Comment 61 for bug 1386005

I have the same problem - and it's not the first time, either. Even though I didn't report a bug, before (just worked around it), I agree with Josh: [K]Ubuntu does not seem to have the QA it should do!

I encounter the same problem again and again on different computers (not sure anymore, but probably all of them using an NVidia card) for quite a few versions/years, already (I think the first time was 10.04 or 12.04, but I'm not sure anymore).

Here's my current scenario:

First the relevant output of lspci:
01:00.0 VGA compatible controller: NVIDIA Corporation GK107 [GeForce GT 740] (rev a1)

And here's what I did:
I installed Kubuntu 15.10 from scratch (no upgrade) with full system encryption. On this machine, I don't use LVM (because I have plenty of RAM and don't need swap), but I encountered the same problem before with the automatic "guided partitioning" setting up LVM in an encrypted container. Thus, LVM has obviously no effect - the problem seems to be related to encryption + graphics card only. On this machine, the root fs (/) lies directly in a LUKS container located on sdc3 (as said: no LVM).

After the fresh installation, which uses the nouveau driver, my screen is entirely blank when booting. Only after I press ESC (grub or plymouth or whatever is in charge seems to switch from graphical to text mode) I see a password prompt. When I press ESC again, it switches back to the graphical mode and I can enter the password there, too (both text + graphical mode work - but only after pressing ESC at least once).

Unfortunately, my system froze far too often. This problem happens with Kubuntu 15.04 too (located on sda), but only once in a week or so. With Kubuntu 15.10 it froze multiple times daily.

Since I suspected the graphics being the cause of the trouble, I wanted to give the binary nvidia driver a try. Thus, I switched to the proprietary driver using the KDE graphical driver manager. AFAIK it does nothing else than installing nvidia-352 and a few other nvidia-* packages.

I then rebooted and the graphical password prompt appeared - but I could not enter anything. I still tried to enter my password + press enter thinking that only the feedback is broken, but no: it does not work at all. Thus, I booted choosing the recovery mode and then selecting "resume".

Btw. in contrast to the nouveau driver, ESC has no effect when booting with the proprietary driver: The system seems completely frozen asking for the disk password during boot.