telnet.netkit

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 c open command implicitly; see the description below.

Options:

• 4 Force IPv4 address resolution.
• 6 Force IPv6 address resolution.
• 8 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.
• E Disables the escape character functionality; that is, sets the escape character to ``no character''.
• L Specifies an 8-bit data path on output. This causes the option to be negotiated on just output.
• a 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 getlogin(3)
• address Use bind(2) on the local socket to bind it to a specific local address.
• d Sets the initial value of the c debug toggle to
• r Emulate rlogin(1) 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.
• tos Sets the IP type-of-service (TOS) option for the telnet connection to the value
• escapechar 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.
• user 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 c open command.
• tracefile Opens for recording trace information. See the c set tracefile command below.
• host Specifies a host to contact over the network.
• port 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 c localchars toggle is (the default for "old line by line"; see below), the user's c quit , c intr , and c flush characters are trapped locally, and sent as protocol sequences to the remote side. If has ever been enabled, then the user's c susp and c eof are also sent as protocol sequences, and c quit is sent as a instead of There are options (see c toggle c autoflush and c toggle c autosynch 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 c quit and c intr ) .

Commands:

The following commands are available. Unique prefixes are understood as abbreviations.

Note that the current version of does not support authentication.

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

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

... The encrypt command controls the protocol option. If was compiled without encryption, the c encrypt command will not be supported.

Valid arguments are as follows:

• [input|output] 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 ?''.
• [input|output] 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 ?''.
• input This is the same as ``encrypt start input''.
• -input This is the same as ``encrypt stop input''.
• output This is the same as ``encrypt start output''.
• -output This is the same as ``encrypt stop output''.
• [input|output] Attempt to begin encrypting. If you do not specify input or output, encryption of both input and output is started.
• status Display the current status of the encryption module.
• [input|output] Stop encrypting. If you do not specify input or output, encryption of both is stopped.
• type 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.

arguments... The c environ 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 c environ command are:

• value 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.
• variable Remove any existing definition of
• variable Mark the specified variable for propagation to the remote host.
• variable 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 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 c environ command.

logout Send the protocol option to the remote host. This command is similar to a c close 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.

type 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.

• character Disable the option, or, if the remote side does not understand the option, then enter "character at a time" mode.
• line Enable the option, or, if the remote side does not understand the option, then attempt to enter "old-line-by-line" mode.
• -isig Attempt to enable (disable) the mode of the option. This requires that the option be enabled.
• -edit Attempt to enable (disable) the mode of the option. This requires that the option be enabled.
• -softtabs Attempt to enable (disable) the mode of the option. This requires that the option be enabled.
• -litecho Attempt to enable (disable) the mode of the option. This requires that the option be enabled.
• ? Prints out help information for the c mode command.

Xo c open Ar host 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.

quit Close any open session and exit An end of file condition on input, when in command mode, will trigger this operation as well.

arguments 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):

• abort Sends the (Abort Processes) sequence.
• ao Sends the (Abort Output) sequence, which should cause the remote system to flush all output the remote system the user's terminal.
• ayt Sends the (Are You There?) sequence, to which the remote system may or may not choose to respond.
• brk Sends the (Break) sequence, which may have significance to the remote system.
• ec Sends the (Erase Character) sequence, which should cause the remote system to erase the last character entered.
• el Sends the (Erase Line) sequence, which should cause the remote system to erase the line currently being entered.
• eof Sends the (End Of File) sequence.
• eor Sends the (End of Record) sequence.
• escape Sends the current escape character.
• ga Sends the (Go Ahead) sequence, which likely has no significance to the remote system.
• getstatus If the remote side supports the command, c getstatus will send the subnegotiation to request that the server send its current option status.
• ip Sends the (Interrupt Process) sequence, which should cause the remote system to abort the currently running process.
• nop Sends the (No Operation) sequence.
• susp Sends the (Suspend Process) sequence.
• synch 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 x 4.2 system -- if it doesn't work, a lower case "r" may be echoed on the terminal).
• cmd
• cmd
• cmd
• cmd 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 c help or c ? to print out help information, including a list of known symbolic names.
• ? Prints out help information for the c send command.

value

value The c set command will set any one of a number of variables to a specific value or to The special value c off turns off the function associated with the variable. This is equivalent to using the c unset command. The c unset command will disable or set to any of the specified variables. The values of variables may be interrogated with the c display command. The variables which may be set or unset, but not toggled, are listed here. In addition, any of the variables for the c toggle command may be explicitly set or unset.

