rshd

rshd, short for remote shell daemon, is the server component of the remote shell (rsh) protocol. It allows a user on one machine to execute commands on a remote machine. The daemon typically runs on the remote host, often started by the Internet super-server (inetd or xinetd), and listens for connections on the shell service, commonly TCP port 514.

When a client connects, rshd authenticates the user using host-based trust mechanisms such as .rhosts and hosts.equiv, or via credentials if configured. If authentication succeeds, the daemon executes the requested command with the privileges of the authenticated remote user and connects the command’s input, output, and error streams to the network connection.

Security considerations: rshd and the rsh protocol transmit data—including commands and potentially sensitive output—in plaintext and rely on weak trust-based authentication. This makes them vulnerable to eavesdropping, interception, and IP spoofing, especially on untrusted networks. As a result, many systems disable rshd by default and restrict its use to tightly controlled environments.

Implementation and availability: rshd has been part of BSD-derived Unix systems and is provided on various Linux distributions through the rsh-server package. In modern deployments, rsh and rshd are largely deprecated in favor of secure alternatives such as SSH. When present, it is typically confined to trusted networks or used where explicit security controls are in place.

See also: rsh, rlogin, rcp, sshd, SSH.