Convert Arch Linux installation from MBR/BIOS to UEFI

After literally years of notebook-only computing I finally built a nice desktop PC, and since I didn’t had enough money to afford an SSD drive right now, I’m borrowing it from my trusty ThinkPad X61s.

The Arch Linux installation I had there was already configured to fit my needs and I wanted to test the real flexibility this distro have to offer, so I converted it from a MBR/BIOS system to a UEFI one, here’s how I did it using only the Arch installation media.

Backup. #

Always make a backup before doing this kind of things.

Analyzing the partition table #

Start the computer from the Arch installation media in UEFI mode first.

The UEFI system relies on a special partition called ”EFI System Partition”, abbreviated in ESP, where the OS bootloader and often its configuration files resides.

So, the first step is to make room on the disk for this partition.

My partition table was composed of:

/dev/sda1: root filesystem
/dev/sda2: swap partition

Since this new PC have enough RAM already, I simply deleted the swap and extended sda1 enough to make a 200MB, ef00 type ESP partition.

Convert the partition table #

To boot with UEFI, you need a gpt partition table and luckily a MBR partition table can become one easily.

Run gdisk /dev/sdX, the software will warn you that if you invoke the w command the partition table will be converted to gpt, and we want exactly that.

Follow the white rabbit #

The last thing to do is pretty much follow the Beginner’s guide :

• mount your root filesystem on /mnt but do not format it
• create a /mnt/boot/uefi mountpoint
• format your ESP partition with mkfs.vfat /dev/sdX
• mount it on the directory created previously
• rebuild your fstab file with genfstab -U /mnt/ > /mnt/etc/fstab to reflect the changes
• chroot in your root
• build a grub.cfg file and then install the bootloader as the guide says.

Done, now your system will boot in UEFI mode!