protocol

The

command is used for interactive communication with another host using the

protocol. It begins in command mode, where it prints a telnet prompt ("telnet> "). If

is invoked with a

argument, it performs an

command implicitly; see the description below.

Options:

Force IPv4 address resolution.

Force IPv6 address resolution.

Request 8-bit operation. This causes an attempt to negotiate the

option for both input and output. By default telnet is not 8-bit clean.

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

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

option to be negotiated on just output.

Attempt automatic login. Currently, this sends the user name via the

variable of the

option if supported by the remote system. The username is retrieved via

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

Sets the initial value of the

toggle to

Emulate

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

to disconnect from the remote host. A ^Z instead of a dot suspends

and a ^] (the default

escape character) generates a normal telnet prompt. These codes are accepted only at the beginning of a line.

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

Sets the escape character to

If no character is supplied, no escape character will be used. Entering the escape character while connected causes telnet to drop to command mode.

Specify

as the user to log in as on the remote system. This is accomplished by sending the specified name as the

environment variable, so it requires that the remote system support the

option. This option implies the

option, and may also be used with the

command.

Opens

for recording trace information. See the

command below.

Specifies a host to contact over the network.

Specifies a port number or service name to contact. If not specified, the

port (23) is used.

Protocol:

Once a connection has been opened,

will attempt to enable the

option. If this fails, then

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

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.

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 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).

If the

option is enabled, or if the

toggle is

(the default for old line by line; see below), the user's

and

characters are trapped locally, and sent as

protocol sequences to the remote side. If

has ever been enabled, then the user's

and

are also sent as

protocol sequences, and

is sent as a

instead of

There are options (see

and

below) which cause this action to flush subsequent output to the terminal (until the remote host acknowledges the

sequence) and flush previous terminal input (in the case of

and

Commands:

The following

commands are available. Unique prefixes are understood as abbreviations.

The

command controls the

protocol option. If

was compiled without authentication, the

command will not be supported. Valid arguments are as follows:

Disable the specified type of authentication. To obtain a list of available types, use the

command.

Enable the specified type of authentication. To obtain a list of available types, use the

command.

List the current status of the various types of authentication.

Note that the current version of

does not support authentication.

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

Display all, or some, of the

and

values (see below).

The encrypt command controls the

protocol option. If

was compiled without encryption, the

command will not be supported.

Valid arguments are as follows:

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

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 ?''.

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

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

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

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

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

Display the current status of the encryption module.

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

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

Note that the current version of

does not support encryption.

The

command is used to propagate environment variables across the

link using the

protocol option. All variables exported from the shell are defined, but only the

and

variables are marked to be sent by default. The

variable is marked to be sent if the

or

command-line options were used.

Valid arguments for the

command are:

Define the variable

to have a value of

Any variables defined by this command are automatically marked for propagation (``exported''). The

may be enclosed in single or double quotes so that tabs and spaces may be included.

Remove any existing definition of

Mark the specified variable for propagation to the remote host.

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 the current set of environment variables. Those marked with a

will be propagated to the remote host. The remote host may still ask explicitly for the rest.

Prints out help information for the

command.

Send the

protocol option to the remote host. This command is similar to a

command. If the remote host does not support the

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.

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

asks the remote host to go into the requested mode. If the remote host says it can, that mode takes effect.

Disable the

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

option, then enter character at a time mode.

Enable the

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

option, then attempt to enter old-line-by-line mode.

Attempt to enable (disable) the

mode of the

option. This requires that the

option be enabled.

Attempt to enable (disable) the

mode of the

option. This requires that the

option be enabled.

Attempt to enable (disable) the

mode of the

option. This requires that the

option be enabled.

Attempt to enable (disable) the

mode of the

option. This requires that the

option be enabled.

Prints out help information for the

command.

Open a connection to the named host. If no port number is specified,

will attempt to contact a

daemon at the standard port (23). The host specification may be a host name or IP address. The

option may be used to specify a user name to be passed to the remote system, like the

command-line option.

When connecting to ports other than the

port,

does not attempt

protocol negotiations. This makes it possible to connect to services that do not support the

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

and the user's

file are executed, in that order.

The format of the telnetrc files is as follows: Lines beginning with a #, and blank lines, are ignored. The rest of the file should consist of hostnames and sequences of

commands 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

will apply to all hosts. Hostnames including

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

is used. Upon connecting to a particular host, the commands associated with that host are executed.

Close any open session and exit

An end of file condition on input, when in command mode, will trigger this operation as well.

Send one or more special

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):

Sends the

(Abort Processes) sequence.

Sends the

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

the remote system

the user's terminal.

Sends the

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

Sends the

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

Sends the

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

Sends the

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

Sends the

(End Of File) sequence.

Sends the

(End of Record) sequence.

Sends the current

escape character.

Sends the

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

If the remote side supports the

command,

will send the subnegotiation to request that the server send its current option status.

Sends the

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

Sends the

(No Operation) sequence.

Sends the

(Suspend Process) sequence.

Sends the

sequence. This sequence causes the remote system to discard all previously typed (but not yet read) input. This sequence is sent as

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

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

Sends the

sequence.

can be either a decimal number between 0 and 255, or a symbolic name for a specific

command.

can also be either

or

to print out help information, including a list of known symbolic names.

Prints out help information for the

command.

The

command will set any one of a number of

variables to a specific value or to

The special value

turns off the function associated with the variable. This is equivalent to using the

command. The

command will disable or set to

any of the specified variables. The values of variables may be interrogated with the

command. The variables which may be set or unset, but not toggled, are listed here. In addition, any of the variables for the

command may be explicitly set or unset.

