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Telnet User Guide
User Telnet (hereafter called Telnet) provides facilities for
communicating with host computers via the ARPA network utilizing
the TELNET protocol. The purpose of the Telnet program is
threefold. It converts various terminals connected to TENEX into
a standard type of terminal called a network virtual terminal
(NVT) by interposing programs in the character streams between
the terminal keyboard and printer and the terminal port on the
host computer. Secondly, it provides information about the
network to assist a user in establishing connections. Thirdly,
it multiplexes the terminal among several remote jobs.
Instructions to the Telnet program are given via the Telnet
Command Interpreter. When in command mode (see below),
characters typed on the user's terminal are read by the Telnet
command interpreter and decoded as commands to perform various
actions by Telnet.
The Telnet command interpreter has two unique features. The
command interpreter will refuse to hear anything it does not
understand. With full-duplex terminals, this means that no echo
will appear for characters which are not valid successors of the
previous input. In any case, the character is ignored and a bell
is typed out. The input stream that has already been typed is
not forgotten however. Therefore, it is only necessary to type
the correct character and not the complete command. This feature
may be turned off with the "no fancy.command.interpret" command.
The other unique feature of the Telnet command interpreter is the
use of question mark to discover what the command interpreter
expects next. Typing a "?" at any time in command mode will
elicit a list of words the command interpreter is expecting.
Thus, typing a "?" when nothing has been typed will yield a list
of all possible top-level commands. Typing "co?" will yield a
list of all commands starting with "co". Typing "connection.to
?" will yield a list of possible arguments to the "connection.to"
The command interpreter provides command completion whenever a
terminator is typed (full-duplex terminals only) and an exact
match is achieved with some command or a unique initial substring
is typed. Command completion may be suppressed with the
"concise" command. Terminators are space, comma, alt-mode, and
carriage return. Terminators are often not distinguished and are
thus equivalent. Where necessary, comma is used to separate list
items, space terminates a command or option and signals the
desire to specify more options, carriage return ends a command
unless more information is necessary. Altmode is the same as
space except that it will cause command completion in those modes
where it is normally suppressed.
As mentioned above, characters typed on the terminal keyboard may
be used in two ways: either as commands to Telnet, or as input to
the remote host. The choice is made on the basis of whether
Telnet is in remote mode or command mode. In command mode,
characters typed on the terminal keyboard are read by the Telnet
command interpreter and decoded as commands to perform various
actions. TELNET is initially in command mode and will revert to
command mode whenever the Telnet escape character (see below) is
The opposite of command mode is remote mode. In remote mode,
characters typed on the keyboard (with certain exceptions) are
not examined by Telnet at all, but are merely passed on to the
remote host computer. Remote mode is normally entered after any
command is executed when the current connection exists. The
"local.mode" command may be used to defeat this. The effect of
the "local.mode" command is cancelled by the "remote.mode"
command or by the "connection.to" or "retrieve.connection"
Escaping Back to Command Mode
At any time, typing the Telnet escape character (initially
control-Z (SUB)) will cause Telnet to stop whatever it is doing
and return to command mode. Occasionally, a slight delay may be
experienced due to the need to clean up whatever was happening at
the time. Telnet announces the switch to command mode by the
appearance of a sharp sign "#" at the left margin. Telnet also
indicates the transition out of command mode by the appearance of
another sharp sign followed by a new line.
WARNING: If you have control-Z anywhere in your programming, you
should change your escape character for Telnet to other than
control-Z to avoid mishaps.
There are two ways to make a connection. Typing "connection.to
<host> [<qualifiers>]" or simply typing "<host> [<qualifiers>]"
will cause a connection attempt to be made. If successful, the
connection will be said to be complete and the terminal will be
placed in remote mode. If unsuccessful, the connection will be
said to be "incomplete because ---" with a reason given; also if
the remote host is down, a line is typed telling why and for how
long. By terminating the host name with a space, one or more
qualifiers may be specified. Ordinarily socket 1 is assumed.
