is the server for the
program. The server provides a remote login facility with
kerberos-based authentication or traditional pseudo-authentication with
privileged port numbers from trusted hosts.
Options supported by
No-op. For backwards compatibility. Hostnames are always verified.
Prevent any authentication based on the user's
file, unless the user is logging in as the superuser.
Disable keep-alive messages.
Enable kerberos authentication.
Do not expect to be spawned by inetd and create a socket and listen on
it yourself.
Specifies the port number it should listen on in case the
flag has been given.
Vacuous, echo "Remote host requires Kerberos authentication" and exit.
Provides an encrypted communications channel. This options requires the
flag.
Specify pathname to an alternative login program.
Use the TCP nodelay option (see setsockopt(2) ).
When a service request is received,
verifies the kerberos ticket supplied by the user.
For non-kerberised connections, 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
and
If the hostname cannot be determined,
the dot-notation representation of the host address is used.
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,
proceeds with the authentication process described in
It then allocates a pseudo terminal (see
and manipulates file descriptors so that the slave
half of the pseudo terminal becomes the
and
for a login process.
The login process is an instance of the
program, invoked with the
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
program. In normal operation, the packet protocol described
in
is invoked to provide
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,
see
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
option is present.
The use of keepalive messages allows sessions to be timed out
if the client crashes or becomes unreachable.
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
is invoked, a null byte is returned as in indication of success.
A
by the server failed.
