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I know there are tons of Questions/Answers about this problem, but even after few hours of search did not give me what I really wanted. Maybe I searched with wrong keyword, but I think this is out of my capability.

I have PC with MSI B450M Mortar, 1 SSD, 1 HDD. And I want my whole system's partition stuff be like this.

  1. SATA SSD, 500GB
    1. 512MB EFI Partition
    2. 140GB Windows(NTFS) Partition (This is where Windows is installed)
    3. 325GB NTFS Partition (This is where I install games etc.)
  2. SATA HDD, 1TB
    1. 500GB NTFS Partition (This is where I install some heavy software)
    2. 100GB ext4 / Partition (This is where Ubuntu's / will be mounted)
    3. 400GB ext4 /home Partition (This is where Ubuntu's /home will be mounted)

Since I don't mainly use Ubuntu but occasionally use it, I don't need SSD for most of Ubuntu stuff. I satisfied with its speed with HDD.



Since I don't know much about 'Windows Boot Manager', I assume it is just for launching Windows. Maybe I can do 'Safe Mode' stuff without it. Thus, I want GRUB to replace WBM. That means, when I turn my PC on, only GRUB will appear(with some cool theme). If I select Windows in GRUB, it will boot to Windows. If I select Ubuntu in GRUB, it will boot to Ubuntu.
(In this case, I don't care about GRUB launching WBM, but only if doing so doesn't impact Windows' boot speed)

I've tried several ways. Since Windows is primary OS for me, I installed Windows first.
(I can't remember everything so I will describe what I remember now)

First, I splitted partition in HDD before installing Ubuntu. I selected 'custom' option thing when installing Ubuntu and selected 'boot loader' partition as /dev/sda1 which Windows Boot Manager is already installed.

It worked well, but boot time was horrible. Booting into Windows and Ubuntu took much much longer. I think this is because GRUB refers config in /boot/grub which is located in HDD, so PC need to search SSD first for EFI and HDD for GRUB config. So, I need to put GRUB thing into EFI partition. My guess is, if I do it, boot time will be fast enough because GRUB gets its config in SSD in same partition as EFI partition.

So I tried to mount EFI partition as /boot when installing, but Ubuntu Installer didn't allow it.
Next attempt was create another 512MB partition next to EFI partition, shrinking Windows partition. I mounted /boot(/dev/sda4 - that's because it was created 4th) and /boot/efi(/dev/sda1 - EFI partition). Well, I don't know why, but it didn't mount /boot, so /dev/sda4 was blank, not used at all.

I even tried to install with Ubuntu Installer's 'Install with Windows Boot Manager' option and I regret it. It created blank, not used partitoin in HDD and put /dev/sdb5 under /dev/sdb3. There was no /dev/sdb4. I personally hate those 'unordered' things, so I gave up with that option.




So, long story short, I want boot loaders act like this.

  1. If WBM act crucial part about 'Safe Mode' etc.
    • GRUB first
      1. If Windows is selected, boot with WBM, boot into Windows
      2. If Ubuntu is selected, boot into Ubuntu
      3. GRUB config/theme located in EFI partition
  2. If WBM act nothing about 'Safe Mode' etc.
    • GRUB only
      1. If Windows is selected, boot into Windows, without WBM
      2. If Ubuntu is selected, boot into Ubuntu
      3. GRUB config/theme located in EFI partition



PS. Don't worry about WBM wiped out. I recovered it with bcdboot C:\Windows /l ko-kr /s K: /f UEFI everytime I formatted EFI partition and recovered WBM.

tetratheta
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  • What you seem to want is the normal default. But grub only boots working Windows. Or when Windows update turns fast start up back on or it needs chkdsk, you have to boot it from UEFI. Or if mostly Windows, set Windows as default, and use UEFI to choose Ubuntu when desired. Ubuntu's Ubiquity installer only installs grub to first drive's UEFI unless you do a work around. To have ESP on HDD. Remove esp flag from Windows - Tim Richardson https://askubuntu.com/questions/16988/how-do-i-install-ubuntu-to-a-usb-key-without-using-startup-disk-creator/1056079#1056079 – oldfred May 22 '21 at 17:46
  • @oldfred So, GRUB cannot launch WBM, right? Thank you for the information. I guess I should try this one, since only other method was 'you must be messed up when you selected /boot in installer, so try it once more' – tetratheta May 23 '21 at 06:03
  • Grub boots working Windows, if UEFI Secure boot is off. Otherwise grub will not boot Windows. Most desktops do not need nor should use separate /boot partition. But if UEFI install you do need the ESP - efi system partition which is more like the MBR with old BIOS installs as it is where the start of booting is , or just part of grub. – oldfred May 23 '21 at 14:43

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