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I'm new to Linux and i have encountered a somewhat difficult problem for me. I currently run my system on Windows 10 installed in BIOS mode. I am trying to dual-boot by installing Ubuntu 16.04 x64 (from a USB stick made bootable with Rufus) on a separate partition to the Windows one (i have 4 : 2 for storage, one for Windows and a free one for Ubuntu) I've tried installing it by booting in legacy mode and with CPM enabled in bios but probably due to the fact that my video card has no VGA port, everytime, after the purple ubuntu loading screen, my monitor stays black. I managed to bypass this by disabling CPM and inserting in the grub command window the parameter "nomodeset" before launching the installer but what is bugging me is that by disabling CPM, my installer goes into UEFI mode due to my boot order being resetted and i'm being warned not to force an UEFI install while having the Windows in BIOS.
Can you help me, pretty please? ^_^


Motherboard : asrock b85 pro4
Video card : nvidia gtx 970 oc
CPU : i5 4460

Bogdan Toma
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  • What does CPM stand for? Did you mean CSM? – You'reAGitForNotUsingGit Mar 30 '17 at 20:49
  • no, i meant bios-compatibility mode. – Bogdan Toma Mar 30 '17 at 21:03
  • I think it is the same. CSM - UEFI Compatibility Support Module (CSM), which emulates a BIOS mode You need nomodeset with nVidia. http://askubuntu.com/questions/162075/my-computer-boots-to-a-black-screen-what-options-do-i-have-to-fix-it With Asrock, make sure you are not using any Asmedia ports, even for DVD/CD. – oldfred Mar 30 '17 at 22:29
  • @oldfred Yes it is the same but the loading screen was so fast i literally had no time to press the arrow key to get to the nomodeset setting...i had that purple screen for not even half a second so i just grabbed an old video card with VGA, installed then put my card back. Thanks for help. – Bogdan Toma Mar 31 '17 at 09:40

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I have several observations:

  • The Compatibility Support Module (CSM; I believe this is what you meant by "CPM") could well be more of a problem than a help to you. See this page of mine for details, but in brief, using the CSM complicates the boot process, leading to a greatly increased risk that you'll accidentally install one OS in one mode and another in the other mode. (The two modes are BIOS/CSM/legacy and EFI/UEFI.) If you had to do it over again I'd say you should disable the CSM and install both Windows and Ubuntu in EFI mode. This is worth considering if you haven't already created lots of user files or spent a lot of time customizing your Windows installation.
  • There's a good chance that the nomodeset trick you describe would work in BIOS mode as well as in EFI mode. Thus, if you want to proceed with a BIOS-mode install of Ubuntu, I recommend you try that.
  • If you really want to, you can install Ubuntu in EFI mode, even on an MBR disk. You'll need to manually create an EFI System Partition (ESP), -- a FAT partition with a type code of 0xEF. I'm not sure if this is possible with the Ubuntu installer; you might need to use fdisk to create the partition and mkdosfs to create a FAT filesystem on it. Once Ubuntu is installed in EFI mode, you'll need to either switch OSes using the firmware's built-in boot manager (typically accessed via Esc, Enter, or a function key at boot time); or install my rEFInd boot manager, edit /boot/efi/EFI/refind/refind.conf to uncomment the scanfor line and add hdbios to its options. The rEFInd approach enables rEFInd to boot Windows in BIOS mode and Ubuntu in EFI mode without dealing with the firmware's (likely very awkward) built-in boot manager. All this said, mixing boot modes in this way is awkward and poorly tested, particularly when your disk uses MBR (as it presumably does). It might or might not work properly on your computer.
  • Another alternative is to convert Windows from booting in BIOS mode to booting in EFI mode, as described on this blog post. You'll then be able to install Ubuntu in EFI mode.
  • You say your disk already has four partitions -- two for Windows, one for shared storage, and one set aside for Ubuntu. Ubuntu prefers to have two partitions, though -- one for its root (/) filesystem and one for swap space. Also, if you decide to boot Ubuntu in EFI mode, you'll need an ESP. Thus, you may need more partitions. If all the current partitions are primary partitions, this won't be possible without jumping through some extra hoops. Since Ubuntu is not yet installed, you can delete its partition, create an extended partition in its place, and create additional partitions inside the extended partition. If you convert to a full-EFI configuration, converting from MBR (with its 4-primary-partition limit) to GPT (with a limit of 128 partitions by default) will be part of the task, which will simplify further partitioning issues.

Of these options, disabling the CSM and re-installing Windows is likely the best option, at least if this is a new enough Windows installation to make the extra effort of re-installing it modest. If Windows is heavily customized, then your task is trickier. Trying nomodeset in BIOS mode might be the best approach in this case. If that fails, I'd try converting Windows to boot in EFI mode, with the caveat that this can be risky, so you should back up your important Windows files first and be prepared to re-install it should things go wrong.

Eliah Kagan
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Rod Smith
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