telnet(1C) TCP/IP R4.11 telnet(1C)
NAME
telnet - log in to another host over network
SYNOPSIS
telnet [-i] [-d] [-o] [-bi] [-bo] [-e] [-e escapechar] [-s] [-l]
[host [port] ]
DESCRIPTION
The telnet command logs in to another host using the TELNET protocol.
If you invoke telnet without arguments, it enters command mode,
indicated by its prompt (telnet>). In this mode, it accepts and
executes the commands listed below. When you invoke telnet with
arguments, it first checks to see if the arguments match the
switches. TELNET then checks to see if the host and port number are
legal. If the arguments are legal, TELNET performs an open command
(see below) with those arguments. If the remote host requests TERM
or window size information, TELNET supplies it.
In order to use the telnet service to create a session on a system
with DG/UX information security, the telnet service must be
authorized for the user name presented.
After a connection has been opened, telnet enters input mode. The
text you type is sent directly to the remote host. The telnet
command provides an eight-bit data path to the network if the local
stty settings provide one. You can toggle the scanning of some
special characters for NVT translation using the localchars command.
You cannot invoke TELNET commands in input mode; however, you can use
the escape character (initially ^]) to enter local mode. While in
local mode, you can invoke a TELNET command. After TELNET executes
the command, it returns you to input mode.
Commands
The following commands are available. You only need to type the
first three letters of any command to uniquely identify it.
bye Close any open TELNET session and exit telnet.
(Go back to the shell, or to the program that
called telnet.) This is the same as the quit
command.
close Close a TELNET connection and return to where
the connection was opened from (for example,
the shell, or TELNET command mode).
crmod Toggle carriage return mode. When enabled,
this mode changes the current setting for CR
in stty(1). If carriage return characters
received from the remote host are mapped to
CR; for example, crmod changes the setting to
NL, where NL is a line feed and a carriage
return. If the current setting in stty is NL,
crmod changes the setting to CR.
debug Toggle debug mode. Also, toggle the ability
to use certain commands. With debug on, the
following commands are enabled: listen, map,
send, and mode. These commands let you wait
for an incoming connection, change character
mappings, and change modes without negotiating
options.
CAUTION: Beware when using the debug command. TELNET
commands can be unpredictable when used in
debug mode.
escape [ string ] Set the TELNET "escape character". Use the
same syntax as for strings in the C
programming language (for example, use double
quotes). If the string is not specified,
telnet will prompt for it.
help [command] Get help. With no arguments, help prints a
help summary. If a command is specified, help
print the help information available about the
command only. The ? command is identical to
the help command.
listen [ port ] Listen on a port for an incoming connection.
This command works only in debug mode. Use
the escape character to abort the connection,
or the Interrupt key (often Ctrl-C) if the
connection has not yet been made.
localchars Toggle the local translation of specific
character sequences into TELNET NVT keyboard
sequences. Translation is off by default. In
the default mode, a special key such as the
stty interrupt key (often set to Ctrl-C) is
passed unmodified to the remote host for
possible processing. For remote UNIX systems,
this is usually preferable. If localchars is
toggled on, the Ctrl-C is intercepted locally
and translated into the standard TELNET
sequence for Interrupt Process (IP). The
remote host then decodes this sequence and
performs whatever actions are required to
interrupt the process. The status command
shows what translations are currently being
done.
log [ logfile ] Instruct TELNET to put the data that the
remote host sends to your terminal to a
logfile. Logging starts when you enter log
with the name of a logfile. Logging stops
when you enter log without an argument. If
the logfile does not exist, it will be
created. If it does, TELNET appends data to
the end of the file. Due to buffering, data
may not be fully written to the logfile until
logging is stopped.
map string NVTchar Substitute a string of your choice for an NVT
character. You can use this command only in
debug mode. NVT characters are: IP, AO, AYT,
EC, EL, BRK, and EOR (see Definitions below
for descriptions of these characters).
mode option type Change mode regardless of negotiated option.
You can use this command only in debug mode.
Option can be one of the following: EC, BI,
BO, or LI (see Definitions below for
descriptions of these options). Type can be
one of the following: on, off, always, never
(see Definitions below for descriptions of
these types).
CAUTION: When using the option types never and always,
you could ask for a particular option that the
remote server does not want. In such a case,
you can expect unusual results during the
connection.
negotiate option type Request negotiation on an option. You can
only request a negotiation; you cannot send an
announcement of the current mode. TELNET does
not notify you that the change has been made
or not. Use the command status to see the
results.
Option can be one of the following: SGA, EC,
BI, BO, ST, TM, or EX (see Definitions below
for descriptions of these options). Type can
be one of the following: on, off, always,
never (see Definitions below for descriptions
of these types).
open host [ port ] Open a connection to the named host. If no
port number is specified, telnet will attempt
to contact a TELNET server at the default
port. The host specification may be either a
hostname (see hosts(4)) or an Internet address
specified in the "dot notation" (see
inet(3N)).
options Toggle viewing of TELNET options processing.
When options viewing is enabled, all TELNET
option negotiations will be displayed.
Options sent by telnet are displayed as
"SENT", while options received from the TELNET
server are displayed as "RCVD".
prompt string Substitute a string of your choice in place of
the normal command prompt.
quit Close any open TELNET session and exit telnet.
