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Xnest - a nested X server
[ options ]
Xnest is both an X client and an X 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 sample server implementation. For more details, please see Xserver(1)
The following additional arguments are supported as well.
Starting up Xnest is just as simple
as starting up xclock(1)
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 oqXnest :1cq
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 oqXnest :2cq
on the command line.
- -display string
- This option specifies the display name of the real server that Xnest should
try to connect to. If it is not provided on the command line, Xnest will
read the DISPLAY environment variable in order to find out this 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 Xnest's performance considerably. It should not be used unless
- 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 sample server implementation 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
the -class and -cc options are specified, the last instance of either option
takes 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,
but it must be supported by the real server. Use xdpyinfo(1)
to obtain 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 color
map will be preallocated. If the user chooses a dynamic class, colors in
the default color map will be available to individual clients for allocation.
- -depth int
- 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, but it
must be supported by the real server. Use xdpyinfo(1)
to obtain a list of
supported visual depths on the real server before starting Xnest.
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 sample server code.
- -geometry WxH+X+Y
option specifies the geometry parameters for the top-level Xnest window.
See lqGEOMETRY SPECIFICATIONSrq in X(7)
for a discusson of this option's
syntax. This window corresponds to the root window of the nested server.
The width W and height H 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. Xnest does not yet support the RANDR
extension for resizing, rotation, and reflection of the root window. If
this option is not specified, Xnest will choose W and H to be 3/4ths the
dimensions of the root window of the real server.
- -bw int
- This option specifies
the border width of the top-level Xnest window. The integer parameter int
must be positive. The default border width is 1.
- -name string
- This option
specifies the name of the top-level Xnest window as string. The default value
is the program name.
- -scrns int
- 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(1)
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 server sample code, which is usually 3.
- This option
tells Xnest to do its own color map 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 color map should be installed in the real server
in the WM_COLORMAP_WINDOWS property of the top-level Xnest window. If this
color map is of the same visual type as the root window of the nested server,
Xnest will associate this color map 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 color map associated
with the top-level Xnest window.
- -parent window_id
- This option tells Xnest to use window_id as the root window instead of
creating a window.
To run clients in the nested server, each client needs
to be given the same display number as the nested server. For example, oqxterm
-display :1cq will start up an xterm process in the first nested server
and oqxterm -display :2cq 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 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. 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, in which case the real server need not support it. Dynamic SHAPE
extension selection support may be considered in further development of
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 color
map. 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 color map at any time.
The color map associated with the top window of the Xnest client need not
be the appropriate color map that the nested server wants installed in
the real server. In the case that a nested client attempts to install a
color map 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 color map 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 color map associated
with the top-level Xnest window. Since most window managers don't yet appear
to implement this convention properly, Xnest can optionally do direct installation
of color maps 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
color map 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.
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
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.
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 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. The xlsfonts(1)
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 case.
Make dynamic the requirement for
the SHAPE extension in the real server, rather than having to recompile
Xnest to turn this requirement on and off.
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.
Xnest should read a customization
input file to provide even greater freedom and simplicity in selecting
the desired layout.
There is no support for backing store and save unders,
but this should also be considered.
Doesn't run well on servers supporting
different visual depths.
Still crashes randomly.
Probably has some memory
Davor Matic, MIT X Consortium
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