Preface

GRUB2 from other distribution cannot boot into distribution using BTRFS as root

I have a multiboot situation consist of Debian, Fedora, OpenSUSE and KaOS. I’m just willing to learn different package managers. This is more like a GRUB2 issue, and not a BTRFS issue, Since I cannot find a GRUB2 community, I blog instead.

Partition

Partition as seen in KDE Partitioner Manager form KaOSx.

  • /dev/sda1 : NTFS : W7

  • /dev/sda8 : Swap

  • /dev/sda7 : Ext4 : Debian

  • /dev/sda9 : Ext4 : Fedora

  • /dev/sda10 : BTRFS : openSUSE Tumbleweed

  • /dev/sda11 : XFS : openSUSE Tumbleweed /home

  • /dev/sda12 : XFS : KaOS

KDE Partitioner Manager

All distro can mount other partition using root privileges. No issue in reading XFS and BTRFS in File Manager.


Distribution Test

GRUB2 installed by openSUSE (BTRFS)

GRUB2 boot successfully to openSUSE. This openSUSE use BTRFS mounted at root /. Of course, the GRUB installed from this openSUSE

GRUB2 installed by Fedora (ext4)

Fedora seems to recognize openSUSE in BTRFS. It shown in grub2-mkconfig, but does not write openSUSE entries to output in /boot/grub2/grub.cfg.

Fedora GRUB2 Issue

$ sudo grub2-mkconfig -o /boot/grub2/grub.cfg 
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-4.11.10-300.fc26.x86_64
Found initrd image: /boot/initramfs-4.11.10-300.fc26.x86_64.img
Found linux image: /boot/vmlinuz-0-rescue-d903a5c6e0a947ccb45d1f9d8d22516e
Found initrd image: /boot/initramfs-0-rescue-d903a5c6e0a947ccb45d1f9d8d22516e.img
mount: /var/lib/os-prober/mount: mount(2) system call failed: No such file or directory.
device-mapper: reload ioctl on osprober-linux-sda6 failed: Device or resource busy
Command failed
Found Windows 7 on /dev/sda1
Found openSUSE Tumbleweed on /dev/sda10
Found KaOS (rolling) on /dev/sda12
Found Debian GNU/Linux 9 (stretch) on /dev/sda7

GRUB2 installed by Debian (ext4)

Debian does not seems to recognize openSUSE at all.

Debian GRUB2 Issue

GRUB2 installed by KaOS (XFS)

KaOS does not seems to recognize openSUSE at all. Same issue with Debian.


Workaround

Failed

I try a workaround, copy paste specific entries from openSUSE’s grub.cfg to Fedora’s grub.cfg.

menuentry 'openSUSE Tumbleweed'  --class opensuse --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-c114d95e-bc0a-4b41-a2db-abd21aa9850f' {
	load_video
	set gfxpayload=keep
	insmod gzio
	insmod part_msdos
	insmod btrfs
	set root='hd0,msdos10'
	if [ x$feature_platform_search_hint = xy ]; then
	  search --no-floppy --fs-uuid --set=root --hint-bios=hd0,msdos10 --hint-efi=hd0,msdos10 --hint-baremetal=ahci0,msdos10 --hint='hd0,msdos10'  c114d95e-bc0a-4b41-a2db-abd21aa9850f
	else
	  search --no-floppy --fs-uuid --set=root c114d95e-bc0a-4b41-a2db-abd21aa9850f
	fi
	echo	'Loading Linux 4.11.8-2-default ...'
	linux	/boot/vmlinuz-4.11.8-2-default root=UUID=c114d95e-bc0a-4b41-a2db-abd21aa9850f  ${extra_cmdline} resume=/dev/disk/by-uuid/b623e30b-c7a5-4f99-a250-45372da4c5b4 splash=silent quiet showopts
	echo	'Loading initial ramdisk ...'
	initrd	/boot/initrd-4.11.8-2-default
}

But it doesn’t work. It said

"error: file '/boot/vmlinuz-4.11.8-2-default' not found"

I have checked that the file “vmlinuz-4.11.8-2-default” is there in btrfs partition. I aware there is option “insmod btrfs”. And I suspect that Fedora’s GRUB2 cannot read BTRFS. The same case also happened with Debian.

What is going on here ? Any solution I can do? A workaround ? I need an enlightenment.

Working

Three workarounds, two responses from Fedora Community, and the third is mine.

  1. Using systemd-boot, forget about GRUB. Require GPT and EFI. Which is I use MBR without EFI.

  2. Create a special /boot partition using ext4 for openSUSE BTRFS. I finally use this method.

  3. Install GRUB2 from openSUSE. I can do it using chroot from openSUSE USB live stick.

Conclusion

It works !

I decide to create /boot partition in /dev/sda13 using /ext4.

But I still wonder, whether there is GRUB2 support for BTRFS, or not.


Thank you for Reading