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TELNET(1)		  BSD General Commands Manual		     TELNET(1)

NAME
     telnet — user interface to the TELNET protocol

SYNOPSIS
     telnet [-468ELadr] [-S tos] [-b address] [-e escapechar] [-l user]
	    [-n tracefile] [host [port]]

DESCRIPTION
     The telnet command is used for interactive communication with another
     host using the TELNET protocol. It begins in command mode, where it
     prints a telnet prompt ("telnet> "). If telnet is invoked with a host
     argument, it performs an open command implicitly; see the description
     below.

     Options:

     -4	     Force IPv4 address resolution.

     -6	     Force IPv6 address resolution.

     -8	     Request 8-bit operation. This causes an attempt to negotiate the
	     TELNET BINARY option for both input and output. By default telnet
	     is not 8-bit clean.

     -E	     Disables the escape character functionality; that is, sets the
	     escape character to ``no character''.

     -L	     Specifies an 8-bit data path on output.  This causes the TELNET
	     BINARY option to be negotiated on just output.

     -a	     Attempt automatic login.  Currently, this sends the user name via
	     the USER variable of the ENVIRON option if supported by the
	     remote system. The username is retrieved via getlogin(3).

     -b address
	     Use bind(2) on the local socket to bind it to a specific local
	     address.

     -d	     Sets the initial value of the debug toggle to TRUE.

     -r	     Emulate rlogin(1).	 In this mode, the default escape character is
	     a tilde. Also, the interpretation of the escape character is
	     changed: an escape character followed by a dot causes telnet to
	     disconnect from the remote host. A ^Z instead of a dot suspends
	     telnet, and a ^] (the default telnet escape character) generates
	     a normal telnet prompt. These codes are accepted only at the
	     beginning of a line.

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

     -e escapechar
	     Sets the escape character to escapechar. If no character is sup‐
	     plied, no escape character will be used.  Entering the escape
	     character while connected causes telnet to drop to command mode.

     -l user
	     Specify user as the user to log in as on the remote system. This
	     is accomplished by sending the specified name as the USER envi‐
	     ronment variable, so it requires that the remote system support
	     the TELNET ENVIRON option. This option implies the -a option, and
	     may also be used with the open command.

     -n tracefile
	     Opens tracefile for recording trace information.  See the set
	     tracefile command below.

     host    Specifies a host to contact over the network.

     port    Specifies a port number or service name to contact. If not speci‐
	     fied, the telnet port (23) is used.

     Protocol:

     Once a connection has been opened, telnet will attempt to enable the
     TELNET LINEMODE option.  If this fails, then telnet will revert to one of
     two input modes: either “character at a time” or “old line by line”
     depending on what the remote system supports.

     When LINEMODE is enabled, character processing is done on the local sys‐
     tem, under the control of the remote system.  When input editing or char‐
     acter echoing is to be disabled, the remote system will relay that infor‐
     mation.  The remote system will also relay changes to any special charac‐
     ters that happen on the remote system, so that they can take effect on
     the local system.

     In “character at a time” mode, most text typed is immediately sent to the
     remote host for processing.

     In “old line by line” mode, all text is echoed locally, and (normally)
     only completed lines are sent to the remote host.	The “local echo char‐
     acter” (initially “^E”) may be used to turn off and on the local echo
     (this would mostly be used to enter passwords without the password being
     echoed).

     If the LINEMODE option is enabled, or if the localchars toggle is TRUE
     (the default for “old line by line“; see below), the user's quit, intr,
     and flush characters are trapped locally, and sent as TELNET protocol
     sequences to the remote side.  If LINEMODE has ever been enabled, then
     the user's susp and eof are also sent as TELNET protocol sequences, and
     quit is sent as a TELNET ABORT instead of BREAK There are options (see
     toggle autoflush and toggle autosynch below) which cause this action to
     flush subsequent output to the terminal (until the remote host acknowl‐
     edges the TELNET sequence) and flush previous terminal input (in the case
     of quit and intr).

