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Changing/Installing Kubuntu/Windows dual-boot and corresponding partitioning

gd flag

I installed Kubuntu 21.04 on a machine with Windows a few days ago. I selected the proposed disk config during the installation and have the following partitions now:

/dev/sda

/dev/sdb

I'd like to place Kubuntu on the SSD for obvious performance reasons now. If I start a new installation I only get the options:

  • Guided - use entire disk
  • Manual

I know some things about partitioning, MBR, boot loaders and the like but I don't know enough to do a manual config for the following:

  1. Leave Windows system (sda2) and data (sdb1) where they are.
  2. Shrink sdb4 to the unallocated size of sda and move it there. (Is this even possible?)
  3. Partition the then unallocated space on sdb for Linux data.

I don't care about where the boot loader is located. It can stay where it is now on sdb.

Abandoning the recently installed Kubuntu on sdb[2|3|4] and achieving the above with a fresh installation is also an option.

oldfred avatar
cn flag
It looks like you have mixed BIOS Windows & UEFI Kubuntu installs. And that means you have newer UEFI hardware. Microsoft has required vendors to install in UEFI boot mode to gpt partiitioned drives since 2012. So did you do your own install and really want the old BIOS/MBR configuration? How you boot install/repair media for both Windows & Ubuntu is how it installs. Best to always boot in one mode or the other and if UEFI hardware to always use UEFI. But you have Windows in BIOS mode. Is reinstalling Windows in UEFI mode possible?
Gerold Broser avatar
gd flag
@oldfred This is a gaming laptop from 2017 with a BIOS from 2016 and according to `dmidecode`: "UEFI is supported". Windows was pre-installed by the OEM. I'd like to avoid reinstalling Windows, since this system is 4 years old, I'm a heavy power user/developer and there's so much configuration and setup in it. I really don't want to spend that much time again for just a secondary OS now that I'm switching to Kubuntu as my primary one.
Gerold Broser avatar
gd flag
@oldfred I think I understand now why installing Kubuntu on sda3 was not presented as an option at installation. I read right now that GPT contains a "dummy" protective MBR which would make the Windows on the same drive unsuable. Is that correct? I also read that MBR can be converted to GPT if there is enough space between MBR and first partition. But that doesn't seem to be the case here.
oldfred avatar
cn flag
You do not want to convert MBR to gpt with a Windows drive. Windows only boots in BIOS mode from MBR and only UEFI from gpt. And with Windows conversion erases drive. There is a complicated conversion process, but those that have posted have ended up reinstalling & restoring from backups. You can dual boot Windows in BIOS mode & Kubuntu in UEFI mode, but only from UEFI boot menu, not from grub. Really more for data only drives and works with LInux with total grub reinstall. Converting to or from GPT - must have good backups. http://www.rodsbooks.com/gdisk/mbr2gpt.html
Gerold Broser avatar
gd flag
@oldfred Thx for the infos. Is it then possible to force the Ubuntu installation to use MBR? I think I don't need the advanced features of GPT for my planned config, do I?
oldfred avatar
cn flag
I recommend gpt, but no you do not have to have it. You can use MBR with Kubuntu in either UEFI or BIOS boot mode. I would keep gpt for any drive that is data only or Linux only. And you can have both an ESP for UEFI boot (in future) and will need a 1MB bios_grub partition, unformated with bios_grub flag for BIOS version of grub on gpt drive. How you boot install or Repair media, UEFI or BIOS, is then how it installs or repairs. Add bios_grub partition and reinstall BIOS version of grub from Kubuntu live installer booted in BIOS mode. Either use Boot-Repair's advanced mode or chroot.
Gerold Broser avatar
gd flag
@oldfred I checked my BIOS setup right now: _UEFI Boot: Disabled_ (and I never changed this). Why did the Kubuntu installation create this `sdb3` partition then?
oldfred avatar
cn flag
Not sure but with most systems the UEFI/CSM setting is for your installed system(s). If USB boot is allowed, then you usually have two boot options in UEFI boot menu of a live installer. One is clearly UEFI and other just shows name/label of flash drive and is for BIOS boot. Also some tools that create live installers, create one that only boots in UEFI mode or only in BIOS mode. So you have to choose correct mode when creating live installer. If UEFI hardware, generally better to have all systems in UEFI mode.
Gerold Broser avatar
gd flag
No further answers required any longer. See [my answer to _"No available connections" after upgrading from 21.04 to 22.04_][A]: > I ended up with abandoning Ubuntu and installing [openSUSE Tumbleweed][OS]. This means a few days of installing/configuring now but I don't have mercy with OSs that do not work as they did before after an upgrade. Fortunately with Linux there's always an alternative. All mount points but `/home` are on the SSD now. That's fine for me. [OS]: https://www.opensuse.org/ [A]: https://askubuntu.com/a/1428571/562424
Gerold Broser avatar
gd flag
@Esther Au contraire, I know very well what an answer to my own question is. Thank you for understanding.
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