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Start Salix from Btrfs root

/ #Salix / #Linux

To start Salix from a Btrfs root partition you have to use Grub.

  • Use the huge kernel
  • Don’t create an initrd.gz and remove an existing /boot/initrd.gz
  • Run grub-mkconfig -o /boot/grub/grub.cfg
  • Check the /boot/grub/grub.cfg file. The linux line should look like this: linux /@/boot/vmlinuz-huge-4.4.13 root=/dev/sda1 ro rootflags=subvol=@ vt.default_utf8=1 quiet
  • Run grub-install /dev/sda

Install from scratch

Some useful informations beforehand:

  • BTRFS actually does not need any partitions. You can create a filesystem and just use subvolumes for different mount points. But if you want to boot from the drive you have to create partitions!
  • You can chose between MSDOS or GPT partition tables. GPT is the future save choice because AFAIK computers with UEFI firmware won’t boot from MSDOS partitions. Furthermore a GPT partition has a PARTUUID, which may be helpful.
  • Both, Lilo and Grub, can boot from MSDOS and GPT partitions, but only Grub can load the kernel from a BTRFS formatted partition. If you want to use Lilo you have to create a /boot partition with a Lilo supported file system, e.g. ext4. Therefore I recommend to use Grub, even if I like the simple design of Lilo much more.
  • For Grub you need some “empty” space at the beginning of the disk. 1 MiB should be enough, but something between 2 and 16 MiB is a save choice. With MSDOS partition table just leave the space unused, with GPT you have to create a small “BIOS boot” (EF02) partition.

Partitions

  • Create a GPT partition table with cgdisk
  • Create a small partition (2 MiB) and set partition type to “BIOS boot” (EF02).
  • Create the btrfs root partition
  • Create other partitions (optional)

Installation

  • Chose your packages and install as usual.
  • On Minimal and Basic installation set up your network connection and access to the internet (this is important). On Full installation you bring up your network by hand after the installation.

Bootloader

  • Skip LILO installation (LILO cannot boot from btrfs)
  • Do not reboot, leave setup instead

Run the following commands:

chroot /mnt
/etc/rc.d/rc.inet1 start
slapt-get -u
slapt-get -i grub
grub-mkconfig -o /boot/grub/grub.cfg
grub-install /dev/sda
exit
reboot

Install on existing partition

If you are using subvolumes you even can install more distributions on a single btrfs filesystem. Your btrfs subvolumes could look like this:

  • @14.1 (root fs of Salix 14.1)
  • @14.2 (root fs of Salix 14.2)
  • @opensuse (root fs of Opensuse)
  • @home (home directory)

Installation

To install in an existing filesystem you have to do:

  • Boot the Salix install CD and leave the setup

  • Mount the top level of your btrfs filesystem, e.g. mount /dev/sda1 /mnt

  • Create a subvolume for your root file system, e.g.:

    cd /mnt btrfs subvol create @14.2 cd umount /mnt

  • Mount the new subvolume, e.g. mount -o subvol=@14.1 /dev/sda1 /mnt

  • Run setup again: setup

  • Don’t touch partitions and don’t format anything. Just went straight to package installation.

Bootloader

  • Skip LILO installation (LILO cannot boot from btrfs)
  • Do not reboot, leave setup instead

Run the following commands

chroot /mnt
/etc/rc.d/rc.inet1 start
slapt-get -u
slapt-get -i grub
grub-mkconfig -o /boot/grub/grub.cfg
grub-install /dev/sda
exit
reboot

fstab

Edit your /etc/fstab and add the subvol=@14.1 mount option to the rootfs.