TELNETD(8C)                          BSD                           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
     indicated by the /etc/services file (see services(5)).

     telnetd operates by allocating a pseudoterminal device (see pty(4)) for a
     client, then creating a login process which has the slave side of the
     pseudoterminal as stdin, stdout, and stderr.  telnetd manipulates the
     master side of the pseudoterminal, 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 characters, 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
     pseudoterminal 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, terminal
     type, and suppress go ahead.

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 4.2BSD telnet, telnetd performs some
     dubious protocol exchanges to try to discover if the remote client is, in
     fact, a 4.2BSD telnet.

     Binary mode has no common interpretation except between similar operating
     systems (the UNIX system in this case).

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

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

     telnetd never sends TELNET go ahead commands.

SEE ALSO
     telnet(1C)