[Pre-Install] Manual partitioning advice for multiboot with Kubuntu 26.04LTS and two more OSs.

[zahtar]

Hello everyone! Happy new LTS release! 🎂🥳

I am thinking of installing kubuntu 26.04 on my laptop, as well as Vanilla OS 2 Orchid, along with the existing win11. I would like to ask for partitioning advice prior installation.

I have installed a 1TB m2 drive to the laptop, cloned the old drive´s partitions with clonezilla and now I have plenty of unallocated space left, around 800GB I think. The windows partitions take up less than 200GB and I am not planning to store data or install any software there.

My current wish is to be able to run all operating systems on my laptop, and hopefully be able to upgrade to kubuntu 28.04 LTS without the system breaking in about two years.

A blog in the vanilla OS website suggests the following for manual partitioning:

• GPT table
• 1GB for /Boot (ext4)
• 512MB for /EFI (fat32)
• 20.5GB ¨for the Root partition pool unformatted.¨, which I do not understand what it means,
• swap for hibernation support
• remaining storage for /var (btrfs)

I do not know whether the author supposed a dedicated drive, but my in-use drive already has a gpt table if I am not mistaken, so it seems I am hopefully ok with that one.

I had a chat with an AI tool which gave me the below suggestion:

• leave everything windows related as-is
• 80GB for Kubuntu root (ext4 or btrfs), mount point /
• 80GB for Orchid root (ext4 or btrfs), mount point /
• 24GB linux swap, shared between Kubuntu and Vanilla
• remaining GB for storage, accessible via all three operating systems. (ntfs)
• install Vanilla, then Kubuntu so I keep the Kubuntu boot loader.
• ¨Use the existing ESP for all bootloaders; do not create a new ESP.¨
• ¨Add the NTFS partition to each OS /etc/fstab using UUID: sudo blkid to get UUID, then mount with ntfs-3g options for Linux.¨

So, my question is, do the above make sense? Is there by chance a different recommended method for manually partitioning before installing multi boot with 2 linux distros + windows?

Thank you in advance!


References:

• https://vanillaos.org/blog/article/2...-devlog-22-nov
• chat gpt5-mini output, on 25 Apr 2026

[INVICTRA]

Yes that looks OK. Should work. Follow AI suggestion.
After you got everything installed then make a backup of the boot partition (ESP) with something like KDE Partition Manager. Because Windows might delete it and recreate it in certain scenarios (Big update, FIX boot etc.). I find it faster to just restore a ESP that windows ****ed up than using live CD to repair Linux boot.

[jlittle]

• install Vanilla, then Kubuntu so I keep the Kubuntu boot loader.

(You'll want to turn on grub's OS prober, by setting GRUB_DISABLE_OS_PROBER=false in /etc/default/grub and running update-grub.)

Some Vanilla update might still trample on the kubuntu boot loader. If Vanilla uses grub, you could uninstall it from Vanilla to stop that. Being familiar with sudo efibootmgr could be useful.

I don't know how Vanilla installs to a btrfs; if it uses subvolumes you could put it and Kubuntu in the same btrfs to economize on space, with some /etc/fstab and grub manipulation.

[zahtar]

Hello, thank you both for your replies!

I installed Vanilla, it went well up to that point, with the exception that it asked to ¨keep EFI¨ in case I multi-boot, with the result not prioritizing its boot loader. From that point on, I needed to press F12 to get the boot menu, where vanilla was available and would boot properly if selected. Otherwise, the laptop used to boot to win11.

I thought this would not be a big deal, since I was ready to install kubuntu and expected its bootloader to take care of things. But this did not happen. The Vanilla option still doesn´t show up in grub, I still need to access the OS by F12 during power up. If I let it boot, grub will just show entries like ¨kubuntu, windows boot loader, UEFI hardware settings¨. This is after entering sudo update-grub

The weird thing is that when running sudo update-grub (I did that twice), the system does detect vanilla, promises that it will update the grub entry, but it doesn´t...

So, two questions:
a) Is there another way to edit grub entries so I get all options in grub? Or make the system properly update the entries automatically?
b) During installation, I didn´t tell kubuntu to use the /EFI partition that I created for Vanilla. I created another one so the new labels and flags cause no errors. Is this ok?


PS: if this conversation needs to move to a post-installation thread, let me know and I´ll rephrease here and create a new one.

[jlittle]

a) Is there another way to edit grub entries so I get all options in grub?

