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RedHat 9 (Linux i386) - man page for in.telnetd (redhat section 8)

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

NAME
     telnetd -- DARPA telnet protocol server

SYNOPSIS
     /usr/sbin/in.telnetd [-hns] [-a authmode] [-D debugmode] [-L loginprg] [-S tos]
			  [-X authtype] [-edebug] [-debug port]

DESCRIPTION
     The telnetd program is a server which supports the DARPA telnet interactive communication
     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 program accepts the following options:

     -a authmode  This option may be used for specifying what mode should be used for authentica-
		  tion.  Note that this option is only useful if telnetd has been compiled with
		  support for authentication, which is not available in the current version.  The
		  following values of authmode are understood:

		  debug  Turns on authentication debugging code.

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

		  valid  Only allow connections when the remote user can provide valid authenti-
			 cation 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 authenti-
			 cation mechanisms, and is thus the same as specifying 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 verification will hap-
			 pen 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   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.

		  exercise  Has not been implemented yet.

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

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

     -L loginprg  This option may be used to specify a different login program.  By default,
		  /bin/login is used.

     -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.

     -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. This is usually useful for controlling remote logins from
		  outside of a firewall.

     -S tos	  Sets the IP type-of-service (TOS) option for the telnet connection to the value
		  tos.

     -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 specific authentication type without having to
		  recompile telnetd.

     If the file /etc/issue.net is present, telnetd will display its contents before the login
     prompt of a telnet session (see issue.net(5)).

     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 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	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 information 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 dis-
			play that is associated with the telnet client.

     DO NEW-ENVIRON	Indicates a desire to be able to request environment variable informa-
			tion, as described in RFC 1572.

     DO ENVIRON 	Indicates a desire to be able to request environment variable informa-
			tion, 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.  issue.net(5)).

FILES
     /etc/services, /etc/issue.net

SEE ALSO
     telnet(1), login(1), issue.net(5),

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.

     The source code is not comprehensible.

Linux NetKit (0.17)			December 29, 1996		      Linux NetKit (0.17)


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