Will Grub overwrite Windows Boot Manager?

[Gat Pelsinger]

I am planning to install Linux on bare metal, and I want to know if I do so, then will grub overwrite the WBM and I would have to go to Windows through grub? What I want is to be able to choose the OS through BIOS and I want WBM to be default.

 

I have another question, till what extent can I isolate my Linux install from the rest of the drive? I will dual boot Windows and Linux on the same drive, so what all can I do for Linux to not be able to access the rest of the drive partitions, incase I accidently wreck something?

[C2dan88]

2 minutes ago, Gat Pelsinger said:

What I want is to be able to choose the OS through BIOS and I want WBM to be default.

Linux requires grub to boot. Windows boot manager will not provide an option to boot linux.

 

I recommend to use grub for choosing which os to boot. However do note window may override grub with windows updates. You'll need to use linux live-cd to repair grub if this occurs

 

5 minutes ago, Gat Pelsinger said:

what all can I do for Linux to not be able to access the rest of the drive partitions

In linux you can use fstab to configure drive/partition so they are not auto mounted. Or you can remove the ntfs-3g package to prevent linux from reading fat/ntfs file systems

 

[OhioYJ]

Where are you installing Linux? On my dual boot machines Linux is installed on a separate SSD so I choose to put the boot manager on on the Linux SSD. It never touches the Windows drive at all.

 

Going through the BIOS to select a boot drive OS is a pain. You can change the default OS in grub, and the amount of time you are given to select one. Just let grub do it's thing. If you want Windows as a default (gross, but personal opinion), set it as the default. I typically choose 3 seconds as my selection time so my boot up time isn't delayed that much.

[Gat Pelsinger]

@C2dan88 @OhioYJ

 

No, what I want is for WBM and grub to show up separately in BIOS boot options. By setting the correct order, Windows will be default but I can always boot in grub manually.

[C2dan88]

14 minutes ago, Gat Pelsinger said:

o, what I want is for WBM and grub to show up separately in BIOS boot options.

Then install linux(, with grub as it is required to boot linux from bios any). This will overrate windows boot temporarily. 

 

To restore windows boot manager. either

• boot to windows installer to perform bootloader repair
• Or  ,boot to linux and use efiboogmgr to set the windows boot manager as higher priority then grub. (assume you installed both os with csm disabled)

Now you can either use bios to boot linux or hammer F8 key (your mobo may differ) to get boot prompt on boot.

[Gat Pelsinger]

@C2dan88

 

So will Windows start to load automatically without any prompt or do I have to go through grub?

[OhioYJ]

1 hour ago, Gat Pelsinger said:

@C2dan88 @OhioYJ

 

No, what I want is for WBM and grub to show up separately in BIOS boot options. By setting the correct order, Windows will be default but I can always boot in grub manually.

 

Well you didn't answer where you are installing Linux (the question I asked). If Linux is on a separate drive, and you install Grub there, then your Windows drive won't be touched. If you insist you can point your BIOS to the Windows drive and it will just boot Windows normally like it always has. If you point it to the Linux drive it will boot grub like it should. 

 

I'm still of the opinion that is overcomplicating it though.

[Gat Pelsinger]

@OhioYJ

2 hours ago, Gat Pelsinger said:

I will dual boot Windows and Linux on the same drive

 

[wasab]

yes and it should. be sure to update the grub config in your linux os if are dual booting it with windows 

 

 

How to Update Grub on Ubuntu and Other Linux Distributions (itsfoss.com)

 

then in grub, you will have the option to select windows on startup. you should probably disable fast boot and the timeout so you have time to get into the grub menu. 

 

12.04 - Is it possible to completely disable Grub timeout? - Ask Ubuntu

[Gat Pelsinger]

@wasab

 

42 minutes ago, wasab said:

then in grub, you will have the option to select windows on startup.

Not what I want. I want to choose grub in BIOS boot options, not directly boot into it.

[wasab]

22 minutes ago, Gat Pelsinger said:

@wasab

 

Not what I want. I want to choose grub in BIOS boot options, not directly boot into it.

Why tho? Windows boot manager can't boot Linux while grub can boot both Linux AND windows.

