How 2 change a multi-boot Grub2 back to a standard boot

English Install/Boot/Login
1

Hi there,

I have a PC with both Windows 7 and OpenSuse 15.1 on disk A (SSD). I have bought another SSD because I intend to put OpenSuse 15.1 on this new disk B and use disk A completely for Win7, which means I would have to remove the linux partitions on A (swap and root) and extend the Win7 partition.

But there is a problem: I used Grub2 for the dual boot and it is unfortunately stored in the root partition. So if I now delete the Linux partitions I will end up with a non bootable system. Though its an UEFI board (Asus M5A99x Evo R2.0) it was installed in Bios compatibility mode.

  1. If I activate in Yast/boot manager the option to write generic code into the MBR, does this mean that it will disable Grub2 and will boot the active partition on disk A?
  2. If I install OpenSuse 15.1 on disk B and try to exclude during the installation every Linux partition on disk A , will the new Grub2 be able to keep the bootable Windows partition in its list ?
  3. Or what else do you guys suggest ?

TIA Joe

2

You will also need to tell it to boot from a partition. Otherwise it may continue to write boot code to the MBR.

If I install OpenSuse 15.1 on disk B and try to exclude during the installation every Linux partition on disk A , will the new Grub2 be able to keep the bootable Windows partition in its list ?

That depends on what you mean by “exclude”. If you just mean to not use those partitions for Leap 15.1, then yes that should do what you want. However, your newly installed system will get a grub menu entry to boot the old 15.1 (from disk A). You can just ignore that entry. Eventually, when you redo things on disk A, an update of the grub menu will remove that entry.

However, one caution: If Windows is installed for Legacy MBR booting, then you need to make sure that you install Leap 15.1 also for legacy booting. If you intend to somehow change Windows 7 to use UEFI booting, then you must install the new 15.1 for UEFI booting. You only get a grub menu entry to boot Windows if Windows is booting the same way as linux.

Or what else do you guys suggest ?

Honestly, install Leap 15.2 instead of Leap 15.1. You will see 15.1 reach its end-of-support shortly. Best to go with 15.2.

3

Hello nrickert,

thanks for your reply.

Downloaded OS 15.2 as suggested and tried to install it from an USB stick.

I set up my own set of partitions on disk B, but during the following process I got an error message that the system would become unbootable, because there would be no efi partition and stopped the installation.

So how can I convince OS 15.2 that indeed it is non an UEFI, but simply an MBR based legacy boot system ?

As I do not need the content of the old OS 15.1 on disk A (the data I want to keep is on disk C & D) , I would like to disable GRUB2 and let the system directly boot the windows parition on disk A. Then OS 15.2 would start in a cleaner, more standard environment …

But how can I convince Grub2 to exactly do that ? Have had already a similar Grub situation with OS 42.x and ended up in an unbootable system. Took me hours to make that pc boot again.

There are several parameters in Yast/Bootloader which sound promising, but the help text is not really helpfull.

I took screenshots, but as this forum does not support the upload of images … So I can only describe those options:

Boot Loader Location :
( ) Boot from Partition
(x) Boot from MBR
( ) Custom Boot Partition

Options:
( ) Set active Flag in Partition Table for Boot Partition
( ) Write generic Boot Code to MBR
( ) Enable Trusted Boot Support

Is option 2. (“Write generic Boot Code to MBR”) disabling the Grub2 ?

The help says:
**Write generic Boot Code to MBR **replace the master boot record of your disk with generic code (OS independend code which boots the active partition)

Does it mean it will disable Grub and just boot the active partition ? Because if not and I remove the OS 15.1 partitons on disk A … Booom!

If it works it would be great as then I could boot directly into Windows and remove the old 15.1 partitions on disk A and expand the Windows partition. Then I could start with the installation of OS 15.2 on disk B. Well if I can convince OS 15.2 to install on a legacy MBR system …

TIA, Joe

4

The install USB can be booted in UEFI mode or it can be booted in legacy MBR booting mode.

You booted it in UEFI mode, so it wanted to install for UEFI booting. That’s what caused the message that you saw.

The best way to avoid this, is to boot the USB installer in legacy mode. How to do that is between you and your BIOS.

If you cannot manage that, there is an alternative. Ignore the message if it occurs just after the partitioning. Then when you see an install summary screen, click on “Booting”. On that screen, change the bootloader from “GRUB2 for EFI” to just “GRUB2”. That should change the bootloader screen to what will be more familiar to you. Make any other changes, then proceed with the install.

As I do not need the content of the old OS 15.1 on disk A (the data I want to keep is on disk C & D) , I would like to disable GRUB2 and let the system directly boot the windows parition on disk A. Then OS 15.2 would start in a cleaner, more standard environment …

If you made the other changes in 15.1 – install generic boot code, boot from a partition – then you should only need to change the active partition to the Windows partition, and Windows should then boot up without using grub.

5

Hi there,
happy new year.

I could install OS 15.2 and the “new” Grub2 could take over in a separate /boot subdir on Disk B. Afterwards I could delete the old OS 15.1 partitions and expand the windows one to the max size of disk A.

And most important … after switching off, the reboot did work like a charm.

So thanks a lot for the help !

Cheers, Joe