If you upgraded Ubuntu 13.10 to Ubuntu 14.04, you might end up with Unity freezing at login time. You boot in to Ubuntu 14.04, enter your credential and the system just hangs up, freezes. If you are lucky, you might see mouse cursor, background wallpaper but nothing else. No Unity launcher, no top panel etc. Basically you will have Ubuntu in an unusable state.
This problem of missing Unity launcher, panel and system freeze can be solved by re-installing Unity. Let’s see how to do that:
Reinstall Unity in Ubuntu 14.04 to fix system freeze issue
Well, since you are stuck with a frozen system, use Ctrl+Alt+F2 key. This will take you to command line interface (instead of the default graphical user interface). You will be asked to enter your credentials. After you enter your username and password, use the following commands one by one to reinstall Unity desktop.
sudo apt-get update sudo apt-get install --reinstall ubuntu-desktop sudo apt-get install unity sudo shutdown -r now
The last command will reboot your system. After the reboot, you should have Unity working as normal.
Fixing Unity freeze issue with Nvidia graphics:
I don’t have experience with Nvidia graphics but I found some people mentioning additional steps for system with Nvidia graphics card. While the above trick worked for my system, I cannot verify the one below. People with Nvidia graphics, please confirm that the steps below work for your system:
Press Ctrl+Alt+F2 to use command line. And after entering username and password, use the following commands one by one:
sudo apt-get update sudo apt-get install --reinstall ubuntu-desktop sudo apt-get install unity sudo apt-get remove --purge nvidia* sudo shutdown -r now
Once you have Unity back to normal at next reboot, just reinstall the Nvidia drivers (you had just removed them).
I hope these quick tips help you to recover your Ubuntu 14.04 from a frozen Unity to a working Unity. Any questions or suggestions are always welcomed.