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TELNETD(8)							    TELNETD(8)

NAME
       telnetd - DARPA TELNET protocol server

SYNOPSIS
       /usr/libexec/telnetd  [-a  authmode]  [-B]  [-D]	 [debugmode] [-e] [-h]
       [-Iinitid] [-l] [-k] [-n] [-rlowpty-highpty] [-s]  [-S  tos]  [-U]  [-X
       authtype] [-w [ip|maxhostlen[,[no]striplocal]]] [-debug [port]]

DESCRIPTION
       The  telnetd command is a server which supports the DARPA standard TEL‐
       NET virtual terminal protocol.  Telnetd	is  normally  invoked  by  the
       internet	 server	 (see  inetd(8)	 for requests to connect to the TELNET
       port as indicated by the /etc/services  file  (see  services(5)).   The
       -debug  option  may  be	used  to start up telnetd manually, instead of
       through inetd(8).  If started up this way, port may be specified to run
       telnetd on an alternate TCP port number.

       The telnetd command accepts the following options:

       -a authmode
	      This  option may be used for specifying what mode should be used
	      for authentication.  Note that this option  is  only  useful  if
	      telnetd  has  been  compiled with support for the AUTHENTICATION
	      option.  There are several valid values for authmode:

	      debug  Turns on authentication debugging code.

	      valid  Only allow connections when the remote user  can  provide
		     valid  authentication  information to identify the remote
		     user, and is allowed  access  to  the  specified  account
		     without providing a password.

	      user   Only  allow  connections when the remote user can provide
		     valid authentication information to identify  the	remote
		     user.   The  login(1) command will provide any additional
		     user verification	needed	if  the	 remote	 user  is  not
		     allowed automatic access to the specified account.

	      other  Only  allow  connections  that supply some authentication
		     information.  This option is currently not	 supported  by
		     any  of  the  existing  authentication mechanisms, and is
		     thus the same as specifying -a valid.

	      none   This is the default state.	 Authentication information is
		     not  required.   If  no  or  insufficient	authentication
		     information is provided, then the login(1)	 program  will
		     provide the necessary user verification.

	      off    This  disables the authentication code.  All user verifi‐
		     cation will happen through the login(1) program.

       -B     Specifies bftp server mode.  In this mode, telnetd causes	 login
	      to  start a bftp(1) session rather than the user's normal shell.
	      In bftp daemon mode, normal logins are  not  supported,  and  it
	      must be used on a port other than the normal TELNET port.

       -D debugmode
	      This  option  may	 be  used for debugging purposes.  This allows
	      telnetd to print out debugging information  to  the  connection,
	      allowing	the user to see what telnetd is doing.	There are sev‐
	      eral possible values for debugmode:

	      options
		     Prints  information  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
		     Displays data written to the pty.

	      encrypt
		     Enables   encryption debugging code.

	      exercise
		     Has not been implemented yet.

       -debug Enables  debugging  on  each  socket  created  by	 telnetd  (see
	      SO_DEBUG in socket(2)).

       -e     This option causes telnetd to refuse unencrypted connections.

       -h     Disables	the printing of host-specific information before login
	      has been completed.

       -I initid
	      This option is only applicable to UNICOS systems prior  to  7.0.
	      It  specifies  the  ID from /etc/inittab to use when init starts
	      login sessions.  The default ID is fe.

       -k     This option is only useful if telnetd  has  been	compiled  with
	      both  linemode and kludge linemode support.  If the -k option is
	      specified, then if  the  remote  client  does  not  support  the
	      LINEMODE	option,	 then  telnetd	will operate in character at a
	      time mode.  It will still support kludge linemode, but will only
	      go into kludge linemode if the remote client requests it.	 (This
	      is done by by the client sending DONT SUPPRESS-GO-AHEAD and DONT
	      ECHO.)   The  -k	option	is  most  useful when there are remote
	      clients that do  not  support  kludge  linemode,	but  pass  the
	      heuristic	 (if they respond with WILL TIMING-MARK in response to
	      a DO TIMING-MARK) for kludge linemode support.

       -l     Specifies line mode.  Tries to force clients to  use  line-at-a-
	      time  mode.  If the LINEMODE option is not supported, it will go
	      into kludge linemode.

