@node rlogind
@chapter rlogind
@cindex rlogind

@command{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.

@command{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:
@enumerate

@item
The server checks the client's source port.  If the port is not in the range
512-1023, the server aborts the connection.

@item
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.
@end enumerate

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 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
client instance of the rlogin 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.


@xref{ruserok, , ruserok, libc, The GNU C Library Reference Manual}, for details.

@section Invoking

The options are as follows :

@table @samp
@item -a
@itemx --verify-hostname
@opindex -a
@opindex --verify-hostname
Ask hostname for verification.

@item -d
@itemx --daemon
@opindex -d
@opindex --daemon
Daemon mode.

@item -l
@itemx --no-rhosts
@opindex -l
@opindex --no-rhosts
Ignore .rhosts file.

@item -L
@itemx --local-domain=NAME
@opindex -L
@opindex --local-domain
Set local domain name.

@item -n
@itemx --no-keepalive
@opindex -n
@opindex --no-keepalive
Do not set SO_KEEPALIVE.

@item -k
@itemx --kerberos
@opindex -k
@opindex --kerberos
Use kerberos IV authentication.

@item -x
@itemx --encrypt
@opindex -x
@opindex --encrypt
Turns on DES encryption for all data passed via the rlogind session.  This may
impact response time and CPU utilization, but provides increased security.

@item -D
@itemx --debug[=LEVEL]
@opindex -D
@opindex -debug
Set debug level, not implemented.

@item -h
@itemx --help
@opindex -h
@opindex --help
Display usage instructions.

@item -V
@itemx --version
@opindex -V
@opindex --version
Display program version.

@item -o
@itemx --allow-root
@opindex -o
@opindex --allow-root
Allow uid == 0 to login, disable by default\n"

@item -p
@itemx --port=PORT
@opindex -p
@opindex --port
Listen on given port (valid only in daemon mode).

@item -r
@itemx --reverse-required
@opindex -r
@opindex --reverse-required
Required  Require reverse resolving of a remote host IP.

@end table

@section 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 is invoked, a null byte is returned as in indication
of success.

@table @samp

@item Try again.
A fork by the server failed.

@end table

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.
