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I already have Windows 8.1 installed and going to install Gentoo on the same drive. Also thinking of using rEFInd.

So do I really have to disable Fast Boot?

If it isn't necessary, what limitations do I get — what instructions do I have to follow to keep this dual-boot working?

Hrisip
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  • Hello and welcome to the U&L stack exchange site! Please review the [Help Center](https://unix.stackexchange.com/help) to get information on how to best post to this site. To get to your question, you should not have to disable fast boot, however when attempting to boot your installer you may not have enough time to press the boot key to reach your install media. You can disable fast boot to give yourself more of a chance to get into BIOS/boot menu. I personally recommend if you are going to dual boot Windows and Linux that, you install them on different disks. – kemotep Oct 25 '18 at 12:41

2 Answers2

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Disabling the BIOS-level Fast Boot feature is only necessary to get enough time to access BIOS/UEFI boot menus, as @kemotep mentioned in question comments.

If you're using rEFInd as your boot menu, that is not typically required, as rEFInd has an adjustable timeout and it can also provide you a boot menu option for accessing the firmware settings (aka "BIOS settings").

On the other hand, the Windows-level Fast Startup feature will typically prevent you from mounting the Windows partitions in Linux, since it acts basically the same as hibernating the Windows OS: Linux sees that Windows has not cleanly unmounted the Windows partitions and so some cached data might held in the hibernation data, waiting to be written to its final place in the Windows filesystem. (In Fast Startup such cached data is likely to be minimal or non-existent, but Linux cannot know that for sure, and so refuses to automatically mount any Windows partitions that have not been cleanly unmounted.)

If you don't need to mount Windows filesystems in Linux (and vice versa), you can keep Fast Startup enabled. Of course that will make it more difficult to exchange files between the operating systems.

Here's how to disable Fast Startup, with pictures. Basically go to Control Panel -> All Control Panel Items -> Power Options -> System Settings, and under the title "Shutdown settings", uncheck the item "Turn on fast startup (recommended)" and click on "Save changes" at the bottom of the window.

When starting the installer for Gentoo, make sure you start it in the UEFI mode. Dual-boot between two operating systems with the same boot style is usually manageable without too much effort; trying to deal with one OS using UEFI and another using legacy BIOS mode is extra tricky and might not be achievable at all, depending on firmware-level limitations.

telcoM
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  • If I use a common ESP (or EFI, however you want to call it partition), is it safe to leave fast boot on? – Balázs Börcsök Jan 12 '23 at 13:59
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    @BalázsBörcsök **Fast Boot** (the BIOS setting) should be safe to leave on, if you can currently access EFI/BIOS firmware settings with it on. Using separate or common ESPs makes no difference. **Fast Startup** (the Windows setting) should be disabled if you want to mount your Windows NTFS filesystems in Linux; otherwise Linux NTFS driver just says "can't mount read/write, Windows is hibernated" because Fast Startup resembles hibernation. – telcoM Jan 12 '23 at 14:39
  • Sorry, I was not clear enough. Is Fast Startup (the Windows feature) safe to turn it on, if I use a common ESP? I do not plan to access my NTFS partitions (like the C: drive) from my Linux system. – Balázs Börcsök Jan 12 '23 at 17:05
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    @BalázsBörcsök Fast Startup has no effect at all on ESP, only to regular Windows partitions (and probably only NTFS at that). So if you don't want to access your NTFS partitions from Linux, Fast Startup should be safe to enable. – telcoM Jan 12 '23 at 17:41
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I recommend disabling fast startup. It is not just the ability to mount Windows drives that might be an issue. Windows may also leave the hardware in a partly initialized state, or a state appropriate for Windows drivers, which might not be undone when you subsequently boot into Linux.

This isn't just theoretical: see this note about problems you can have with your WiFi card with fast boot enabled.

BeeOnRope
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