<SOLVED> Grub Menu Not Discovering Windows 10 on other Drive

[Auzzz]

Solved due to the two posts by Dragon and Pbear below. Thank you both again

Hi all,

Linux / computer noob here. I recently added Linux onto my system and have been having a hard time getting Windows and Linux to boot successfully together. At first, I couldn't get Mint to boot at all, which required me to fresh install windows, remove the drive containing windows, then install Linux on a separate hard drive, so the boot loader wouldn't be loaded onto my Windows drive. I currently can boot into both systems, however, when the GRUB comes up for Mint, Windows 10 isn't an option. I can boot into Windows by selecting the drive via my BIOS boot order. I have tried:

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 sudo os-prober 

This does not find windows. I think it has to do with the fact that Windows in UEFI and my Mint is not. I am looking to see if there is a solution to get Windows onto the GRUB without doing a re-install (if possible) due to the headache I had getting both OS onto my computer in the first place.

I tried doing some digging on this forum, google, and Youtube for additional help, but couldn't find solutions that I understood for my exact scenario. I would get a little lost in the sauce on one solution, move to another one, and I think I am mixing up some solutions. I really appreciate any guidance that anyone can provide. Thank you in advance for any help. Below are some details that I hope are pertinent to my problem:

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System:    Kernel: 5.4.0-110-generic x86_64 bits: 64 compiler: gcc v: 9.4.0 Desktop: Cinnamon 5.2.7 
           wm: muffin 5.2.1 dm: LightDM 1.30.0 Distro: Linux Mint 20.3 Una base: Ubuntu 20.04 focal 
Machine:   Type: Desktop Mobo: Micro-Star model: MPG X570 GAMING PLUS (MS-7C37) v: 2.0 
           serial: <filter> UEFI [Legacy]: American Megatrends v: A.70 date: 01/09/2020 
CPU:       Topology: 8-Core model: AMD Ryzen 7 3700X bits: 64 type: MT MCP arch: Zen 
           L2 cache: 4096 KiB 
           flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 sse4a ssse3 svm bogomips: 115200 
           Speed: 2200 MHz min/max: 2200/3600 MHz boost: enabled Core speeds (MHz): 1: 2200 2: 2200 
           3: 2191 4: 2200 5: 2199 6: 2199 7: 2199 8: 2199 9: 2199 10: 2199 11: 2200 12: 2199 
           13: 2200 14: 2200 15: 2200 16: 2200 
Drives:    Local Storage: total: 2.05 TiB used: 20.77 GiB (1.0%) 
           ID-1: /dev/nvme0n1 vendor: Samsung model: SSD 970 EVO Plus 250GB size: 232.89 GiB 
           speed: 31.6 Gb/s lanes: 4 serial: <filter> rev: 1B2QEXM7 scheme: GPT 
           ID-2: /dev/sda vendor: Western Digital model: WD10EZEX-00BN5A0 size: 931.51 GiB 
           speed: 6.0 Gb/s rotation: 7200 rpm serial: <filter> rev: 1A01 temp: 37 C scheme: MBR 
           ID-3: /dev/sdb vendor: Samsung model: SSD 860 EVO 1TB size: 931.51 GiB speed: 6.0 Gb/s 
           serial: <filter> rev: 4B6Q scheme: MBR 
Partition: ID-1: / size: 913.74 GiB used: 20.57 GiB (2.3%) fs: ext4 dev: /dev/dm-1 
           ID-2: /boot size: 703.5 MiB used: 210.1 MiB (29.9%) fs: ext4 dev: /dev/sdb5 
           ID-3: swap-1 size: 976.0 MiB used: 0 KiB (0.0%) fs: swap dev: /dev/dm-2 

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$ efibootmgr
EFI variables are not supported on this system.

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$ lsblk
NAME                MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
sda                   8:0    0 931.5G  0 disk  
└─sda1                8:1    0 931.5G  0 part  
sdb                   8:16   0 931.5G  0 disk  
├─sdb1                8:17   0   512M  0 part  /boot/efi
├─sdb2                8:18   0     1K  0 part  
├─sdb5                8:21   0   731M  0 part  /boot
└─sdb6                8:22   0 930.3G  0 part  
  └─sdb6_crypt      253:0    0 930.3G  0 crypt 
    ├─vgmint-root   253:1    0 929.3G  0 lvm   /
    └─vgmint-swap_1 253:2    0   976M  0 lvm   [SWAP]
nvme0n1             259:0    0 232.9G  0 disk  
├─nvme0n1p1         259:1    0   100M  0 part  
├─nvme0n1p2         259:2    0    16M  0 part  
├─nvme0n1p3         259:3    0 232.3G  0 part  
└─nvme0n1p4         259:4    0   509M  0 part  

[DisturbedDragon]

Both must be installed BIOS or UEFI. You cannot mix. I would re-install Mint in UEFI mode.

