Ubuntu | Windows startup items for dual systems cannot be found to fix

Dual system windows10, ubuntu 16.04, after reinstalling ubuntu, the startup item of windows cannot be found when booting, and the solution is found on the Internet:

Open terminal
Grant permission first

sudo chmod 777/boot/grub/grub.cfg

Modify again

sudo grub-mkconfig >/boot/grub/grub.cfg

or:

sudo update-grub