display manager - LightDM shows blank screen with cursor

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display manager - LightDM shows blank screen with cursor

Postby furquan » 2017-05-10 12:45

I'm using Debian Sid (unstable) amd64 and when trying to login via LightDM, it shows a blank screen with a blinking cursor at the top-left corner.

I installed Debian (somewhere around Dec 2016) using the Debian live "standard" iso flashed onto a USB-drive. It was a minimal install (without X) so I installed Xfce with LightDM (using the default GTK greeter) on it. I upgraded to Testing after a week of using this installation and have used that without any (major) problems so far. A few weeks back, when Ubuntu dropped Unity in favor of GNOME, I decided to try it on Debian. It worked perfectly fine with LightDM but there was no sleep button so I installed GDM. It installed and worked OK but I decided to switch back to LightDM because GDM was hardly configurable and theming it was a pain.

So I apt purge'd gdm3 and switched back to LightDM. But when I rebooted Debian, it was showing a blank screen with a blinking cursor at the top-left corner. I immediately opened tty1 (CTRL + ALT + F1) and typed startx which dropped me into Xfce. I tried searching the web for a solution but all hits I got were related to Arch (or an Arch-based distro) and it was all due to a bug in Arch (now resolved) which was not my case. Seeing no apparent solution, I reinstalled GDM and it again worked perfectly and booted me into GNOME.

But I noticed a strange problem with GDM; though I was able to boot into GNOME (both on X and Wayland) I wasn't able to boot into Xfce. It would just drop me back to the login prompt. So I tried opening a TTY to see if startx works, strangely CTRL+ALT+F1 didn't work so I had to use TTY2 instead. Predictably, startx on TTY2 logged me into Xfce so I logged out and when I tried to switch back to the GUI using CTRL+ALT+F7, I was dropped to a blank screen with a cursor blinking in the top-corner. I switched to TTY1 and I was taken to the GDM prompt. So yeah, GDM (and the display server) was, for some unknown reason, on TTY1!

At this point, logging into GNOME from GDM (on TTY1) has no effect whatsoever on GNOME (i.e. logout works, sleep works, etc) but it can't login to Xfce. I installed XDM and it works the same as startx and it properly starts from TTY7 but unfortunately I can't change session so it can only login to Xfce.

Summing up the problems what I can conclude is that:
  • LightDM doesn't work, boots into a blank screen
  • GDM does work but for some reason it's on TTY1. It also can't log into Xfce.
  • startx at any TTY drops me into Xfce
  • XDM works, is on TTY7 and logs into Xfce. There's no option to change session.

I thought something must have broke during updates so I did an update -- unsurprisingly Testing was up-to-date. A friend of mine (who has been using Debian for considerably longer than I have) told me that it must be some bug and Testing takes a long time to fix if it breaks so I should switch to Sid. I did upgrade to Sid but the problems persist.

I'm using an Intel machine with a 3GHz x2 processor and 4GB of RAM. I've installed no dedicated GPU on this machine so I'm using the Intel-integrated graphics.
Right now I'm using no display-manager and I'm typing this on Xfce started through startx on TTY1. If anyone has any idea for a fix then it would be greatly appreciated.
Debian Sid - GNOME (with tiling extensions), Xfce. Generic Intel machine with G2030 3.0GHz x2 CPU, 8GB RAM and a generic GPU.

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Re: display manager - LightDM shows blank screen with cursor

Postby arochester » 2017-05-10 20:28

A friend of mine (who has been using Debian for considerably longer than I have) told me that it must be some bug and Testing takes a long time to fix if it breaks so I should switch to Sid. I did upgrade to Sid but the problems persist.


Using Sid if you can't sort out all your own problems is not a good idea.

Have you tried purging all your Display Managers and then reinstalling LightDM?

To some extent you should be able to start different Desktops from the command line e.g. startlxde, startkde and startkde - although Gnome tends to be different and might need configuration.

Look at e.g. https://journalxtra.com/linux/desktop-r ... ktop-back/ from Solution Five: Reconfigure the display manager and https://wiki.debian.org/LightDM
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Re: display manager - LightDM shows blank screen with cursor

Postby furquan » 2017-05-11 05:40

arochester wrote:Have you tried purging all your Display Managers and then reinstalling LightDM?


Yes I have tried that already. I apt-purge'd all *dm and gdm3 (which also removed gnome and gnome-core) and reinstalled lightdm.

Now when I try starting lightdm with:
Code: Select all
sudo systemctl start lightdm.service

I'm again taken to the same black screen with a cursor blinking in the top-left corner. I rebooted and the same blank screen greets me.

Right now, I've reinstalled gdm3 because it's a dependency of gnome but I'm not using it. I've found another DM called LXDM which is the display-manager for LXDE and it does seem to work. It is just the same as xdm but it can also change sessions (thus allowing me to log into GNOME which XDM didn't do) but it does not allow logging into GNOME with Wayland. Also, when I boot the machine I'm dropped to TTY1 with the login prompt after the plymouth animation ends. I switch to TTY7 and see the LXDM prompt and then I'm able to log into GNOME. I'm increasingly convinced that it's a bug but I'm not sure how I can be affected when I didn't do any updates (there were none to do because Testing has been quiet for a while).

Edit: Here's the lightdm.log just after booting into Debian: https://pastebin.com/raw/FdB2pFGq . And restarting lightdm with systemctl restart also doesn't help.

