Triple boot - looking to reinstall CentOS 7 without affecting order !

aztec11us

good evening everyone!



I have the following set-up:



an i7 with 2 HDDs:



First HDD) a 3 TB HDD dedicated to a licensed Windows 10 pro 64 bits



Second HDD) a 2 TB HDD shared between 2 linux distros: a CentOS 7 KDE and a Linux Mint 18 Cinnamon (both 64 bits)



-----------------------------------------------



I bought this PC as bare-bones (without and os).



First, i proceeded to install the Windows 10 64, on the 3TB HDD (on the first HDD). So windows has an entire HDD all to itself.





Then, on the second HDD, the 2 TB one, i proceeded to install, in the following order:

1) CentOS 7 KDE all inclusive (i used a USB stick to boot and install)

and then:

2) Linux Mint 18 Cinnamon with its GRUB2.



So, the Linux Mint 18's GRUB2 controls all booting proccesses and boot order.



On the Linux Mint 18, i also have grub-customizer.



The attached screenshots both show the same thing:

Screenshot 1 --- is the shell with the command df -h

and

Screenshot 2 -- same thing, except i used the disks utility of Mint 18 Cinnamon



In either screenshot, you will see the following:

- sda: is the 3 TB windows hdd

- sdb: is tne 2 TB hdd which is shared between the linux partitions.



On sdb:

sdb 1, sdb2 and sdb 3 --- all these belong to the CentOS 7 installation

sdb 4, sdb 5 and sdb 6 --- all these belong to the Mint 18 Cinnamon installation (this is the one which also controls the GRUB2)



PROBLEM: seeing as i have an AMD Radeon RX470 4 GBDDR5 graphics board, i tried to install the official drivers in CentOS 7.



This operation went great in Linux Mint 18...but not good at all in CentOS 7!



Now i want to re-install the CentOS 7, but i do not want to mess up the grub2 bootloader (and centos 7 also has grub2!)



if i do a regular re-install it will mess up the GRUb2 by re-writing it!



How precisely do i reinstall CentOS 7, without affecting/re-writing the GRUB2, and without affecting the other OSes boot order?



Thanks