E pur si muove

Encrypted hard disk: LVM on LUKS

Sunday, August 19, 2007

There are of course about a million other guides on how to use encrypted disks out there. However I did run into some trouble when trying this, so here mine. Specificly I address the issue of getting an encrypted root disk, with the root being on a Logical Volume Management (LVM) as most other guides only seem to describe how to setup a random disk/partition encrypted. I'm not going to duplicate the other guides too much, so read a reasonable one (like this one) first. The last special case is that I copy all the data accross once the disk is ready, otherwise I could have just used the debian-installer which does a great job.

This entire operation was done while being booted from a grml life cd, with the backups of the data on a USB disk

Firstly you need to partition your disk. Create 2 partitions, one small one for /boot which will stay unencrypted, and the other as large as you fancy. The boot partition should be a normal Linux partition (0x83) while the other one I did set to Linux LVM (0x8e), but I don't think that matters. The boot partition is simple: format it (e.g. mkfs -t ext3 /dev/hda1) and copy the data on it. The other partition is going to be a LUKS volume, on which we will create an LVM Physical Volume (PV) with a Volume Group (VG) on with several Logical Volumes (LV), say, / and /home. Let's do this:

~# cryptsetup luksFormat /dev/hda2
<asks for password>
~# cryptsetup luksOpen /dev/hda2 luksvolume
<asks for password>

The luksvolume part is the name of the volume for the device mapper, the disk will now appear in /dev/mapper/luksvolume. Great! Let's create our LVM setup on it:

~# pvcreate /dev/mapper/luksvolume
~# vgcreate mygroup /dev/mapper/luksvolume
~# lvcreate -L 10G -n root mygroup
~# lvcreate -L 10G -n home mygroup

The volumes are now available as /dev/mapper/mygroup-root and /dev/mapper/mygroup-home or via the symlinks /dev/mygroup/root and /dev/mygroup/home. Again, create your favourite filesystems on it and copy the data accross.

We're almost there, but not quite. The disk needs to be bootable, so mount the root partition somewhere and mount the boot partition inside it, then install grub on it: grub-install --root-directory=/mnt/newroot, time to double check /mnt/newroot/boot/grub/menu.lst and make sure all is fine in there.

Now make sure the encrypted disk will work when booting. For the following it is easiest to chroot /mnt/newroot as the command doesn't deal with alternative roots yet. So in the chroot write the /etc/crypttab:

# <target name> <source device> <key file> <options>
luksvolume      /dev/hda2       none       luks

Hopefully one day that would be enough, currently this was completely irelevant in this setup however (this file is only relevant for non-root encrypted disks currently). So you need to create another file, /etc/initramfs-tools/conf.d/cryptroot:


Now recreate the initrd using update-initramfs -u and you should be all set. Get out of the chroot and boot the disk.

This should work on both Debian and Ubuntu, however when you're using Ubuntu you may get some funny results when it needs the password while usplash is running. It will quit usplash but not tell you it is waiting for a password, check out this bug report for some possible solutions.

Sunday, August 19, 2007 |


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