rlogind is the server for the rlogin program (see rlogin invocation). The server provides a remote login facility with authentication based on privileged port numbers from trusted hosts.
rlogind listens for service requests at the port indicated in the ‘login’ service specification. When a service request is received the following protocol is initiated:
Once the source port and address have been checked, rlogind proceeds with the authentication process described rshd invocation. It then allocates a pseudo terminal, 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 program, invoked with the -f option if authentication has succeeded. If automatic authentication fails, the user is prompted to log in as if on a standard terminal line.
The parent of the login process manipulates the master side of the pseudo 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’ is invoked to provide C-S/C-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. 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.
Transport-level keepalive messages are enabled unless the -n
option is client instance of the
rlogin program. The use of
keepalive messages allows sessions to be timed out if the client
crashes or becomes unreachable.
See ruserok, for details.
The options are as follows:
All initial diagnostic messages are indicated by a leading byte with a value of 1, after which any network connections are closed. If there are no errors before login is invoked, a null byte is returned as in indication of success.
The authentication procedure used here assumes the integrity of each client machine and the connecting medium. This is insecure, but is useful in an “open” environment.