     Commands:

     The following telnet commands are available. Unique prefixes are under‐
     stood as abbreviations.

     auth argument ...
		The auth command controls the TELNET AUTHENTICATE protocol
		option.	 If telnet was compiled without authentication, the
		auth command will not be supported.  Valid arguments are as
		follows:

		disable type  Disable the specified type of authentication.
			      To obtain a list of available types, use the
			      auth disable ? command.

		enable type   Enable the specified type of authentication.  To
			      obtain a list of available types, use the auth
			      enable ? command.

		status	      List the current status of the various types of
			      authentication.

		Note that the current version of telnet does not support
		authentication.

     close	Close the connection to the remote host, if any, and return to
		command mode.

     display argument ...
		Display all, or some, of the set and toggle values (see
		below).

     encrypt argument ...
		The encrypt command controls the TELNET ENCRYPT protocol
		option. If telnet was compiled without encryption, the encrypt
		command will not be supported.

		Valid arguments are as follows:

		disable type [input|output]
			      Disable the specified type of encryption.	 If
			      you do not specify input or output, encryption
			      of both is disabled.  To obtain a list of avail‐
			      able types, use ``encrypt disable ?''.

		enable type [input|output]
			      Enable the specified type of encryption.	If you
			      do not specify input or output, encryption of
			      both is enabled.	To obtain a list of available
			      types, use ``encrypt enable ?''.

		input	      This is the same as ``encrypt start input''.

		-input	      This is the same as ``encrypt stop input''.

		output	      This is the same as ``encrypt start output''.

		-output	      This is the same as ``encrypt stop output''.

		start [input|output]
			      Attempt to begin encrypting.  If you do not
			      specify input or output, encryption of both
			      input and output is started.

		status	      Display the current status of the encryption
			      module.

		stop [input|output]
			      Stop encrypting.	If you do not specify input or
			      output, encryption of both is stopped.

		type type     Sets the default type of encryption to be used
			      with later ``encrypt start'' or ``encrypt stop''
			      commands.

		Note that the current version of telnet does not support
		encryption.

     environ arguments...
		The environ command is used to propagate environment variables
		across the telnet link using the TELNET ENVIRON protocol
		option.	 All variables exported from the shell are defined,
		but only the DISPLAY and PRINTER variables are marked to be
		sent by default.  The USER variable is marked to be sent if
		the -a or -l command-line options were used.

		Valid arguments for the environ command are:

		define variable value
			    Define the variable variable to have a value of
			    value. Any variables defined by this command are
			    automatically marked for propagation
			    (``exported'').  The value may be enclosed in sin‐
			    gle or double quotes so that tabs and spaces may
			    be included.

		undefine variable
			    Remove any existing definition of variable.

		export variable
			    Mark the specified variable for propagation to the
			    remote host.

		unexport variable
			    Do not mark the specified variable for propagation
			    to the remote host. The remote host may still ask
			    explicitly for variables that are not exported.

		list	    List the current set of environment variables.
			    Those marked with a * will be propagated to the
			    remote host. The remote host may still ask explic‐
			    itly for the rest.

		?	    Prints out help information for the environ com‐
			    mand.

     logout	Send the TELNET LOGOUT protocol option to the remote host.
		This command is similar to a close command. If the remote host
		does not support the LOGOUT option, nothing happens.  But if
		it does, this command should cause it to close the connection.
		If the remote side also supports the concept of suspending a
		user's session for later reattachment, the logout command
		indicates that the session should be terminated immediately.

     mode type	Type is one of several options, depending on the state of the
		session.  Telnet asks the remote host to go into the requested
		mode. If the remote host says it can, that mode takes effect.

		character     Disable the TELNET LINEMODE option, or, if the
			      remote side does not understand the LINEMODE
			      option, then enter “character at a time“ mode.

		line	      Enable the TELNET LINEMODE option, or, if the
			      remote side does not understand the LINEMODE
			      option, then attempt to enter “old-line-by-line“
			      mode.