Thus without a qualifier, the connection will be made to the
"logger" on the remote system. By using an octal number as a
qualifier, the connection will be made to the socket so
specified. A set of names is available for specifying the socket
desired. This set consists of names for all the standard
The "wait" qualifier may be used to camp-on the connection. This
qualifier causes Telnet to repeat the attempt to connect in the
event of a failure until it finally succeeds. An initial failure
causes a message to that effect to be printed. When the attempt
finally succeeds, bells are typed out to wake the user up. The
attempt to connect may be aborted by typing the Telnet escape
The "load.settings.from..." qualifier (possibly qualified with
"no") may be used to cause (inhibit) the mode flags to be
initialized from the mode file. When inhibited, the current
modes are used.
The "name.for.connection" qualifier may be used to specify a name
for this connection other than the one assigned by Telnet. A
name for the connection may also be given later by the
The "disconnect" command is used to close the current connection.
This will not necessarily log you out from the remote host so you
should perform the logout procedure for that host before
disconnecting. The disconnect command takes an optional argument
specifying the name of a particular connection to be
disconnected. See multiple connections and connection names
In the event that the network connections are severed by a
network failure, the message "IO error for connection <name>" is
printed, the connection is disconnected, and Telnet reverts to
command mode. This may happen even if the error occurs on a
connection which is not current. If the remote host initiates a
disconnect, a message to that effect is printed and the same
action is taken.
If the remote host on the current connection stops responding
when input is being sent, a line is typed, "Host not responding
on connection xxx." (In this case the connection is NOT lost.)
When the remote host resumes operating, the user is informed:
"Service restored on connection xxx."
Telnet allows several options concerned with echoing. Echos may
be generated by the terminal, by Telnet, or by the remote host.
Telnet determines if the terminal is generating echoes when
started by examining the mode word for the terminal. The
"terminal.type.is" command may be used to change this.
If the terminal is echoing, then Telnet will do everything
possible to cause the remote host to not generate echoes, and
Telnet will not generate echoes itself. If the terminal is not
generating echoes, then Telnet determines whether it should echo
or not by information in the mode file (if any) or by the "echo
remote"/"echo local" commands, or by information sent from the
Telnet keeps the remote host informed about how echoing is being
done and if the remote host is suitably equipped, it will follow
along. If not, then the user will have to give commands to the
remote host to achieve the proper echoing. Telnet also will
respond to commands from the remote host concerning who should be
echoing. If Telnet believes the terminal is doing its own
echoing, it will respond to any request from the remote host to
not echo by an "I'll echo" command.
Line-Buffering and End of Line Conventions
Telnet provides an optional line buffer for use with
line-oriented operating systems. In this mode, characters typed
in remote mode are stored in a local buffer up through an end of
line. Prior to the end of line, the currently buffered line may
be edited using control-A (SOH) or control-H (BS) to delete
characters, control-X (CAN) to delete everything, and control-R
(DC2) to retype the current contents. Telnet always converts the
TENEX EOL into the NVT EOL. TENEX in turn converts a carriage
return into the TENEX EOL. Thus typing a carriage return will
cause the buffered line to be transmitted. Linefeed may also be
used to terminate a line. In this case, the transmitted line
will end with only linefeed, not the NVT EOL.
Telnet provides an optional linefeed echo for carriage return.
If the remote host provides a linefeed also, then the echo
generated by Telnet should be suppressed with the "echo no
linefeed.for.carriage.return" command. In remote echo mode,
Telnet generates no echos whatsoever. In this mode, all echos
must be provided by the remote host.
