rlogind, in.rld - remote login server
login stream tcp nowait root /usr/sbin/in.rld in.rld
tcpd login /usr/sbin/in.rld
Rlogind is the server for the rlogin(1) program. 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; see services(5). When a service request
is received the following protocol is initiated:
1) The server checks the client's source port. If the port is not in
the range 0-1023, the server aborts the connection.
2) The server checks the client's source address and requests the
corresponding host name (see gethostbyaddr(3), hosts(5) and
named(8)). If the hostname cannot be determined, the dot-notation
representation of the host address is used.
Once the source port and address have been checked, rlogind allocates a
pseudo terminal (see tty(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(8), 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 tty(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.
All diagnostic messages are returned on the connection associated with
the stderr, after which any network connections are closed. An error is
indicated by a leading byte with a value of 1.
A fork by the server failed.
The user's login shell could not be started.
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.
A facility to allow all data exchanges to be encrypted should be present.
A more extensible protocol should be used.