• ayt 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.
• 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, say, a password).
• eof 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 c eof character.
• erase If is in c localchars mode (see c toggle c localchars below), if is operating in "character at a time" mode, then when this character is typed, a sequence (see c send c ec above) is sent to the remote system. The initial value for the erase character is taken to be the terminal's c erase character.
• escape This is the escape character (initially "^[") which causes entry into command mode (when connected to a remote system).
• flushoutput If is in c localchars mode (see c toggle c localchars below) and the c flushoutput character is typed, a sequence (see c send c ao above) is sent to the remote host. The initial value for the flush character is taken to be the terminal's c flush character.
• forw1
• forw2 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.
• interrupt If is in c localchars mode (see c toggle c localchars below) and the c interrupt character is typed, a sequence (see c send c ip above) is sent to the remote host. The initial value for the interrupt character is taken to be the terminal's c intr character.
• kill If is in c localchars mode (see c toggle c localchars below), c and if is operating in "character at a time" mode, then when this character is typed, a sequence (see c send c el above) is sent to the remote system. The initial value for the kill character is taken to be the terminal's c kill character.
• lnext If is operating in or "old line by line" mode, then this character is taken to be the terminal's c lnext character. The initial value for the lnext character is taken to be the terminal's c lnext character.
• quit If is in c localchars mode (see c toggle c localchars below) and the c quit character is typed, a sequence (see c send c brk above) is sent to the remote host. The initial value for the quit character is taken to be the terminal's c quit character.
• reprint If is operating in or "old line by line" mode, then this character is taken to be the terminal's c reprint character. The initial value for the reprint character is taken to be the terminal's c reprint character.
• rlogin This is the rlogin mode escape character. Setting it enables rlogin mode, as with the command-line option (q.v.)
• start If the option has been enabled, then this character is taken to be the terminal's c start character. The initial value for the kill character is taken to be the terminal's c start character.
• stop If the option has been enabled, then this character is taken to be the terminal's c stop character. The initial value for the kill character is taken to be the terminal's c stop character.
• susp If is in c localchars mode, or is enabled, and the c suspend character is typed, a sequence (see c send c susp above) is sent to the remote host. The initial value for the suspend character is taken to be the terminal's c suspend character.
• tracefile This is the file to which the output, caused by c netdata or c option tracing being will be written. If it is set to then tracing information will be written to standard output (the default).
• worderase If is operating in or "old line by line" mode, then this character is taken to be the terminal's c worderase character. The initial value for the worderase character is taken to be the terminal's c worderase character.
• ? Displays the legal c set

commands.

state The c slc 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 c ip or c quit ) or line editing characters (like c erase and c kill ) . By default, the local special characters are exported.

• check 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.
• export 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.
• import 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 c slc command.

status 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 c set and c unset commands. More than one flag may be toggled at once. The state of these flags may be examined with the c display command. Valid flags are:

• authdebug Turns on debugging for the authentication code. This flag only exists if authentication support is enabled.
• autoflush If c autoflush and c localchars are both then when the c ao , or c quit characters are recognized (and transformed into sequences; see c set 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
• autodecrypt 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.

autologin 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 c open command or on the command line.

autosynch If c autosynch and c localchars are both then when either the c intr or c quit characters is typed (see c set above for descriptions of the c intr and c quit characters), the resulting sequence sent is followed by the sequence. This procedure c should 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

binary Enable or disable the option on both input and output.

inbinary Enable or disable the option on input.

outbinary Enable or disable the option on output.

crlf 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

crmod 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

debug Toggles socket level debugging (useful only to the c super user ) . The initial value for this toggle is

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

localchars If this is then the c flush , c interrupt , c quit , c erase , and c kill characters (see c set above) are recognized locally, and transformed into (hopefully) appropriate control sequences (respectively c ao , c ip , c brk , c ec , and c el ; see c send 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 c localchars is ignored, and assumed to always be If has ever been enabled, then c quit is sent as c abort , and c eof and suspend are sent as c eof and c susp , see c send above).

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

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

prettydump When the c netdata toggle is enabled, if c prettydump is enabled the output from the c netdata 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.

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

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

verbose_encrypt When the c verbose_encrypt 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 c toggle commands.

z Suspend This command only works when the user is using the

command Execute a single command in a subshell on the local system. If c command is omitted, then an interactive subshell is invoked.

command 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.

The command appeared in x 4.2 .

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 c eof 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.