		isig (-isig)  Attempt to enable (disable) the TRAPSIG mode of
			      the LINEMODE option.  This requires that the
			      LINEMODE option be enabled.

		edit (-edit)  Attempt to enable (disable) the EDIT mode of the
			      LINEMODE option.	This requires that the
			      LINEMODE option be enabled.

		softtabs (-softtabs)
			      Attempt to enable (disable) the SOFT_TAB mode of
			      the LINEMODE option.  This requires that the
			      LINEMODE option be enabled.

		litecho (-litecho)
			      Attempt to enable (disable) the LIT_ECHO mode of
			      the LINEMODE option.  This requires that the
			      LINEMODE option be enabled.

		?	      Prints out help information for the mode com‐
			      mand.

     open host [[-l] user][- port]
		Open a connection to the named host.  If no port number is
		specified, telnet will attempt to contact a telnet daemon at
		the standard port (23).	 The host specification may be a host
		name or IP address.  The -l option may be used to specify a
		user name to be passed to the remote system, like the -l com‐
		mand-line option.

		When connecting to ports other than the telnet port, telnet
		does not attempt telnet protocol negotiations. This makes it
		possible to connect to services that do not support the telnet
		protocol without making a mess. Protocol negotiation can be
		forced by placing a dash before the port number.

		After establishing a connection, any commands associated with
		the remote host in /etc/telnetrc and the user's .telnetrc file
		are executed, in that order.

		The format of the telnetrc files is as follows: Lines begin‐
		ning with a #, and blank lines, are ignored.  The rest of the
		file should consist of hostnames and sequences of telnet com‐
		mands to use with that host. Commands should be one per line,
		indented by whitespace; lines beginning without whitespace are
		interpreted as hostnames.  Lines beginning with the special
		hostname ‘DEFAULT’ will apply to all hosts.  Hostnames includ‐
		ing ‘DEFAULT’ may be followed immediately by a colon and a
		port number or string.	If a port is specified it must match
		exactly with what is specified on the command line.  If no
		port was specified on the command line, then the value
		‘telnet’ is used.  Upon connecting to a particular host, the
		commands associated with that host are executed.

     quit	Close any open session and exit telnet.	 An end of file condi‐
		tion on input, when in command mode, will trigger this opera‐
		tion as well.

     send arguments
		Send one or more special telnet protocol character sequences
		to the remote host.  The following are the codes which may be
		specified (more than one may be used in one command):

		abort	Sends the TELNET ABORT (Abort Processes) sequence.

		ao	Sends the TELNET AO (Abort Output) sequence, which
			should cause the remote system to flush all output
			from the remote system to the user's terminal.

		ayt	Sends the TELNET AYT (Are You There?) sequence, to
			which the remote system may or may not choose to
			respond.

		brk	Sends the TELNET BRK (Break) sequence, which may have
			significance to the remote system.

		ec	Sends the TELNET EC (Erase Character) sequence, which
			should cause the remote system to erase the last char‐
			acter entered.

		el	Sends the TELNET EL (Erase Line) sequence, which
			should cause the remote system to erase the line cur‐
			rently being entered.

		eof	Sends the TELNET EOF (End Of File) sequence.

		eor	Sends the TELNET EOR (End of Record) sequence.

		escape	Sends the current telnet escape character.

		ga	Sends the TELNET GA (Go Ahead) sequence, which likely
			has no significance to the remote system.

		getstatus
			If the remote side supports the TELNET STATUS command,
			getstatus will send the subnegotiation to request that
			the server send its current option status.

		ip	Sends the TELNET IP (Interrupt Process) sequence,
			which should cause the remote system to abort the cur‐
			rently running process.

		nop	Sends the TELNET NOP (No Operation) sequence.

		susp	Sends the TELNET SUSP (Suspend Process) sequence.

		synch	Sends the TELNET SYNCH sequence.  This sequence causes
			the remote system to discard all previously typed (but
			not yet read) input.  This sequence is sent as TCP
			urgent data (and may not work if the remote system is
			a 4.2BSD system -- if it doesn't work, a lower case
			“r” may be echoed on the terminal).

		do cmd

		dont cmd

		will cmd

		wont cmd
			Sends the TELNET DO cmd sequence.  cmd can be either a
			decimal number between 0 and 255, or a symbolic name
			for a specific TELNET command.	cmd can also be either
			help or ? to print out help information, including a
			list of known symbolic names.

