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I have Windows 10 dual boot with CentOS. However, I can't access CentOS, my machine start automatically with Windows, and there is no Grub screen to choose CentOS. Can you guys help me? Thanks.

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    Does the system use legacy/BIOS or UEFI? In which order did you install the OS's? Apr 7 '18 at 2:30
  • Even more questions: When not BIOS, is it UEFI (PC) or EFI (e.g. Mac)? Which CentOS? Did you actually install grub without errors?
    – reichhart
    Apr 7 '18 at 23:07
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I made a Tutorial on the installation of Grub on CentOS 7:

Dual Boot Installation with Grub

Installation of Grub2 and dual boot with windows 10

If your Grub configuration is not as you like follow this tutorial. First reinstall Grub.

sudo yum reinstall grub2-tools

Login as root in a terminal

su

In another terminal , get information about your Windows 10 hard drive, in my case it was named '/dev/sdb1'

sudo fdisk -l

In my configuration, my windows 10 disk was on another hard drive. Follow only if you are in the same situation.

In the root terminal, navigate to the grub configuration directory

 cd  /etc/grub.d/

Now we must find the UUID of your Windows 10 hard drive, enter this command in your non-root terminal

ls -l /dev/disk/by-uuid

Find the UUID code next to your disk something like: 40S863A9D8619F12

Now in the root terminal enter the command:

nano 40_custom

Inside this file enter your windows 10 configuration using GRUB standard. Use the UUID code previously found inside the configuration. In my case my config is:

menuentry 'Windows 10' {
        insmod ntfs
        insmod ntldr
        insmod part_msdos
        insmod search_fs_uuid
        search --fs-uuid --no-floppy --set=root 40S863A9D8619F12
        ntldr /bootmgr
}

Save and exit nano. Now we need to generate a new GRUB configuration file. Enter the command:

grub2-mkconfig --output=/boot/grub2/grub.cfg

Voilà !!!! Try the configuration with a fresh restart

Source: http://dareneiri.github.io/Configuring-Grub-2-on-CentOS-7/ https://ihaveabackup.net/article/grub2-entry-for-windows-10-uefi

(Optional) Install GRUB customizer

If you want to have a sexy GRUB menu you can install grub-customizer using this tutorial: https://centos.pkgs.org/7/epel-x86_64/grub-customizer-5.0.6-1.el7.x86_64.rpm.html

you can find more tutorial at: https://github.com/Winterhart/CentOS7-Setup/

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