Dell's e6430 discrete graphics card on Debian

Some new laptops have two graphics cards. One power-efficient integrated with CPU and one powerful discrete (separate board).

Bumblebee project provides support for NVIDIA Optimus laptops. Installing and usage is straightforward and described here. In short (if you want proprietary drivers):

1. make sure you have contrib and non-free repositories enabled 
2. Install packages:
   # apt-get install nvidia-glx nvidia-kernel-dkms bumblebee-nvidia primus
3. Installing nvidia driver package will automatically set it as a default rendering engine but it's not desired. Normally 3D would be rendered by integrated Intel card, so do:
   # update-alternatives --set glx /usr/lib/mesa-diverted

Normally this should be it, but unfortunately in current debian testing there is a bug causing an output:

$ optirun glxgears
[   42.214557] [ERROR]Cannot access secondary GPU - error: Could not load GPU driver
[   42.214599] [ERROR]Aborting because fallback start is disabled.

To fix this in file /etc/bumblebee/bumblebee.conf in section [driver-nvidia] change line:
KernelDriver=nvidia
to:
KernelDriver=nvidia-current