X Version 11 (Release 6.1)
nested X server
Xnest is a client and a server. Xnest is a client of the
real server which manages windows and graphics requests on its behalf.
Xnest is a server to its own clients. Xnest manages
windows and graphics requests on their behalf. To these clients
Xnest appears to be a conventional server.
Xnest supports all standard options of the
server implementation. The following additional arguments are
This option specifies the display name of the real server that
Xnest should try to connect with. If it is not provided on the
command line Xnest will read the DISPLAY environment
variable in order to find out the same information.
This option tells Xnest to synchronize its window and graphics
operations with the real server. This is a useful option for
debugging, but it will slow down the performance considerably. It
should not be used unless absolutely necessary.
This option tells Xnest to utilize full regeneration of real
server objects and reopen a new connection to the real server each
time the nested server regenerates. The
regenerates all objects in the server when the last client of this
server terminates. When this happens, Xnest by default
maintains the same top level window and the same real server
connection in each new generation. If the user selects full
regeneration, even the top level window and the connection to the real
server will be regenerated for each server generation.
This option specifies the default visual class of the nested server.
It is similar to the -cc option from the set of standard options
except that it will accept a string rather than a number for the
visual class specification. The string must be one of the following
six values: StaticGray, GrayScale, StaticColor,
PseudoColor, TrueColor, or DirectColor. If both,
-class and -cc options are specified, the last instance of
either option assumes precedence. The class of the default visual of
the nested server need not be the same as the class of the default
visual of the real server; although, it has to be supported by the
real server. See the
manual page for a list of supported visual
classes on the real server before starting Xnest. If the user
chooses a static class, all the colors in the default colormap will be
preallocated. If the user chooses a dynamic class, colors in the
default colormap will be available to individual clients for
This option specifies the default visual depth of the nested server.
The depth of the default visual of the nested server need not be the
same as the depth of the default visual of the real server; although,
it has to be supported by the real server. See
manual page for a
list of supported visual depths on the real server before starting
This option tells Xnest to use the software screen saver. By
default Xnest will use the screen saver that corresponds to the
hardware screen saver in the real server. Of course, even this screen
saver is software generated since Xnest does not control any
actual hardware. However, it is treated as a hardware screen saver
within the Xsco server code.
This option specifies geometry parameters for the top level
Xnest windows. These windows corresponds to the root windows of
the nested server. The width and height specified with this option
will be the maximum width and height of each top level Xnest
window. Xnest will allow the user to make any top level window
smaller, but it will not actually change the size of the nested server
root window. As of yet, there is no mechanism within the Xsco
server implementation to change the size of the root window after
screen initialization. In order to do so, one would probably need to
extend the X protocol. Therefore, it is not likely that this will be
available any time soon. If this option is not specified Xnest
will choose width and height to be 3/4 of the dimensions of the root
window of the real server.
This option specifies the border width of the top level Xnest
window. The integer parameter must be a positive number. The default
border width is 1.
This option specifies the name of the top level Xnest window.
The default value is the program name.
This option specifies the number of screens to create in the nested
server. For each screen, Xnest will create a separate top level
window. Each screen is referenced by the number after the dot in the
client display name specification. For example, xterm -display
:1.1 will open an xterm client in the nested server with the
display number :1 on the second screen. The number of screens
is limited by the hard coded constant in the Xsco server code,
which is usually 3.
This option tells Xnest to do its own colormap installation by
bypassing the real window manager. For it to work properly the user
will probably have to temporarily quit the real window manager. By
default Xnest will keep the nested client window whose colormap
should be installed in the real server in the
WM_COLORMAP_WINDOWS property of the top level Xnest
window. If this colormap is of the same visual type as the root
window of the nested server, Xnest will associate this colormap
with the top level Xnest window as well. Since this does not
have to be the case, window managers should look primarily at the
WM_COLORMAP_WINDOWS property rather than the colormap
associated with the top level Xnest window.
Starting up Xnest is as simple as starting up
from a terminal emulator. If a user wishes to run Xnest on the same
workstation as the real server, it is important that the nested server
is given its own listening socket address. Therefore, if there is a
server already running on the user's workstation, Xnest will
have to be started up with a new display number. Since there is
usually no more than one server running on a workstation, specifying
Xnest :1 on the command line will be sufficient for most users.
