“The system is running in low-graphics mode” error upon Ubuntu Upgrade (Nvidia Graphics Card)

I found this issue today while upgrading my Ubuntu desktop from 14.10 to 15.04. The upgrade went by smoothly, until I rebooted and X failed to start with the dreaded error message: “The system is running in low-graphics mode”. I currently have a NVIDIA GeForce GTS 450, which is using the nvidia-304 driver. After digging around, I found that the x.org file had been delete(?), so I took the following steps to recover.

Assuming you cannot login to GUI, choose either the console terminal from the presented options, or drop to the terminal with (control)+(alt)+(f1)
Ensure the latest driver is installed. You will need to reboot if this is required.
```
$ sudo apt-get install nvidia-current
```
Install the tool “nvidia-settings”. This will create the x.org file.
```
$ sudo apt-get install nvidia-settings
```
Run the nvidia-settings command and restart.
```
$ sudo nvidia-settings
```
```
$ sudo shutdown -r
```
Change permission of .Xauthority. This might not be required, but in my case, the .Xauthority in my user directory became owned by root, so this needed to corrected.
```
$ sudo chmod $USER:USER ~/.Xauthority
```

Now back to playing some TF2 🙂