       -n     Disable TCP keep-alives.	Normally telnetd enables the TCP keep-
	      alive  mechanism	to  probe  connections that have been idle for
	      some period of time to determine if the client is	 still	there,
	      so  that idle connections from machines that have crashed or can
	      no longer be reached may be cleaned up.

       -r lowpty-highpty
	      This option is only enabled when telnetd is compiled for UNICOS.
	      It  specifies  an	 inclusive range of pseudo-terminal devices to
	      use.  If the system has sysconf variable	_SC_CRAY_NPTY  config‐
	      ured, the default pty search range is 0 to _SC_CRAY_NPTY; other‐
	      wise, the default range is 0 to 128.  Either lowpty  or  highpty
	      may be omitted to allow changing either end of the search range.
	      If lowpty is omitted, the - character is still required so  that
	      telnetd can differentiate highpty from lowpty.

       -s     This  option is only enabled if telnetd is compiled with support
	      for SecurID cards.  It causes the -s option to be passed	on  to
	      login(1),	 and  thus  is only useful if login(1) supports the -s
	      flag to indicate that only SecurID validated logins are allowed,
	      and is usually useful for controlling remote logins from outside
	      of a firewall.

       -S tos

       -U     This option causes telnetd to refuse connections from  addresses
	      that cannot be mapped back into a symbolic name via the gethost‐
	      byaddr(3) routine.

       -w [ip|maxhostlen[,[no]striplocal]]
	      Controls the form of the remote  hostname	 passed	 to  login(1).
	      Specifying  ip  results  in  the numeric IP address always being
	      passed to login(1).  Specifying a number, maxhostlen,  sets  the
	      maximum length of the hostname passed to login(1) before it will
	      be passed as a numeric IP address.  If maxhostlen is 0, then the
	      system  default,	as determined by the utmp or utmpx structures,
	      is used.	The nostriplocal and striplocal options, which must be
	      preceded	by  a  comma,  control	whether	 or not the local host
	      domain is stripped from the remote hostname.   By	 default,  the
	      equivalent of striplocal is in effect.

       -X authtype
	      This option is only valid if telnetd has been built with support
	      for the authentication option.  It disables the use of  authtype
	      authentication,  and  can	 be used to temporarily disable a spe‐
	      cific authentication type without having to recompile telnetd.

       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
       process.

       When  a	TELNET	session is started up, telnetd sends TELNET options to
       the client side indicating a willingness to  do	the  following	TELNET
       options, which are described in more detail below:

	    DO AUTHENTICATION
	    WILL ENCRYPT
	    DO TERMINAL TYPE
	    DO TSPEED
	    DO XDISPLOC
	    DO NEW-ENVIRON
	    DO ENVIRON
	    WILL SUPPRESS GO AHEAD
	    DO ECHO
	    DO LINEMODE
	    DO NAWS
	    WILL STATUS
	    DO LFLOW
	    DO TIMING-MARK

       The pseudo-terminal allocated to the client is configured to operate in
       “cooked” mode, and with XTABS and CRMOD enabled (see tty(4)).

       Telnetd has support for enabling locally the following TELNET options:

       WILL ECHO	    When the LINEMODE option is enabled, a  WILL  ECHO
			    or	WONT  ECHO will be sent to the client to indi‐
			    cate the current state of terminal echoing.	  When
			    terminal  echo is not desired, a WILL ECHO is sent
			    to indicate that telnetd will take care of echoing
			    any	 data that needs to be echoed to the terminal,
			    and then nothing is echoed.	 When terminal echo is
			    desired, a WONT ECHO is sent to indicate that tel‐
			    netd will not be doing any	terminal  echoing,  so
			    the	 client should do any terminal echoing that is
			    needed.

       WILL BINARY	    Indicates that the client is willing to send  a  8
			    bits of data, rather than the normal 7 bits of the
			    Network Virtual Terminal.

       WILL SGA		    Indicates that it will not be sending IAC  GA,  go
			    ahead, commands.

       WILL STATUS	    Indicates  a  willingness to send the client, upon
			    request, of	 the  current  status  of  all	TELNET
			    options.

       WILL TIMING-MARK	    Whenever  a DO TIMING-MARK command is received, it
			    is always responded to with a WILL TIMING-MARK

       WILL LOGOUT	    When a DO LOGOUT is received,  a  WILL  LOGOUT  is
			    sent  in  response, and the TELNET session is shut
			    down.

