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NAME    [Toc]    [Back]

     tn3270 - full-screen remote login to IBM VM/CMS

SYNOPSIS    [Toc]    [Back]

     tn3270 [-d] [-n filename] [-t commandname] [sysname [port]]

DESCRIPTION    [Toc]    [Back]

     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
     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

     The options are as follows:

     -d      Turn on socket-level tracing (for superuser only).

             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.

             Specify  a  UNIX  command  to process IBM 4994-style
transparent mode
             data received from the remote IBM machine.

             The name of the remote system.  If the  remote  name
is not specified,
  the  user will be prompted for a command (see

     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
     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,
     map3270(5))  or  in an environment variable MAP3270 (and, if
     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

     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

     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    [Toc]    [Back]

     tn3270 checks the  following  environment  variables:  TERM,
     MAP3270[A...].    Information  on  these  can  be  found  in
mset(1).  tn3270 also
 checks SHELL, KEYBD, and API3270.

FILES    [Toc]    [Back]


NOTES    [Toc]    [Back]

     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.
     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

SEE ALSO    [Toc]    [Back]

     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    [Toc]    [Back]

     The tn3270 command appeared in 4.3BSD.

BUGS    [Toc]    [Back]

     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      3.6                           July      27,     1991
[ Back ]
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