lsblk -f

NAME       MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
loop0        7:0    0  92.9M  1 loop /run/miso/sfs/livefs
loop1        7:1    0   1.2G  1 loop /run/miso/sfs/mhwdfs
loop2        7:2    0   1.8G  1 loop /run/miso/sfs/desktopfs
loop3        7:3    0 939.3M  1 loop /run/miso/sfs/rootfs
sda          8:16   1  14.9...

I’m running Manjaro alongside Windows on a Dell XPS 13 Plus (9320), using BTRFS for the / and /home mount points and a FAT32 partition for the EFI system. After an update, I lost the GRUB bootloader. In this tutorial, you’ll learn how to reinstall GRUB on a BTRFS and UEFI system using a Live USB.

Identify Partitions

To begin, check which partitions belong to your Manjaro installation. Run the following command:

lsblk -f

You’ll get an output like this:

NAME       MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
loop0        7:0    0  92.9M  1 loop /run/miso/sfs/livefs
loop1        7:1    0   1.2G  1 loop /run/miso/sfs/mhwdfs
loop2        7:2    0   1.8G  1 loop /run/miso/sfs/desktopfs
loop3        7:3    0 939.3M  1 loop /run/miso/sfs/rootfs
sda          8:16   1  14.9G  0 disk /run/miso/bootmnt
sda1         8:17   1   4.2G  0 part
sda2         8:18   1     4M  0 part
nvme0n1    259:0    0 476.9G  0 disk
nvme0n1p1  259:1    0   240M  0 part
nvme0n1p2  259:2    0   128M  0 part
nvme0n1p3  259:3    0 299.2G  0 part
nvme0n1p4  259:4    0   1.2G  0 part
nvme0n1p5  259:5    0 104.3G  0 part
nvme0n1p6  259:6    0   300M  0 part
nvme0n1p7  259:7    0   1.1G  0 part
nvme0n1p8  259:8    0    52G  0 part
nvme0n1p9  259:9    0  17.1G  0 part
nvme0n1p10 259:10   0   1.4G  0 part

In my case, the partition layout is as follows:

• nvme0n1p6 –> EFI system
• nvme0n1p8 –> / partition
• nvme0n1p5 –> /home partition

Mount the Top-level BTRFS Volume

As Manjaro is installed on a BTRFS partition, identify which subvolumes are available in the root partition to mount the system correctly.

First, mount the / partition:

sudo mount -o subvolid=5 /dev/nvme0n1p8 /mnt

Replace /dev/nvme0n1p8 with the corresponding / partition of your installation.

Now, list available subvolumes:

sudo btrfs subvolume list /mnt

You’ll get an output like this:

ID 256 gen 87366 top level 5 path @
ID 257 gen 87347 top level 5 path @cache
ID 258 gen 87365 top level 5 path @log

If you have the /home directory in the same root partition, you may get the @home subvolume listed.

Mount the Correct Root Subvolume

Once identified, mount the correct root volume:

sudo umount /mnt
sudo mount -o subvol=@ /dev/nvme0n1p8 /mnt

Replace /dev/nvme0n1p8 with the corresponding / partition of your installation.

Create Mount Points

These folders should already exist; we are just ensuring they are present before mounting.

sudo mkdir -p /mnt/var/cache
sudo mkdir -p /mnt/var/log

Mount the Subvolumes

Mount the cache subvolume:

sudo mount -o subvol=@cache /dev/nvme0n1p8 /mnt/var/cache

Replace /dev/nvme0n1p8 with the corresponding / partition of your installation.

Mount the log subvolume:

sudo mount -o subvol=@log /dev/nvme0n1p8 /mnt/var/log

Replace /dev/nvme0n1p8 with the corresponding / partition of your installation.

(Optional) Mount the separate home partition:

sudo mount /dev/nvme0n1p5 /mnt/home

Replace /dev/nvme0n1p5 with the corresponding /home partition of your installation.

Now, verify that all necessary BTRFS subvolumes are mounted and that the mount options are correct (specifically, ensure they are listed as rw for read-write). Run the following command:

mount | grep btrfs

You’ll get an output like this:

/dev/nvme0n1p8 on /mnt type btrfs (rw,relatime,ssd,discard=async,space_cache=v2,subvolid=256,subvol=/@)
/dev/nvme0n1p8 on /mnt/var/cache type btrfs (rw,relatime,ssd,discard=async,space_cache=v2,subvolid=257,subvol=/@cache)
/dev/nvme0n1p8 on /mnt/var/log type btrfs (rw,relatime,ssd,discard=async,space_cache=v2,subvolid=258,subvol=/@log)
/dev/nvme0n1p5 on /mnt/home type btrfs (rw,relatime,ssd,discard=async,space_cache=v2,subvolid=5,subvol=/)

Mount the EFI Partition

Finally mount the EFI partition by running the following command:

sudo mount /dev/nvme0n1p6 /mnt/boot/efi

Replace /dev/nvme0n1p6 with the corresponding EFI partition of your installation.

Bind System Directories

Next, bind the system directories. These ‘virtual’ folders act as a bridge between the Live USB and your Manjaro installation, allowing the repair tools to interact with your hardware:

sudo mount --bind /dev  /mnt/dev
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys  /mnt/sys
sudo mount --bind /run  /mnt/run

Chroot and Reinstall GRUB

Now that all subvolumes and partitions are mounted, and system directories are bound, you can access your Manjaro installation and reinstall GRUB. Run the following commands:

sudo chroot /mnt
grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=Manjaro --recheck
grub-mkconfig -o /boot/grub/grub.cfg

GRUB is reinstalled and the bootloader would appear after rebooting.