telnet(1C) C2 Trusted DG/UX 5.4.2T telnet(1C)
NAME
telnet - log in to another host over network
SYNOPSIS
telnet [-i] [-d] [-o] [-bi] [-bo] [-e] [-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.
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
(see Using TCP/IP on the DG/UX System for more details on character
translation). 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.
Licensed material--property of copyright holder(s) 1
telnet(1C) C2 Trusted DG/UX 5.4.2T telnet(1C)
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
Licensed material--property of copyright holder(s) 2
telnet(1C) C2 Trusted DG/UX 5.4.2T telnet(1C)
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
Licensed material--property of copyright holder(s) 3
telnet(1C) C2 Trusted DG/UX 5.4.2T telnet(1C)
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.
Licensed material--property of copyright holder(s) 4
telnet(1C) C2 Trusted DG/UX 5.4.2T telnet(1C)
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.
-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.
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.
Licensed material--property of copyright holder(s) 5
telnet(1C) C2 Trusted DG/UX 5.4.2T telnet(1C)
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
Licensed material--property of copyright holder(s) 6
telnet(1C) C2 Trusted DG/UX 5.4.2T 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) 7