,
• by SSH key — more secure; the user holds a private key and places the corresponding public key on the server.

After logging in, the administrator works in the system shell through the command line. The protocol also supports secure file transfer (via SFTP and SCP) and connection tunneling — routing other services' traffic through the encrypted channel.

SSH in practice

SSH is a daily tool for administrators, developers and DevOps engineers. It is used to configure servers, install software, deploy applications, review logs and manage services. Secure file transfer over SFTP is built on it, and automation and deployment systems connect to servers precisely over SSH. For security it is recommended to disable password login in favor of keys, restrict access with a firewall, and use tools such as fail2ban to block suspicious connection attempts.