For each server running on the workstation the display number needs to
be incremented by one. Thus, if you wish to start another
Xnest, you will need to type Xnest :2 on the command line.
To run clients in the nested server each client needs to be given the
same display number as the nested server. For example, xterm
-display :1 will start up an xterm in the first nested server
and xterm -display :2 will start an xterm in the second
nested server from the example above. Additional clients can be
started from these xterms in each nested server.
Xnest as a client
Xnest behaves and looks to the real server and other real
clients as another real client. It is a rather demanding client,
however, since almost any window or graphics request from a nested
client will result in a window or graphics request from Xnest to
the real server. Therefore, it is desirable that Xnest and the
real server are on a local network, or even better, on the same
machine. As of now, Xnest assumes that the real server supports
the shape extension. There is no way to turn off this assumption
dynamically. Xnest can be compiled without the shape extension
built in, and in that case the real server need not support it. The
dynamic shape extension selection support should be considered in
further development of Xnest.
Since Xnest need not use the same default visual as the the real
server, the top level window of the Xnest client always has its
own colormap. This implies that other windows' colors will not be
displayed properly while the keyboard or pointer focus is in the
Xnest window, unless the real server has support for more than
one installed colormap at any time. The colormap associated with the
top window of the Xnest client need not be the appropriate
colormap that the nested server wants installed in the real server.
In the case that a nested client attempts to install a colormap of a
different visual from the default visual of the nested server,
Xnest will put the top window of this nested client and all
other top windows of the nested clients that use the same colormap
into the WM_COLORMAP_WINDOWS property of the top level
Xnest window on the real server. Thus, it is important that the
real window manager that manages the Xnest top level window
looks at the WM_COLORMAP_WINDOWS property rather than the
colormap associated with the top level Xnest window. Since most
window managers appear to not implement this convention properly as of
yet, Xnest can optionally do direct installation of colormaps
into the real server bypassing the real window manager. If the user
chooses this option, it is usually necessary to temporarily disable
the real window manager since it will interfere with the Xnest
scheme of colormap installation.
Keyboard and pointer control procedures of the nested server change
the keyboard and pointer control parameters of the real server.
Therefore, after Xnest is started up, it will change the
keyboard and pointer controls of the real server to its own internal
defaults. Perhaps there should be a command line option to tell
Xnest to inherit the keyboard and pointer control parameters
from the real server rather than imposing its own. This is a future
Xnest as a server
Xnest as a server looks exactly like a real server to its own
clients. For the clients there is no way of telling if they are
running on a real or a nested server.
As already mentioned, Xnest is a very user friendly server when
it comes to customization. Xnest will pick up a number of
command line arguments that can configure its default visual class and
depth, number of screens, etc. In the future, Xnest should read
a customization input file to provide even greater freedom and
simplicity in selecting the desired layout. Unfortunately, there is
no support for backing store and save under as of yet, but this should
also be considered in the future development of Xnest.
The only apparent intricacy from the users' perspective about using
Xnest as a server is the selection of fonts. Xnest
manages fonts by loading them locally and then passing the font name
to the real server and asking it to load that font remotely. This
approach avoids the overload of sending the glyph bits across the
network for every text operation, although it is really a bug. The
proper implementation of fonts should be moved into the os
layer. The consequence of this approach is that the user will have to
worry about two different font paths -- a local one for the nested
server and a remote one for the real server -- since Xnest does
not propagate its font path to the real server. The reason for this
is because real and nested servers need not run on the same file
system which makes the two font paths mutually incompatible. Thus, if
there is a font in the local font path of the nested server, there is
no guarantee that this font exists in the remote font path of the real
server. Xlsfonts client, if run on the nested server will list
fonts in the local font path and if run on the real server will list
fonts in the remote font path. Before a font can be successfully
opened by the nested server it has to exist in local and remote font
paths. It is the users' responsibility to make sure that this is the
This server has not been thoroughly tested and debugged. It:
will not run well on servers supporting different visual depths.
still crashes randomly.
probably has some memory leaks.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004