Multi-booting BTRFS installs made easier with Calamares ***UPDATE*** Ubiquity can be edited also

[oshunluvr]

DECLAIMER: This has only been tested on KDEneon Stable in a virtual machine.

Calamares:

I was reading some Calamares documentation and saw where the latest versions allow the distro developer to customize not only the mount points but also the BTRFS subvolume names.

This is notable because some of us like to install multiple distros to a single BTRFS file system. The default subvolumes used by *buntus when using BTRFS are "@" for root and "@home" for home. This is fine and dandy until you want to install a second distro. Then you have to edit fstab and grub.cfg and rename the subvolumes before installing the second (or third or fourth) distro. A typo can be disastrous! So I went looking...

...and found it!

Using a KDEneon ISO, the subvolume names are in this file: /lib/X86_64-linux-gnu/calamares/modules/mount/main.py

On line 165 , you'll find these entries:

...subvolume="/@"...
...subvolume'"/@home"...

It's as simple as changing those two subvolume names and then launching the installer.

My process:

1. Boot to the KDEneon ISO.
2. Select "Try before installing" rather than "Install".
3. Open Konsole and edit the file above: sudo nano /lib/X86_64-linux-gnu/calamares/modules/mount/main.py
4. Scroll to line 165 and change the subvolume names (I used @neon and @neon_home) and save the file.
5. Run the installer.

That's it! I felt this was much easier and quicker than a post-install edit of grub.cfg and fstab and rebooting, then running update-grub.

Things to note:

• I used a virtual machine and have not tested this on bare metal but I have no reason to believe the results would vary.
• The actual line in the above edited file may change with distros or versions so you may have to search for "@" and "@home" in the file.
• This may not be obvious to everyone; You're editing a file in a "live" environment so "saving" your edit only lasts until the first reboot. If you want to do this again, or mess up your install and want to reinstall, you have to do the edit again - and every time you reboot.

I don't know if Kubuntu plans to move to Calamares anytime soon, so I'm going to go looking into Ubiquity next...

...see post below.

[claydoh]

I don't know if Kubuntu plans to move to Calamares anytime soon

They should, Lubuntu already does iirc. if they Ubuntu doesn't update the installer, it is a sane move to make.
Calamares has become pretty stable.

On the live session, look at /calamares on the root directory for some config files as well. Might be some useful bits to hack on there
Used to have to edit the fstab setup in there for btrfs until the past couple of weeks - they updated Calamares to the current release for neon, which fixed that, among other things.

[oshunluvr]

Yeah, I went through those files. I was specifically searching only for @ and @home and didn't dig any deeper than that.

[oshunluvr]

Ubiquity:

This tested in a VM using Kubuntu 23.10 newest ISO.

The 2 files to be edited are:

• /usr/lib/partman/fstab.d/btrfs
• /usr/lib/partman/mount.d/70btrfs

/usr/lib/partman/fstab.d/btrfs

Lines 31, 32, and 37 contain: subvol=@ or subvol=@home

I edited these to @2310 and @2310_home


/usr/lib/partman/mount.d/70btrfs

Lines 21, 22, 24, 28, 29, 31, and 32 all contain: @ or @home

As above, I edited these to @2310 or @2310_home


The total process was the same as in the first post. Only the file names and location were changed and more specific edits were required.

All the above warnings apply and make sure you get ALL the @ and @homes edited!