Edit2: Is it normal for GDM to start on TTY1? Because a discussion on Arch forums (https://bbs.archlinux.org/viewtopic.php?id=189998) seems to indicate that you'd have to recompile GDM in order to make it start on TTY7. Is compiling GDM on a binary distribution like Debian a good idea? But even if GDM normally starts on TTY1 it isn't going to help me much because I need to log in to Xfce as well (which GDM can't).
Debian Sid - GNOME (with tiling extensions), Xfce. Generic Intel machine with G2030 3.0GHz x2 CPU, 8GB RAM and a generic GPU.

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Re: display manager - LightDM shows blank screen with cursor

Postby furquan » 2017-05-11 15:53

It looks like LightDM is lost hope. I don't think I can recover it anymore so I've apt-purge'd it and gone back to GDM (which still starts on TTY1). The GNOME guys must have broken something because I'm not able to use LightDM only after installing and using GDM.

Though GDM cannot start an Xfce session I can start it on another TTY with startx.

The link to the guide you gave was awesome. I tried everything up to Solution-Six but stopped short of apt-purging my desktop because I wasn't sure how I can go back to the original configuration. Unfortunately nothing helped and LightDM stayed as dead as ever. And I've yet to find a way to compel GDM to start on TTY7 (apart from recompiling).

Thanks for all the help but I guess fixing this is impossible.

And now that I'm on Sid, should I go back to Testing and is it even possible to do so?
Debian Sid - GNOME (with tiling extensions), Xfce. Generic Intel machine with G2030 3.0GHz x2 CPU, 8GB RAM and a generic GPU.

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Re: display manager - LightDM shows blank screen with cursor

Postby oswaldkelso » 2017-05-11 17:57

Sounds like a systemd issue to be I'd check the bug reports
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Re: display manager - LightDM shows blank screen with cursor

Postby edbarx » 2017-05-12 11:07

If a package is broken, more precisely, if a pakage has missing files, you can force a reinstall of the package with:
Code: Select all
apt-get install --reinstall broken-package

In the case breakage that is caused by a broken user configuration, that has also to be removed or corrected.
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Re: display manager - LightDM shows blank screen with cursor

Postby phenest » 2017-05-12 13:47

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Re: display manager - LightDM shows blank screen with cursor

Postby furquan » 2017-05-13 07:38

edbarx wrote:If a package is broken, more precisely, if a pakage has missing files, you can force a reinstall of the package with:
Code: Select all
apt-get install --reinstall broken-package

In the case breakage that is caused by a broken user configuration, that has also to be removed or corrected.


That's what the guide that @arochester linked me to advised (https://journalxtra.com/linux/desktop-r ... ktop-back/). I've done it several times to many different packages (the window-system window-manager, display-manager, etc). It doesn't work.

I'm guessing that either LightDM is broken (less likely) or GNOME broke it (more likely). Either way, LightDM is my only option because GDM:
  • Starts on TTY1
  • Makes logging into Xfce impossible (have to use startx)
Debian Sid - GNOME (with tiling extensions), Xfce. Generic Intel machine with G2030 3.0GHz x2 CPU, 8GB RAM and a generic GPU.

"You know you're brilliant, but maybe you'd like to understand what you did 2 weeks from now." -- Linus Torvalds
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Re: display manager - LightDM shows blank screen with cursor

Postby phenest » 2017-05-13 18:53

I installed Debian Jessie in a VM to test this. I installed Gnome and XFCE. I installed Slim and LightDM as alternative login greeters. I have tried trying logging into Gnome and XFCE using all 3 login managers.

Result: Works as expected.
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Re: display manager - LightDM shows blank screen with cursor

Postby Bulkley » 2017-05-13 22:06

arochester wrote:Using Sid if you can't sort out all your own problems is not a good idea.


+1
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Re: display manager - LightDM shows blank screen with cursor

Postby furquan » 2017-05-14 07:57

phenest wrote:I installed Debian Jessie in a VM to test this. I installed Gnome and XFCE. I installed Slim and LightDM as alternative login greeters. I have tried trying logging into Gnome and XFCE using all 3 login managers.

Result: Works as expected.


That's why I'm sure this has to do with a bug introduced in the later updates. I've never had Testing break up on me (but I'm not using it for long enough to testify that). Now that I'm on Sid, perhaps it will get fixed soon. I hope.
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Re: display manager - LightDM shows blank screen with cursor

Postby phenest » 2017-05-14 08:43

I tried the same test with Debian Stretch (upgraded from Jessie). Same results. Works as expected.
furquan wrote:Now that I'm on Sid, perhaps it will get fixed soon. I hope.

Have you submitted a bug report?
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Re: display manager - LightDM shows blank screen with cursor

Postby furquan » 2017-05-14 12:14

phenest wrote:I tried the same test with Debian Stretch (upgraded from Jessie). Same results. Works as expected.
furquan wrote:Now that I'm on Sid, perhaps it will get fixed soon. I hope.

Have you submitted a bug report?


No I thought it's best to leave it alone till it gets resolved in another update :-P

Honestly, it's not that big of an issue right now. GNOME is my primary desktop (granted it starts from TTY1 but that doesn't matter if everything else works fine) and I can always startx to log in to Xfce. But I'm sure that it's not caused by my configuration (I've apt-purge'd and reinstalled all suspecting packages) and is rather a bug (something similar was reported on Arch forums a while back but it was an Arch-specific issue and it got quickly resolved).
Debian Sid - GNOME (with tiling extensions), Xfce. Generic Intel machine with G2030 3.0GHz x2 CPU, 8GB RAM and a generic GPU.

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Re: display manager - LightDM shows blank screen with cursor

Postby phenest » 2017-05-14 13:30

furquan wrote:No I thought it's best to leave it alone till it gets resolved in another update :-P

How is it going to be fixed if you don't report it? If I'm not having a problem, chances are neither are lots of other users, therefore neither the maintainer nor the developer know there is an issue.
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