(Go back to the shell, or to the program that
called telnet.)
resume Exit local mode and continue any suspended
remote mode. Returning to remote mode does
not automatically produce a shell prompt,
refresh the screen, or enter any characters.
You may take these actions yourself.
send NVTchar Send NVT special characters across your
network connection. (You can use this command
only in debug mode.) You can substitute any
of the following for NVTchar: Sync, IP, AO,
AYT, EC, EL, BRK, or EOR (see Definitions
below for descriptions of these characters).
shell [ command ] Create a shell process without terminating
TELNET. If you have a network connection, it
will remain suspended until you terminate the
shell process. Terminate the shell process by
entering the exit command. The ! command is
identical to the shell command.
status Show the current status of telnet parameters.
This includes the host to which you are
connected, the local character translations,
and the state of debugging.
terminator string Add string to the list of terminators.
Terminators determine when to ship characters
in line mode. The list of terminators
includes the default characters (see below)
and any you specify. They cannot be the
escape character or NVT special characters.
The default terminators are:
New Line
End-of-file character
Each character in the string you specify will
be a terminator.
un-term string Cancel terminator status for specified
characters.
z Suspend telnet. This command works only when
the user is using DG/UX csh(1); it interacts
with the C shell's job control facilities.
When you issue a suspend command, you are then
placed in the C shell. To return to the
telnet session, type fg job#. Job# is the job
number that was returned when you suspended
the TELNET session. See csh(1) for more
information on how the C shell handles job
control.
? [ command ] Get help. With no arguments, ? prints a help
summary. If a command is specified, ? print
the help information available about the
command. This is a synonym for the help
command.
! [ command ] Create a shell process without terminating
TELNET. If you have a network connection, it
will remain suspended until you terminate the
shell process. Terminate the shell process by
entering the exit command. This command is
identical to the shell command.
Switches
Some of the commands shown above are available as switches. Switches
let you issue commands when you execute telnet, without having to
enter command mode first. The following table shows the available
switches, their corresponding commands, and definitions:
Switch Command Definition
-istype Negotiate Negotiate binary input option.
-ostype Negotiate Negotiate binary output option.
-d Debug mode Turn debug mode on.
-estype Negotiate Negotiate remote echo option.
-e escapechar Escape Sets the telnet escape chaacter.
-sstype Negotiate Negotiate remote side suppress-go-ahead
option.
-l[port] Listen Listen for connections on the given
port number.
-bi, -bo These mode switches send and receive
the data as is, with no translation
from either side. All control
characters are received and not
ignored.
The argument stype indicates whether or not you want the option.
You must substitute either the letter a, for always, or the letter n,
for never.
The argument escapechar specifies the initial telnet escape
character. If escapechar is an empty string (most shells will
require quotes), then the telnet escape character mechanism will be
disabled.
For the argument [port], you must substitute the port number of the
connection you are monitoring. If you do not specify a port number,
telnet will assign one to you.
Definitions
This section describes the NVT characters, options, and types that
are used with the commands map, mode, negotiate, and send. The NVT
characters are as follows:
NVT Character Meaning
Sync A TCP urgent notification with the
command data mark (DM).
Interrupt process (IP) Suspends, interrupts, aborts, or
terminates a user process.
Break character (BRK) Sends the appropriate break character to
the remote process.
Abort output (AO) Allows a process to run to completion,
but does not send the output to the
user's terminal.
Are you there (AYT) Provides the user with visible evidence
that the system is still up and running.
Erase character (EC) Deletes the last preceding character or
printed position the user types.
Printed position means several
characters that are a result of
overstrikes.
Erase line (EL) Deletes all the data on the current line
of input.
End of record (EOR) Allows the user to flush the input
buffer before a terminator character is
encountered.
The strings used for option in the commands mode and negotiate are as
follows:
Option Meaning
SGA Suppress go-aheads
EC Foreign echoing (for negotiate)
EC Local echoing (for mode)
BI Binary input
BO Binary output
ST Status
TM Timing mark
EX Extended option
LI Line mode
telnet(1C) TCP/IP R4.11 telnet(1C)
When using the command mode, substitute one of the following strings
for type:
Type Function
on Turns on the mode regardless of the option that
normally controls it. However, if the option is
negotiated after your change, the mode changes to
correspond with the change in the option.
off Turns off the mode regardless of the option that
normally controls it. However, if the option is
negotiated after your change, the mode changes to
correspond with the change in the option.
always Turns the mode on and leaves it on regardless of
the option. Mode is changed when you invoke the
change or when you close the connection. When you
close the connection, the mode returns to the
default setting.
never Turns the mode off and leaves it off regardless of
the option. Mode changes when you invoke the
change or when you close the connection. When you
close the connection, the mode returns to the
default setting.
When using the command negotiate, substitute one of the following
strings for type:
String Function
on Try to negotiate an option on. All future
requests to negotiate the option off will be
honored.
off Try to negotiate an option off. All future
requests to negotiate the option on will be
honored.
always Try to negotiate an option on. All future
requests from the server program to negotiate the
option off will be honored. However, the user
program immediately sends one request to the
server to negotiate the option back on.
never Demands an option to be negotiated off and left
off. All future requests to negotiate it on will
be refused. You must know whether or not the
server will abort when that option is refused.
SEE ALSO
rlogin(1C), telnetd(1M), inet(3N), hosts(4).
Licensed material--property of copyright holder(s)