rsh

RSH, short for Remote Shell, is a family of network services and programs that allow users to run commands on a remote machine without performing an interactive login. It originated with BSD Unix and became part of many UNIX-like systems. The core components typically include the client program rsh, the server daemon rshd, and related utilities such as rlogin and rcp. Together they provide remote command execution, remote login, and remote file copying.

Operation is straightforward: a user on a local host runs rsh with a target host and a command. The client connects to the remote host’s rshd (by default on a designated TCP port) and transmits the requested command. If the remote host accepts the request under its trust relationship, often defined in /etc/hosts.equiv or ~/.rhosts, rshd executes the command with the invoking user’s privileges and sends back the standard output and error to the client.

Security considerations are central to the history of RSH. The protocol relies on host-based trust and generally transmits data in plaintext, including credentials and commands. This makes it vulnerable to eavesdropping, spoofing, and unauthorized access, particularly on untrusted networks. Although a Kerberos-enabled variant existed to provide stronger authentication, the core rsh protocol is widely regarded as insecure. Consequently, rsh and its related services have been deprecated or disabled by default on many modern systems, with SSH (Secure Shell) preferred for secure remote command execution.

In modern contexts, RSH is typically encountered only in legacy environments or specific compatibility scenarios. It serves as a historical reference in the evolution of remote administration tools.