[pbear]

... so the boot loader wouldn't be loaded onto my Windows drive.

Why do you think that's a bad thing? It's standard procedure. Indeed, what you are attempting to force is considered bad practice.

Anyhoo, to my knowledge, there's no way for Linux booted in BIOS mode to detect Windows in UEFI and add to the Grub menu. As the Dragon says, you should reinstall Mint in UEFI mode.

I can tell you how to keep Mint from putting its boot loader on the Windows drive, but let's discuss why that worries you.

[Auzzz]

Both must be installed BIOS or UEFI. You cannot mix. I would re-install Mint in UEFI mode.

Hello - sorry for the delay in my response but thank you very much for taking the time to respond to my post. I reinstalled Mint as UEFI and now have Windows and Mint listed in GRUB. Thank you again for the help.

[Auzzz]

... so the boot loader wouldn't be loaded onto my Windows drive.

Why do you think that's a bad thing? It's standard procedure. Indeed, what you are attempting to force is considered bad practice.

Anyhoo, to my knowledge, there's no way for Linux booted in BIOS mode to detect Windows in UEFI and add to the Grub menu. As the Dragon says, you should reinstall Mint in UEFI mode.

I can tell you how to keep Mint from putting its boot loader on the Windows drive, but let's discuss why that worries you.

Hi Pbear - sorry to you as well for my delay in response and thank you so much for the help. When I was troubleshooting another issue I had some other user on some other resource recommended disconnecting the windows drive to install Linux on its own drive. So I did that and ran into the GRUB issue. After reading your comment I realized that you are right and it doesn't matter if the boot loader was on the Windows drive lol. Thank you again for the help very much appreciated.

[pbear]

After reading your comment I realized that you are right and it doesn't matter if the boot loader was on the Windows drive lol.

Understand, this is a subject over which reasonable minds can differ, but I would say the majority of experienced Linux users will agree putting all the boot loaders in one EFI partition is best practice. It's also how UEFI was designed to work. Another thing to know - and to my mind the fatal flaw in the keep-the-systems-separate strategy - is that it's not possible. Sure, one can have two EFI partitions, but what really matters are the boot order settings in NVRAM. Your computer has only one of those.

If at some future date you find a Windows update is interfering with Linux boot, the problem won't be in the EFI partition. Rather, it will be in the NVRAM settings. You fix that by booting a live session and running efibootmgr. No need to learn how to do that today. Not likely to come up and you won't remember the details anyway. Deal with if and when ...

[ramussons]

Both must be installed BIOS or UEFI. You cannot mix. I would re-install Mint in UEFI mode.

My experience is different.
I have a HP laptop with Windows 10 on a GPT main drive and Linux Mint on a second hard drive (using a CDROM adapter) in MBR.
Obviously, there will be no option of boot OS of choice, with the GPT getting priority and Windows not detecting the Linux.
I made a GPT install Penstick for Linux, booted up and using the Boot Repair made changes to the Bootup sequence in the EFI partition.
Now Linux Boots first and the GRUB gives me an option to choose Ubuntu or Windows.

[ramussons]

Here are the screen shots.

[Auzzz]

After reading your comment I realized that you are right and it doesn't matter if the boot loader was on the Windows drive lol.

Understand, this is a subject over which reasonable minds can differ, but I would say the majority of experienced Linux users will agree putting all the boot loaders in one EFI partition is best practice. It's also how UEFI was designed to work. Another thing to know - and to my mind the fatal flaw in the keep-the-systems-separate strategy - is that it's not possible. Sure, one can have two EFI partitions, but what really matters are the boot order settings in NVRAM. Your computer has only one of those.

If at some future date you find a Windows update is interfering with Linux boot, the problem won't be in the EFI partition. Rather, it will be in the NVRAM settings. You fix that by booting a live session and running efibootmgr. No need to learn how to do that today. Not likely to come up and you won't remember the details anyway. Deal with if and when ...

Good to know. I have been daily driving Mint since my post with Windows on my computer as well just for gaming the games that Linux can't run and for work. I like it a lot but still have so much that I need to learn so thank you for the context that you just provided. I will note this down in case I run into a problem in the future. But thank you again for taking the time to reach out and provide some guidance. It is much appreciated!