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Login
Stucked in your desktop/laptop ubuntu’s login screen means , you enter your password then screen goes black then login screen appears again and again in loop , here are three easy troubleshooting methods you can follow to resolve your problem.
Error Info
$ cat ~/.xsession-errors
Now see and identify what is causing the problem.
Method 1
Login in console mode using Ctrl + Alt + F1 or Ctrl + Alt + F2 then:
$ chown $USER:$USER .Xauthority
If it doesn’t work try renaming.
$ mv .Xauthority .Xauthority.bak
Then press Ctrl + Alt + F7 to go back to login screen, if these all solution doesn't work, then uninstall and install again lightdm:
Method 2
# For re-configuring $ sudo dpkg-reconfigure lightdm
Re-installing
$ sudo apt-get purge lightdm && sudo apt-get install lightdm
Or install gdm in place of lightdm:
$ sudo apt-get purge lightdm && sudo apt-get install gdm