Migrage Root from Physical Disk Partition to LV and Rebuild the Bootloader

1. Install Tools for Generating Initramfs

emerge -avt genkernel

# both genkernel and dracut are fine,
# 'darcut' is more recommended.
emerge -avt dracut

• For genkernel

  • FILE /etc/default/grub Adding dolvm as a kernel boot parameter
  • GRUB_CMDLINE_LINUX="dolvm"

• For dracut

  • FILE /etc/default/grub Adding LVM support to the kernel boot parameters
  • GRUB_CMDLINE_LINUX="rd.lvm.lv=vg00/lv_root"

2. Create LV and Migrate Data

# choose your own name for root fs
# in this case, VG: vg00, LV: lv_root
lvcreate -L 15G -n /dev/vg00/lv_root
mkfs.ext4 /dev/vg00/lv_root

mkdir /mnt/new_root
mount /dev/vg00/lv_root /mnt/new_root

# sync data form / to /mnt/new_root
# exclude the filesystems already mounted
rsync -av --progress --exclude=/boot --exclude=/proc --exclude=/media --exclude=/mnt --exclude=/sys $(df -h | awk '{print $NF}' | grep -E "/[a-z][a-z]*" | awk '{print "--exclude="$1}' | xargs) /* /mnt/new_root

3. Change Root Directory to New Place

mount -t proc /proc /mnt/new_root/proc

mkdir -p /mnt/new_root/{run,dev,proc,sys}

mount --rbind /dev /mnt/new_root/dev
mount --rbind /sys /mnt/new_root/sys
mount --rbind /run /mnt/new_root/run

chroot /mnt/new_root /bin/bash

[host@user]# df -h /
Filesystem                Size  Used Avail Use% Mounted on
/dev/mapper/vg00-lv_root  9.8G  9.1G  141M  99% 

# mount filesystems
[host@user]# mount -a
mount: /var: mount point does not exist.
       dmesg(1) may have more information after failed mount system call.
mount: /opt: mount point does not exist.
       dmesg(1) may have more information after failed mount system call.

# create directories not exist
# names depends on your own environment
mkdir -p /{home,var,var,opt,usr/portage,root}

# mount all again
mount -a

# verify mount status
df -h

4. Add Kernel Support

General setup  --->
    [*] Initial RAM filesystem and RAM disk (initramfs/initrd) support

General setup  --->
    () Initramfs source file(s)
    [*]   Support initial ramdisk/ramfs compressed using gzip 
    []   Support initial ramdisk/ramfs compressed using bzip2
    []   Support initial ramdisk/ramfs compressed using LZMA 
    []   Support initial ramdisk/ramfs compressed using XZ   
    []   Support initial ramdisk/ramfs compressed using LZO  
    []   Support initial ramdisk/ramfs compressed using LZ4

5. Generate New Kernel Image

cd /usr/src/linux
make && make modules_install && mount /boot && make install

6. Modify Filesystems Configuration

# file: /etc/fstab
vi /etc/fstab

# Before
/dev/sda3 / ext4 noatime 0 1

# After
/dev/vg00/lv_root / ext4 noatime 0 1

7. Add Grub Boot Paramenter

# Add line to file '/etc/default/grub'
vi /etc/default/grub

# Before
GRUB_CMDLINE_LINUX=""
# After
GRUB_CMDLINE_LINUX="rd.lvm.lv=vg00/lv_root"

8. Gerenate Initramfs with 'dracut' or 'genkernel'

# only if option 'noauto' is set for '/boot' line in the file '/etc/fstab'
mount /boot

# if initramfs file exists, add option '--force'
dracut -a lvm --kver=x.y.zz-gentoo

# or generate initramfs with 'genkernel'
genkernel --lvm initramfs

9. Configure Bootloader

# verify boot parameter 'rd.lvm.lv' is effective
# check the UUID of root filesystem is the same with
# the output of command 'blkid /dev/vg00/lv_root'

grub-mkconfig 2>/dev/null| grep lvm
blkid /dev/vg00/lv_root

# regenerate GRUB boot menu
grub-mkconfig -o /boot/grub/grub.cfg

# sync the cache to local disk and reboot the system
sync && shutdown -r now