Issue

• How can I convert a RHEL system from using UEFI to using legacy BIOS?
• Is it possible to conver boot LUN from GPT to MBR without losing data and configuration?
• How to convert boot LUN from GPT to MBR (i.e. UEFI boot to Legacy Only)?
• The machine is installed with UEFI boot enabled, now is it possible to make it Legacy only?

Resolution

1. Before beginning: Make a backup of the main disk
   The following steps have been tested by engineers in Red Hat Support; however, the risk of mistakes causing damage is high when using programs that modify partition tables, so taking a backup first is highly recommended

2. Install the gdisk package if it's not already installed

   Raw

   yum install gdisk

3. Use the gdisk command to convert the main disk's GPT to MBR
   (Replace /dev/sda as appropriate)

   Raw

   gdisk /dev/sda <<EOFrga2t283wyEOF

4. Reconfigure GRUB
   (Replace /dev/sda as appropriate)

   • RHEL 6

     Raw

     cp -a /boot/efi/EFI/redhat/grub.conf /boot/grub/grub-install /dev/sda

   • RHEL 7

     Raw

     rm -f /etc/grub2-efi.cfg /boot/grub2/grubenvyum install grub2grub2-install --target=i386-pc /dev/sdagrub2-mkconfig | sed -r 's/(linux|initrd)efi/\116/' >/etc/grub2.cfg