TN3270(1) General Commands Manual TN3270(1)
tn3270 - full-screen remote login to IBM VM/CMS
Tn3270 permits a full-screen, full-duplex connection from a VAX UNIX machine to an IBM machine running VM/CMS giving the appearance of
being logged in directly to the remote machine on an IBM 3270 terminal. Of course you must have an account on the machine to which you
wish to connect in order to log in. Tn3270 looks to the user in many respects like the Yale ASCII Terminal Communication System II.
Tn3270 is actually a modification of the Arpanet TELNET user interface (see telnet(1)) that interprets and generates raw 3270 control
Emulation of the 3270 terminal is done in the Unix process. This emulation involves mapping 3270-style commands from the host into appro-
priate sequences to control the user's terminal screen. Tn3270 uses curses(3x) and the /etc/termcap file to do this. The emulation also
involves simulating the special 3270 keyboard keys (program function keys, etc.) by mapping sequences of keystrokes from the ASCII key-
board into appropriate 3270 control strings. This mapping is terminal dependent and is specified in a description file,
/usr/share/misc/map3270, (see map3270(5)) or in an environment variable MAP3270 (see mset(1)). Any special function keys on the ASCII key-
board are used whenever possible. If an entry for the user's terminal is not found, tn3270 looks for an entry for the terminal type
unknown. If this is not found, tn3270 uses a default keyboard mapping (see map3270(5)).
The first character of each special keyboard mapping sequence is either an ASCII escape (ESC), a control character, or an ASCII delete
(DEL). If the user types an unrecognized function key sequence, tn3270 sends an ASCII bell (BEL), or a visual bell if defined in the
user's termcap entry, to the user's terminal and nothing is sent to the IBM host.
If tn3270 is invoked without specifying a remote host system name, it enters local command mode, indicated by the prompt ``tn3270>''. In
this mode, tn3270 accepts and executes the following commands:
open connect to a remote host
close close the current connection
quit exit tn3270
z suspend tn3270
status print connection status
? print help information
Other common telnet commands are not available in tn3270. Tn3270 command mode may also be entered, after connecting to a host, by typing a
special escape character (typically control-C).
While in command mode, any host login session is still alive but temporarily suspended. The host login session may be resumed by entering
an empty line (press the RETURN key) in response to the command prompt. A session may be terminated by logging off the foreign host, or by
typing ``quit'' or ``close'' while in local command mode.
mset(1), telnet(1), termcap(3x), termcap(5), map3270(5), Yale ASCII Terminal Communication System II Program Description/Operator's Manual
Performance is slow and uses system resources prodigiously.
Not all 3270 functions are supported, nor all Yale enhancements.
4.3 Berkeley Distribution November 27, 1996 TN3270(1)
Check Out this Related Man Page
telnet - user interface to the TELNET protocol
The interface is used to communicate with another host using the TELNET protocol. If is invoked without arguments, it enters command mode,
which is indicated by the prompt, telnet>. In this mode, accepts and executes the commands listed below. If it is invoked with arguments,
it performs an open command (see below) with those arguments.
Once a connection is opened, enters input mode. The 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, text is sent to the remote host as it is typed. In line-by-line mode, text is echoed
locally and only completed lines are sent to the remote host. The local-echo-character, initially ^E. turns the local echo on and off,
which is useful when you want to enter passwords without them echoing to the screen.
In either mode, if the localchars toggle is TRUE (the default in line mode), then the user's quit, intr, and flush characters are trapped
locally and sent as TELNET protocol sequences to the remote side. Options such as toggle autoflush and toggle autosynch flush previous
terminal input, as in quit and intr, in addition to flushing subsequent output to the terminal until the remote host acknowledges the TEL-
To issue commands when in input mode, precede them with the escape character, initially the control character followed by a right bracket
(^]). When in command mode, use the normal terminal editing conventions.
The following commands are available:
open host [ port ]
Opens a connection to the named host. If no port number is specified, attempts to contact a TELNET server at the default
port. The host specification may be either a host name or an Internet address specified in the dot notation. For further
information, see and
close Closes a TELNET session and returns to command mode.
quit Closes any open TELNET session and exits
z Suspends This command only works when the user is using the
mode type The type is either line, for line-by-line mode, or character, for character-at-a-time mode. The local host asks the remote
host for permission to go into one or the other mode. The remote host enters the requested mode if it is capable of it.
status Shows the current status of This includes the peer one is connected to, as well as the state of debugging.
display [ argument... ]
Displays all, or some, of the set and toggle values (see below).
? [ command ]
Accesses on-line help. With no arguments, prints a help summary. If a command is specified, prints the help information
for that command.
