rlogind

rlogind is the remote login daemon that implements the rlogin service used by early Unix systems to provide remote sessions over a TCP connection. It runs on a server to accept connections from rlogin clients and facilitates remote user logins. Traditionally, rlogind is started by a super-server such as inetd or xinetd and listens on TCP port 513.

Authentication in rlogind historically relies on trust relationships defined by .rhosts in the user's home directory or hosts.equiv, allowing login without a password when the connecting host and user are deemed trusted. Because the protocol transmits data in cleartext and uses weak host-based authentication, it is vulnerable to interception and IP spoofing.

Due to security concerns, rlogind has fallen out of use on many modern systems. Administrators typically disable the service or block it with a firewall, and substitute SSH (sshd) for remote access, as SSH provides encrypted communication and stronger authentication. If rlogind remains installed, it should be kept behind a firewall and not exposed to untrusted networks.

Historically, rlogind was part of the BSD/rsh/rlogin toolset and was widely used in the 1980s and 1990s. Today it is often removed or disabled in favor of more secure alternatives.

Related topics include rsh, rlogin clients, inetd/xinetd, and ssh.