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.\"     @(#)telnet.1    8.5 (Berkeley) 3/1/94

.\"     $Id: telnet.1,v 1.1 2002-03-25 22:32:02 simons Exp $

.\"

.Dd March 1, 1994

.Dt TELNET 1

.Os BSD 4.2

.Sh NAME

.Nm telnet

.Nd user interface to the

.Tn TELNET

protocol

.Sh SYNOPSIS

.Nm

.Op Fl 8EFKLacdfrx

.Op Fl S Ar tos

.Op Fl X Ar authtype

.Op Fl e Ar escapechar

.Op Fl k Ar realm

.Op Fl l Ar user

.Op Fl n Ar tracefile

.Oo

.Ar host

.Op Ar port

.Oc

.Sh DESCRIPTION

The

.Nm

command

is used to communicate with another host using the

.Tn TELNET

protocol.

If

.Nm

is invoked without the

.Ar host

argument, it enters command mode,

indicated by its prompt

.Pq Nm telnet\&> .

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

If it is invoked with arguments, it performs an

.Ic open

command with those arguments.

.Pp

Options:

.Bl -tag -width indent

.It Fl 8

Specifies an 8-bit data path.  This causes an attempt to

negotiate the

.Dv TELNET BINARY

option on both input and output.

.It Fl E

Stops any character from being recognized as an escape character.

.It Fl F

If Kerberos V5 authentication is being used, the

.Fl F

option allows the local credentials to be forwarded

to the remote system, including any credentials that

have already been forwarded into the local environment.

.It Fl K

Specifies no automatic login to the remote system.

.It Fl L

Specifies an 8-bit data path on output.  This causes the

.Dv BINARY

option to be negotiated on output.

.It Fl N

Prevents IP address to name lookup when destination host is given

as an IP address.

.It Fl S Ar tos

Sets the IP type-of-service (TOS) option for the telnet

connection to the value

.Ar tos,

which can be a numeric TOS value

or, on systems that support it, a symbolic

TOS name found in the

.Pa /etc/iptos

file.

.It Fl X Ar atype

Disables the

.Ar atype

type of authentication.

.It Fl a

Attempt automatic login.

Currently, this sends the user name via the

.Ev USER

variable

of the

.Ev ENVIRON

option if supported by the remote system.

The name used is that of the current user as returned by

.Xr getlogin 2

if it agrees with the current user ID,

otherwise it is the name associated with the user ID.

.It Fl c

Disables the reading of the user's

.Pa \&.telnetrc

file.  (See the

.Ic toggle skiprc

command on this man page.)

.It Fl d

Sets the initial value of the

.Ic debug

toggle to

.Dv TRUE .

.It Fl e Ar escapechar

Sets the initial

.Nm

escape character to

.Ar escapechar .

If

.Ar escapechar

is omitted, then

there will be no escape character.

.It Fl f

If Kerberos V5 authentication is being used, the

.Fl f

option allows the local credentials to be forwarded to the remote system.

.It Fl k Ar realm

If Kerberos authentication is being used, the

.Fl k

option requests that

.Nm

obtain tickets for the remote host in

realm

.Ar realm

instead of the remote host's realm, as determined by

.Xr krb_realmofhost 3 .

.It Fl l Ar user

When connecting to the remote system, if the remote system

understands the

.Ev ENVIRON

option, then

.Ar user

will be sent to the remote system as the value for the variable

.Ev USER .

This option implies the

.Fl a

option.

This option may also be used with the

.Ic open

command.

.It Fl n Ar tracefile

Opens

.Ar tracefile

for recording trace information.

See the

.Ic set tracefile

command below.

.It Fl r

Specifies a user interface similar to

.Xr rlogin 1 .

In this

mode, the escape character is set to the tilde (~) character,

unless modified by the

.Fl e

option.

.It Fl x

Turns on encryption of the data stream if possible.  This

option is not available outside of the United States and

Canada.

.It Ar host

Indicates the official name, an alias, or the Internet address

of a remote host.

