Moving the root filesystem to an LVM volume in etch

What is the problem?

I experienced quite some trouble when migrating etch to an LVM volume. Thus I documented the process below.

Afterwards I found this posting, which claims, that it should not be a problem at all, if you start it correctly. Please read that post and try if it works for you, before you continue reading.

Details of migration

• split the active raid 1 mirror:

  mdadm --fail /dev/md2 /dev/hdb5
  mdadm --remove /dev/md2 /dev/hdb5

• create a new raid 1 mirror:

  mdadm --create /dev/md3 --raid-devices=2 --raid-level=mirror /dev/hdb5 missing

• create an LVM physical volume, a volume group and the logical volume:

  pvcreate /dev/md3
  vgcreate base-lvm /dev/md3
  lvcreate -n root -L 5G base-lvm
  mkfs.ext3 /dev/base-lvm/root

• copy the old system to the new volume:

  mount /dev/base-lvm/root /mnt
  cp -axv / /mnt/

• backup the current initrd file and the menu.lst:

  cp /boot/initrd-XXX /boot/initrd-XXX_before_lvm
  cp /boot/grub/menu.lst /boot/grub/menu.lst_before_lvm

• chroot into the new system on lvm:

  mount --bind /dev /mnt/dev
  mount --bind /boot /mnt/boot
  chroot /mnt
  mount /proc
  mount /sys

• change the root filesystem in /etc/fstab:

  /dev/base-lvm/root      /               ext3    noatime,errors=remount-ro 0       1

• copy the following script to /usr/share/initramfs-tools/hooks/lvm:

  PREREQ=""
  
  prereqs()
  {
          echo "$PREREQ"
  }
  
  case $1 in
  prereqs)
          prereqs
          exit 0
          ;;
  esac
  
  if [ ! -x /sbin/lvm ]; then
          exit 0
  fi
  
  . /usr/share/initramfs-tools/hook-functions
  
  if [ -e /etc/lvm/lvm.conf ]; then
          mkdir -p ${DESTDIR}/etc/lvm
          cp /etc/lvm/lvm.conf ${DESTDIR}/etc/lvm/
  fi
  
  copy_exec /sbin/lvm /sbin
  # this is the self-made stuff to get it running under etch ...
  cp -a /sbin/lv* $DESTDIR/sbin
  cp -a /sbin/vg* $DESTDIR/sbin
  cp -a /sbin/pv* $DESTDIR/sbin
  cp -a /lib/lvm-200 $DESTDIR/lib
  cp -a /lib/lvm-default $DESTDIR/lib
  # also copy the required libraries
  ldd /lib/lvm-200/lvm | cut -f 1 -d " " | cut -f 2 | sed s#^l#/lib/l# | while read fname
    do    test -e $DESTDIR$fname || cp "$fname" $DESTDIR$fname
   done
  
  for x in dm_mod dm_snapshot dm_mirror; do
          manual_add_modules ${x}
  done

  • the script is heavily based

• run update-initramfs -u

• change the root device for grub:

  • update the placeholder in /boot/grub/menu.lst:

    # kopt=root=/dev/mapper/base--lvm-root ro

    • BEWARE: in etch you must use the /dev/mapper/XXXX location (instead of the /dev/vg/lv-style)

  • update the grub menu file:

    update-grub

• reboot

• hope for mercy