Ubuntu – No GUI after Kubuntu 18.04 LTS upgrade from 17.10

17.1018.04kubuntulightdmupgrade

I have an MSI GP72 Laptop. I upgraded from 17.10 → 18.04 LTS a few hours ago today. The upgrade process itself went well. (Unlike this question, I'm using the final official release.)

However, while I can boot the system, I can only get a terminal. The GUI is nowhere to be seen.

What I need is help in:

  • finding what/where the error is, and
  • fixing it so that I can get the GUI back

Any and all help is appreciated.

I've been unable to find explicit error reports. Here're a few of the places I've already checked:

  • /var/log/syslog
  • /var/log/kern.log
  • /var/log/boot.log

The boot.log entries show [OK]s for the services, including [OK] Started Login Service.. Interestingly, the lightdm entry shows up as follows

...
[OK] Started LSB: GNOME Display Manager.
[OK] Started Permit User Sessions.
[OK] Started Disk Manager.
     Starting Network Manager Script Dispatcher Service...
     Starting Hold until boot process finishes up...
     Starting Light Display Manager...
...
[OK] Started Network Manager Script Dispatcher Service.
...

Checking the status of lightdm.service shows the following (I've omitted date stamps with <date> to avoid clutter):

$ systemctl status lightdm.service
lightdm.service - LSB: Start lightdm
  Loaded: loaded (/etc/init.d/lightdm; generated)
  Active: active (exited) since <date>; 1h 2min ago
    Docs: man:systemd-sysv-generator(8)
 Process: 3251 ExecStop=/etc/init.d/lightdm stop (code=exited, status=0/SUCCESS)
 Process: 3327 ExecStart=/etc/init.d/lightdm start (code=exited, status=0/SUCCESS)

<date> msi-hive systemd[1]: Starting LSB: Start lightdm...
<date> msi-hive systemd[1]: Started LSB: Start lightdm.

So, for whatever reason the service seems to exit after getting launched and its exit code is "successful".

The systemctl start lightdm.service command simply returns to the terminal and shows nothing (i.e. no output, errors, etc). Changing to other terminals using the Ctrl + Alt + F1-F8 keys doesn't show a working GUI elsewhere either.

Please note the meta announcement stating that Ubuntu Bionic Beaver 18.04 LTS is now released, and posts about it are (generally) No Longer Offtopic.

Best Answer

TL;DR; Run sudo apt-get install lightdm to let the system discover and install missing dependencies. In this case, the upgrade appears to have removed bindfs, so it had to be re-installed.

It turns out that the lightdm package was left in a broken state after upgrading. The sudo dpkg-reconfigure lightdm command ended up exiting with an error and saying that the lightdm package was broken or not completely installed.

So, running sudo apt-get install lightdm again after the upgrade had completed showed that bindfs was not installed. While, according to apt-cache show lightdm, the bindfs package shows up under the 'Suggests' category, letting the process install the package actually allowed the service to run as expected and fixed the problem.

It seems that this package is actually required by lightdm to work, but is (incorrectly) not listed as such, so lightdm ends up in a broken state after upgrading.

To fix this, just re-install it to make sure dependencies are met.

Related Question