Linux: Boot from LVM

For those who don't know. Yes, it is possible to boot Linux directly from LVM without legacy /boot partition. If you don't need fancy graphic for GRUB then configuration is really simple but first prerequisites:

• only GRUB version 1.9*, 2.00 and newer support booting from LVM
• there should be enough "space" before first partition on disk
• during installation correct modules should be selected (or simply all)

First partition should start at 2048 sector otherwise there is not enough free space for GRUB. If your boot device looks like this one:

# fdisk -l /dev/sda

Disk /dev/sda: 640.1 GB, 640135028736 bytes, 1250263728 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xc3b3f0e3

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1            2048  1250263727   625130840   8e  Linux LVM

then continue with next steps. If first partition start lower sector number, then you should shift(move) it first.

If you compare GRUB2 configuration with configuration of legacy GRUB then you find it looks similar. Here is my configuration of GRUB2:

# grub.cfg for phoebe

set default="0"
set timeout="3"

insmod part_msdos
insmod lvm
insmod ext2

set root=lvm/vg_phoebe-lv_boot

menuentry "Gentoo GNU/Linux" {
        linux /vmlinuz root=/dev/vg_phoebe/lv_root rootfstype=ext4 nodetect dolvm quiet net.ifnames=0
        initrd /initramfs
}

menuentry "Memory test (memtest86+)" {
        linux16 /memtest86plus/memtest.bin
}

# EOF

Most important part is insmod. This will instruct GRUB to load proper modules which are essential for access to boot logical volume (ext2 module cover also ext3 and ext4).

Note: "set root" statement changed between version 1.99 and 2.00. Correct syntax is following:

• 1.99 -> set root="(vg_phoebe-lv_boot)"
• 2.00 -> set root=lvm/vg_phoebe-lv_boot

As last step is important to store GRUB2 in boot area of disk. If you don't care that all modules are installed (as me also) then invoke:

# grub-install /dev/sda
Installation finished. No error reported.

It should finish with no errors (of course) and installation can take longer than similar task for legacy GRUB. If you want only specific modules installed then use --install-modules option for grub-install