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RSH / REMSH
Remote Shell (rsh or remsh) is a legacy protocol designed to execute shell commands on a remote Unix system in a non-interactive fashion. It operates primarily over TCP, allowing administrators or automated systems to issue single commands remotely. Despite its historical usage, RSH is largely deprecated due to its insecure design, transmitting data in plaintext, including user credentials, posing significant security risks in modern network environments..
Remote Shell (RSH) is part of the Berkeley r-commands suite, enabling users to execute single, non-interactive commands remotely. Unlike interactive sessions offered by protocols like Telnet or SSH, RSH executes the specified command and then disconnects. It is primarily used for scripting, remote system administration, and automation, particularly in trusted local network environments.
RSH communicates over TCP port 514. Authentication is traditionally based on trust relationships defined in .rhosts or /etc/hosts.equiv files, which determine user mapping and access permissions without requiring passwords, relying heavily on trust between systems. As such, it was commonly used within secured, internal networks with known hosts.
Due to the lack of encryption and strong authentication mechanisms, RSH protocols have fallen out of favor. Today's best practices replace RSH with Secure Shell (SSH), which provides robust encryption and authentication, addressing the security deficiencies inherent in RSH.