I updated Ubuntu 16.04 to 17.04 and now my login screen is freezed with no access to touchpad and keyboard! I opened in grub mode there sudo apt-get update is not working either! What do ido? It is showing unable to unlink read only files /var/lib when i try to update
I had this same problem more recently, when upgrading from 16.04 LTS to 16.04.5. That was a bad idea, the screen began freezing at the session login. So when your new to ubuntu like I am, don't upgrade to a version that isn't stable (LTS) unless you've got time on your hands !
Option 1 : upgrade from 16.04.5 to 18.04 LTS, the latest stable version.
Option 2 : Change your display manager (gdm3, lightDM)
sudo dpkg-reconfigure MANAGER
Option 3: If you have random freezing, then make sure you have the right drivers for your graphics card =>
sudo ubuntu-drivers autoinstall
To upgrade despite the login freeze, do it either as root (which you can do by booting into a root shell in recovery mode) or by entering Ctrl + Shift + F2/F3 when at the login interface and, connecting to your session without the graphical interface (I found that connecting to the WIFI to get the update was easier using this last option).
Hope this helps anyone else that makes the same mistake !