		?	Prints out help information for the send command.

     set argument value

     unset argument value
		The set command will set any one of a number of telnet vari‐
		ables to a specific value or to TRUE.  The special value off
		turns off the function associated with the variable. This is
		equivalent to using the unset command.	The unset command will
		disable or set to FALSE any of the specified variables.	 The
		values of variables may be interrogated with the display com‐
		mand.  The variables which may be set or unset, but not tog‐
		gled, are listed here.	In addition, any of the variables for
		the toggle command may be explicitly set or unset.

		ayt	If telnet is in localchars mode, or LINEMODE is
			enabled, and the status character is typed, a TELNET
			AYT sequence is sent to the remote host.  The initial
			value for the "Are You There" character is the termi‐
			nal's status character.

		echo	This is the value (initially “^E”) which, when in
			“line by line” mode, toggles between doing local echo‐
			ing of entered characters (for normal processing), and
			suppressing echoing of entered characters (for enter‐
			ing, say, a password).

		eof	If telnet is operating in LINEMODE or “old line by
			line” mode, entering this character as the first char‐
			acter on a line will cause this character to be sent
			to the remote system.  The initial value of the eof
			character is taken to be the terminal's eof character.

		erase	If telnet is in localchars mode (see toggle localchars
			below), and if telnet is operating in “character at a
			time” mode, then when this character is typed, a
			TELNET EC sequence (see send ec above) is sent to the
			remote system.	The initial value for the erase char‐
			acter is taken to be the terminal's erase character.

		escape	This is the telnet escape character (initially “^[”)
			which causes entry into telnet command mode (when con‐
			nected to a remote system).

		flushoutput
			If telnet is in localchars mode (see toggle localchars
			below) and the flushoutput character is typed, a
			TELNET AO sequence (see send ao above) is sent to the
			remote host.  The initial value for the flush charac‐
			ter is taken to be the terminal's flush character.

		forw1

		forw2	If TELNET is operating in LINEMODE, these are the
			characters that, when typed, cause partial lines to be
			forwarded to the remote system.	 The initial value for
			the forwarding characters are taken from the termi‐
			nal's eol and eol2 characters.

		interrupt
			If telnet is in localchars mode (see toggle localchars
			below) and the interrupt character is typed, a TELNET
			IP sequence (see send ip above) is sent to the remote
			host.  The initial value for the interrupt character
			is taken to be the terminal's intr character.

		kill	If telnet is in localchars mode (see toggle localchars
			below), and if telnet is operating in “character at a
			time” mode, then when this character is typed, a
			TELNET EL sequence (see send el above) is sent to the
			remote system.	The initial value for the kill charac‐
			ter is taken to be the terminal's kill character.

		lnext	If telnet is operating in LINEMODE or “old line by
			line“ mode, then this character is taken to be the
			terminal's lnext character.  The initial value for the
			lnext character is taken to be the terminal's lnext
			character.

		quit	If telnet is in localchars mode (see toggle localchars
			below) and the quit character is typed, a TELNET BRK
			sequence (see send brk above) is sent to the remote
			host.  The initial value for the quit character is
			taken to be the terminal's quit character.

		reprint
			If telnet is operating in LINEMODE or “old line by
			line“ mode, then this character is taken to be the
			terminal's reprint character.  The initial value for
			the reprint character is taken to be the terminal's
			reprint character.

		rlogin	This is the rlogin mode escape character. Setting it
			enables rlogin mode, as with the r command-line option
			(q.v.)

		start	If the TELNET TOGGLE-FLOW-CONTROL option has been
			enabled, then this character is taken to be the termi‐
			nal's start character.	The initial value for the kill
			character is taken to be the terminal's start charac‐
			ter.

