Reboot and repair after windows and ubuntu are installed again

After windows and ubuntu are re-installed on both systems, the boot fix for windows 7 is reinstalled in the notebook today. After that, windows 7 is directly started and there is no linux option. solution: 1. Find a linux liveCD disc or start it with a USB flash disk. 2. Enter linux liveCD, open the terminal, and run the sudo passwd root command to set the root password, switch to root 3, use fdisk-l to list the disks, and find the linux partitions. My boot is separately partitioned, Which is sda9, depending on your computer. 4. Run mount/dev/sda9/mnt to mount it. 5. Run the grub-install-root -- directory =/mnt/dev/sda command to install grub, after the reboot is completed, the boot will be restored.