telnetd

NAME

       telnetd - DARPA TELNET protocol server

SYNOPSIS

       /etc/telnetd  [-debug  [port]] [-l] [-L login_program] [-D
       options] [-D report] [-D exercise] [-D netdata]  [-D  pty-
       data]

DESCRIPTION

       Telnetd is a server which supports the DARPA standard TEL-
       NET 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/ser-
       vices  file (see services(5)).  If the -debug may be used,
       to start up telnetd manually, instead of through inetd(8).
       If  started up this way, port may be specified to run tel-
       netd on an alternate TCP port number.

       The -D option may be used for  debugging  purposes.   This
       allows  telnet  to  print out debugging information to the
       connection, allowing the  user  to  see  what  telnetd  is
       doing.  There are several modifiers: options prints infor-
       mation about the negotiation  of  TELNET  options,  report
       prints  the  options  information,  plus  some  additional
       information about what processing  is  going  on,  netdata
       displays the data stream received by telnetd, ptydata dis-
       plays data written to the pty, and exercise has  not  been
       implemented yet.

       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 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, to do
       remote flow control, and to receive terminal type informa-
       tion, terminal speed information, and window size informa-
       tion 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-ter-
       minal  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:  linemode,  binary,  terminal  type,  terminal
       speed, window size, toggle flow  control,  environment,  X
       display location, and suppress go ahead.
       If  the  file /etc/issue.net is present, telnetd will show
       its contents before the login prompt of a  telnet  session
       (see issue.net(5)).

SEE ALSO

       telnet(1), issue.net(5)

BUGS

       Some TELNET commands are only partially implemented.

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

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

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

       Telnetd never sends TELNET go ahead commands.