Impossible to detect Virtual Box graphics card

[Mary Goes]

Hi, all.
I have a problem.

I use Linux(CentOS) that is in the real partitions with Virtual Box + guest-additions.
But when it starts form the real partition without using VirtualBox, xorg.conf is changed automatically,
and the driver that is not "vboxvideo" but the driver used for my real machine is specified in xorg.conf.
After that, x server cannot detect Virtual Box graphics card("vboxvideo") when it starts in Virtual Box again.
(x error message: "no devices detected")
I don't want to configure xorg.conf manually each time to start it form VirtualBox after booted without it.
How should I do to make xorg detect it automatically?

[Technologov]

You'r setup is very specific one.

Don't know how to help in this case, but in general, isn't it easier to keep two separate "/" root partitions, with shared "/home" partition?
This could solve your problem.

[Sasquatch]

Another option is to make an init script that checks what hardware you have (check for the VB video adapter) and let it run before X starts. Then in the script itself you let it copy one of the two xorg.conf files, one with your bare metal configuration and one with your VM configuration, to xorg.conf and let X start properly that way.