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TELNETD(8C)                                                        TELNETD(8C)

       telnetd, in.telnetd - TCP/IP TELNET protocol server


       This  program  is  available  with the Networking software installation
       option.  Refer to for information on how to install optional software.

       telnetd is a server which supports the TCP/IP standard  TELNET  virtual
       terminal  protocol.   telnetd  is  invoked  by the internet server (see
       inetd(8C)), normally for requests to connect  to  the  TELNET  port  as
       indicated 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 its standard input, output, and error.  telnetd
       manipulates the master side of the  pseudo-terminal,  implementing  the
       TELNET  protocol  and  passing characters between the remote client and
       the login process.

       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, ICRNL, and ONLCR enabled (see

       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.


       Postel, Jon, and Joyce Reynolds, ``Telnet Protocol Specification,'' RFC
       854, Network Information Center, SRI International, Menlo Park, Calif.,
       May 1983.

       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

       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.

       telnetd can only support 64 pseudo-terminals.

                               18 December 1989                    TELNETD(8C)