Macbook Pro, booting to Ubuntu on BTRFS

[Anand Patil]

Hi everyone,

I've created a partition on my Macbook Pro, booted Ubuntu from a USB
stick using refind 0.8.4, formatted the partition as BTRFS, and
installed Ubuntu to it using ubiquity.

I then roughly followed the instructions here:
http://randomtutor.blogspot.com/2014/01/installing-ubuntu-on-retina-macbook-pro_19.html
by adding the following lines to /Volumes/ESP/EFI/BOOT/refind.conf :

fs0: load btrfs_x64.efi
fs0: map -r

The other options in that blog post didn't seem necessary:
btrfs_x64.efi seems to already be on the driver search path, and
'scanfor internal' is already the default behavior.

I then followed the instructions here:
http://www.rodsbooks.com/refind/drivers.html for btrfs. I added

also_scan_dirs @/boot

to refind.conf. I then generated
/Volumes/ESP/EFI/BOOT/refind_linux.conf, corrected the device path (my
btrfs partition is /dev/disk0s4), and added the rootflags option from
the above link, so refind_linux.conf looks like this:

"Boot with standard options" "ro root=/dev/disk0s4 rootflags=subvol=@"

"Boot to single-user mode" "ro root=/dev/disk0s4
rootflags=subvol=@ single"

"Boot with minimal options" "ro root=/dev/disk0s4 rootflags=subvol=@"

I didn't make any other changes to the configuration.

Ubuntu shows up in the boot menu,
saying 'Boot @\boot\vmlinuz-3.13.0-32-generic from Ubuntu'. When I
select it, I briefly see a screen that says

rEFInd - Booting OS
Starting vmlinuz-3.13.0-32-generic
Using load options "initrd-@\boot\initd.img-3.13.0-32-generic

followed by some log messages, and finally I see a message that says

BusyBox v1.21.1 (Ubuntu 1:1.21.0-1ubuntu1) built-in shell (ash)

and am dropped at a shell with prompt (intramfs). If I push ctrl-d, I
get a message saying "can't open /root/dev/console: no such file" and
a kernel panic.

Most of the advice on the internet for this error seems to say that
the volume is corrupted, but I ran 'btrfs check' on /dev/sda4 and it
seemed to be fine. I also booted from a USB stick, mounted /dev/sda4,
and verified that @/boot/vmlinuz-3.13.0-32-generic exists.

I feel like I'm almost there, any help would be much appreciated.

Thanks,
Anand Patil

[Roderick W. Smith]

/dev/disk0s4 is an OS X partition specifier, not a Linux one. Chances are this corresponds to /dev/sda4, although if you've got multiple disks, it's possible that OS X and Linux would number them differently, so it could be something else. It's generally safer to specify a volume by UUID or label because these are usually invariant, although using a device file is perfectly OK for short-term use or if you're careful to adjust them if you repartition in a way that changes the partition number.

[Anand Patil]

Hi Roderick, thanks for the response. I did test the partition numbers when booting from a live cd, and they were the same, so hopefully this will fix it. I'll test as soon as I get back to the macbook.

[Anand Patil]

Hi Roderick,

I replaced /dev/disk0s4 with /dev/sda4, then tried the uuid of the volume (obtained by running blkid from the intramfs shell) and also the uuid_sub of the volume, but no dice.

I also noticed that, when I added options such as 'quiet' and 'splash', as you did here: http://www.rodsbooks.com/refind/linux.html , I didn't notice any difference in the output. That makes me wonder whether I'm making refind_linux.conf available to rEFInd correctly. I currently have it in the same folder as refind.conf, which is /Volumes/ESP/EFI/BOOT.

Thanks again,
Anand

[Anand Patil]

Hey hey! Got it working. I had to put my refind_linux.conf in @/boot in the actual btrfs volume, not where I had it. To do that, I had to boot Ubuntu from a usb stick, mount the btrfs volume, and create the text file in there. How awesome is this!

In case anyone gets here from Google, the steps were, with @ being the root subvolume:

• Add to /Volumes/ESP/EFI/BOOT/refind.conf

fs0: load btrfs_x64.efi
fs0: map -r
also_scan_dirs @/boot

• Boot Ubuntu from a USB stick, mount the btrfs volume, and write the following into @/boot/refind_linux.conf

"Boot with standard options" "ro root=/dev/sda4 rootflags=subvol=@"
"Boot to single-user mode" "ro root=/dev/sda4
rootflags=subvol=@ single"
"Boot with minimal options" "ro root=/dev/sda4 rootflags=subvol=@"

As Roderick said earlier, I should replace the /dev/sda4's with uuid's, but note that the mac and ubuntu uuid's are different.

Thanks for your help!
Anand

[Roderick W. Smith]

The following two lines do nothing in refind.conf:

fs0: load btrfs_x64.efi
fs0: map -r

Those are EFI shell commands (and prompts), which rEFInd can't parse.

Most partitions have one UUID and one GUID (called a "PARTUUID" in some Linux utilities). The UUID is a filesystem-level ID, which is embedded in the filesystem itself. The GUID is part of the partition table, and identifies the partition. (There's also a partition type code GUID.) Chances are you're thinking that the UUID is Linux-specific and the GUID is Mac-specific, but that's not the case; it's just that some tools will show the UUID and others show the GUID.

The /boot/refind_linux.conf file is Linux-specific, so you should use Linux device identifiers and conventions in it. Most distributions use filesystem UUIDs to identify devices, as in UUID=9b6f62b3-dab2-4abc-987e-32d769a01068. You could instead use a partition's GUID by using the PARTUUID= syntax. I don't know how that would work with a Btrfs volume, though. If you want to experiment with this, you can create new entries in /boot/refind_linux.conf -- duplicate existing ones, modify them, and then select them when you reboot by hitting F2 or Insert and picking your modified entry from the list.