.\" Copyright (c) 1983 Regents of the University of California.

.\" All rights reserved. The Berkeley software License Agreement

.\" specifies the terms and conditions for redistribution.

.\"

.\" @(#)telnet.1c 6.5 (Berkeley) 5/10/86

.\"

.TH TELNET 1 "May 10, 1986"

.UC 5

.SH NAME

telnet \- user interface to the \s-1TELNET\s0 protocol

.SH SYNOPSIS

telnet [

.I host

[

.I port

] ]

.SH DESCRIPTION

.I Telnet

is used to communicate with another host using the

.B TELNET

protocol.

If

.I telnet

is invoked without arguments, it enters command mode,

indicated by its prompt (\*(lqtelnet>\*(rq).

In this mode, it accepts and executes the commands listed below.

If it is invoked with arguments, it performs an

.B open

command (see below) with those arguments.

.PP

Once a connection has been opened,

.I telnet

enters an input mode.

The input mode entered will be either \*(lqcharacter at a time\*(rq

or \*(lqline by line\*(rq

depending on what the remote system supports.

.PP

In \*(lqcharacter at a time\*(rq mode, most

text typed is immediately sent to the remote host for processing.

.PP

In \*(lqline by line\*(rq mode, all text is echoed locally,

and (normally) only completed lines are sent to the remote host.

The \*(lqlocal echo character\*(rq (initially \*(lq^E\*(rq) may be used

to turn off and on the local echo

(this would mostly be used to enter passwords

without the password being echoed).

.PP

In either mode, if the

.I localchars

toggle is TRUE (the default in line mode; see below),

the user's

.IR quit ,

.IR intr ,

and

.I flush

characters are trapped locally, and sent as

.B TELNET

protocol sequences to the remote side.

There are options (see

.B toggle

.I autoflush

and

.B toggle

.I autosynch

below)

which cause this action to flush subsequent output to the terminal

(until the remote host acknowledges the

.B TELNET

sequence) and flush previous terminal input

(in the case of

.I quit

and

.IR intr ).

.PP

While connected to a remote host,

.I telnet

command mode may be entered by typing the

.I telnet

\*(lqescape character\*(rq (initially \*(lq^]\*(rq).

When in command mode, the normal terminal editing conventions are available.

.PP

.B COMMANDS

.PP

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

.BR mode ,

.BR set ,

.BR toggle ,

and

.B display

commands).

.PP

.TP

.B open \fIhost\fP \fR[\fP \fIport\fP \fR]\fP

.br

Open a connection to the named host.

If no port number

is specified,

.I telnet

will attempt to contact a

.B TELNET

server at the default port.

The host specification may be either a host name (see

.IR hosts (5))

or an Internet address specified in the \*(lqdot notation\*(rq (see

.IR inet (3N)).

.TP

.B close

.br

Close a

.B TELNET

session and return to command mode.

.TP

.B quit

.br

Close any open

.B TELNET

session and exit

.IR telnet .

An end of file (in command mode) will also close a session and exit.

.TP

.B z

.br

Suspend

.IR telnet .

This command only works when the user is using the

.IR csh (1).

.TP

.B mode \fItype\fP

.br

.I Type

is either

.I line

(for \*(lqline by line\*(rq mode)

or

.I character

(for \*(lqcharacter at a time\*(rq 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.

.TP

.B status

.br

Show the current status of

.IR telnet .

This includes the peer one is connected to, as well

as the current mode.

.TP

.B display \fR[\fP \fIargument...\fP \fR]\fP

.br

Displays all, or some, of the

.B set

and

.B toggle

values (see below).

.TP

.B ? \fR[\fP \fIcommand\fP \fR]\fP

.br

Get help. With no arguments,

.I telnet

prints a help summary.

If a command is specified,

.I telnet

will print the help information for just that command.

.TP

.B send \fIarguments\fP

.br

Sends 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):

.RS

.TP

.I escape

.br

Sends the current

.I telnet

escape character (initially \*(lq^]\*(rq).

.TP

.I synch

.br

Sends the

.B 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 4.2 BSD system -- if

it doesn't work, a lower case \*(lqr\*(rq may be echoed on the terminal).

.TP

.I brk

.br

Sends the

.B TELNET BRK

(Break) sequence, which may have significance to the remote

system.

.TP

.I ip

.br

Sends the

.B TELNET IP

(Interrupt Process) sequence, which should cause the remote

system to abort the currently running process.

.TP

.I ao

.br

Sends the

.B TELNET AO

(Abort Output) sequence, which should cause the remote system to flush

all output

.B from

the remote system

.B to

the user's terminal.

.TP

.I ayt

.br

Sends the

.B TELNET AYT

(Are You There)

sequence, to which the remote system may or may not choose to respond.

.TP

.I ec

.br

Sends the

.B TELNET EC

(Erase Character)

sequence, which should cause the remote system to erase the last character

entered.

.TP

.I el

.br

Sends the

.B TELNET EL

(Erase Line)

sequence, which should cause the remote system to erase the line currently

being entered.

.TP

.I ga

.br

Sends the

.B TELNET GA

(Go Ahead)

sequence, which likely has no significance to the remote system.

.TP

.I nop

.br

Sends the

.B TELNET NOP

(No OPeration)

sequence.

.TP

.I ?

.br

Prints out help information for the

.B send

command.

.RE

.TP

.B set \fIargument value\fP

.br

Set any one of a number of

.I telnet

variables to a specific value.

