Installing Linux is a little trickier with Windows 8 now that Microsoft has implemented the UEFI system, instead of the BIOS system. I hope this guide will help at least some people out, because I would hate for people to be forced into Windows just because of UEFI and secure boot! The horror.
I'm using a Toshiba Satellite P75 A7200, and some of the guides I've read left out information that I needed for my specific computer, so I might be including extras that you might not need for your computer. The two main things I had to do that most guides didn't include were:
--Add in a fix to the script at the GRUB screen during installation; this was due to a hanging black screen at startup.
--I had to manually partition the hard drive, because the Ubuntu installer didn't recognize that Windows 8 was already on the computer.
OK, so here's how you do it. I'm assuming you already have a LiveUSB or LiveCD made with an ISO image.
1.) Start Windows 8 and navigate to the Disk Manager. Right-click the largest/main partition and click "Shrink volume." I typed in 15000. I guess that is a good solid number. That's all you have to do in Windows. I used this video to partition the disk:
2.) You will have to make sure you boot the USB instead of just booting back into Windows. To do this, go to the right-hand sidebar, click on PC Settings at the bottom, go to General, and scroll down "Advanced Startup." Click on this, then go to Troubleshooting>Advanced>UEFI Firmware Settings. This will restart your computer at the BIOS screen. Insert your LIVEUSB or LiveCD.
3.) On the BIOS screen, disable Secure Boot. I don't know if it matters since Ubuntu supposedly supports Secure Boot now, but I did this anyway. You don't have to change to CMS Legacy Boot. Also, change the boot order so the USB or CD boots first. Then press F10 to save and continue.
4.) Hopefully now you will get to the GRUB screen. You can either try Ubuntu or just install it if you are feeling daring, but before I did this I had to press 'e' and then revise the script. Before "quiet splash," I included "acpi _ osi=Linux acpi _ backlight=vendor". Then it should load without issue into the Ubuntu GUI.
5.) While installing, if the installer doesn't recognize the existing Windows OS, you will have to select the "Something else" option and manually partition. In the end, Windows 8 will still be there, so don't worry. Select the partition you created and within it create a swap partition at about 10% of the size of the partition itself. The video I linked above explains this much better than I can. Then complete the installation.
6.) If you try to reboot the computer and it loads onto a black screen again, don't fear. Restart the computer using the LiveCD and install boot-repair from the LiveCD:
sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update sudo apt-get install boot-repair
In boot-repair, just click on the "Recommended" button and let it do its work. It will fix the GRUB screen so you can see Ubuntu and Windows, although Windows is named something weird in the menu, it still works. Restart the computer.
7.) You should see the GRUB screen. Select Ubuntu and press 'e'. Repeat step 4 so you can get into Ubuntu. To fix the black screen problem permanently, edit this line in /etc/default/grub:
GRUB _ CMDLINE _ LINUX _ DEFAULT="acpi _ osi=Linux acpi _ backlight=vendor quiet splash"
Then in a terminal, do "sudo update-grub" and restart.
Everything should work successfully! If not, keep trying! Mandelbaum! Mandelbaum! Mandelbaum!