.It Ar port

Indicates a port number (address of an application).  If a number is

not specified, the default

.Nm

port is used.

.El

.Pp

When in rlogin mode, a line of the form ~.  disconnects from the

remote host; ~ is the

.Nm

escape character.

Similarly, the line ~^Z suspends the

.Nm

session.

The line ~^] escapes to the normal

.Nm

escape prompt.

.Pp

Once a connection has been opened,

.Nm

will attempt to enable the

.Dv TELNET LINEMODE

option.

If this fails, then

.Nm

will revert to one of two input modes:

either \*(Lqcharacter at a time\*(Rq

or \*(Lqold line by line\*(Rq

depending on what the remote system supports.

.Pp

When

.Dv LINEMODE

is enabled, character processing is done on the

local system, under the control of the remote system.  When input

editing or character echoing is to be disabled, the remote system

will relay that information.  The remote system will also relay

changes to any special characters that happen on the remote

system, so that they can take effect on the local system.

.Pp

In \*(Lqcharacter at a time\*(Rq mode, most

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

.Pp

In \*(Lqold line 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

If the

.Dv LINEMODE

option is enabled, or if the

.Ic localchars

toggle is

.Dv TRUE

(the default for \*(Lqold line by line\*(Rq; see below),

the user's

.Ic quit  ,

.Ic intr ,

and

.Ic flush

characters are trapped locally, and sent as

.Tn TELNET

protocol sequences to the remote side.

If

.Dv LINEMODE

has ever been enabled, then the user's

.Ic susp

and

.Ic eof

are also sent as

.Tn TELNET

protocol sequences,

and

.Ic quit

is sent as a

.Dv TELNET ABORT

instead of

.Dv BREAK .

There are options (see

.Ic toggle

.Ic autoflush

and

.Ic toggle

.Ic autosynch

below)

which cause this action to flush subsequent output to the terminal

(until the remote host acknowledges the

.Tn TELNET

sequence) and flush previous terminal input

(in the case of

.Ic quit

and

.Ic intr  ) .

.Pp

While connected to a remote host,

.Nm

command mode may be entered by typing the

.Nm

\*(Lqescape character\*(Rq (initially \*(Lq^]\*(Rq).

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

.Pp

The following

.Nm

commands are available.

Only enough of each command to uniquely identify it need be typed

(this is also true for arguments to the

.Ic mode  ,

.Ic set ,

.Ic toggle  ,

.Ic unset ,

.Ic slc  ,

.Ic environ ,

and

.Ic display

commands).

.Pp

.Bl -tag -width "mode type"

.It Ic auth Ar argument ...

The auth command manipulates the information sent through the

.Dv TELNET AUTHENTICATE

option.  Valid arguments for the

.Ic auth

command are:

.Bl -tag -width "disable type"

.It Ic disable Ar type

Disables the specified type of authentication.  To

obtain a list of available types, use the

.Ic auth disable \&?

command.

.It Ic enable Ar type

Enables the specified type of authentication.  To

obtain a list of available types, use the

.Ic auth enable \&?

command.

.It Ic status

Lists the current status of the various types of

authentication.

.El

.It Ic close

Close a

.Tn TELNET

session and return to command mode.

.It Ic display Ar argument ...

Displays all, or some, of the

.Ic set

and

.Ic toggle

values (see below).

.It Ic encrypt Ar argument ...

The encrypt command manipulates the information sent through the

.Dv TELNET ENCRYPT

option.

.Pp

Note:  Because of export controls, the

.Dv TELNET ENCRYPT

option is not supported outside of the United States and Canada.

.Pp

Valid arguments for the

.Ic encrypt

command are:

.Bl -tag -width Ar

.It Ic disable Ar type Ic [input|output]

Disables the specified type of encryption.  If you

omit the input and output, both input and output

are disabled.  To obtain a list of available

types, use the

.Ic encrypt disable \&?

command.