Several status commands are available for discovering facts about
the network. None of these commands will affect the state of the
current connection. The status commands include where.am.I,
status.of, netstatus, and socket.map. These commands are
Several commands are available to send characters which do not
appear on the terminal. "Code" takes an octal (decimal if
precede by "D", hexadecimal if preceded by "H") argument and
sends the character with that code. The word "code" may be
omitted and just the argument typed. "Control" takes a character
argument and sends the corresponding control character (the low
order five bits of the character) is sent. The "!break!" command
sends the NVT break character which is mapped by some systems
into the equivalent of the attention, quit or break key which
appears on some terminals.
To facilitate operation with systems requiring frequent use of
special characters or lower/upper case graphics which a
particular terminal may lack (e.g. 33 Teletypes have no lower
case), case shift characters may be defined for upper/lower
character/lock shifts and characters may defined which will
translate into attention or break (NVT 201), and the synch
sequence. The "case.shift.prefix.for", "attention.character=",
and "synch.character=" commands are available to independently
set each of these characters. In addition, a character may be
defined ("quote.prefix" command) to be a single character quote.
The character following this character is always sent regardless
of any special action it may otherwise have.
If possible, case shift characters will be used to indicate the
case of both input and output. Thus the case shift characters
may not be echoed when typed but rather before the output.
All special characters are listed by the "current.modes.are"
command. This includes the escape character and the clear output
To leave Telnet, it is first necessary to return to command mode
by typing the escape character. This is because while in remote
mode all characters except the escape character are passed on to
the remote host or modify characters passed to the remote host.
Once in command mode, you may return to the EXEC by typing
control-C (ETX) or by using the "quit" command. Continuing from
the EXEC will resume with no loss. The "logout" command will
disconnect from any remote job and logout your local job. The
"exec" command will start up an inferior EXEC under Telnet. From
this inferior EXEC, it is possible to perform assemblies or any
other task involving the running of subsystems. The "run"
command allows an arbitrary program to be run in an inferior fork
of Telnet. The "run" may be interrupted by the Telnet escape
Telnet provides a facility for multiplexing a user's terminal
among several remote jobs thus allowing several simultaneous
activities. This is done by giving a name for each connection as
it is created. The user may specify the name, or Telnet will
default the name to a number. The "retrieve.connection..."
command causes the named connection to be made current and remote
mode to be entered. Non-current connections remain active, but
any output received is buffered until that connection again
becomes active. Terminal input goes only to the currently active
Telnet may be made to announce the receipt of output on a
non-current connection with the "signal.waiting.output" command;
it may also be caused to hunt for and switch to any active
connection-- see "wait.for.any.active.connection" and
The name of the current connection may be changed after it is
established by means of the "name.for.current.connection"
command. The name so specified may be up to 6 characters in
length and must be unique.
Telnet provides a means of saving on a file a copy of the
typescript for a session. This is useful for producing hard copy
of the session when using a scope terminal or for producing
documentation of procedures or demonstrations. Telnet is started
with no typescript file assigned. The "typescript.to.file"
command may be used to assign one, either the default temporary
file TELNET.TYPESCRIPT;S in the LOGIN directory, or one named by
the user. The typescript consists of a nearly exact copy of what
appears on the terminal with the exception of that which occurs
during the execution of the "exec" or "run" or "ddt" commands.
"Nearly" refers to slight differences in the spelling of file
names in certain Telnet commands. For privacy, the typescript
file is given a protection that allows no access to anyone but
The output stream may be diverted to some other file with the
"divert.output.to.file" command. While diverting output, Telnet
sends all output to the indicated file and sends a line to the
terminal only when the terminal's output buffer is empty. Thus
the terminal monitors the transmission of the stream to the file.
The diverted output consists only of characters from the remote
host. Telnet commands and responses do not appear in the
diverted information. This mode is useful as a primitive file
transfer mechanism or to allow printing of large amounts of
terminal output to be done with the lineprinter. It is cancelled
by "no divert.output ...".
