TELNET, TN, TN3270(1c,C) AIX TCP/IP User's Guide TELNET, TN, TN3270(1c,C)
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telnet, tn, tn3270
PURPOSE
Provides the TELNET interface for logging in to a foreign host.
SYNTAX
+------+ +---------------------+ +--------------------+
telnet, tn ---| |--| |--| |-...
+- -d -+ +- -n net_trace_file -+ +- -e terminal_type -+
+-------------------+
...-| +--------+ |--|
+- host -| |-+
+- port -+
DESCRIPTION
The telnet command implements the TELNET protocol, which allows remote login to
other hosts. It uses the Transmission Control Protocol (TCP) m m u nicate
with other hosts in the network. The tn command is identical to the telnet
command, and in the following discussion, telnet means either the telnet
command or the tn command. The tn3270 command is used to connect to an IBM
main frame system and is equivalent to running telnet -e3270.
The telnet command operates in two different modes: command mode and input
mode. When issued without arguments, telnet enters command mode, as indicated
by the "telnet>" prompt. In this mode, the subcommands listed under
"Parameters" can be executed.
If the telnet command is issued with arguments, it performs a n open subcommand
with those arguments, then enters input mode. The type of input mode is either
character-at-a-time or line-by-line, depending on what the remote system
supports.
In character-at-a-time mode, most text typed is immediately sent to the remote
host for processing. In line-by-line mode, all text is echoed locally and
completed lines are sent to the remote host. The local echo character is used
to shut the local echo off and turn it back on. Its initial value is Ctrl-E.
In either input mode, if toggle localchars is true (see "Parameters"), the
user's QUIT, INTR : , and FLUSH characters are trapped locally and sent as
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TELNET sequences to the remote host. The toggle autoflush and toggle autosynch
subcommands cause this action to flush subsequent output to the terminal until
the remote host acknowledges the TELNET sequence and to flush previous terminal
input (in the case of QUIT and INTR).
To enter telnet command mode while connected to a remote host , type the TELNET
escape key sequence. The default escape sequence is Ctrl-T.
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You may use screen-oriented programs on a host with which you are communicating
through telnet. The telnet comman d will pass the name of your local terminal
type through to the remote host when you first connect to it. If the remote
host supports terminal-negotiation and does not recognize the name of you r
terminal, telnet will attempt to negotiate a mutually acceptable terminal type
with the remote host. If you are using an HFT terminal (such as the System/370
console), telnet can emulate either a DEC VT100 terminal or an IBM 3270
terminal. If your local terminal is not an HFT, telnet usually can emulate an
IBM 3270 terminal. If you can use the vi command (see the AIX System/370 Text
Formatting Guide and the A Operating System Commands Reference for information
on the vi command) on your terminal, then telnet can emulate a 3270 using your
terminal. If none of the terminals telnet can emulate are acceptable to the
remote host, the original terminal type will be used. You may specify a
terminal-type to be emulated. If you do so, telnet will not negotiate for
terminal type with the remote host. You can bypass terminal emulation and
negotiation altogether by asking telnet to emulate terminal "none."
To override the terminal negotiation from the console, use the EMULATE
environment variable or the -e option. To determine whether terminal-type
negotiation is performed, the following list describes the order of the telnet
command processing:
o The -e command line flag. (No negotiation)
o The EMULATE environment variable. (No negotiation)
o If the first two items are not present, terminal-type negotiation occurs
automatically.
If the client and the server negotiate to use a 3270 data stream, the keyboard
mapping to be used is determined by the following precedence:
$HOME/.3270keys User's 3270 keyboard mapping.
/etc/3270.keys Default 3270 keyboard mapping.
The telnet command supports these 3270 terminal types: 3277-1 , 3277-2, 3278-2,
3278-3, 3278-4, and 3278-5. If you are using the telnet command in 3270 mode
on a color display, the colors and fields are displayed the same as those of an
actual 3279 display.
RESTRICTIONS
The mouse cannot be used as an input device with the telnet command.
The telnet command does not support the APL data stream.
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ENVIRONMENT VARIABLES
The following environment variables can be used with the telnet k command:
EMULATE Specifies type of terminal for telnet to emulate. If giv e the -e
flag overrides this variable. The value of EMULATE ma y be set to
vt100, but telnet will only try to emulate a vt100 if you are using
an HFT terminal. If the type to emulate is 3270, telnet will do so
on any terminal (as long as that terminal can be used with vi).