There's at least 3 ways to do this:

1. edit the file /etc/grub.d/40_custom to have the menu entries you need, then run sudo update-grub,
2. create the file /boot//grub/custom.cfg with the desired entries; no update-grub needed.
3. eschew the whole update-grub machinery altogether, and maintain manually grub.cfg.

No. 3 is a big step but I have done it for years and I claim that it's easier and far more reliable in the long term.

With any of these methods menu entries for a *buntu install can look like this:

menuentry 'Kubuntu' --class ubuntu --class gnu-linux --class gnu --class os {
    search --no-floppy --label --set=root your-label

    linux /@/boot/vmlinuz root=LABEL=your-label ro rootflags=subvol=@
    initrd /@/boot/initrd.img
}
​

Adjust your-label to suit. More conservatively you can use the UUID instead; change --label to --fs-uuid and LABEL to UUID, and put in the UUID instead of the label, twice.

Or make the system properly update the entries automatically?

Note that entries like the above boot the latest kernel and initrd ("initial ram disk') so don't have to be updated when a new kernel arrives. I have gone years without needing to touch an entry.

[barfly]

Laptops have many different keys for accessing the bios, but the majority use either F2 or F8. This is not the same as a temporary F12 to get a drop-down list of bootable options.

You need to get into the bios proper, and there will be an option for permanently selecting the correct (for you) o/s to be your primary boot system. Then reboot and you should then boot straight into your flavour of choice without having to press the F12 key for the drop-down boot menu.

Cheers Tony

[zahtar]

There's at least 3 ways to do this:
...
eschew the whole update-grub machinery altogether, and maintain manually grub.cfg.
No. 3 is a big step but I have done it for years and I claim that it's easier and far more reliable in the long term.
...

Note that entries like the above boot the latest kernel and initrd ("initial ram disk') so don't have to be updated when a new kernel arrives. I have gone years without needing to touch an entry.

John that sounds fantastic!!! I am already researching, I think I´d better start a new post regarding this and return here for final conclusions regarding the partitioning. Thanks for the idea!

..., and there will be an option for permanently selecting the correct (for you) o/s to be your primary boot system.

Tony, what I am looking for is to be able to have a grub menu during bootup with all three choices available. So I won´t have to enter the F12 boot menu etc. Thanks for your suggestion though!

[claydoh]

Tony, what I am looking for is to be able to have a grub menu during bootup with all three choices available. So I won´t have to enter the F12 boot menu etc. Thanks for your suggestion though!

Set your primary boot OS in the BIOS to whichever one you prefer, Let's use Kubuntu as the choice here as an example. Make sure in Kubuntu, you have os_prober enabled. Run sudo update-grub to detect and add other OS installs to its grub menu.
So, when you reboot, you should be seeing Kubuntu's Grub menu with Windows and Vanilla options.

That's it.


Every time you have a kernel update in Kubuntu, it will run update-grub for you. But if you added a new OS install or or wipe one, you will need to do this manually. In Kubuntu.
Also, any kernel update in Vanilla will not be picked up in Kubuntu's grub menu until grub is updated in Kubuntu. It will boot the previous kernel for Vanilla until Kubuntu's grub is updated, and sees the new kernel in Vanilla.

Each OS install has its own bootloader, and each Linux install has its own boot menu. Selecting Kubuntu (or Vanilla) as the main boot option, you are getting the boot menu from that OS. This is the one you need to focus some regular updating on.

It is not a bad idea to have os_prober enabled in Vanilla as well, so it also detects and updates the other OS installs when grub is updated. This is good as a fallback, in case something happens to Grub on Kubuntu, and vice-versa.

It is not as much work as it sounds unless you are a massive distrohopper. This could easily be scripted as well.

[zahtar]

Hello claydoh, thank you for your response.

I already have GRUB_DISABLE_OS_PROBER=false in /etc/default/grub as jlittle suggested in post #3.

sudo update-grubgives the following output, but no vanilla entry is added to the grub menu after reboot. Am I perhaps missing something?

