Install dual boot with Kubuntu 25.04 on separate 2nd drive, manual partitioning?

[greylander]

Hello, I'm planning to install Kubunu on a secondary drive where Windows 10 is on the first drive.

I want to be sure the Kubuntu installer does not mess with the existing window EFI boot loader. Various guides indicate manual partitioning but are not up to date with 25.04 and latest installer, so far as I can tell. It seems that trying "side by side", at least by my interpretation of what the installer indicated it would do, would result in modifying the existing EFI boot partition rather than make an independent EFI with grub on the 2nd drive. My attempt to do manual partitioning left me unclear whether it would do the right thing, so I aborted the install.

I'm hoping I can following instructions similar to this guide for Ubuntu dual boot, https://merox.dev/blog/windows-11-ub...al-boot-guide/ though it is a bit sparse on specifics for the 2-drive scenario. Also, I think the partition options and manual partition settings look a bit different with the Kubuntu installer vs Ubuntu installer, and I want to make sure I set things like partition type, mount, flags, & "use as" correctly.

So hoping for clarification on exactly what to do, or will the installer support what I'm trying to do? If not -- then do I need to do some workaround like using gparted to make all the right partitions before running the install?

I've also seen other guides & forum posts suggesting either removing or disabling(in bios) the first drive before installing linux on second drive. This is followed by a step where the first drive is re-enabled then boot into the new linux and run a command that sets up the grub to be aware of Windows. Thus the Linux boot setup knows about windows and can let me boot into it, but the Windows boot setup has no idea the linux installation even exists.

Although I'd prefer to try the latest greatest Kubuntu, would switching to 24.10 be a better option for some reason?

Other details in case they matter or if any knows any gotchas or other considerations I should be aware of:
-- not sure it matters but the second drive has an existing secondary windows partition -- hoping that doesn't really change anything about "installing linux on 2nd drive" as long as I just use remaining free space on that drive.
-- this is a UEFI / GPT system
-- Razer Blade 15 (2020) with Windows 10, GeForce RTX 2070

Ideally would prefer to not have to pull out the first drive SSD and just have the Kubuntu installer do the right thing (i.e. not touch the Windows installatoin & drive at all, and have its own separate EFI boot loader partition that can boot into windows or Kubuntu).

I think maybe I just need to clear on all manual partitions I need to create and exactly what settings to use for them. But recommendations of doing things differently or "best practices" welcome.

Apologies if I'm mangling terminology above.

Thanks!

[Qqmike]

I think you will find this recent post useful:

GRUB Issue
https://www.kubuntuforums.net/forum/...204-grub-issue

Please try to read it from start to finish (2 pages, but it goes pretty fast).

[greylander]

I think you will find this recent post useful:

GRUB Issue
https://www.kubuntuforums.net/forum/...204-grub-issue

Please try to read it from start to finish (2 pages, but it goes pretty fast).

Yes, thanks! That looks like it addresses what I'm after. Just need to make sure I have a separate ESP partition that can use grub to select boot OS, since Windows wants to keep control of its own ESP partition.

Just need to be sure I set up the partitions correctly (whether within the installer, or with gparted outside of the installer) and in such a way that the installer will use them. Now need to read through all of it carefully.

[Qqmike]

Now need to read through all of it carefully.

Yes.
You'll note that there is no need to pull that Windows drive. The author there unmounted the Windows drive.
I do not use Windows, as I indicated in that thread.
However, I'm pretty sure that instead of unmounting the Windows drive, you could disable the Windows ESP by (temporarily) turning off the boot flag on it. You could do this using gparted, for example.

[greylander]

Yes.
You'll note that there is no need to pull that Windows drive. The author there unmounted the Windows drive.
I do not use Windows, as I indicated in that thread.
However, I'm pretty sure that instead of unmounting the Windows drive, you could disable the Windows ESP by (temporarily) turning off the boot flag on it. You could do this using gparted, for example.

I'm looking at your writeup, about using two ESPs, and you mention Kubuntu's Calamares installer lets me pick which ESP to use. Does that mean I should not even need to disable the Windows ESP (let along remove the drive)?

Also, at what point should I see this choice? Will it just automatically use a new ESP partition if I've created one in the manual partitioning step? Or will I get a choice after that step? (Thus far, I haven't moved beyond specifying the partitions but not actually creating them or continuing beyond that point, since the button just says "install" and I don't want to screw something up if I haven't specified correctly and there is not a subsequent choice of ESP to use or confirmation after that step.

Maybe I'm overly worried, since I guess Windows will just repair its own ESP if my Kubuntu install messed with it. Worst case I just reinstall Kubuntu?

[greylander]

After some additional research, I think in Calamares installer, the ESP (EFI) partition that is used by the installer will be selected by setting the mount point of the partition I want as /boot/efi, yes?

[Qqmike]

I want as /boot/efi, yes?

Yes -- that's the mount point always, for any ESP.

Notes
-- GRUB will remember which ESP you've used when GRUB was installed.
So when you are in your OS, and you issue sudo grub-install or sudo update-grub, GRUB will use the ESP that was used when GRUB was installed in that OS (the OS that you are in now when you issue those commands).
-- The command df /boot/efi -- shows you the ESP partition the OS is using (the OS that you are currently booted into when you issue that command).

[Qqmike]

you mention Kubuntu's Calamares installer lets me pick which ESP to use. Does that mean I should not even need to disable the Windows ESP (let along remove the drive)?

The Calamares installer is supposed to show you a drop-down menu of ESPs to choose from. I do believe that's what I saw when I did the experiments.
Windows always seems to be the hassle.
In that thread, the author was taking no chances, I guess.
If you unmount an ESP, of if you hide it (by temporarily removing its boot flag), then the installer will only see the ESP(s) that are visible (not unmounted or hidden).

Also, at what point should I see this choice?

While you are specifying the use of the partitions (root(/), /home, /swap, etc.).
That choice (of specifying the ESP), for me, was at the top of the screen! (Yes, it was, at the top, in kind of small letters, as I recall.)

Maybe I'm overly worried, since I guess Windows will just repair its own ESP if my Kubuntu install messed with it. Worst case I just reinstall Kubuntu?

No, your should worry! haha I'm the same way, along with most of the people here. Plan ahead, take no chances (or reduce your uncertainties).
Worst case, yes, you can re-install Kubuntu easily.
And, reading the posts around here, I think that Windows can (somehow) fix its bootloader.
ALSO ...
There is, ya know, Boot-Repair, which can come in real handy-dandy at times:
https://help.ubuntu.com/community/Boot-Repair
(I do believe it can even fix a Windows bootloader.)

[claydoh]

We are overcomplicating things, maybe

In calamares, at least on KDE neon and Kubuntu 24.10 and 25.04 for using a separate drive and separate EFi, this can be done very easily using the automated install option

here is one:
Note "tech" is the existing OS install, and VDA is the second drive here



Selecting the desired drive and using the "erase disk" (yes, poor wording!), note what it proposes at the bottom.
Then, on the confirmation page, it....confirms


Now, doing a manual install, you do need to manually create/designate the efi partition and set it as /boot/efi with the boot flag, or it will complain. But it won't use the existing partition on the other disk unless you tell it to, as far as I can see.
(this test is still installing)

Even if you used one efi partition, the actual bootloaders for each OS are still completely separate. The only thing that changes sometimes is Windows updates or BIOS updates resetting the boot order in the BIOS settings.
m
The whole removing/disconnecting the windows drive is old habit and Internet Memory, and is not necessary but of course not harmful. Older Kubuntu and other installers may have benefitted from doing this at some point.
I haven't done this myself since at least 2016.