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 telnet(1)							   telnet(1)




 NAME
      telnet - user interface to the TELNET protocol

 SYNOPSIS
      telnet [[options]host [port]]

 DESCRIPTION
      telnet is used to communicate with another host using the TELNET
      protocol.	 If telnet is invoked without arguments, it enters command
      mode, indicated by its prompt (telnet>&gt&gt>).	In this mode, it accepts and
      executes the commands listed below.  If telnet is invoked with
      arguments, it performs an open command (see below) with those
      arguments.

      Once a connection has been opened, telnet enters an input mode.  The
      input mode will be either ``character at a time'' or ``line by line'',
      depending on what the remote system supports.

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

      In ``line by line'' mode, all text is echoed locally, and (normally)
      only completed lines are sent to the remote host.	 The ``local echo
      character'' (initially ^E) can be used to turn off and on the local
      echo (this would mostly be used to enter passwords without the
      password being echoed).

      In either mode, if the localchars toggle is TRUE (the default in line
      mode; see below), the user's quit and intr characters are trapped
      locally, and sent as TELNET protocol sequences to the remote side.
      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 acknowledges the TELNET sequence) and flush
      previous terminal input (in the case of quit and intr).

      While connected to a remote host, telnet command mode can be entered
      by typing the telnet ``escape character'' (initially ^]).	 When in
      command mode, the normal terminal editing conventions are available.

      telnet supports eight-bit characters when communicating with the
      server on the remote host.  To use eight-bit characters you may need
      to reconfigure your terminal or the remote host appropriately (see
      stty(1)).	 Furthermore, you may have to use the binary toggle to
      enable an 8-bit data stream between telnet and the remote host.  Note
      that some remote hosts may not provide the necessary support for
      eight-bit characters.

      If, at any time, telnet is unable to read from or write to the server
      over the connection, the message Connection closed by foreign host. is
      printed on standard error.  telnet then exits with a value of 1.




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 telnet(1)							   telnet(1)




      telnet supports the TAC User ID (also known as the TAC Access Control
      System, or TACACS User ID) option.  Enabling the option on a host
      server allows the user to telnet into that host without being prompted
      for a second login sequence.  The TAC User ID option uses the same
      security mechanism as rlogin for authorizing access by remote hosts
      and users.  The system administrator must enable the (telnetd) option
      only on systems which are designated as participating hosts.  The
      system administrator must also assign to each user of TAC User ID the
      very same UID on every system for which he is allowed to use the
      feature.	(See telnetd(1M) and the Managing Systems and Workgroups
      manual)

      The following telnet options are available:

      -8	Enable cs8 (8 bit transfer) on local tty.

      -ec	Set the telnet command mode escape character to be ^c
		instead of its default value of ^].

      -l	Disable the TAC User ID option if enabled on the client, to
		cause the user to be prompted for login username and
		password. Omitting the -l option executes the default
		setting.

    Commands
      The following commands are available in command mode.  You need only
      type enough of each command to uniquely identify it (this is also true
      for arguments to the mode, set, toggle, and display commands).

      open host [port]
		     Open a connection to the named host at the indicated
		     port.  If no port is specified, telnet attempts to
		     contact a TELNET server at the standard TELNET port.
		     The hostname can be either the official name or an
		     alias as understood by gethostbyname() (see
		     gethostent(3N)), or an Internet address specified in
		     the dot notation as described in hosts(4).	 If no
		     hostname is given, telnet prompts for one.

      close	     Close a TELNET session.  If the session was started
		     from command mode, telnet returns to command mode;
		     otherwise telnet exits.

      quit	     Close any open TELNET session and exit telnet.  An end
		     of file (in command mode) will also close a session and
		     exit.

      z		     Suspend telnet.  If telnet is run from a shell that
		     supports job control, (such as csh(1) or ksh(1)), the z
		     command suspends the TELNET session and returns the
		     user to the shell that invoked telnet.  The job can



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 telnet(1)							   telnet(1)




		     then be resumed with the fg command (see csh(1) or
		     ksh(1)).

      mode mode	     Change telnet's user input mode to mode, which can be
		     character (for ``character at a time'' mode) or line
		     (for ``line by line'' mode).  The remote host is asked
		     for permission to go into the requested mode.  If the
		     remote host is capable of entering that mode, the
		     requested mode is entered.	 In character mode, telnet
		     sends each character to the remote host as it is typed.
		     In line mode, telnet gathers user input into lines and
		     transmits each line to the remote host when the user
		     types carriage return, linefeed, or EOF (normally ^D;
		     see stty(1)).  Note that setting line-mode also sets
		     local echo.  Applications that expect to interpret user
		     input character by character (such as more, csh, ksh,
		     and vi) do not work correctly in line mode.

      status	     Show current status of telnet.  telnet reports the
		     current escape character.	If telnet is connected, it
		     reports the host to which it is connected and the
		     current mode.  If telnet is not connected to a remote
		     host, it reports No connection. Once telnet has been
		     connected, it reports the local flow control toggle
		     value.

      display [argument ...]
		     Displays all or some of the set and toggle values (see
		     below).

      ? [command]    Get help.	With no arguments, telnet prints a help
		     summary.  If a command is specified, telnet prints the
		     help information available about that command only.
		     Help information is limited to a one-line description
		     of the command.

      ! [shell_command]
		     Shell escape.  The SHELL environment variable is
		     checked for the name of a shell to use to execute the
		     command.  If no shell_command is specified, a shell is
		     started and connected to the user's terminal.  If SHELL
		     is undefined, /usr/bin/sh is used.

      send arguments Sends one or more special character sequences to the
		     remote host.  Each argument can have any of the
		     following values (multiple arguments can be specified
		     with each send command):

			  escape    Sends the current telnet escape
				    character (initially ^]).




