Jtdcftul

I installed Ubuntu 18.04 yesterday, done some app installation and configurations and went to sleep. This morning, the login simply didn't work: the system is unable to log into my session, even with the correct password. Every time I try it, it flashes the screen into black and purple, the mouse pointer is available, but it flashes back to the login screen again: no error message prompts and I spent quite some time amusing myself trying to win it by attrition =). I also tried switch over to Wayland, and the same result: screen flashes to black, couple of seconds later, I'm back at the login stage.

There is nothing wrong with my password, since I can log into my user account on the Terminal (CTRL+ALT+F1). Once there, I did a sudo apt update/upgrade in the hopes it'd fix something, but my system was up to date and it didn't solve anything after I rebooted.

I've seen a lot of similar reports on the internet and the only solution that it seemed worthwhile to my noobish eyes was removing/deleting the .Xauthority file. But when I tried it, the return I got was that there was no such file on my Home directory. The other solutions applied to people upgrading their systems - mine was a fresh install - or with pretty specific hardware and conditions that don't apply to me.

So, what should I do to fix this?

I had the same problem.

Then I found out that I accidentally changed the ownership of my /home/username directory to root.

So you can go to the terminal by CTRL+ALT+F1, and change the username directory ownership with

sudo chown username:username -R /home/username

I ended up solving this by disabling secure boot on my notebook. As I understand, my issue was caused by wonky Nvidia drivers.

Experienced the same problem today for the first time since moving on to Beaver. Weirdly immediately post full wizard install.

Initially I thought it was a Wayland issue but despite attempts to force other compositors the issue remained until I cracked-open a Shell and removed my freshly created user /home folder. Upon the next initialisation of my chosen GDM I was shown the new user config wizard and all has been fine since.

I just spent WAAAY too much time solving this issue. What finally solved the issue was replacing the /usr/local/lib/libreadline.so.7 library with a link to /lib/x86_64-linux-gnu/libreadline.so.7

sudo mv /usr/local/lib/libreadline.so.7 /usr/local/lib/back.libreadline.so.7

sudo mv /usr/local/lib/libreadline.so   /usr/local/lib/back.libreadline.so

sudo ln -s /lib/x86_64-linux-gnu/libreadline.so.7  /usr/local/lib/libreadline.so.7

sudo ln -s /usr/local/lib/libreadline.so.7  /usr/local/lib/libreadline.so

A good indication that there was a problem was that gawk did not work because of the same missing external in libreadline with:

$ gawk

gawk: symbol lookup error: /usr/local/lib/libreadline.so.7: undefined symbol: UP

My ~/.Xauthority was fine, no amounts of updates made any difference.
Right after my upgrade from to Ubuntu 18.04.1, my system would stop booting in the middle somewhere. I switched to lightdm from gdm3 with

sudo dpkg-reconfigure lightdm

and the system would boot but then I could not login.

I hope this can help somebody.

In my case, the issue was linked to my home directory beeing encrypted with ecryptfs, it seems.

I logged in to the console (Ctrl+Alt+F1), and installed ecryptfs-utils :

sudo apt-get install ecryptfs-utils

It solved the problem.