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TELNETD(8)			   BSD System Manager's Manual			       TELNETD(8)

NAME
     telnetd -- DARPA TELNET protocol server

SYNOPSIS
     /usr/libexec/telnetd [-Uhlkns] [-D debugmode] [-Iinitid] [-S tos] [-X authtype]
			  [-a authmode] [-edebug] [-p loginprog] [-rlowpty-highpty] [-u len]
			  [-debug [port]]

DESCRIPTION
     The telnetd command is a server which supports the DARPA standard TELNET 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  Turn on authentication debugging code.

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

	     valid  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 mech-
		    anisms, 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    Disable the authentication code.  All user verification will happen through
		    the login(1) program.

     -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 several possible values for debugmode:

	     options   Print information about the negotiation of TELNET options.

	     report    Print the options information, plus some additional information about what
		       processing is going on.

	     netdata   Display the data stream received by telnetd.

	     ptydata   Display data written to the pty.

	     exercise  Has not been implemented yet.

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

     -edebug
	     If telnetd has been compiled with support for data encryption, then the -edebug
	     option may be used to enable encryption debugging code.

     -p loginprog
	     Specify an alternate login(1) command to run to complete the login.  The alternate
	     command must understand the same command arguments as the standard login.

     -h      Disable 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 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      Specify line mode. Try 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 vari-
	     able _SC_CRAY_NPTY configured, the default pty search range is 0 to _SC_CRAY_NPTY;
	     otherwise, 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 - char-
	     acter 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 fire-
	     wall.

     -S tos

     -u len  This option is used to specify the size of the field in the utmp structure that
	     holds the remote host name.  If the resolved host name is longer than len, the dot-
	     ted decimal value will be used instead.  This allows hosts with very long host names
	     that overflow this field to still be uniquely identified.	Specifying -u0 indicates
	     that only dotted decimal addresses should be put into the utmp file.

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

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

     Telnetd operates by allocating a pseudo-terminal device (see pty(4)) for a client, then cre-
     ating 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 indi-
     cating 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 indicate 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 telnetd will not be doing any terminal
			echoing, so the client should do any terminal echoing that is needed.

     WILL BINARY	Indicate 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		Indicate that it will not be sending IAC GA, go ahead, commands.

     WILL STATUS	Indicate 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	Indicate 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		Indicate 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	Indicate a desire to be able to request information about the speed of
			the serial line to which the client is attached.

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

     DO NEW-ENVIRON	Indicate a desire to be able to request environment variable information,
			as described in RFC 1572.

     DO ENVIRON 	Indicate a desire to be able to request environment 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 auto-
			matic login.

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

NOTES
     By default telnetd will read the he, hn, and im capabilities from /etc/gettytab and use that
     information (if present) to determine what to display before the login: prompt. You can also
     use a System V style /etc/issue file by using the if capability, which will override im.
     The information specified in either im or if will be displayed to both console and remote
     logins.

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

SEE ALSO
     bftp(1), login(1), gettytab(5), telnet(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 operating 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.

HISTORY
     IPv6 support was added by WIDE/KAME project.

BSD					  March 1, 1994 				      BSD
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