The input stream to a remote job may be taken from a file instead
of the local terminal by means of the command
"take.input.stream.from.file". Telnet blocks terminal input to
the connection current when the file is specified, and transmits
characters from the named file (echoing as usual according to
current modes). However, input to other connections and in
command mode is from the user's terminal. When the given file
reaches EOF the file is closed and released, and input reverts to
the terminal. The user may also manually cancel file input by
escaping to command mode and giving "no take.input ...". This
mode is useful for routine sequences performed in the remote job.
Note that a connection must be established and current when input
to it is diverted to a file.
Telnet Command Summary
Connection.to <host> or host name
Performs ICP to connect to the indicated host.
Options are available for specifying initial
connection socket name or number, and initializing
modes from the mode file via the following
subcommands. Note that if <host name> is used as
a command, only the NAME of a SERVER host may be
given (e.g., BBN-TENEX). The argument for
"Connection.to" may be any host name or an octal
An ICP is performed to connect to the
indicated service socket. Normally
socket 1 is assumed.
Sets socket to 1.
The connection attempt is repeated until
Sets the name for this connection as
Determines whether to use current mode
settings or to load new ones from the
Disconnects the current connection. This will not
necessarily log you out from the remote host.
Perform the necessary operations before
Disconnects the connection with the specified
Connects to BBN socket 15600031 where-in the
RSEXEC (Resource-Sharing Executive) is found.
Performs ICP with the indicated host and prints
Sets echo mode according to the following
Turns off echoes generated by Telnet and
signals the remote computer to generate
echoes. Some hosts are not yet equipped
to handle this signal and may require
additional action to cause the remote
computer to generate echoes. If Telnet
believes it is connected to a local
half-duplex terminal, it will complain
about remote echoes but do it anyway.
Turns on Telnet generated echoes and
signal the remote computer to not
generate echoes. Note that Telnet never
generates echoes for terminals it
believes have local echo of their own.
TENEX translates carriage return to EOL,
Telnet sends the EOL as the TELNET EOL
(i.e. carriage return-linefeed). For
some systems, the TELNET EOL is
translated into carriage return. For
these systems, the appropriate echo is
carriage return. Other systems
translate the TELNET EOL into carriage
return-linefeed. For these systems the
appropriate echo is carriage
return-linefeed. This subcommand causes
the latter echo to be generated.
[no] control.character.echo.for <list of
Turns on local echoes for the indicated
control characters. Normally only
control-G,J, and M (bell, linefeed, and
carriage return) are enabled.
Allows the user to change Telnet's opinion of his
terminal according to the following subcommands.
Each command may be preceded by the word "no" to
negate its meaning.
Terminal generates its own echoes.
Terminal does not generate its own
The terminal has lower case characters.
If connected, this command prevents Telnet from
returning to remote mode after each command.
If connected, this command causes Telnet to return
to remote mode after each command. If not
connected, it does nothing.
May appear before some commands to reverse their
Prints the state of connection terminal mode
flags, and all special characters.
Causes each character typed to be transmitted as
it is typed.
Causes Telnet to accumulate a line of text before
transmitting. A line ends on linefeed or EOL or
altmode (esc). The line may be edited with
control-A, X, and R.
Causes lower case letters to be transmitted as
their upper case equivalents.
Causes upper case letters to be transmitted as
their lower case equivalents.
Causes all characters to pass through Telnet and
TENEX untouched. This is needed for special
terminals such as the IMLAC using special
character stream protocols.
Allows the specification of the four case shift
characters according the following four
Same as the "Lower" command. Subsequent
upper case input will be converted to
Converts the following letter to lower
Same as "Raise" command. Subsequent
lower case input will be converted to
Converts the following character to
Causes all following characters to be unshifted.
I.e. undoes both an upper case lock and a lower
Causes the following character to be transmitted
without regard to any special significance it may
The specified character will be converted to the
TELNET synch sequence. The TELNET synch sequence
is used to cause the remote host examine its input
stream to the current point for any special
characters (interrupts, attentions etc.). All
non-special may be thrown away.
The specified character will be converted to the
TELNET break or attention character. This
character is equivalent to the attention, quit, or
break key on certain terminals and may be
necessary for using some systems. The !Break!
command generates the same character.
