Public bug reported:

Let me start by excusing myself, if some of the technical terms used are
wrong. Although I do see myself as quite tech savvy, this is pretty far
away from my usual territory.

I've been running with a partition layout like this for a while:

* An extended partition with 3 logical partitions in it:
  * A small, unencrypted partition for /boot
  * Another, encrypted partition for /
  * And the last partition, encrypted for /home

I initially based this layout more or less on the way the Ubuntu
installer does it if I just let it do it for me, except that I have
/home on a separate partition.

With the release of Xenial Xerus, I decided to do a clean installation.
I also decided to wipe the existing partitions and recreate the same
setup, but with different partition sizes. And so I did, by choosing the
"Something else" option on the "Installation type" step in the
installer. Installation went fine and all.

But upon boot, the splash screen stayed there for a long time. Where I
would expect the passphrase prompt for the disk encryption key to
appear, nothing happened. After some time, I was dropped to busybox with
an `(initramfs)` prompt.

Since then, I've spend a whole day trying to find a fix. And I think I
succeeded. But it seems like the installer is missing something. So let
me try to explain what I did to make this work, hoping that it gives
someone capable of fixing the installer a clue about what's wrong with
it.

Several people on the internet suggested that I ran `cryptsetup` from
`initramfs` prompt. But that command wasn't available. After doing more
research on the interwebz, I managed to fix this by doing 3 things after
mounting and chrooting the encrypted root partition from the Live USB:

1) I read somewhere that `cryptsetup` would only be part of `initramfs`
if `crypttab` was present. I followed a suggestion to manually edit the
file `/etc/crypttab`, which was missing(!), and entered the proper
settings for my 2 encrypted partitions. This of course had to match with
what the decrypted partitions were called in `/etc/fstab`.

2) Then I followed another suggestion to add the following modules to
`/etc/initramfs-tools/modules`:

aes-x86_64
sha512-ssse3
xts
dm-mod
dm-crypt

I have no idea whether this had any actual influence on the success, but
-- from the names of the modules -- it sounds plausible that I needed at
least some of those.

3) Finally, I ran `update-initramfs` with some arguments along the lines
of `-uck all` (which seemed to form some quite appropriate words after
hours of searching for answers without any luck at all).

After a reboot, I was finally prompted to enter the disk passphrase and
eventually got to the login greeter. Phew!

Along the way, I also did several other things, but I tried to remember
to always revert those changes if they did not work. Other things
_might_ have been changed manually, though, for this to work, but I
believe that it was the things mentioned above that did the trick.

** Affects: ubuntu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1575658

Title:
  Unable to boot from encrypted partition after fresh install of 16.04

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