4.3BSD - /usr/man/cat8/telnetd.0

TELNETD(8C)                                                        TELNETD(8C)


NAME
       telnetd - DARPA TELNET protocol server

SYNOPSIS
       /etc/telnetd

DESCRIPTION
       Telnetd  is  a  server which supports the DARPA standard TELNET virtual
       terminal protocol.  Telnetd is invoked  by  the  internet  server  (see
       inetd(8)), normally for requests to connect to the TELNET port as indi‐
       cated by the /etc/services file (see services(5)).

       Telnetd operates by allocating a pseudo-terminal  device  (see  pty(4))
       for a client, then creating a login process which has the slave side of
       the pseudo-terminal as stdin, stdout, and stderr.  Telnetd  manipulates
       the  master side of the pseudo-terminal, implementing the TELNET proto‐
       col and passing characters between the remote client and the login pro‐
       cess.

       When  a  TELNET  session is started up, telnetd sends TELNET options to
       the client side indicating a willingness to do remote echo  of  charac‐
       ters,  to  suppress  go ahead, and to receive terminal type information
       from the remote client.  If the remote client is  willing,  the  remote
       terminal  type  is  propagated  in the environment of the created login
       process.  The pseudo-terminal allocated to the client is configured  to
       operate  in  “cooked”  mode,  and  with  XTABS  and  CRMOD enabled (see
       tty(4)).

       Telnetd is willing to do: echo, binary, suppress go ahead,  and  timing
       mark.   Telnetd is willing to have the remote client do: binary, termi���
       nal type, and suppress go ahead.

SEE ALSO
       telnet(1C)

BUGS
       Some TELNET commands are only partially implemented.

       The TELNET protocol allows for the exchange of the number of lines  and
       columns on the user’s terminal, but telnetd doesn’t make use of them.

       Because  of  bugs  in the original 4.2 BSD telnet(1C), telnetd performs
       some dubious protocol exchanges to try to discover if the remote client
       is, in fact, a 4.2 BSD telnet(1C).

       Binary mode has no common interpretation except between similar operat‐
       ing systems (Unix in this case).

       The terminal type name received from the remote client is converted  to
       lower case.

       The packet interface to the pseudo-terminal (see pty(4)) should be used
       for more intelligent flushing of input and output queues.

       Telnetd never sends TELNET go ahead commands.


4.2 Berkeley Distribution        May 28, 1986                      TELNETD(8C)