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 telnet(1)							   telnet(1)




			  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 to
				    some systems -- if it doesn't work, a
				    lower case ``r'' may be echoed on the
				    terminal).

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

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

			  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.

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

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

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

			  nop	    Sends the TELNET NOP (No OPeration)
				    sequence.

			  ?	    Prints out help information for the send
				    command.

      set variable_name value
		     Set any one of a number of telnet variables to a
		     specific value.  The special value off turns off the
		     function associated with the variable.  The values of



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 telnet(1)							   telnet(1)




		     variables can be shown by using the display command.
		     The following variable_names can be specified:

			  echo This is the value (initially ^E) which, when
			       in line-by-line mode, toggles between doing
			       local echoing of entered characters (for
			       normal processing), and suppressing echoing
			       of entered characters (for entering, for
			       example, a password).

			  escape
			       This is the telnet escape character
			       (initially ^]) which causes entry into telnet
			       command mode (when connected to a remote
			       system).

			  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.

			  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.

			  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 character is
			       ^O.

			  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 character is
			       taken to be the terminal's erase 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



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 telnet(1)							   telnet(1)




			       character is typed, a TELNET EL sequence (see
			       send el above) is sent to the remote system.
			       The initial value for the kill character is
			       taken to be the terminal's kill character.

			  eof  If telnet is operating in line-by-line mode,
			       entering this character as the first
			       character on a line causes 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.

      toggle arguments ...
		     Toggle (between TRUE and FALSE ) various flags that
		     control how telnet responds to events.  More than one
		     argument can be specified.	 The state of these flags
		     can be shown by using the display command.	 Valid
		     arguments are:

			  localchars
			       If TRUE, the flush, interrupt, quit, erase,
			       and kill characters (see set above) are
			       recognized locally, and transformed into
			       appropriate TELNET control sequences
			       (respectively ao, ip, brk, ec, and el; see
			       send above).  The initial value for this
			       toggle is TRUE in line-by-line mode, and
			       FALSE in character-at-a-time mode.

			  autoflush
			       If autoflush and localchars are both TRUE,
			       whenever the ao, intr, 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.

			  autosynch
			       If autosynch and localchars are both TRUE,
			       when either the intr or quit character 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 discarding
			       all previously typed input until both of the
			       TELNET sequences have been read and acted



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 telnet(1)							   telnet(1)




			       upon.  The initial value of this toggle is
			       FALSE.

			  binary
			       Enable or disable the TELNET BINARY option on
			       both input and output.  This option should be
			       enabled in order to send and receive 8-bit
			       characters to and from the TELNET server.

			  crlf If TRUE, end-of-line sequences are sent as an
			       ASCII carriage-return and line-feed pair.  If
			       FALSE, end-of-line sequences are sent as an
			       ASCII carriage-return and NUL character pair.
			       The initial value for this toggle is FALSE.

			  crmod
			       Toggle carriage return mode.  When this mode
			       is enabled, any carriage return characters
			       received from the remote host are mapped into
			       a carriage return and a line feed.  This mode
			       does not affect those characters typed by the
			       user; only those received.  This mode is only
			       required for some hosts that require the
			       client to do local echoing, but output
			       ``naked'' carriage returns.  The initial
			       value for this toggle is FALSE.

			  echo Toggle local echo mode or remote echo mode.
			       In local echo mode, user input is echoed to
			       the terminal by the local telnet before being
			       transmitted to the remote host.	In remote
			       echo, any echoing of user input is done by
			       the remote host.	 Applications that handle
			       echoing of user input themselves, such as C
			       shell, Korn shell, and vi (see csh(1),
			       ksh(1), and vi(1)), do not work correctly
			       with local echo.

			  options
			       Toggle viewing of TELNET options processing.
			       When options viewing is enabled, all TELNET
			       option negotiations are displayed.  Options
			       sent by telnet are displayed as ``SENT'',
			       while options received from the TELNET server
			       are displayed as ``RCVD''.  The initial value
			       for this toggle is FALSE.

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



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 telnet(1)							   telnet(1)




			  ?    Displays the legal toggle commands.

 RETURN VALUE
      In the event of an error, or if the TELNET connection is closed by the
      remote host, telnet returns a value of 1.	 Otherwise it returns zero
      (0).

 DIAGNOSTICS
      The following diagnostic messages are displayed by telnet:

	   Error!  Could not retrieve authentication type.
		There are two authentication mechanisms used by TELNET.	 One
		authentication mechanism is based on Kerberos and the other
		is not.	 The type of authentication mechanism is obtained
		from a system file which is updated by inetsvcs_sec.  If the
		system file on either the local host or the remote host does
		not contain known authentication types, the above error is
		displayed.

	   telnet/tcp: Unknown service
		telnet was unable to find the TELNET service entry in the
		services(4) database.

	   hostname: Unknown host
		telnet was unable to map the host name to an Internet
		address.  Your next step should be to contact the system
		administrator to check whether there is an entry for the
		remote host in the hosts database (see hosts(4)).

	   ?Invalid command
		An invalid command was typed in telnet command mode.

	   system call>&gt&gt>: ...
		An error occurred in the specified system call.	 See the
		appropriate manual entry for a description of the error.

 AUTHOR
      telnet was developed by the University of California, Berkeley.

 SEE ALSO
      csh(1), ksh(1), login(1), rlogin(1), stty(1), telnetd(1M),
      inetsvcs_sec(1M), hosts(4), services(4), termio(7).












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