TNESC Specifies an alternate TELNET escape character, other than the
default Ctrl-T. You can use TNESC to change the telnet escape
sequence. To cha n the sequence, set TNESC to the octal value of
the character you want to use and export TNESC. Refer to the AIX
Operating System Technical Reference for a table that maps octal
values to their ASCII equivalents.
For more information on using environment variables, see the env command in the
AIX Operating System Commands Reference.
FLAGS
The telnet, tn command options are:
-d Turns debugging mode on.
-e terminaltype
Overrides terminal-type negotiation. Possible values for terminal
type are vt100, 3270 and none.
-n net_trace_file
Records network trace information in the file specified by
net_trace_file.
PARAMETERS
For each of the subcommands listed below, you only need to type enough letters
to uniquely identify the command. (For example, q is sufficient for the quit
command.) This is also true for the arguments to emulate, display, mode, set,
and toggle.
The subcommands for telnet and tn are:
? [command]
Requests help on telnet. Without arguments, the telnet command prints a
help summary. If a command is specified, the telnet command prints help
information for just that command.
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close
Closes the TELNET connection. If telnet was started with a hostname on the
command line, close exits telnet. Otherwise, close returns to command
mode.
display [argument]
Displays all of the set and toggle values if no argument is specified.
Otherwise, lists only those values that matches the argument.
emulate terminaltype
Overrides terminal type negotiation with the specified terminaltype.
Possible choices are:
? - Prints help information.
3270 - Emulates a 3270 terminal.
none - Specifies no emulation.
vt100 - Emulates a DEC VT100 terminal (only on hft).
All output received from the remote host is processed by the specified
emulator. The initial terminal type to emulate can be specified through the
EMULATE environment variable or the -e option to the telnet command.
mode type
Specifies the current input mode. When type is line, the mode is line by
line. When type is character, the mode is character at a time. Permission
is requested from the remote host before entering the requested mode, and
if the remote host supports it, the new mode is entered.
open host [port]
Opens a connection to the specified host. The host specification can be
either a host name or an Internet address in dotted decimal form. If no
port is given, the telnet command attempts to contact a TELNET server at
the default port.
quit
Closes a TELNET connection and exits telnet. An END-OF-FILE in command
mode also closes the connection and exits.
send arguments
Sends one or more arguments (special character sequences) to the remote
host. Multiple arguments are separated by spaces.
The following arguments can be used:
? - Prints help information for the send command.
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ao - Sends the TELNET AO (Abort Output) sequence, which causes the
remote host to flush all output from the remote system to the local
terminal.
ayt - Sends the TELNET AYT (Are You There) sequence, to which the
remote system can respond.
brk - Sends the TELNET BRK (Break) sequence.
ec - Sends the TELNET EC (Erase Character) sequence, which causes the
remote host to erase the last character entered.
el - Sends the TELNET EL (Erase Line) sequence, which causes the
remote system to erase the line currently being entered.
escape - Sends the current telnet escape character (Ctrl-T by default).
ga - Sends the TELNET GA (Go Ahead) sequence.
ip - Sends the TELNET IP (Interrupt Process) sequence, which causes
the remote system to cancel the currently running process.
nop - Sends the TELNET NOP (No Operation) sequence.
synch - Sends the TELNET SYNC sequence.
set variable value
Sets a TELNET variable to the specified value. The special value off
cancels the function associated with the variable name entered. The
display command can be used to query the current setting of each variable.
The variables that can be specified are:
echo - Toggles between local echo of entered characters and suppressing
local echo. Local echo is used for normal processing, while
suppressing the echo is used for entering text that should not
appear on the display, such as passwords. This variable can only
be used in line-by-line mode.
EOF - Defines the END-OF-FILE character for telnet. When telnet is in
line-by-line mode, entering the EOF character as the first
character on a line sends the character to the remote host. The
initial value for the EOF character is the terminal's EOF
character.
erase - Defines the erase character for telnet. When telnet is in
character-at-a-time mode and localchars is true, typing the erase
character sends the TELNET EC sequence to the remote host. The
initial value for the erase character is the terminal's erase
character.
