Ubuntu Trusty 14.04 (Linux Kernel 3.19.0-65) install NVIDIA GeForce 780M driver

Recently, after an kernel upgrade, my laptop cannot detect external monitors anymore. Finding a solution takes me two days – here’s a note in case I need to do it again in the future.

• google keyword: ubuntu+nvidia+driver; ubuntu+nvidia+dual/multi monitor 
• re-install ubuntu, get a clean environment 
• disable UEFI secure boot is required 
• still need to download and run official nvidia driver install script - NVIDIA-Linux-x86_64->.

run

  $ add-apt-repository ppa:graphics-drivers/ppa
  $ sudo add the graphics-drivers ppa
  $ sudo apt-get update
  $ sudo ubuntu-drivers autoinstall // in order to disable UEFI secure boot

Since I tried lots of steps and finally worked, which steps are nessesary or not is never known. Here’s the packages related to nvidia I currently installed:

[NOTE]
During installation with NVIDIA-Linux-x86_64->.

run , remember0. follow the steps recommended on Ask-Ubuntu forum to disable x-server
1. don't install source for next kernel upgrage
2. generate new key-pair
3. remove old key
4. re-start x-server ($ sudo service lightdm start)

Hope this pose help someone also.