Recent updates cause hang in startup

[Steve the Pocket]

Last night, I was prompted to do a bunch of updates, so I let it download and install them. About 20% of the way through, according to the progress bar, it stopped and reset the update window and prompted me to reboot. So I did. About ten seconds into the splash screen, the hard drive sounds stopped and there was no further sign that anything was happening. Hitting Esc to show the text output of the bootup revealed that it had stopped after the lines

Starting Mount network filesystems
Stopping Mount network filesystems

As I was writing this down, two more lines appeared:

cups
Starting CUPS printing spooler

Then it stopped for good. I tried restarting into recovery mode, enabling the networking, and running the package repair thing. This downloaded a great deal of data (possibly the remainder of the unfinished update?) but after rebooting again, the problem remained. Then I tried booting straight into a root command line and running apt-get update and apt-get upgrade. This removed about a gigabyte of files, but still no fix. Any idea what I can do at this point? My setup started with a fresh install of 12.04, upgraded to 14.04 Alpha 2 using kubuntu-devel-release-upgrade, and has received maybe two system updates since. No third-party drivers.

[Snowhog]

Boot in to recovery (single user) mode. No Desktop, just a command line. Then type:

sudo apt-get install -f

Let it finish. Then type:

sudo apt-get update

Let it finish. Then type:

sudo apt-get dist-upgrade

When it finishes, type:

sudo shutdown -r now

[Steve the Pocket]

No luck. Same deal, hangs after "Starting Mount network filesystems" and "Stopping Mount network filesystems". FYI, it didn't acquire or install anything when I did the apt-get install -f, but grabbed about 4 megs during the dist-upgrade.

[kubicle]

Just to make sure (because you said your upgrade removed quite a few files)...check if kubuntu-desktop package is installed (this should pull in all the packages that are part of the default install that might have been removed during upgrade). I'd propose the following (you can omit the "sudos" if you're in a root shell):

1. sudo dpkg --configure -a
(configure all packages that might have been left unconfigured)
2. sudo apt-get install kubuntu-desktop

[Steve the Pocket]

Yep, that did it. How did kubuntu-desktop disappear in the first place, d'you think? And why did the boot process hang instead of dropping to the command line or output some sort of error message that KDE wasn't found or something?

[kubicle]

How did kubuntu-desktop disappear in the first place, d'you think?

I can't tell for sure, but it can happen if you perform a dist-upgrade when there is a newer version of a dependancy package available on the servers but a compatible dependant package isn't (in such a case apt might upgrade the dependancy, but remove the incompatible dependant package. This is why you should always halt the upgrade if an upgrade wants to remove a lot of packages (and either wait a while to see if there's a dependancy mismatch or try to figure out what is the cause).

You could get hints of what happened by checking the apt and dpkg logs in /var/log/ (these record all apt/dpkg runs)

And why did the boot process hang instead of dropping to the command line or output some sort of error message that KDE wasn't found or something?

KDE basically comes to play after you log in graphically...since you didn't get to the graphical login, I'd think you were missing packages that are lower in the boot stack (I'm guessing either the display server or display manager). And you were probably left on virtual terminal 7 (VT7, which is were the X server should start in...but in your case, didn't). There probably were command line terminals on VT1-6 (these would have been accessible with Ctrl+Alt+F1 [or F2-F6]), but this of course isn't immediately apparent if you're sitting on VT7.