Converting an existing installation to LUKS using luksipc

This is a burst of notes that I wrote in an e-mail in June when asked about it, and I'm not going to have any better steps since I don't remember even that amount as back then. I figured it's better to have it out than not.

So... if you want to use LUKS In-Place Conversion Tool, the notes below on converting a shipped-with-Ubuntu Dell XPS 13 Developer Edition (2015 Intel Broadwell model) may help you. There were a couple of small learnings to be had...
 
The page http://www.johannes-bauer.com/linux/luksipc/ itself is good and without errors, although funnily uses reiserfs as an example. It was only a bit unclear why I did save the initial_keyfile.bin since it was then removed in the next step (I guess it's for the case you want to have a recovery file hidden somewhere in case you forget the passphrase).

For using the tool I booted from a 14.04.2 LTS USB live image and operated there, including downloading and compiling luksipc in the live session. The exact reason of resizing before luksipc was a bit unclear to me at first so I simply indeed resized the main rootfs partition and left unallocated space in the partition table.

Then finally I ran ./luksipc -d /dev/sda4 etc.

I realized I want /boot to be on an unencrypted partition to be able to load the kernel + initrd from grub before entering into LUKS unlocking. I couldn't resize the luks partition anymore since it was encrypted... So I resized what I think was the empty small DIAGS partition (maybe used for some system diagnostic or something, I don't know), or possibly the next one that is the actual recovery partition one can reinstall the pre-installed Ubuntu from. And naturally I had some problems because it seems vfatresize tool didn't do what I wanted it to do and gparted simply crashed when I tried to use it first to do the same. Anyway, when done with getting some extra free space somewhere, I used the remaining 350MB for /boot where I copied the rootfs's /boot contents to.

After adding the passphrase in luks I had everything encrypted etc and decryptable, but obviously I could only access it from a live session by manual cryptsetup luksOpen + mount /dev/mapper/myroot commands. I needed to configure GRUB, and I needed to do it with the grub-efi-amd64 which was a bit unfamiliar to me. There's also grub-efi-amd64-signed I have installed now but I'm not sure if it was required for the configuration. Secure boot is not enabled by default in BIOS so maybe it isn't needed.

I did GRUB installation – I think inside rootfs chroot where I also mounted /dev/sda6 as /boot (inside the rootfs chroot), ie mounted dev, sys with -o bind to under the chroot (from outside chroot) and mount -t proc proc proc too. I did a lot of trial and effort so I surely also tried from outside the chroot, in the live session, using some parameters to point to the mounted rootfs's directories...

I needed to definitely install cryptsetup etc inside the encrypted rootfs with apt, and I remember debugging for some time if they went to the initrd correctly after I executed mkinitramfs/update-initramfs inside the chroot.

At the end I had grub asking for the password correctly at bootup. Obviously I had edited the rootfs's /etc/fstab to include the new /boot partition, I changed / to be "UUID=/dev/mapper/myroot /     ext4    errors=remount-ro 0       ", kept /boot/efi as coming from the /dev/sda1 and so on. I had also added "myroot /dev/sda4 none luks" to /etc/crypttab. I seem to also have GRUB_CMDLINE_LINUX="cryptdevice=/dev/sda4:myroot root=/dev/mapper/myroot" in /etc/default/grub.

The only thing I did save from the live session was the original partition table if I want to revert.

So the original was:

Found valid GPT with protective MBR; using GPT.
Disk /dev/sda: 500118192 sectors, 238.5 GiB
Logical sector size: 512 bytes
...
First usable sector is 34, last usable sector is 500118158
Partitions will be aligned on 2048-sector boundaries
Total free space is 6765 sectors (3.3 MiB)  
Number  Start (sector)    End (sector)  Size       Code  Name
1            2048         1026047   500.0 MiB   EF00  EFI system partition
2         1026048         1107967   40.0 MiB    FFFF  Basic data partition
3         1107968         7399423   3.0 GiB     0700  Basic data partition
4         7399424       467013631   219.2 GiB   8300
5       467017728       500117503   15.8 GiB    8200

And I now have:

Number  Start (sector)    End (sector)  Size       Code  Name
1            2048         1026047   500.0 MiB   EF00  EFI system partition
2         1026048         1107967   40.0 MiB    FFFF  Basic data partition
3         1832960         7399423   2.7 GiB     0700  Basic data partition
4         7399424       467013631   219.2 GiB   8300
5       467017728       500117503   15.8 GiB    8200
6         1107968         1832959   354.0 MiB   8300

So it seems I did not edit DIAGS (and it was also originally just 40MB) but did something with the recovery partition while preserving its contents. It's a FAT partition so maybe I was able to somehow resize it after all.

The 16GB partition is the default swap partition. I did not encrypt it at least yet, I tend to not run into swap anyway ever in my normal use with the 8GB RAM.

If you go this route, good luck! :D