NAME

telnet - user interface to a remote system using the TELNET protocol

SYNOPSIS

telnet [ host [ port ] ]

DESCRIPTION

telnet communicates with another host using the TELNET protocol. If telnet is invoked without arguments, it enters command mode, indicated by its prompt telnet>. In this mode, it accepts and executes the commands listed below. If it is invoked with arguments, it performs an open command (see ``Telnet Commands'' below) with those arguments.

Once a connection has been opened, telnet enters input mode. In this mode, text typed is sent to the remote host. The input mode entered 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) may 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, intr, and flush characters are trapped locally, and sent as TELNET protocol sequences to the remote side. There are options (see toggle, autoflush, and toggle, autosynch) 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 may be entered by typing the telnet escape character (initially ^]). When in command mode, the normal terminal editing conventions are available.

USAGE

Telnet Commands

The following commands are available. Only enough of each command to uniquely identify it need be typed (this is also true for arguments to the mode, set, toggle, and display commands).

open host [ port ]

Open a connection to the named host. If no port number is specified, telnet will attempt to contact a TELNET server at the default port. The host specification may be either a host name [see hosts(4)] or an Internet address specified in the dot notation [see inet(7)].

close

Close any open TELNET session and exit telnet. An EOF (in command mode) will also close a session and exit.

quit Same as close, above.

z Suspend telnet. This command only works when the user is using a shell that supports job control, such as sh(1).

mode type

type is either line (for line by line mode) or character (for character at a time 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 will be entered.

status

Show the current status of telnet. This includes the peer one is connected to, as well as the current mode.

display [ argument... ]

Display all, or some, of the set and toggle values (see toggle, arguments).

? [ command ]

Get help. With no arguments, telnet print a help summary. If a command is specified, telnet will print the help information for just that command.

send arguments

Send one or more special character sequences to the remote host. The following are the arguments which may be specified (more than one argument may be specified at a time):

escape

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

synch

Send the TELNET SYNCH sequence. This sequence discards all previously typed (but not yet read) input on the remote system. This sequence is sent as TCP urgent data (and may not work if the remote system is a 4.2 BSD system - if it does not work, a lower case r may be echoed on the terminal).

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

ip Send the TELNET IP (Interrupt Process) sequence, which aborts the currently running process on the remote system.

ao Sends the TELNET AO (Abort Output) sequence, which flushes 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 erases 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 argument 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 variables may be interrogated with the display command. The variables which may be specified are:

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

escape

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

interrupt

If telnet is in localchars mode (see toggle localchars) and the interrupt character is typed, a TELNET IP sequence (see send and ip) 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 local-
     chars)  and  the quit character is typed, a TELNET
     BRK sequence (see send, brk) 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) and the flushoutput character is typed, a TELNET AO sequence (see send, ao) is sent to the remote host. The initial value for the flush character is taken to be the terminal's flush character.

erase

If telnet is in localchars mode (see toggle localchars), and if telnet is operating in character at a time mode, then when this character is typed, a TELNET EC sequence (see send, ec) 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 local-
     chars), and if telnet is operating in character at
     a time mode, then when this character is typed,  a
     TELNET  EL  sequence (see send, el) is sent to the
     remote system.  The initial  value  for  the  kill
     character is taken to be the terminal's kill char-
     acter.

eof If telnet is operating in line by line mode, entering this character as the first character on a line sends this character 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 may be specified. The state of these flags may be interrogated with the display command. Valid arguments are:

autoflush

If autoflush and localchars are both TRUE, then when the ao, intr, or quit characters are recognized (and transformed into TELNET sequences; see set for details), telnet refuses to display any data on the user's terminal until the remote system acknowledges (using 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)].

autosynch

If autosynch and localchars are both TRUE, then when either the intr or quit characters are typed (see set 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.

crmod

Toggle RETURN mode. When this mode is enabled, most RETURN characters received from the remote host will be mapped into a 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 RETURN, but never LINEFEED. The initial value for this toggle is FALSE.

debug

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

localchars

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

netdata

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

options

Toggle the display of some internal telnet protocol processing (having to do with TELNET options). The initial value for this toggle is FALSE.

?    Display the legal toggle commands.

SEE ALSO

rlogin(1), sh(1), stty(1), hosts(4), inet(7).

NOTES

Do not attempt to run layers(1) while using telnet.

There is no adequate way for dealing with flow control.

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

There is enough settable state to justify a file.

In line by line mode, the terminal's EOF character is only recognized (and sent to the remote system) when it is the first character on a line.