NAME

layers - layer multiplexor for windowing terminals

SYNOPSIS

layers [-s] [-t] [-D [-m max-pkt] [-d] [-p] [-h modlist] [-f
file] [layersys-prgm]

DESCRIPTION

layers manages asynchronous windows [see layers(5)] on a windowing terminal. Upon invocation, layers finds an unused xt(7) channel group and associates it with the terminal line on its standard output. It then waits for commands from the terminal.

Command-line options:

-s Report protocol statistics on standard error at the end of the session after you exit from layers. The statistics may be printed during a session by invoking the program xts(1M).

-t Turn on xt(7) driver packet tracing, and produces a trace dump on standard error at the end of the session after you exit from layers. The trace dump may be printed during a session by invoking the program xtt(1M).

-D Send debugging messages to standard error.

-m max-pkt

Set maximum size for the data part of regular xt packets sent from the host to the terminal. Legal values are 32 to 252. This option also implies that regular rather than network xt protocol should be used. See xtproto(5).

-d If a firmware patch has been downloaded, print out the sizes of the text, data, and bss portions of the firmware patch on standard error.

-p If a firmware patch has been downloaded, print the down-loading protocol statistics and a trace on standard error.

-h modlist

Push a list of STREAMS modules separated by a comma on a layer.

-f file Start layers with an initial configuration specified
        by  file.   Each line of the file represents a layer
        to be created, and has the following format:

          origin_x origin_y corner_x corner_y command_list

The coordinates specify the size and position of the layer on the screen in the terminal's coordinate system. If all four are 0, the user must define the layer interactively. command_list, a list of one or more commands, must be provided. It is executed in the new layer using the user's shell (by executing: $SHELL -i -c "command_list"). This means that the last command should invoke a shell, such as /usr/bin/sh. (If the last command is not a shell, then, when the last command has completed, the layer will not be functional.)

layersys-prgm

A file containing a firmware patch that the layers command downloads to the terminal before layers are created and command_list is executed.

Each layer is in most ways functionally identical to a separate terminal. Characters typed on the keyboard are sent to the standard input of the UNIX system process attached to the current layer (called the host process), and characters written on the standard output by the host process appear in that layer. When a layer is created, a separate shell is established and bound to the layer. If the environment variable SHELL is set, the user gets that shell: otherwise, /usr/bin/sh is used. In order to enable communications with other users via write(1), layers invokes the command relogin(1M) when the first layer is created. relogin(1M) will reassign that layer as the user's logged-in terminal. An alternative layer can be designated by using relogin(1M) directly. layers will restore the original assignment on termination.

Layers are created, deleted, reshaped, and otherwise manipulated in a terminal-dependent manner. For instance, the AT&T 630 MTG terminal provides a mouse-activated pop-up menu of layer operations. The method of ending a layers session is also defined by the terminal. If a user wishes to take advantage of a terminal-specific application software package, the environment variable DMD should be set to the path name of the directory where the package was installed. Otherwise DMD should not be set.

EXAMPLES

A typical startup command is:
     layers -f startup
where startup contains
     8 8 700 200 date ; pwd ; exec $SHELL
     8 300 780 850 exec $SHELL

The command
     layers -h FILTER,LDTERM
pushes the STREAMS modules FILTER and LDTERM on  each  layer
that is opened.

FILES

/dev/xt/??[0-7]
/usr/lib/layersys/lsys.8;7;3
$DMD/lib/layersys/lsys.8;?;?

SEE ALSO

ismpx(1), jterm(1), jwin(1), sh(1), write(1).
relogin(1M),  wtinit(1M),   xts(1M),   xtt(1M),   jagent(5),
layers(5),  xtproto(5), and xt(7).
libwindows(3X) in the Programmer's Reference Manual.

NOTES

The xt(7) driver supports  an  alternate  data  transmission
scheme  known  as  ENCODING  MODE.   This  mode makes layers
operation possible even over data links which intercept con-
trol characters or do not transmit 8-bit characters.  ENCOD-
ING MODE is selected either by setting  a  setup  option  on
your  windowing terminal or by setting the environment vari-
able DMDLOAD to the value hex before running layers:
     DMDLOAD=hex; export DMDLOAD
If, after executing layers -f file, the  terminal  does  not
respond in one or more of the layers, often the last command
in the command_list for that layer did not invoke a shell.

To access this version of layers, make sure /usr/bin appears before any other directory, such as $DMD/bin, you have in your path that contains a layers program. [For information about defining the shell environmental variable PATH in your .profile, see profile(4).] Otherwise, if there is a terminal-dependent version of layers, you may get it instead of the correct one.

layers sends all debugging and error  messages  to  standard
error.   Therefore, when invoking layers with the -D, -d, or
-p option, it is necessary to redirect standard error  to  a
file.  For example,
     layers -D 2>layers.msgs

If layers encounters an error condition and standard error is not redirected, the last error encountered will be printed when the layers commands exits.

When using layers the mimimum acceptable baud rate is 1200. Behavior of layers is unpredictable when using baud rate below 1200.

When using V7/BSD/Xenix applications (e.g., the jim  editor)
layers should be invoked as
     layers -h ldterm,ttcompat
This pushes the ttcompat module on each window and  converts
the BSD interface into the termio(7) interface.