Cannot login after kernel upgrade

Hi. I just upgraded from Stretch to Buster. And now when I use kernel 4.15(used in Buster) at login screen when I type login and password it goes to desktop for 1second and then I get kicked back to login screen.
When I use old kernel, that one from Stretch I can login.
DE: XFCE
lightdm.service - Light Display Manager Loaded: loaded (/lib/systemd/system/lightdm.service; indirect; vendor preset:

If you update to an unstable version, then misfuntion does occur.

Originally Posted by Keruskerfuerst If you update to an unstable version, then misfuntion does occur.

Is there a way to fix it ?

Moving from Stable to Testing is not an upgrade.

- Testing includes fewer bug fixes than stable and less timely security updates. It changes frequently and though it will break less often than unstable, the chances of complete breakage are still notably more than stable. It is for this reason that moving to testing is not an 'upgrade'.

- The clue to 'testing' is in its name. Its raison d'être is to find fixes for the next stable release.

- Testing will not function as well as stable and is not recommend as a primary system, daily driver or for anyone where productivity is key.

- Testing is the future Debian stable, the future version 10. It is not version 10 yet. Stable is currently 9.4.

- Testing is not a rolling release distribution as some consider it to be, it is a development version.

Please see the below for more information. I strongly recommend you read this post:

http://forums.debian.net/viewtopic.php?p=531279#p531279

and

https://www.debian.org/releases/testing/

Testing still breaks, but just not "as badly" [to quote the Wiki] as unstable

As already stated, breakage does occur in Testing which can sometimes disable your access to the entire system.

Unless you are willing to file bug reports and are using Testing on a secondary/tertiary machine I would move back to Stable.

It would be helpful to know what your video chip set is. You may want to make sure that you have firmware installed:

https://packages.debian.org/buster/f...-linux-nonfree

I am using the 4.15.0-2-amd64 version of the kernel on a laptop with AMD graphics and the lightdm desktop manager, and I do not see the problem you describe. My laptop is running Debian stable with the exception of the linux-image and nonfree firmware taken from sid.

Have a look at /var/log/Xorg.0.log and dmesg.

Logs

there are errors in that log, so your X could not be started.
like: (EE) Failed to load module "nv" (module does not exist, 0)

Originally Posted by pan64 there are errors in that log, so your X could not be started. like: (EE) Failed to load module "nv" (module does not exist, 0)

That's what I found when I google. So that is what I need to do

What counts is what kernel was running when the nvidia module was built, since it was built using the header files for that kernel, and it was installed where that kernel can find it to load. If you're running a different kernel now than you were when you built the nvidia module, you'll have to rebuild the nvidia module and reinstall it.

I use nouveau, I uninstall and install it back and reconfigure, but still I have same problem, can you help me please

I do not think it is a problem with X, because lightdm is running with the correct display. You might want to take a look at this:

https://www.computersnyou.com/4947

Or you could just try purging and re-installing lightdm to see if that corrects the problem:

apt-get purge lightdm && sudo apt-get install lightdm