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
- -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
- -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
- -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
- 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
’ 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 xterm
s 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
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,
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
property of the top-level Xnest
the real server. Thus, it is important that the real window manager that
manages the Xnest
top-level window looks at the
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
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
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
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 the
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
the keyboard and pointer control parameters from the real server rather than
imposing its own.
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
The proper implementation of fonts should be moved into the os
Doesn't run well on servers supporting different visual depths.
Still crashes randomly.
Probably has some memory leaks.
Davor Matic, MIT X Consortium