[1] The r-commands were developed in 1982 by the Computer Systems Research Group at the University of California, Berkeley, based on an early implementation of TCP/IP (the protocol stack of the Internet).
[2] The CSRG incorporated the r-commands into their Unix operating system, the Berkeley Software Distribution (BSD).
[2][3] The r-commands were a significant innovation, and became de facto standards for Unix operating systems.
RFC 1282, in which it was defined, states: "The rlogin facility provides a remote-echoed, locally flow-controlled virtual terminal with proper flushing of output."
[18] rwho's daemon, rwhod, maintains a database of the status of Unix systems on the local network.
Just as the uptime command shows how long a Unix system has been running since the last restart, ruptime requests a status report from all computers on the local network.
[19] Those r-commands which involve user authentication (rcp, rexec, rlogin, and rsh) share several serious security vulnerabilities: Due to these problems, the r-commands fell into relative disuse (with many Unix and Linux distributions no longer including them by default).