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escape - Specifies the telnet escape character, which puts telnet into
command mode when connected to a remote host. This character can
also be specified in octal in the TNESC environment variable.
flushoutput
- Defines the flush character for telnet. When localchars is true,
typing the flushoutput character sends the TELNET AO sequence to
the remote host. The initial value for the flush character is
Ctrl-O. If the remote host is running AIX, flushoutput, unlike the
other special characters defined by set, only works in localchars
mode since it has no termio equivalent.
interrupt
- Defines the interrupt character for telnet. When localchars is
true, typing the interrupt character sends the TELNET IP sequence
to the remote host. The initial value for the interrupt character
is the terminal's interrupt character.
kill - Defines the kill character for telnet. When telnet is in
character-at-a-time mode and localchars is true, typing the kill
character sends the TELNET EL sequence to the remote host. The
initial value for the kill character is the terminal's kill
character.
quit - Defines the quit character for telnet. When localchars is true,
typing the quit character sends the TELNET BRK sequence to the
remote host. The initial value for the quit character is the
terminal's quit character.
status
Shows the status of telnet, including the current mode and the currently
connected remote host.
toggle arguments
Toggles one or more arguments that control how telnet responds to events.
Possible values are true and false. Multiple arguments are separated by
spaces. The display command can be used to query the current setting of
each argument.
The following arguments can be used:
? - Displays valid arguments to toggle.
autoflush
- If autoflush and localchars are both true, then when the AO,
INTR, and QUIT characters are recognized and transformed into
TELNET sequences, telnet does not display any data on the user's
terminal until the remote system acknowledges (with a TELNET timing
mark option) that it has processed those TELNET sequences. The
initial value of autoflush is true if the terminal has not done an
stty noflsh and false if it has.
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autosynch
- If autosynch and localchars are both true, then typing the INTR
or QUIT character sends that character's TELNET sequence, followed
by the TELNET SYNC sequence. This procedure causes the remote host
to discard all previously typed input until both of the TELNET
sequences have been read and acted upon. The initial value of this
toggle is false.
crmod - Toggles carriage return mode. When set to true, most carriage
return characters received from the remote host are mapped into a
carriage return followed by a line feed. This mode does not affect
the characters typed by the user, only those received from the
remote host. This mode is useful when the remote host sends only a
carriage return and not a line feed. The initial value of this
toggle is false.
debug - Toggles debugging at the socket level. This argument can only be
entered by a user with superuser privileges. The initial value of
this toggle is false.
localchars
- Determines the handling of TELNET special characters. When this
value is true, the ERASE, FLUSH, INTERRUPT, KILL, and QUIT
characters are recognized locally and transformed into the
appropriate TELNET control sequences (EC, AO, IP, BRK, and EL,
respectively). The initial value of localchars is true in
line-by-line mode and false in character-at-a-time mode.
netdata - Toggles the display of all network data (in hexadecimal format).
The data is written to standard output unless a net_trace_file is
specified with the -n flag on the telnet command line. The initial
value of this toggle is false.
options - Toggles the display of some internal TELNET processing options.
The initial value of this toggle is false.
z - Suspends this TELNET session. If the user's shell does not
support job control (assumed to be true if no stty susp character
has been set), then this command will open a sub-shell on the local
host. The shell started is the one specified by the SHELL
environment variable. When the shell is exited, telnet returns to
its previous mode.
EXAMPLES
1. To log in to host1 and do terminal type negotiation:
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$ tn host1
Trying...
Connected to host1.
Escape character is '^T'.
AIX telnet (host1)
login: _
2. To log in to host1 as a vt100 (no terminal type negotiation):
$ EMULATE=vt100; export EMULATE
$ tn host1
Trying...
Connected to host1.
Escape character is '^T'.
AIX telnet (host1)
login: _
$ tn -e vt100 host1
Trying...
Connected to host1.
Escape character is '^T'.
AIX telnet (host1)
login: _
FILES
$HOME/.3270keys Defines user's 3270 keyboard mapping.
/etc/3270.keys Default 3270 keyboard mapping.
RELATED INFORMATION
In this book: "telnetd."
pty device driver, refer to AIX Operating System Technical Reference.
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