.It Ic enable Ar type Ic [input|output]

Enables the specified type of encryption.  If you

omit input and output, both input and output are

enabled.  To obtain a list of available types, use the

.Ic encrypt enable \&?

command.

.It Ic input

This is the same as the

.Ic encrypt start input

command.

.It Ic -input

This is the same as the

.Ic encrypt stop input

command.

.It Ic output

This is the same as the

.Ic encrypt start output

command.

.It Ic -output

This is the same as the

.Ic encrypt stop output

command.

.It Ic start Ic [input|output]

Attempts to start encryption.  If you omit

.Ic input

and

.Ic output,

both input and output are enabled.  To

obtain a list of available types, use the

.Ic encrypt enable \&?

command.

.It Ic status

Lists the current status of encryption.

.It Ic stop Ic [input|output]

Stops encryption.  If you omit input and output,

encryption is on both input and output.

.It Ic type Ar type

Sets the default type of encryption to be used

with later

.Ic encrypt start

or

.Ic encrypt stop

commands.

.El

.It Ic environ Ar arguments...

The

.Ic environ

command is used to manipulate the

variables that my be sent through the

.Dv TELNET ENVIRON

option.

The initial set of variables is taken from the users

environment, with only the

.Ev DISPLAY

and

.Ev PRINTER

variables being exported by default.

The

.Ev USER

variable is also exported if the

.Fl a

or

.Fl l

options are used.

.Pp

Valid arguments for the

.Ic environ

command are:

.Bl -tag -width Fl

.It Ic define Ar variable value

Define the variable

.Ar variable

to have a value of

.Ar value.

Any variables defined by this command are automatically exported.

The

.Ar value

may be enclosed in single or double quotes so

that tabs and spaces may be included.

.It Ic undefine Ar variable

Remove

.Ar variable

from the list of environment variables.

.It Ic export Ar variable

Mark the variable

.Ar variable

to be exported to the remote side.

.It Ic unexport Ar variable

Mark the variable

.Ar variable

to not be exported unless

explicitly asked for by the remote side.

.It Ic list

List the current set of environment variables.

Those marked with a

.Cm *

will be sent automatically,

other variables will only be sent if explicitly requested.

.It Ic \&?

Prints out help information for the

.Ic environ

command.

.El

.It Ic logout

Sends the

.Dv TELNET LOGOUT

option to the remote side.

This command is similar to a

.Ic close

command; however, if the remote side does not support the

.Dv LOGOUT

option, nothing happens.

If, however, the remote side does support the

.Dv LOGOUT

option, this command should cause the remote side to close the

.Tn TELNET

connection.

If the remote side also supports the concept of

suspending a user's session for later reattachment,

the logout argument indicates that you

should terminate the session immediately.

.It Ic mode Ar type

.Ar Type

is one of several options, depending on the state of the

.Tn TELNET

session.

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.

.Bl -tag -width Ar

.It Ic character

Disable the

.Dv TELNET LINEMODE

option, or, if the remote side does not understand the

.Dv LINEMODE

option, then enter \*(Lqcharacter at a time\*(Rq mode.

.It Ic line

Enable the

.Dv TELNET LINEMODE

option, or, if the remote side does not understand the

.Dv LINEMODE

option, then attempt to enter \*(Lqold-line-by-line\*(Rq mode.

.It Ic isig Pq Ic \-isig

Attempt to enable (disable) the

.Dv TRAPSIG

mode of the

.Dv LINEMODE

option.

This requires that the

.Dv LINEMODE

option be enabled.

.It Ic edit Pq Ic \-edit

Attempt to enable (disable) the

.Dv EDIT

mode of the

.Dv LINEMODE

option.

This requires that the

.Dv LINEMODE

option be enabled.

.It Ic softtabs Pq Ic \-softtabs

Attempt to enable (disable) the

.Dv SOFT_TAB

mode of the

.Dv LINEMODE

option.

This requires that the

.Dv LINEMODE

option be enabled.

