Windows startup item in grub does not have Windows boot after installing Ubuntu

My question:

When installing the system, choose Grub installed on the SDB disk

Http://forum.ubuntu.org.cn/viewtopic.php?f=139&t=474289&start=15

Background

Download the Ubuntu kylin16.04.1 ISO installation package, burn it to the U disk, install it on a PC with Win 7, and the computer has freed up 100G of free space.
When you install Ubuntu using the option "Ubuntu and Windows Coexist", the system automatically divides the 100G free space into 96G storage and 4G swap space.
After successful installation, the Grub page becomes the Kylin image (boot is still sda1, but is rewritten by the Ubuntu system), where there is no WIN8 startup item, only the Utuntu startup item.

Reference attempt

Enter Ubuntu system, run sudo fdisk-l, find boot is still sda1,win8 boot disk in Sda2,ubuntu system installed in SDA7 and SDA8
Gedit/boot/grub/grub.cfg
Edit Reference http://wenku.baidu.com/view/f99c198ec1c708a1294a4456.html
sudo update-grub
You can find the start of Win8
Another: If you suspect that you don't need to change grub.cfg, you can use the sudo update-grub command directly.

Http://blog.5ibc.net/p/88875.html

Dd

Windows startup item in grub does not have Windows boot after installing Ubuntu