Switch monitor with xrandr command line

Set viewsonic as main, then hp:
xrandr --auto --output eDP-1 --mode 1920x1080 --right-of HDMI-1-2

Set hp as main, then viewsonic:
xrandr --auto --output HDMI-1-2 --mode 1920x1080 --right-of eDP-1

Turn off hp:
xrandr --auto --output eDP-1 --off  --right-of HDMI-1-2

Turn off viewsonic:
xrandr --auto --output HDMI-1-2 --off  --right-of eDP-1

setup nvidia for hp pavilion gaming 15

1. Reboot
2. F10 enter BIOS
3. System Configureation -> power -> Security Boot
4. disable 
5. Follow the screen message, enter 4-digit then press enter
6. boot into ubuntu
7. sudo apt purge nvidia* 
8. sudo apt update
9. sudo apt-add-repository ppa:graphics-drivers/ppa
10. Run 額外驅動程式，click Nvidia-430
11. Reboot

software-properties-gtk no working 無: 套件庫 額外驅動程式

cf: https://askubuntu.com/questions/789966/software-updates-crashes-and-will-not-open
Reinstall with this line:

sudo aptitude reinstall apt apt-utils aptdaemon aptdaemon-data update-manager update-manager-core dbus

accented european letter in bibtex

{\"a} {\^e} {\`i} {\.I} {\o} {\'u} {\aa} {\c c} {\u g} {\l} {\~n} {\H o} {\v r} {\ss}

Enable HP Pavilion HDMI for Ubuntu

1. 額外的驅動程式，click 430
2. 輸入 security password
3. reboot
4. enroll emks ( something like this ?),  DO NOT just click continue, Have to enroll first ！
5. reboot
6. HDMI should be ok.
7. check if the module is enabled by issuing:
   lsmod | grep nvidia
   or
   run nvidia-settings

Install operation system on SD fron linux

sudo dd bs=4M if=ubuntu-18.04.2-preinstalled-server-arm64+raspi3.img of=/dev/sdX status=progress conv=fsync