SSHServer

An SSH server is software that implements the Secure Shell protocol to provide encrypted remote login and other services over an insecure network. It allows an administrator or user to authenticate, execute commands, and transfer files between a client machine and a server. The software typically listens on port 22 but may be configured to another port.

OpenSSH sshd is the most widely used implementation on Unix-like systems; other options include Dropbear for embedded or resource-constrained devices, and Windows deployments such as Microsoft OpenSSH Server or commercial products like Bitvise SSH Server.

Key features include support for public-key authentication, password authentication, and other methods; secure tunnels and port forwarding; X11 forwarding; and the SFTP subsystem for secure file transfer. Administrators can control access with configuration files (for example, sshd_config) and service management commands; common options cover permitted authentication methods, allowed users, chrooting, and session controls.

Security practice emphasizes using key-based authentication, disabling root logins and password-based access, keeping software up to date, and implementing rate limiting or intrusion protection. Operational considerations include log monitoring, integration with identity stores, audit trails, and periodic reconfiguration as needs evolve.