Options supported by rlogind
The -h, -l, and -L flags are not used if PAM (Pluggable Authentication Module) support is in use. In this case the same effects can be achieved by editing /etc/pam.conf
The -h and -l options should also not be trusted without verifying that they work as expected with the particular version of libc installed on your system (and should be tested again after any libc update) because some versions of libc may not honor the internal flags used by rlogind As the -L option bypasses the libc functions entirely, it is not subject to this problem.
Also note that the design of the .rhosts system is COMPLETELY INSECURE except on a carefully firewalled private network. Always use the -L option under all other circumstances. Also, since rlogind does not encrypt communications, it should not, in general, be used at all. Consider ssh(8).
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 proceeds with the authentication process described in rshd(8). It then 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 -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(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.
Transport-level keepalive messages are enabled unless the -n option is present. The use of keepalive messages allows sessions to be timed out if the client crashes or becomes unreachable.
A facility to allow all data exchanges to be encrypted should be present.
A more extensible protocol should be used.