Some concrete technical tips in Ubuntu for my future myself

These solutions are not in another place of internet by now~

How to put a CA certificate in a wifi config with Gnome 3

Gnome 3 networking manager have a weird bug that doesn't allow to save a wifi config when you choose a CA certificate.
In that case, complete the form without adding the CA certificate, and then:

1. Open a terminal
2. Write "cd /etc/NetworkManager/system-connections/" to go to the directory where configs are saved
3. Write "sudo gedit SSID" where SSID is the name of the wifi spot and gedit is the text editor
4. Under the line "[802-1x]" add the line "ca-cert=PATH" where path is the file path to your ca certificate (ex. /home/user/certificate.der)

How to see the Nvidia card temperature using bumblebee

optirun nvidia-settings -c :8 -q gpucoretemp

How to completely erase the contents of a USB device

Even Gparted was unable to create a new partition table on it!
WARNING it will erase all!
dd if=/dev/zero of=/dev/[name of the device] bs=512 count=[bit number of the device capacity]
(I'm not sure about the count parameter)