[MULTI BOOT] Dual Boot on Multi Drive All Linux System

[petrux]

I will be installing Kubuntu 20.04 on a multi-drive desktop. Currently openSUSE 15.1 with ext 4 occupies sdc, and openSUSE 13.1 occupies sda. The openSUSE 15.1 install recognizes 13.1 and provides the dual boot choice in the boot menu. Kubuntu will be installed on sda and will occupy the entire disk, replacing 13.1. My question is, will the Kubuntu install recognize openSUSE 15.1 on sdc and offer a boot choice? The Kubuntu installation provides no explanation about other OSs on the system (no Windows here). I?ve never seen this situation explained. Looking for some guidance.

[claydoh]

It should - the installer scans for boot info for other OSs and adds them to the grub menu, just like openSUSE saw the other install. Just make sure that Kubuntu is set to be the first boot option in your bios.
If you prefer Opensuse to be the primary boot OS, you will just need to update its grub, which should discover and add Kubuntu to its grub menu after you install the new OS.

As each OS has its own boot loader (unless you are running fairly old hardware) all that really matters is that the Grub boot menu for the primary OS is updated if there have been updates to the secondary OS, or another one is added or replaced.

And, again, as each OS has its own boot loader and grub menu, if there are problems, you can manually choose one via your system's boot drive selection hotkey.

[oshunluvr]

I have not been able to successfully install Kubuntu 20.04 or above in legacy (non-uefi) mode. I'm not saying it won't work for you as it might be related to what BIOS you have. In my case, I have not been able to get a 20.04 ISO to allow a non-UEFI install even though I have legacy mode set on my PC. I eventually resorted to doing a new Ubuntu Server 20.04 Legacy install (there's a special ISO without EFI on it) and then installing the Kubuntu Desktop afterward.

Why this matters is, I'm guessing you are using a legacy configuration. What may happen is, at install time, the installer will fail if you do not have a pre-configured EFI partition. If you encounter this, you have a few options:

1. You can install without a boot-loader (start Ubiquity from the command line with the -b switch) and let opensuse be your primary boot install.
2. You can let Kubuntu have sda with an EFI partition and go ahead with an EFI install. Then boot opensuse and let opensuse be your primary boot install.
3. You can install Kubuntu in EFI mode and then convert the opensuse install to EFI mode. Then either install can be the primary boot install.
4. Do what I did and have a regular legacy install by install Ubuntu Server Legacy 20.04 and then install Kubuntu desktop.

For #s 1 and 2, just running "sudo update-grub" from opensuse should detect the Kubuntu install and be able to boot it.
#3 requires some work on your opensuse install but it's been done. You can find instructions on the web.
#4 isn't as time consuming as it sounds and worked for me. It's initially faster than a "normal" Kubuntu install because not all the extra stuff is automatically installed like LibreOffice. However, you may have to add those sort of things afterward. This was fine with me because I prefer to pick my own stuff anyway.

Hopefully, none of the above will apply to you and it will be smooth sailing. Regardless, it's much better to have multiple drives when dual booting. Having more than one drive set up as a boot drive is extra security against mucking up GRUB somehow.

[petrux]

Thanks much for both explanations. That’s what I was missing about the boot process after a new OS install, and the grub update (this is a UEFI system). I’ll still be working in openSUSE while setting up Kubuntu, so it’s nice to boot either OS quickly. It will be a bit before I do the Kubuntu install, and will report the results.

[oshunluvr]

Well than I wouldn't expect any problems. Note that one of my biggest objections to UEFI is there's actually no way to have a true boot backup. There can only be one EFI partition so if that drive fails or has an issue or even if GRUB has a problem, you may be left in an unbootable condition. With legacy boot it's easy - just have more than one drive bootable. I have seen articles where there was a hacky attempt to have more than 1 EFI partition but it was a real sketchy. I wonder if one could duplicate the EFI partition on a thumb drive and boot from it? In any case, probably a good idea to make a mirror partition of the EFI partition and just not set it as an EFI partition. Then at least you could repair from it.

[claydoh]

There can only be one EFI partition

That is not true. I have two EFI partitions on my PC, one on my HDD that has Windows on one of its partitions, and one on my main ssd with KDE Neon.

Similar setup on my laptop.


When I have done test installs of other distros on my laptop, I put the boot files on the HDD's EFI (along with the OS) , and can use that to boot any of my OSs if necessary.

[oshunluvr]

Well last I read it couldn't be done. That's good to know. I couldn't get it to work on my work computer

[Qqmike]

It's always been true that you can have as many EFI's as you want.
Going way back to my early how-to's ...

Dual-booting: How to Use Multiple ESPs
https://www.kubuntuforums.net/showthread.php/43221-GRUB-2-A-Guide-for-Users?p=376040&viewfull=1#post376040

This material is incorporated into the above two how-to's: "UEFI for Kubuntu--simplified. And ... some dual-booting tips for Kubuntu" and "UEFI Simplified, a quicker version."

... more from:

UEFI, GPT, ESP, GRUB2-EFI, (dual)-booting, fixing things
https://www.kubuntuforums.net/showth...l=1#post412601

You just have to set them up correctly, and manage them correctly. I've tested it with 3 or 4 EFI's, fwiw.

[petrux]

The Kubuntu install was flawless. Made sda/Kunbutu primary in the BIOS, and got the dual boot option. Then updated grub in openSUSE (you can do that in YaST with one click, I discovered), and made openSUSE/sdc primary for now, so dual boot options either way. All good, and thanks, again.