rlogin

Rlogin is a remote login program and the associated protocol used to log into a remote host over a TCP/IP network. It originated with BSD Unix and was widely used in Unix and Linux environments during the 1980s and 1990s as part of the BSD r-utilities, which also included rsh and rcp.

Operation: The rlogind service listens on TCP port 513. A user on the local host can invoke rlogin to connect to a remote host, optionally specifying a different login name with the -l option. Once connected, the remote shell is started on the target as if the user had logged in locally.

Authentication and security: Rlogin commonly relies on host-based authentication using the .rhosts file or hosts.equiv on the remote host. If the client host and user are trusted according to these files, access is granted without a password. Data transmitted during the session is not encrypted, making rlogin susceptible to eavesdropping, spoofing, and other attacks. This design, together with brittle host-based trust assumptions, is considered insecure on untrusted networks.

Status and alternatives: With the rise of Secure Shell (SSH), rlogin fell out of favour and many systems disable the rlogind service by default. SSH provides encrypted communication and stronger authentication, and is the recommended replacement for remote login tasks on modern systems. In practice, rlogin remains available for compatibility on some older or specialized systems but is rarely used in new deployments.

See also: rsh, rcp, rlogind, SSH.