If

is in localchars mode, or

is enabled, and the status character is typed, a

sequence is sent to the remote host. The initial value for the "Are You There" character is the terminal's status character.

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, say, a password).

If

is operating in

or old line by line 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

character.

If

is in

mode (see

below),

if

is operating in character at a time mode, then when this character is typed, a

sequence (see

above) is sent to the remote system. The initial value for the erase character is taken to be the terminal's

character.

This is the

escape character (initially ^]) which causes entry into

command mode (when connected to a remote system).

If

is in

mode (see

below) and the

character is typed, a

sequence (see

above) is sent to the remote host. The initial value for the flush character is taken to be the terminal's

character.

If

is operating in

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.

If

is in

mode (see

below) and the

character is typed, a

sequence (see

above) is sent to the remote host. The initial value for the interrupt character is taken to be the terminal's

character.

If

is in

mode (see

below),

if

is operating in character at a time mode, then when this character is typed, a

sequence (see

above) is sent to the remote system. The initial value for the kill character is taken to be the terminal's

character.

If

is operating in

or old line by line mode, then this character is taken to be the terminal's

character. The initial value for the lnext character is taken to be the terminal's

character.

If

is in

mode (see

below) and the

character is typed, a

sequence (see

above) is sent to the remote host. The initial value for the quit character is taken to be the terminal's

character.

If

is operating in

or old line by line mode, then this character is taken to be the terminal's

character. The initial value for the reprint character is taken to be the terminal's

character.

This is the rlogin mode escape character. Setting it enables rlogin mode, as with the

command-line option (q.v.)

If the

option has been enabled, then this character is taken to be the terminal's

character. The initial value for the kill character is taken to be the terminal's

character.

If the

option has been enabled, then this character is taken to be the terminal's

character. The initial value for the kill character is taken to be the terminal's

character.

If

is in

mode, or

is enabled, and the

character is typed, a

sequence (see

above) is sent to the remote host. The initial value for the suspend character is taken to be the terminal's

character.

This is the file to which the output, caused by

or

tracing being

will be written. If it is set to

then tracing information will be written to standard output (the default).

If

is operating in

or old line by line mode, then this character is taken to be the terminal's

character. The initial value for the worderase character is taken to be the terminal's

character.

Displays the legal

commands.

The

command (Set Local Characters) is used to set or change the state of the the special characters when the

option has been enabled. Special characters are characters that get mapped to

commands sequences (like

or

or line editing characters (like

and

By default, the local special characters are exported.

Verify the current settings for the current special 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.

Switch to the local defaults for the special characters. The local default characters are those of the local terminal at the time when

was started.

Switch to the remote defaults for the special characters. The remote default characters are those of the remote system at the time when the

connection was established.

Prints out help information for the

command.

Show the current status of

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

Toggle (between

and

various flags that control how

responds to events. These flags may be set explicitly to

or

using the

and

commands. More than one flag may be toggled at once. The state of these flags may be examined with the

command. Valid flags are:

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

If

and

are both

then when the

or

characters are recognized (and transformed into

sequences; see

above for details),

refuses to display any data on the user's terminal until the remote system acknowledges (via a

option) that it has processed those

sequences. The initial value for this toggle is

if the terminal user had not done an "stty noflsh", otherwise

(see

When the

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.

If the remote side supports the

option,

attempts to use it to perform automatic authentication. If the

option is not supported, the user's login name is propagated using the

option. Setting this flag is the same as specifying the

option to the

command or on the command line.

If

and

are both

then when either the

or

characters is typed (see

above for descriptions of the

and

characters), the resulting

sequence sent is followed by the

sequence. This procedure

cause the remote system to begin throwing away all previously typed input until both of the

sequences have been read and acted upon. The initial value of this toggle is

Enable or disable the

option on both input and output.

Enable or disable the

option on input.

Enable or disable the

option on output.

If this is

then carriage returns will be sent as

If this is

then carriage returns will be send as

The initial value for this toggle is

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

Toggles socket level debugging (useful only to the

The initial value for this toggle is

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

If this is

then the

and

characters (see

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

control sequences (respectively

and

see

above). The initial value for this toggle is

in old line by line mode, and

in character at a time mode. When the

option is enabled, the value of

is ignored, and assumed to always be

If

has ever been enabled, then

is sent as

and

and

are sent as

and

see

above).

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

Toggles the display of some internal

protocol processing (having to do with

options). The initial value for this toggle is

When the

toggle is enabled, if

is enabled the output from the

command will be formatted in a more user-readable format. Spaces are put between each character in the output, and the beginning of

escape sequences are preceded by a '*' to aid in locating them.

When the skiprc toggle is

does not read the telnetrc files. The initial value for this toggle is

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

When the

toggle is

prints out a message each time encryption is enabled or disabled. The initial value for this toggle is

This flag only exists if encryption support is available.

Displays the legal

commands.

Suspend

This command only works when the user is using the

Execute a single command in a subshell on the local system. If

is omitted, then an interactive subshell is invoked.

Get help. With no arguments,

prints a help summary. If a command is specified,

will print the help information for just that command.

uses at least the

and

environment variables. Other environment variables may be propagated to the other side via the

option.

global telnet startup values

user customized telnet startup values

The

command appeared in

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

the terminal's

character is only recognized (and sent to the remote system) when it is the first character on a line.

The source code is not comprehensible.