The special value \*(lqoff\*(rq turns off the function associated with

the variable.

The values of variables may be interrogated with the

.B display

command.

The variables which may be specified are:

.RS

.TP

.I echo

.br

This is the value (initially \*(lq^E\*(rq) which, when in

\*(lqline by line\*(rq mode, toggles between doing local echoing

of entered characters (for normal processing), and suppressing

echoing of entered characters (for entering, say, a password).

.TP

.I escape

.br

This is the

.I telnet

escape character (initially \*(lq^[\*(rq) which causes entry

into

.I telnet

command mode (when connected to a remote system).

.TP

.I interrupt

.br

If

.I telnet

is in

.I localchars

mode (see

.B toggle

.I localchars

below)

and the

.I interrupt

character is typed, a

.B TELNET IP

sequence (see

.B send

.I ip

above)

is sent to the remote host.

The initial value for the interrupt character is taken to be

the terminal's

.B intr

character.

.TP

.I quit

.br

If

.I telnet

is in

.I localchars

mode (see

.B toggle

.I localchars

below)

and the

.I quit

character is typed, a

.B TELNET BRK

sequence (see

.B send

.I brk

above)

is sent to the remote host.

The initial value for the quit character is taken to be

the terminal's

.B quit

character.

.TP

.I flushoutput

.br

If

.I telnet

is in

.I localchars

mode (see

.B toggle

.I localchars

below)

and the

.I flushoutput

character is typed, a

.B TELNET AO

sequence (see

.B send

.I ao

above)

is sent to the remote host.

The initial value for the flush character is taken to be

the terminal's

.B flush

character.

.TP

.I erase

.br

If

.I telnet

is in

.I localchars

mode (see

.B toggle

.I localchars

below),

.B and

if

.I telnet

is operating in \*(lqcharacter at a time\*(rq mode, then when this

character is typed, a

.B TELNET EC

sequence (see

.B send

.I ec

above)

is sent to the remote system.

The initial value for the erase character is taken to be

the terminal's

.B erase

character.

.TP

.I kill

.br

If

.I telnet

is in

.I localchars

mode (see

.B toggle

.I localchars

below),

.B and

if

.I telnet

is operating in \*(lqcharacter at a time\*(rq mode, then when this

character is typed, a

.B TELNET EL

sequence (see

.B send

.I el

above)

is sent to the remote system.

The initial value for the kill character is taken to be

the terminal's

.B kill

character.

.TP

.I eof

.br

If

.I telnet

is operating in \*(lqline by line\*(rq mode, entering this character

as the first character 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

.B eof

character.

.RE

.TP

.B toggle \fIarguments...\fP

.br

Toggle (between

TRUE

and

FALSE)

various flags that control how

.I telnet

responds to events.

More than one argument may be specified.

The state of these flags may be interrogated with the

.B display

command.

Valid arguments are:

.RS

.TP

.I localchars

.br

If this is

TRUE,

then the

.IR flush ,

.IR interrupt ,

.IR quit ,

.IR erase ,

and

.I kill

characters (see

.B set

above) are recognized locally, and transformed into (hopefully) appropriate

.B TELNET

control sequences

(respectively

.IR ao ,

.IR ip ,

.IR brk ,

.IR ec ,

and

.IR el ;

see

.B send

above).

The initial value for this toggle is TRUE in \*(lqline by line\*(rq mode,

and FALSE in \*(lqcharacter at a time\*(rq mode.

.TP

.I autoflush

.br

If

.I autoflush

and

.I localchars

are both

TRUE,

then when the

.IR ao ,

.IR intr ,

or

.I quit

characters are recognized (and transformed into

.B TELNET

sequences; see

.B set

above for details),

.I telnet

refuses to display any data on the user's terminal

until the remote system acknowledges (via a

.B TELNET

.I Timing Mark

option)

that it has processed those

.B TELNET

sequences.

The initial value for this toggle is TRUE if the terminal user had not

done an "stty noflsh", otherwise FALSE (see

.IR stty(1)).

.TP

.I autosynch

If

.I autosynch

and

.I localchars

are both

TRUE,

then when either the

.I intr

or

.I quit

characters is typed (see

.B set

above for descriptions of the

.I intr

and

.I quit

characters), the resulting

.B TELNET

sequence sent is followed by the

.B TELNET SYNCH

sequence.

This procedure

.B should

cause the remote system to begin throwing away all previously

typed input until both of the

.B TELNET

sequences have been read and acted upon.

The initial value of this toggle is FALSE.

.TP

.I crmod

.br

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.

.TP

.I debug

.br

Toggles socket level debugging (useful only to the

.IR super user ).

The initial value for this toggle is FALSE.

.TP

.I options

.br

Toggles the display of some internal

.I telnet

protocol processing (having to do with

.B TELNET

options).

The initial value for this toggle is FALSE.

.TP

.I netdata

.br

Toggles the display of all network data (in hexadecimal format).

The initial value for this toggle is FALSE.

.TP

.I ?

.br

Displays the legal

.B toggle

commands.

.RE

.SH BUGS

.PP

There is no adequate way for dealing with flow control.

.PP

On some remote systems, echo has to be turned off manually when in

\*(lqline by line\*(rq mode.

.PP

There is enough settable state to justify a

.RI . telnetrc

file.

.PP

No capability for a

.RI . telnetrc

file is provided.

.PP

In \*(lqline by line\*(rq mode, the terminal's

.I eof

character is only recognized (and sent to the remote system)

when it is the first character on a line.