Sourcingfile `/etc/default/grub'
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-7.0.0-15-generic
Found initrd image: /boot/initrd.img-7.0.0-15-generic
Found linux image: /boot/vmlinuz-7.0.0-14-generic
Found initrd image: /boot/initrd.img-7.0.0-14-generic
Found memtest86+ 64bit EFI image: /boot/mt86+x64
Found memtest86+ 32bit EFI image: /boot/mt86+ia32
Found memtest86+ 64bit image: /boot/mt86+x64
Found memtest86+ 32bit image: /boot/mt86+ia32
Warning: os-prober will be executed to detect other bootable partitions.
Its output will be used to detect bootable binaries on them and create new boot entries.
grub-probe: error: disk `lvmid/fl06Sj-rdhf-mwFU-5eul-MZ9j-clMy-2wM6QI/rTVF8w-iJ5x-JKaJ-FPqf-V6pq-c0cE-0yqsmH' not found.
grub-probe: error: disk `lvmid/fl06Sj-rdhf-mwFU-5eul-MZ9j-clMy-2wM6QI/EUc5M2-4gYk-Tdub-6mSl-yLAJ-WN9G-2ZavHt' not found.
Found Windows Boot Manager on /dev/nvme0n1p1@/efi/Microsoft/Boot/bootmgfw.efi
Found Vanilla OS 2.0 (2.0) on /dev/mapper/vos--root-root--a
Adding boot menu entry for UEFI Firmware Settings ...
done

The current state is:
The 1st OS to boot is Kubuntu, grub menu shows kubuntu, advanced settings, memory test (two options), windows boot manager and UEFI settings. Both Kubuntu and windows will boot fine from that menu if I choose either one, but Vanilla is absent, despite having been detected during update-grub. The only way currently to boot vanilla is from the F12 menu during powerup.


EDIT: another attempt with chatgpt, gave me the idea that maybe this is due to Vanilla Safe Boot. So the suggestion is to add a custom entry:

sudo nano /etc/grub.d/40_custom

menuentry "Vanilla OS (chainload EFI)" {
search --fs-uuid --no-floppy --set=root [uuid value]
chainloader /EFI/vanilla/shimx64.efi
}
​

Is this safe to attempt?

[barfly]

John that sounds fantastic!!! I am already researching, I think I´d better start a new post regarding this and return here for final conclusions regarding the partitioning. Thanks for the idea!





Tony, what I am looking for is to be able to have a grub menu during bootup with all three choices available. So I won´t have to enter the F12 boot menu etc. Thanks for your suggestion though!

When you install new o/s's, they usually bump up their boot loader as first entry in the machine's bios. So in order to get your PRIMARY o/s to boot first you will need to set that in the bios.
After sorting that you then boot into that system and run "update-grub" (with the o/s prober enabled) and that will then give you all the other options in your grub boot screen. If you get the wrong o/s to be first in the bios order you will always have to do the f12 thing! That is what I meant in my earlier post - sorry if I was not clear.
Cheers Tony

[zahtar]

thanks for the clarification mate, but I´ve already done this. The kubuntu partition has the priority indeed and its bootloader is the one that boots. Os-prober is activated, update-grub detects Vanilla, but does not add any entry to the grub menu.

I attempted adding a custom entry in the 40_custom file, but it still doesn´t work.

Maybe it is the safe boot that vanilla uses? who knows...

[jlittle]

grub-probe: error: disk `lvmid/fl06Sj-rdhf-mwFU-5eul-MZ9j-clMy-2wM6QI/rTVF8w-iJ5x-JKaJ-FPqf-V6pq-c0cE-0yqsmH' not found.
grub-probe: error: disk `lvmid/fl06Sj-rdhf-mwFU-5eul-MZ9j-clMy-2wM6QI/EUc5M2-4gYk-Tdub-6mSl-yLAJ-WN9G-2ZavHt' not found.

Well, the OS prober did not cope with the Vanilla OS setup; I could only guess at why, as the errors are mysterious. Some kind of logical volume arrangement.

sudo nano /etc/grub.d/40_custom

menuentry "Vanilla OS (chainload EFI)" {
search --fs-uuid --no-floppy --set=root [uuid value]
chainloader /EFI/vanilla/shimx64.efi
}
​

That looks like it might work. I thought shimx64.efi is needed with secure boot, and if you've got that on I don't know what happens. Does the ESP have /EFI/vanilla, and /EFI/vanilla/shimx64.efi?

What does /boot/grub/grub.cfg from within Vanilla OS say in the first menu entry?

[zahtar]

hello, thank you for your reply and sorry for taking so long to respond. I only have time in weekends to experiment with this, and the last one was very very busy.

I´ll take a look in the /efi folder in my laptop and Iĺl get back to you. If I remember correctly /efi was mounted on a separate fat32 partition which might not be visible, but I can´t remember right now. I also think that grub.cfg was not accessible either (due to being atomic/immutable?), but I cant remember that, sorry.

I´ll check and give a proper reply whenever I find time for it.