NAME
rlogind —
remote login server
SYNOPSIS
DESCRIPTION
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.
Options supported by
rlogind:
-
-
- -a
- Ask hostname for verification.
-
-
- -l
- Prevent any authentication based on the user's
“.rhosts” file, unless the user is logging
in as the superuser.
-
-
- -n
- Disable keep-alive messages.
-
-
- -L
- Log all successful accesses to
syslogd(8) as
auth.info
messages.
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:
- The server checks the client's source port. If the port is
not in the range 512-1023, the server aborts the connection.
- The server checks the client's source address and requests
the corresponding host name (see
getnameinfo(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 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
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(1)
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.
At the end of a login session,
rlogind invokes the
ttyaction(3) facility with an
action of "rlogind" and user "root" to execute
site-specific commands.
DIAGNOSTICS
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(1) is invoked, a
null byte is returned as in indication of success.
-
-
- Try
again.
- A fork(2) by
the server failed.
SEE ALSO
login(1),
ruserok(3),
ttyaction(3),
rshd(8)
HISTORY
The
rlogind command appeared in
4.2BSD.
BUGS
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.
rlogind intentionally rejects accesses from IPv4 mapped
address on top of
AF_INET6
socket, since IPv4 mapped
address complicates host-address based authentication. If you would like to
accept connections from IPv4 peers, you will need to run
rlogind on top of
AF_INET
socket,
not
AF_INET6
socket.