		stop	If the TELNET TOGGLE-FLOW-CONTROL option has been
			enabled, then this character is taken to be the termi‐
			nal's stop character.  The initial value for the kill
			character is taken to be the terminal's stop charac‐
			ter.

		susp	If telnet is in localchars mode, or LINEMODE is
			enabled, and the suspend character is typed, a TELNET
			SUSP sequence (see send susp above) is sent to the
			remote host.  The initial value for the suspend char‐
			acter is taken to be the terminal's suspend character.

		tracefile
			This is the file to which the output, caused by
			netdata or option tracing being TRUE, will be written.
			If it is set to “-”, then tracing information will be
			written to standard output (the default).

		worderase
			If telnet is operating in LINEMODE or “old line by
			line“ mode, then this character is taken to be the
			terminal's worderase character.	 The initial value for
			the worderase character is taken to be the terminal's
			worderase character.

		?	Displays the legal set (unset) commands.

     slc state	The slc command (Set Local Characters) is used to set or
		change the state of the the special characters when the TELNET
		LINEMODE option has been enabled.  Special characters are
		characters that get mapped to TELNET commands sequences (like
		ip or quit) or line editing characters (like erase and kill).
		By default, the local special characters are exported.

		check	    Verify the current settings for the current spe‐
			    cial characters.  The remote side is requested to
			    send all the current special character settings,
			    and if there are any discrepancies with the local
			    side, the local side will switch to the remote
			    value.

		export	    Switch to the local defaults for the special char‐
			    acters.  The local default characters are those of
			    the local terminal at the time when telnet was
			    started.

		import	    Switch to the remote defaults for the special
			    characters.	 The remote default characters are
			    those of the remote system at the time when the
			    TELNET connection was established.

		?	    Prints out help information for the slc command.

     status	Show the current status of telnet.  This includes the name of
		the remote host, if any, as well as the current mode.

     toggle arguments ...
		Toggle (between TRUE and FALSE) various flags that control how
		telnet responds to events.  These flags may be set explicitly
		to TRUE or FALSE using the set and unset commands.  More than
		one flag may be toggled at once.  The state of these flags may
		be examined with the display command.  Valid flags are:

		authdebug     Turns on debugging for the authentication code.
			      This flag only exists if authentication support
			      is enabled.

		autoflush     If autoflush and localchars are both TRUE, then
			      when the ao, or quit characters are recognized
			      (and transformed into TELNET sequences; see set
			      above for details), telnet refuses to display
			      any data on the user's terminal until the remote
			      system acknowledges (via a TELNET TIMING MARK
			      option) that it has processed those TELNET
			      sequences.  The initial value for this toggle is
			      TRUE if the terminal user had not done an "stty
			      noflsh", otherwise FALSE (see stty(1)).

		autodecrypt   When the TELNET ENCRYPT option is negotiated, by
			      default the actual encryption (decryption) of
			      the data stream does not start automatically.
			      The autoencrypt (autodecrypt) command states
			      that encryption of the output (input) stream
			      should be enabled as soon as possible.

			      Note that this flag exists only if encryption
			      support is enabled.

		autologin     If the remote side supports the TELNET
			      AUTHENTICATION option, telnet attempts to use it
			      to perform automatic authentication.  If the
			      TELNET AUTHENTICATION option is not supported,
			      the user's login name is propagated using the
			      TELNET ENVIRON option.  Setting this flag is the
			      same as specifying the a option to the open com‐
			      mand or on the command line.

		autosynch     If autosynch and localchars are both TRUE, then
			      when either the intr or quit characters is typed
			      (see set above for descriptions of the intr and
			      quit characters), the resulting telnet sequence
			      sent is followed by the TELNET SYNCH sequence.
			      This procedure should cause the remote system to
			      begin throwing away all previously typed input
			      until both of the telnet sequences have been
			      read and acted upon.  The initial value of this
			      toggle is FALSE.

