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
$ prime-select nvidia // Grub bootloader will update // *Reboot
That should do it on Ubuntu 16+