Rlogind listens for service requests at the port indicated in the ``login'' service specification; see services(5). When a service request is received the following protocol is initiated:
Once the source port and address have been checked, rlogind allocates a pseudo terminal (see pty(4)), and manipulates file descriptors so that the slave half of the pseudo terminal becomes the stdin , stdout , and stderr for a login process. The login process is an instance of the login(1) program, invoked with the -r option. The login process then proceeds with the authentication process as described in rshd(8C), but if automatic authentication fails, it reprompts the user to login as one finds on a standard terminal line.
The parent of the login process manipulates the master side of the pseduo terminal, operating as an intermediary between the login process and the client instance of the rlogin program. In normal operation, the packet protocol described in pty(4) is invoked to provide ^S/^Q type facilities and propagate interrupt signals to the remote programs. The login process propagates the client terminal's baud rate and terminal type, as found in the environment variable, ``TERM''; see environ(7). The screen or window size of the terminal is requested from the client, and window size changes from the client are propagated to the pseudo terminal.
``Try again.''
A
fork
by the server failed.
``/bin/sh: ...''
The user's login shell could not be started.
A facility to allow all data exchanges to be encrypted should be present.
A more extensible protocol should be used.