rlogind - remote login server
rlogind [ -aln ]
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 speci-
fication; see services(5). When a service request is received the following protocol is
1) The server checks the client's source port. If the port is not in the range
512-1023, the server aborts the connection.
2) The server checks the client's source address and requests the corresponding host
name (see IR gethostbyaddr (3), hosts(5) 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 option is given, the addresses for the hostname
are requested, verifying that the name and address correspond. Normal authentica-
tion is bypassed if the address verification fails.
Once the source port and address have been checked, rlogind proceeds with the authentica-
tion 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 auto-
matic 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 pseudo terminal, oper-
ating 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 pro-
vide ^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 ter-
minal 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
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.
A fork by the server failed.
login(1), ruserok(3), rshd(8)
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.
4.2 Berkeley Distribution September 11, 1989 RLOGIND(8)