Sends one or more special character sequences to the remote host. One or more of the following arguments can be specified:
Sends the current escape character (initially the control character followed by a right bracket, ^]).
Sends the TELNET SYNCH sequence. This sequence causes the remote system to discard input that was previously entered
but that it has not yet read. This sequence is sent as TCP urgent data and may not work if the remote system is a
4.2 BSD system. If it does not work, a lower case r may be echoed on the terminal screen.
Sends the TELNET BRK (Break) sequence, which may have significance to the remote system.
Sends the TELNET IP (Interrupt Process) sequence, which causes the remote system to abort the currently running
Sends the TELNET AO (Abort Output) sequence, which causes the remote system to flush all output from the remote sys-
tem to the user's terminal.
Sends the TELNET AYT (Are You There) sequence. The remote system may or may not respond.
Sends the TELNET EC (Erase Character) sequence, which causes the remote system to erase the last character entered.
Sends the TELNET EL (Erase Line) sequence, which causes the remote system to erase the line currently being entered.
Sends the TELNET GA (Go Ahead) sequence. Often this sequence has no significance to the remote system.
Sends the TELNET NOP (No OPeration) sequence.
Prints out help information for the send command.
set argument value
Sets a variable to a specific value. The off value turns off the function associated with the variable. The current values
of variables can be displayed with the display command.
The following variables that can be specified:
Toggles between local echoing of entered characters, and suppressing echoing of entered characters when in line-by-line mode.
The value is initially ^E.
Enters the command mode when you are connected to a remote system. The value is initially the control character followed by
a left bracket (^[).
Sends a TELNET IP sequence (see send ip above) to the remote host if is in localchars mode (see toggle localchars below) and
the interrupt character is typed. The initial value for the interrupt character is the terminal's intr character.
Sends a TELNET BRK sequence (see send brk above) to the remote host if is in localchars mode (see toggle localchars below)
and the quit character is typed. The initial value for the quit character is the terminal's quit character.
Sends a TELNET AO sequence (see send ao above) to the remote host if telnet is in localchars mode (see toggle localchars
below) and the flushoutput character is typed. The initial value for the flush character is the terminal's flush character.
Sends a TELNET EC sequence (see send ec above) to the remote system if telnet is in localchars mode (see toggle localchars
below), and if telnet is operating in character-at-time mode. The initial value for the erase character is the terminal's
Sends a TELNET EL sequence (see send el above) to the remote system if is in localchars mode (see toggle localchars below)
and if is operating in character-at-a-time mode. The initial value for the kill character is the terminal's kill character.
Sends this character to the remote system if is operating in line-by-line mode and this character is entered as the first
character on a line. The initial value of the eof character is the terminal's eof character.
Toggles (between TRUE and FALSE) flags that control how responds to events. More than one argument may be specified and the current
value of these flags can be displayed with the display command. Valid arguments for the command are the following:
Causes the flush, interrupt, quit, erase, and kill characters to be recognized locally and transformed into appropriate TEL-
NET control sequences if this flag is set to TRUE. (See set above). The appropriate TELNET control sequences are: ao, ip,
brk, ec, and el, respectively. For more information see the command. The initial value for this toggle is TRUE in line-by-
line mode, and FALSE in character-at-a-time mode.
Causes the command to not display any data on the user's terminal until the remote system acknowledges (via a TELNET Timing
Mark option) that it recognized and processed the following TELNET sequences: ao, intr, or quit. Both autoflush and
localchars must be TRUE for autoflush to work in this manner. The initial value for this toggle is TRUE if the terminal user
did not specify Otherwise it is FALSE. For further information, see
Causes the TELNET SYNCH sequence to follow the TELNET sequence that is initiated when either the intr or quit character is
typed. The autosynch flag works in this manner when both the autosynch and localchars are TRUE. This procedure should cause
the remote system to begin throwing away all previously typed input until both of the TELNET sequences have been read and
acted upon. The initial value of this toggle is FALSE.
Toggles carriage return mode. When this mode is enabled, most carriage return characters received from the remote host are
mapped into a carriage return followed by a line feed. It is useful only when the remote host sends carriage returns but
never line feeds. The initial value for this toggle is FALSE.
Toggles socket level debugging which is useful only to the superuser. The initial value for this toggle is FALSE.
Toggles the display of internal protocol processing that deals with TELNET options. The initial value for this toggle is
Toggles the display of all network data (in hexadecimal format). The initial value for this toggle is FALSE.
Displays the legal toggle commands.
In line-by-line mode, the terminal's EOF character is only recognized and sent to the remote system when it is the first character on a