Turns off automatic command completion. Saves
typeout at the expense of readability.
The opposite of concise.
Commands are checked character by character. If a
character does not fit, it is ignored and not
echoed (full duplex terminals only).
Causes all subsequent output from the remote
computer to be written on the specified file. Use
"No divert..." to stop this.
Causes subsequent input to the remote host on the
current connection to be read from the specified
file; input to other connections and in command
mode is still from the user's terminal. File is
automatically closed and released at EOF; user may
force this by "No take.input...", after escaping
to command mode.
A record of the session is kept on a file
including both input and output. This is useful
for providing hard copy with scope terminals.
The file kept is TELNET.TYPESCRIPT;S in
the LOGIN (not connected) directory.
typescript.to.file <filename> <cr>
The named file receives the typescript.
The typescript file (if any) is closed
and released; subsequent terminal
activity is not saved.
The specified character becomes the Telnet escape
character. This character must be a TENEX
interrupt character. "?" will type what these
WARNING: If you have anywhere in your programming
a control-Z you should change your escape
character in TELNET to other than control-Z to
The specified character becomes the clear output
buffer character. Typing this character generates
an interrupt which causes the terminal output
buffer and any accumulated output to be cleared.
Prints the file <SYSTEM>TELNET.HELP on the user's
Looks up the given identifier in the Help file and
prints the accompanying description; an efficient
way to read the Help text. Type "describe ?" to
get a list of identifiers; command recognition
operates on input of identifier.
Prints a list of all current connection on the
system. Optional arguments may be used to select
a particular host and a particular connection
Runs the specified file. Like the EXEC's run
Returns from Telnet to the superior fork (usually
the EXEC). May be continued with no loss.
Logs out the local job (not the remote one).
Requires confirmation with a carriage return.
Re-initializes Telnet producing an essentially
Enters ddt. If ddt is not loaded, this will
result in an unexpected interrupt. No harm is
done if this happens.
Starts up an inferior EXEC under Telnet. This
EXEC may be used like an ordinary EXEC to run
subsystems etc without disturbing any existing
connections. The Telnet escape character will
return to Telnet however.
Transmits the character specified by the argument.
The argument is a taken as an octal number unless
preceded by "d" for decimal or "h" for
hexadecimal. The argument may be preceded by "o"
The "code" command argument may be used as a
command by itself and will cause the indicated
code to be transmitted.
Transmits the TELNET break character.
Transmits the TELNET synch sequence. Occasionally
the "!synch!" command will work where the synch
character will not since the command bypasses the
buffering which may interfere with the use of the
Causes the current mode flags to be saved on the
<SYSTEM>TELNET.MODES file under the specified
host. Requires write access to the file and is
thus not available to ordinary users.
Retrieves the connection previously saved under
the specified name.
Used with multiple connections to wait for and
switch attention to the next connection that has
any output waiting. Useful when several
independent tasks are being run and you wish to
know when one completes and switch to that task.
Used to switch between tasks on several
connections which may each be inactive for long
periods. If the current connection is inactive on
both input and output for a given number of
minutes, Telnet will begin to hunt for any other
active connection. If and only if one is found,
that connection is made current. The "inactivity
time constant" may be specified as any positive
integral number of minutes if the "auto.switch..."
command is terminated by a space. A <cr>
terminator invokes the default value of 2 minutes.
"No auto.switch..." disables this feature (current
connection remains current until manually
Prints a summary of the local job, system, user,
terminal and the remote host and socket.
Causes all non-current connections to print a
message when output becomes available.
Lists all current host names with corresponding
octal host numbers.
Lists the name, local socket, foreign host, and
foreign socket of all connections.
Marks all connections to the specified host as
dead and sends a reset to that host. Requires
wheel or operator special capability.
An initial semi-colon causes the remainder of the
line to be ignored. Useful for comments or typing