Ubuntu 11.04 - disable NVIDIA graphics card

Depending on which driver you are using for the nVidia card (nouveau, nv or nvidia) - you should be able to see it with lsmod - the solution is to blacklist it to udev. For example, if your driver is nouveau, edit the /etc/modprobe.d/blacklist.conf and append a line containing blacklist nouveau, then reboot and lsmod again - it shouldn't be there any more.

From the terminal:

$ prime-select intel
// Grub bootloader will update
// *Reboot

To reenable:

$ prime-select nvidia
// Grub bootloader will update
// *Reboot

That should do it on Ubuntu 16+