RLOGIND(8) BSD System Manager's Manual RLOGIND(8)
rlogind -- remote login server
Rlogind is the server for the rlogin(1) program. The server provides a remote login facil-
ity with authentication based on privileged port numbers from trusted hosts.
Options supported by rlogind:
-a Ask hostname for verification.
-h Permit use of superuser ``.rhosts'' files.
-l Prevent any authentication based on the user's ``.rhosts'' file. If the user is log-
ging in as the superuser and the -h option is used, ``.rhosts'' processing is still
-L Prevent any authentication based on ``.rhosts'' or ``hosts.equiv'' information.
-n Disable keep-alive messages.
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.
Rlogind listens for service requests at the port indicated in the ``login'' service specifi-
cation; see services(5). When a service request is received the following protocol is ini-
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 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 authentication is bypassed if the address ver-
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 manipu-
lates 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 authenti-
cation 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, operat-
ing as an intermediary between the login process and the client instance of the rlogin pro-
gram. 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 envi-
ronment 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
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 unreach-
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.
The rlogind command appeared in 4.2BSD.
Linux NetKit (0.17) March 16, 1991 Linux NetKit (0.17)