       WILL ENCRYPT	    Only sent if telnetd is compiled with support  for
			    data  encryption,  and  indicates a willingness to
			    decrypt the data stream.

       Telnetd has support for enabling remotely the following TELNET options:

       DO BINARY	     Sent to  indicate	that  telnetd  is  willing  to
			     receive an 8 bit data stream.

       DO LFLOW		     Requests  that  the  client  handle  flow control
			     characters remotely.

       DO ECHO		     This is not really	 supported,  but  is  sent  to
			     identify  a  4.2BSD  telnet(1) client, which will
			     improperly respond with WILL  ECHO.   If  a  WILL
			     ECHO  is  received,  a  DONT ECHO will be sent in
			     response.

       DO TERMINAL-TYPE	     Indicates a desire to be able to request the name
			     of	 the  type of terminal that is attached to the
			     client side of the connection.

       DO SGA		     Indicates that it does not need  to  receive  IAC
			     GA, the go ahead command.

       DO NAWS		     Requests  that  the client inform the server when
			     the window (display) size changes.

       DO TERMINAL-SPEED     Indicates a desire to be able to request informa‐
			     tion  about the speed of the serial line to which
			     the client is attached.

       DO XDISPLOC	     Indicates a desire to be able to request the name
			     of	 the X windows display that is associated with
			     the telnet client.

       DO NEW-ENVIRON	     Indicates a desire to be able to request environ‐
			     ment  variable  information,  as described in RFC
			     1572.

       DO ENVIRON	     Indicates a desire to be able to request environ‐
			     ment  variable  information,  as described in RFC
			     1408.

       DO LINEMODE	     Only sent if telnetd is compiled with support for
			     linemode, and requests that the client do line by
			     line processing.

       DO TIMING-MARK	     Only sent if telnetd is compiled with support for
			     both linemode and kludge linemode, and the client
			     responded with  WONT  LINEMODE.   If  the	client
			     responds with WILL TM, the it is assumed that the
			     client supports kludge linemode.  Note  that  the
			     -k option can be used to disable this.

       DO AUTHENTICATION     Only sent if telnetd is compiled with support for
			     authentication, and indicates  a  willingness  to
			     receive  authentication information for automatic
			     login.

       DO ENCRYPT	     Only sent if telnetd is compiled with support for
			     data  encryption,	and indicates a willingness to
			     decrypt the data stream.

FILES
       /etc/services
       /etc/inittab (UNICOS systems only)
       /etc/iptos (if supported)
       /usr/ucb/bftp (if supported)

SEE ALSO
       telnet(1), login(1), bftp(1) (if supported)

STANDARDS
       RFC-854	   TELNET PROTOCOL SPECIFICATION
       RFC-855	   TELNET OPTION SPECIFICATIONS
       RFC-856	   TELNET BINARY TRANSMISSION
       RFC-857	   TELNET ECHO OPTION
       RFC-858	   TELNET SUPPRESS GO AHEAD OPTION
       RFC-859	   TELNET STATUS OPTION
       RFC-860	   TELNET TIMING MARK OPTION
       RFC-861	   TELNET EXTENDED OPTIONS - LIST OPTION
       RFC-885	   TELNET END OF RECORD OPTION
       RFC-1073	   Telnet Window Size Option
       RFC-1079	   Telnet Terminal Speed Option
       RFC-1091	   Telnet Terminal-Type Option
       RFC-1096	   Telnet X Display Location Option
       RFC-1123	   Requirements for Internet Hosts -- Application and Support
       RFC-1184	   Telnet Linemode Option
       RFC-1372	   Telnet Remote Flow Control Option
       RFC-1416	   Telnet Authentication Option
       RFC-1411	   Telnet Authentication: Kerberos Version 4
       RFC-1412	   Telnet Authentication: SPX
       RFC-1571	   Telnet Environment Option Interoperability Issues
       RFC-1572	   Telnet Environment Option

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 discover if the remote client
       is, in fact, a 4.2 BSD telnet(1).

       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.

       Telnetd never sends TELNET IAC GA (go ahead) commands.

								    TELNETD(8)
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