9   X-META-X Option DYNAMICSERVER

9.1 Operation
9.2 Configuration
      9.2.1 Screen
9.3 Resource manager

9.1   Operation

The option DYNAMICSERVER allows to connect and disconnect X Window servers at runtime.

With the additional option FAILSAFE (10 X-META-X Option FAILSAFE) the X-META-X proxy even detects the breakdown of an X Window server, disconnects it, and deletes the corresponding screens from the configuration. The X Window clients are not affected.

9.2   Configuration

The statement

options [+|-]dynamicServer 

enables or disables the option. However, only options which are covered by the license key (3 Licensing) may be enabled. The default setting - no additional options - corresponds to the X-META-X base product.

9.2.1   Screen

Screens of screen type (6.12 Screen) or window type (8.2.1 Screen) may be deleted from or added to the configuration during run-time using the configuration program xmetaxtool (19 X-META-X-TOOL configuration tool).

When starting the X-META-X proxy, at least one screen must be configured. The common subset of the servers' resources and capabilities cannot be reduced by adding a screen. For instance, one cannot add a monochrome screen to an all-color configuration.

If the X-META-X proxy cannot at least contact all potential screens at start-up, the common resources and capabilities have to be defined in advance (6.10 Common resources and capabilities).

9.2.1.1   Screen tags

The screen sub-statement

    tags {[+|-]probeOnly|static|none}... 

specifies certain features of a screen:

• A screen marked probeOnly will be used only at startup of the X-META-X proxy for determining the subset of common resources and capabilities (6.10 Common resources and capabilities) and for calculating the meta screen dimensions (6.11.2 Dimensions of a meta screen) before it is deleted from the current configuration. So the proxy can take screens into account which are to be controlled later.
• static determines that the screen cannot be deleted from a configuration, even with the DYNAMICSERVER option. This may be used to avoid the X-META-X resource manager (9.3 Resource manager).

These screen tags cannot be modified when the xmetax program is running.

9.2.1.2   Priority

An xmetax program may be driven out by a second one from a screen. The screen is automatically deleted from the configuration of the first X-META-X proxy and included into the new configuration. This is useful, if, for instance, a specialized screen, like a wall display, has to be interactively associated to alternating meta screens.

Therefore, each screen - each controlled X Window server actually - gets a priority value. If a screen has to be associated to another meta screen, it is released only if its priority value increases. This new priority value can be decreased at once to avoid escalation.

The screen sub-statement

    priority priority [later_priority] 

specifies both priority values. The default values are 0, i.e. driving out is impossible.

9.3   Resource manager

If not at least one screen of each meta screen has the static tag (6.12.9 Screen tags), the X-META-X proxy may be configured in such a way, that it does not control any real X Window server at all. In this case, for independently managing the X11 requests - windows, pixmaps, fonts, etc. -, the virtual X Window server xvx is automatically started on the computer which executes the X-META-X proxy as resource manager. With respect to resources, the resource manager acts like an additional X Window server. However, it never needs explicit configuration nor can it be configured.

The resource manager always gets the screen tags atom, color, doNotEnter, font, glx, image, and static (6.12.9 Screen tags) regardless of the particular configuration. This affects the lookup of color names, which is done with respect to the color database in the directory $XMETAX_ETC/rgb/. If the color name lookup should equal the lookup of a certain X Window server, the color database must be changed according to its color definitions (usually in the file /usr/lib/X11/rgb.txt):

$XMETAX_HOME/bin/copyRgb file_with_color_definitions 

One may avoid the resource manager using the static screen tag (9.2.1.1 Screen tags).