Ubuntu boot issue Records

Preface two problems recently encountered: 1. ubuntu disappears after windows is reinstalled. 2. I have also installed the centos system. I want to set the centos as the default introduction.

Two problems recently encountered: 1. ubuntu disappears after windows is reinstalled. 2. I also installed centos. I want to set centos as the default boot system.

So I checked the information and recorded it.

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Enter the missing ubuntu

In windows, you can install easyBCD and add ubuntu.

When adding a bootstrap program, you must first select it. By default, the bootstrap program is the first one. to ensure security, the second one is also added.

Select ubuntu.

Select the partition where your ubuntu instance is located. if you are not sure about the partition, add each partition and start the system one by one.

Select the default boot system. the general boot system is in/boot/grub/menu. lst or/boot/grub. cfg.
In row 13, you can see set default = "0" or default 0 (search if no value is found ).
This number is the one that is guided by default. You can modify the system you want to start by default.
Update the boot list

Generally, after windows is installed, the linux boot will not be displayed, so you cannot enter linux.

After installing a software in windows, we can go to linux. after entering the software, we need to update the boot list.
Use the following command to update the file.

Sudo grub-install/dev/sda sudo update-grub