.It Ic litecho Pq Ic \-litecho

Attempt to enable (disable) the

.Dv LIT_ECHO

mode of the

.Dv LINEMODE

option.

This requires that the

.Dv LINEMODE

option be enabled.

.It Ic \&?

Prints out help information for the

.Ic mode

command.

.El

.It Xo

.Ic open Ar host

.Op Fl l Ar user

.Oo Op Fl

.Ar port Oc

.Xc

Open a connection to the named host.

If no port number

is specified,

.Nm

will attempt to contact a

.Tn TELNET

server at the default port.

The host specification may be either a host name (see

.Xr hosts  5  )

or an Internet address specified in the \*(Lqdot notation\*(Rq (see

.Xr inet 3 ) .

The

.Fl l

option may be used to specify the user name

to be passed to the remote system via the

.Ev ENVIRON

option.

When connecting to a non-standard port,

.Nm

omits any automatic initiation of

.Tn TELNET

options.  When the port number is preceded by a minus sign,

the initial option negotiation is done.

After establishing a connection, the file

.Pa \&.telnetrc

in the

users home directory is opened.  Lines beginning with a # are

comment lines.  Blank lines are ignored.  Lines that begin

without white space are the start of a machine entry.  The

first thing on the line is the name of the machine that is

being connected to.  The rest of the line, and successive

lines that begin with white space are assumed to be

.Nm

commands and are processed as if they had been typed

in manually to the

.Nm

command prompt.

.It Ic quit

Close any open

.Tn TELNET

session and exit

.Nm telnet  .

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

.It Ic send Ar arguments

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):

.Pp

.Bl -tag -width escape

.It Ic abort

Sends the

.Dv TELNET ABORT

(Abort

processes)

sequence.

.It Ic ao

Sends the

.Dv TELNET AO

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

all output

.Em from

the remote system

.Em to

the user's terminal.

.It Ic ayt

Sends the

.Dv TELNET AYT

(Are You There)

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

.It Ic brk

Sends the

.Dv TELNET BRK

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

system.

.It Ic ec

Sends the

.Dv TELNET EC

(Erase Character)

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

entered.

.It Ic el

Sends the

.Dv TELNET EL

(Erase Line)

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

being entered.

.It Ic eof

Sends the

.Dv TELNET EOF

(End Of File)

sequence.

.It Ic eor

Sends the

.Dv TELNET EOR

(End of Record)

sequence.

.It Ic escape

Sends the current

.Nm

escape character (initially \*(Lq^\*(Rq).

.It Ic ga

Sends the

.Dv TELNET GA

(Go Ahead)

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

.It Ic getstatus

If the remote side supports the

.Dv TELNET STATUS

command,

.Ic getstatus

will send the subnegotiation to request that the server send

its current option status.

.It Ic ip

Sends the

.Dv TELNET IP

(Interrupt Process) sequence, which should cause the remote

system to abort the currently running process.

.It Ic nop

Sends the

.Dv TELNET NOP

(No OPeration)

sequence.

.It Ic susp

Sends the

.Dv TELNET SUSP

(SUSPend process)

sequence.

.It Ic synch

Sends the

.Dv TELNET SYNCH

sequence.

This sequence causes the remote system to discard all previously typed

(but not yet read) input.

This sequence is sent as

.Tn TCP

urgent

data (and may not work if the remote system is a

.Bx 4.2

system -- if

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

.It Ic do Ar cmd

.It Ic dont Ar cmd

.It Ic will Ar cmd

.It Ic wont Ar cmd

Sends the

.Dv TELNET DO

.Ar cmd

sequence.

.Ar Cmd

can be either a decimal number between 0 and 255,

or a symbolic name for a specific

.Dv TELNET

command.

.Ar Cmd

can also be either

.Ic help

or

.Ic \&?

to print out help information, including

a list of known symbolic names.

.It Ic \&?

Prints out help information for the

.Ic send

command.

.El

.It Ic set Ar argument value

.It Ic unset Ar argument value

The

.Ic set

command will set any one of a number of

.Nm

variables to a specific value or to

.Dv TRUE .