 

If that's what you are looking for, you need two hard drive. One that has Linux, one that has windows and in your bios, select windows drive as your default boot drive. You won't be able to boot Linux unless you select Linux drive as your default boot drive 

[Gat Pelsinger]

@wasab

 

I don't understand. Why can't there be 2 separate boot managers on the EFI partition? Completely separate from each other.

[wasab]

21 minutes ago, Gat Pelsinger said:

@wasab

 

I don't understand. Why can't there be 2 separate boot managers on the EFI partition? Completely separate from each other.

Because you tell bios to select a drive to boot from so it is whatever boot manager on that drive. Do you ever see an option in your bios menu that allow you to select what boot manager on a drive? 

 

Maybe there is a way but idk. You have to search it up yourself. You will likely need to do advanced and manual partitioning of the drive to make sure everything is working. Not recommended, you will likely lose all your data and brick your os. 

 

I personally always keep my linux and windows separate and never partition for two to live side by side on a share drive when dual booting. I am not big fan of messing around with drive partition and risk losing all my data. 

 

I also have heard horror stories of windows install manager "accidentally" deleting your linux partition and what not so yeah.... two drives are safer. 

[Eigenvektor]

10 hours ago, Gat Pelsinger said:

I don't understand. Why can't there be 2 separate boot managers on the EFI partition? Completely separate from each other.

The BIOS only allows you to select the boot device on a physical level. It's the boot manager's job to select the OS to boot on the logical level. Having two boot managers on the same drive makes no sense, how would you switch between them? A pre-boot manager?

 

11 hours ago, Gat Pelsinger said:

Not what I want. I want to choose grub in BIOS boot options, not directly boot into it.

Then you'll need two drives and use the BIOS to switch between them. The BIOS will simply load whatever boot manager is on the selected drive, it doesn't know what GRUB is in particular.

[Gat Pelsinger]

@wasab @Eigenvektor

 

Well I tried it in a VM and everything is straightforward. First I installed Windows on the whole drive and then shrunk the main partition to install Linux in the empty space. I then proceeded to install Linux on that partition. GRUB did become the default boot loader, but in BIOS I changed the order and put WBM on top. Now without any prompt the system directly boots into Windows, and to boot into Linux, I would have to go through the BIOS boot menu. This was so straightforward, why did you guys think it wasn't possible to put 2 boot managers on the same drive?

 

Well now that's done, so what all do I need to do to keep both of the boot managers at peace? I heard Windows and sometimes even Linux can overwrite each other's boot managers. But I think Linux's can be handled. I think there is an option in GRUB's config file which works but idk about Windows. Well I won't be mad to re-install GRUB if it ever gets destroyed, not that I update Windows often.

[wasab]

53 minutes ago, Gat Pelsinger said:

why did you guys think it wasn't possible to put 2 boot managers on the same drive?

Probably because you are doing it in a vm?

 

Try it in real disk. If you get it working, all the power to you. 

[Eigenvektor]

2 hours ago, Gat Pelsinger said:

Well I tried it in a VM and everything is straightforward.

You are correct, I apologize. My BIOS boot menu does allow me to select between "UEFI OS" and "Windows Boot Manager". The first one goes to Grub. Though I see no particular reason to ever use it. Instead of hammering F11 during boot, I just wait until Grub pops up and can select between Windows and Linux all the same.

 

2 hours ago, wasab said:

Try it in real disk. If you get it working, all the power to you. 

Just tried on my system, it does indeed work.

 

2 hours ago, Gat Pelsinger said:

Well now that's done, so what all do I need to do to keep both of the boot managers at peace?

This is what my primary disk looks like:

Spoiler

As you can see, there are two EFI partitions, one created by Windows ("EFI system partition") and one for Linux (/boot/efi). As you can see I could've gotten away with a lot less space for the Linux partition.

 

This setup has been running without any issues since 2021. I've had the same scheme on my previous computer with Windows 7, 8, 8.1 and 10, never ran into issues with system updates.

[wasab]

24 minutes ago, Eigenvektor said:

You are correct, I apologize. My BIOS boot menu does allow me to select between "UEFI OS" and "Windows Boot Manager". The first one goes to Grub. Though I see no particular reason to ever use it. Instead of hammering F11 during boot, I just wait until Grub pops up and can select between Windows and Linux all the same.

Cool, i guess it is technically feasible even if extremely redundant.