Can't login to Ubuntu 14.04 after upgrade

What worked for the original poster was: recursively correcting the permissions of their home directory.

sudo chmod -R ug+rwx /home/[username]

To be more specific, the problem is with the .Xauthority in your home folder. You simply need to change its permissions to yourself or, as it was in my case, it was owned by root, so I needed to change the owner to my user. This way you don't need to change the permissions for every file in your home folder.

I am having the same problem. Fixed by chown the whole home directory.

chown -R [user-name]:[user-name] /home/[user-name]

details in this post Unable to mount home-directory for user after fresh install 14.04

In my case my /home filesystem is on a separate partition, and after an update, for some reason the entry in my /etc/fstab to mount /home had been commented out. Booted into recovery mode to get a root shell so that I could edit /etc/fstab and re-instate the entry.

I tried this and it worked for me:

sudo apt-get install --reinstall ubuntu-session

(Source)

I had that too. It seems that 14.04 uses something called ubuntu-session for login, while the old 12.04 used something called unity-desktop. Since I tried to upgrade from the desktop itself, there were problems deleting it, and I was barred from logging in the next time.

To fix, boot the machine, and as soon as the grub loader comes up, scroll down to "Advanced options for Ubuntu" which will probably be the 2nd entry. Hit enter. On the next page, choose "Ubuntu, with Linux 3.13.0-30 (recovery mode)" or a similar entry. It could be the 2nd entry on that page. This brings up some recovery options.

Scroll down to the thing that says "network Enable networking" and hit enter. This is IMPORTANT, otherwise Ubuntu can't find the files it needs on the internet. After networking is enabled, scroll to "dpkg Repair broken packages" and hit enter. That should install the needed ubuntu-session, delete the old unity-desktop, and fix up any other things that were missed also.