The special value

.Ic off

turns off the function associated with

the variable, this is equivalent to using the

.Ic unset

command.

The

.Ic unset

command will disable or set to

.Dv FALSE

any of the specified functions.

The values of variables may be interrogated with the

.Ic display

command.

The variables which may be set or unset, but not toggled, are

listed here.  In addition, any of the variables for the

.Ic toggle

command may be explicitly set or unset using

the

.Ic set

and

.Ic unset

commands.

.Bl -tag -width escape

.It Ic ayt

If

.Tn TELNET

is in localchars mode, or

.Dv LINEMODE

is enabled, and the status character is typed, a

.Dv TELNET AYT

sequence (see

.Ic send ayt

preceding) is sent to the

remote host.  The initial value for the \*(LqAre You There\*(Rq

character is the terminal's status character.

.It Ic echo

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).

.It Ic eof

If

.Nm

is operating in

.Dv LINEMODE

or \*(Lqold line 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

.Ic eof

character.

.It Ic erase

If

.Nm

is in

.Ic localchars

mode (see

.Ic toggle

.Ic localchars

below),

.Sy and

if

.Nm

is operating in \*(Lqcharacter at a time\*(Rq mode, then when this

character is typed, a

.Dv TELNET EC

sequence (see

.Ic send

.Ic ec

above)

is sent to the remote system.

The initial value for the erase character is taken to be

the terminal's

.Ic erase

character.

.It Ic escape

This is the

.Nm

escape character (initially \*(Lq^[\*(Rq) which causes entry

into

.Nm

command mode (when connected to a remote system).

.It Ic flushoutput

If

.Nm

is in

.Ic localchars

mode (see

.Ic toggle

.Ic localchars

below)

and the

.Ic flushoutput

character is typed, a

.Dv TELNET AO

sequence (see

.Ic send

.Ic ao

above)

is sent to the remote host.

The initial value for the flush character is taken to be

the terminal's

.Ic flush

character.

.It Ic forw1

.It Ic forw2

If

.Nm

is operating in

.Dv 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 terminal's

eol and eol2 characters.

.It Ic interrupt

If

.Nm

is in

.Ic localchars

mode (see

.Ic toggle

.Ic localchars

below)

and the

.Ic interrupt

character is typed, a

.Dv TELNET IP

sequence (see

.Ic send

.Ic ip

above)

is sent to the remote host.

The initial value for the interrupt character is taken to be

the terminal's

.Ic intr

character.

.It Ic kill

If

.Nm

is in

.Ic localchars

mode (see

.Ic toggle

.Ic localchars

below),

.Ic and

if

.Nm

is operating in \*(Lqcharacter at a time\*(Rq mode, then when this

character is typed, a

.Dv TELNET EL

sequence (see

.Ic send

.Ic el

above)

is sent to the remote system.

The initial value for the kill character is taken to be

the terminal's

.Ic kill

character.

.It Ic lnext

If

.Nm

is operating in

.Dv LINEMODE

or \*(Lqold line by line\*(Rq mode, then this character is taken to

be the terminal's

.Ic lnext

character.

The initial value for the lnext character is taken to be

the terminal's

.Ic lnext

character.

.It Ic quit

If

.Nm

is in

.Ic localchars

mode (see

.Ic toggle

.Ic localchars

below)

and the

.Ic quit

character is typed, a

.Dv TELNET BRK

sequence (see

.Ic send

.Ic brk

above)

is sent to the remote host.

The initial value for the quit character is taken to be

the terminal's

.Ic quit

character.

.It Ic reprint

If

.Nm

is operating in

.Dv LINEMODE

or \*(Lqold line by line\*(Rq mode, then this character is taken to

be the terminal's

.Ic reprint

character.

The initial value for the reprint character is taken to be

the terminal's

.Ic reprint

character.

.It Ic rlogin

This is the rlogin escape character.

If set, the normal

.Nm

escape character is ignored unless it is