rlogind
—
remote login server
The rlogind
utility 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
:
-D
- Set TCP_NODELAY socket option. This improves responsiveness at the expense
of some additional network traffic.
-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.
The rlogind
utility 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
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 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.
- /etc/hosts
-
- /etc/hosts.equiv
-
$HOME
/.rhosts
-
- /var/run/nologin
-
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.
The rlogind
utility appeared in
4.2BSD.
IPv6 support was added by WIDE/KAME project.
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.