Xnest - a nested X server
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.
is a server to its own clients. Xnest
manages windows and
graphics requests on their behalf. To these clients, Xnest
be a conventional server.
supports all standard options of the sample server implementation.
For more details, please see Xserver
(1). The following additional
arguments are supported as well.
- -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 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 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
- -class string
- 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
- 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
sample server code.
- This option specifies the geometry parameters for the top-level
Xnest window. See “GEOMETRY SPECIFICATIONS” 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
- 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. Unfortunately, window managers are
not very good at doing that yet so this option might come in handy.
- -parent window_id
- This option tells Xnest to use window_id as the root window
instead of creating a window.
Starting up Xnest
is just as simple as starting up xclock
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
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
’ 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 process 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.
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
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 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 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) 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
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.
The proper implementation of fonts should be moved into the
Doesn't run well on servers supporting different visual depths.
Still crashes randomly.
Probably has some memory leaks.
Davor Matic, MIT X Consortium