		binary	      Enable or disable the TELNET BINARY option on
			      both input and output.

		inbinary      Enable or disable the TELNET BINARY option on
			      input.

		outbinary     Enable or disable the TELNET BINARY option on
			      output.

		crlf	      If this is TRUE, then carriage returns will be
			      sent as <CR><LF>.	 If this is FALSE, then car‐
			      riage returns will be send as <CR><NUL>.	The
			      initial value for this toggle is FALSE.

		crmod	      Toggle carriage return mode.  When this mode is
			      enabled, most carriage return characters
			      received from the remote host will be mapped
			      into a carriage return followed by a line feed.
			      This mode does not affect those characters typed
			      by the user, only those received from the remote
			      host.  This mode is not very useful unless the
			      remote host only sends carriage return, but
			      never line feed.	The initial value for this
			      toggle is FALSE.

		debug	      Toggles socket level debugging (useful only to
			      the super user).	The initial value for this
			      toggle is FALSE.

		encdebug      Turns on debugging information for the encryp‐
			      tion code.  Note that this flag only exists if
			      encryption support is available.

		localchars    If this is TRUE, then the flush, interrupt,
			      quit, erase, and kill characters (see set above)
			      are recognized locally, and transformed into
			      (hopefully) appropriate TELNET control sequences
			      (respectively ao, ip, brk, ec, and el; see send
			      above).  The initial value for this toggle is
			      TRUE in “old line by line” mode, and FALSE in
			      “character at a time” mode.  When the LINEMODE
			      option is enabled, the value of localchars is
			      ignored, and assumed to always be TRUE.  If
			      LINEMODE has ever been enabled, then quit is
			      sent as abort, and eof and are sent as eof and
			      susp, see send above).

		netdata	      Toggles the display of all network data (in
			      hexadecimal format).  The initial value for this
			      toggle is FALSE.

		options	      Toggles the display of some internal telnet pro‐
			      tocol processing (having to do with telnet
			      options).	 The initial value for this toggle is
			      FALSE.

		prettydump    When the netdata toggle is enabled, if
			      prettydump is enabled the output from the
			      netdata command will be formatted in a more
			      user-readable format.  Spaces are put between
			      each character in the output, and the beginning
			      of telnet escape sequences are preceded by a '*'
			      to aid in locating them.

		skiprc	      When the skiprc toggle is TRUE, telnet does not
			      read the telnetrc files.	The initial value for
			      this toggle is FALSE.

		termdata      Toggles the display of all terminal data (in
			      hexadecimal format).  The initial value for this
			      toggle is FALSE.

		verbose_encrypt
			      When the verbose_encrypt toggle is TRUE, TELNET
			      prints out a message each time encryption is
			      enabled or disabled.  The initial value for this
			      toggle is FALSE. This flag only exists if
			      encryption support is available.

		?	      Displays the legal toggle commands.

     z		Suspend telnet.	 This command only works when the user is
		using the csh(1).

     ! [command]
		Execute a single command in a subshell on the local system.
		If command is omitted, then an interactive subshell is
		invoked.

     ? [command]
		Get help.  With no arguments, telnet prints a help summary.
		If a command is specified, telnet will print the help informa‐
		tion for just that command.

ENVIRONMENT
     Telnet uses at least the HOME, SHELL, DISPLAY, and TERM environment vari‐
     ables.  Other environment variables may be propagated to the other side
     via the TELNET ENVIRON option.

FILES
     /etc/telnetrc  global telnet startup values
     ~/.telnetrc    user customized telnet startup values

HISTORY
     The Telnet command appeared in 4.2BSD.

NOTES
     On some remote systems, echo has to be turned off manually when in “old
     line by line” mode.

     In “old line by line” mode or LINEMODE the terminal's eof character is
     only recognized (and sent to the remote system) when it is the first
     character on a line.

BUGS
     The source code is not comprehensible.

Linux NetKit (0.17)		August 15, 1999		   Linux NetKit (0.17)
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