The rlogind daemon listens for service requests at the port indicated in the login service specification; see services(4). When a service request is received, the following protocol is initiated: The server checks the client's source port. If the port is not in the range 512 to 1023, the server aborts the connection. The server checks the client's source address and requests the corresponding hostname (see gethostbyaddr(3), hosts(4) and named(8). If the hostname cannot be determined, the dot-notation representation of the host address is used. If the hostname is in the same domain as the server (according to the last two components of the domain name), or if the -a flag is given, the addresses for the hostname are requested, verifying that the name and address correspond. Normal authentication is bypassed if the address verification fails.
Once the source port and address have been checked, rlogind proceeds with the authentication process described in rshd(8). It then allocates a pseudoterminal (see pty(7)), and manipulates file descriptors so that the slave half of the pseudoterminal becomes the stdin, stdout, and stderr for a login process. The login process is an instance of the login(1) 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 -l option prevents any authentication based on the user's .rhosts file, unless the user is logging in as the superuser.
The parent of the login process manipulates the master side of the pseudoterminal, 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(7) is invoked to provide <Ctrl-s>/<Ctrl-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 TERM environment variable. The screen or window size of the terminal is requested from the client, and window size changes from the client are propagated to the pseudoterminal.
Transport-level, keep-alive messages are enabled unless the -n flag is present. The use of keep-alive messages allows sessions to be timed out if the client crashes or becomes unreachable.
Note that 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.
Specifies the command path
Functions: ruserok(3) delim off