TN3270(1) OpenBSD Reference Manual TN3270(1)
NAME
tn3270 - full-screen remote login to IBM VM/CMS
SYNOPSIS
tn3270 [-d] [-n filename] [-t commandname] [sysname [port]]
DESCRIPTION
tn3270 permits a full-screen, full-duplex connection from a UNIX machine
to an IBM (or compatible) machine. tn3270 gives the appearance of being
logged in to the remote machine from an IBM 3270 terminal. Of course,
you must have an account on the machine to which you 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)) which will, in certain
circumstances, interpret and generate raw 3270 control streams.
The options are as follows:
-d Turn on socket-level tracing (for superuser only).
-n filename
Specify a file to receive network trace data output (from
commands toggle netdata and toggle options, see telnet(1)); the
default is for output to be directed to the standard error file.
-t commandname
Specify a UNIX command to process IBM 4994-style transparent mode
data received from the remote IBM machine.
sysname
The name of the remote system. If the remote name is not
specified, the user will be prompted for a command (see below).
port The port to connect to on the remote system. Normally, tn3270
attempts to connect to the standard TELNET port (port 23) on the
remote machine.
When tn3270 first connects to the remote system, it will negotiate to go
into 3270 mode. Part of this negotiation involves telling the remote
system what model 3270 it is emulating. In all cases, tn3270 emulates a
3278 terminal. To decide which specific model, tn3270 looks at the
number of lines and columns on the actual terminal (as defined in the
TERM environment variable; see termcap(5)). The terminal (or window in
which tn3270 is running, on multiple window systems) must have at least
80 columns and 24 lines, or tn3270 will not go into emulation mode. If
the terminal does have at least 80 columns and at least 24 lines, the
following table describes the emulation:
minimum_size emulated
(rows*columns) terminal
-------------- ------------
27*132 3278 model 5
43*80 3278 model 4
32*80 3278 model 3
24*80 3278 model 2
Emulation of the 3270 terminal is done in the UNIX process. This
emulation involves mapping 3270-style commands from the host into
appropriate sequences to control the user's terminal screen. tn3270 uses
curses(3) and the /usr/share/misc/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 keyboard
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 (and, if necessary, MAP3270A, MAP3270B, and so on - see mset(1)).
Any special function keys on the ASCII keyboard 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 all the commands of telnet(1), plus one
additional command:
transcom Specify UNIX command for IBM 4994-style transparent mode
processing.
tn3270 command mode may also be entered, after connecting to a host, by
typing a special escape sequence. If tn3270 has succeeded in negotiating
3270 mode with the remote host, the escape sequence will be as defined by
the map3270 (see map3270(5)) entry for the user's terminal type
(typically control-C); otherwise the escape sequence will initially be
set to the single character `^]' (control right square bracket).
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.
ENVIRONMENT
tn3270 checks the following environment variables: TERM, MAP3270,
MAP3270[A...]. Information on these can be found in mset(1). tn3270
also checks SHELL, KEYBD, and API3270.
FILES
/usr/share/misc/termcap
/usr/share/misc/map3270
NOTES
The IBM 4994-style transparent mode command is invoked when tn3270
receives IBM 4994-style transparent output from the remote host. Output
and input pipes are created for communication between the two processes.
The pipes are closed when a 3270 clear command is received from the
remote hosts, signalling the end of transparent mode output. Transparent
mode is necessary for sending ASCII control characters over the 3270
terminal connection; ASCII graphics terminal support is accomplished this
way. Developers of transcom commands should note that the transcom stdin
pipe end will be in CBREAK mode, with ECHO and CRMOD turned off.
SEE ALSO
mset(1), telnet(1), curses(3), termcap(3), map3270(5), termcap(5)
Yale ASCII Terminal Communication, System II Program
Description/Operator's Manual, IBM SB30-1911.
HISTORY
The tn3270 command appeared in 4.3BSD.
BUGS
tn3270 is slow and uses system resources prodigiously.
Not all 3270 functions are supported, nor all Yale enhancements.
Error conditions (attempting to enter data in a protected field, for
example) should cause a message to be sent to the user's terminal instead
of just ringing a bell.
OpenBSD 4.8 May 31, 2007 OpenBSD 4.8