Reinstall Ubuntu on a dual-system machine

Recently, I need to reinstall the Ubuntu on Dell XPS 6 series. Here is the recording.

I follow the tutorial to install the ubuntu without deleting other data. By the method, the data that are not in the same partition with the OS will be left in the disk.

The basic steps are:

• Create a live USB
• Reinstall Ubuntu by choosing something else for installation type. link
  • Find the partition for OS.
  • Remove the partition and install the new ubuntu system on it.

Some Issues:

1. I met with these problems mostly because the machine I deal with has dual systems: ubuntu and windows. So after I reinstall ubuntu, I will stuck in the GRUB command line view.
   • How to use grub to run ubuntu: link
   • Solution: Change boot from UEFL to Legacy
   • How to change Grub Graphic UI waiting time: link
2. Auto mount the external disk on startup: link