Recently, the Linux operating system on my laptop no longer boots. It seems
that the boot sector for GRUB bootloader is corrupted. I tried to
reinstall GRUB with an Ubuntu LiveCD; however, I have encountered some
problem related to Btrfs file system (which is the file system for my root
After several attempts, I finally reinstalled GRUB to the hard disk. I feel that it will be good idea to write the steps down, since I can't find any useful suggestion at the time of writing.
Before changing anything, it will be better to understand the situation
beforehand. Check the status and find the correct device file with
fdisk -l command or the GParted GUI tool.
For example, on my laptop, the main hard drive is
according to the result of
/dev/SDA1is the partition for the EFI firmwares, which is a FAT32 partition.
/dev/SDA4is the root file system for the Linux installation, which is a Btrfs partition.
Besides, I would like to reinstall GRUB to
After gathering the necessary information, we can start our work. In summary, there are three steps:
- Mount the file systems.
- Switch to the root file system with
chrootcommand and fix the problem inside the chroot.
- Unmount the file systems.
I will elobrate them in the following paragraphs.
Mount the File Systems
First, create a directory as a mount point for root file system:
$ sudo mkdir mnt
Second, mount the root file system with:
$ sudo mount -o subvol=@ /dev/SDA4 mnt
Notice that it is required to specify the Btrfs subvolume with the
-o subvol= option. We will explain this later. On the default Ubuntu
installation, the subvolume for the root file system is named after
Third, mount the special file system for the chroot:
$ for i in dev dev/pts sys proc run; do sudo mount --bind /$i mnt/$i; done
Fourth, if you are using UEFI, you should mount the EFI boot partition as well:
$ sudo mount /dev/SDA1 mnt/boot/efi
Change Root and Reinstall GRUB
Now, we can switch to the root file system with the
$ sudo chroot mnt
In the chroot, we can reinstall the GRUB bootloader with:
> grub-install /dev/SDA
Remarks: If you see the error messages like "
cannot find a device for
...", then it is possible that some partition is not mounted properly. As a
grub-probe can't detect the devices for the existing
For example, in my first attempt, I have seen the following error message:
grub-install: error: cannot find a device for /boot/grub (is /dev mounted?)
This is due to the fact that the Btrfs subvolume was mentioned in the
configuration file but I didn't specify the
subvol= option when I was
mounting the root file system in the first attempt. If you encounter similar
error messages, double check the
/etc/fstab and the mount options.
Now, we can verify the GRUB installation and update the configuration files with:
> grub-install --recheck /dev/SDA > update-grub
Finally, leave the chroot with:
Unmount the File Systems
Now, we would like to unmount the file systems so that the changes can be flushed properly.
First, unmount the EFI partition (if available):
$ sudo umount mnt/boot/efi
Second, unmount the special file systems:
$ for i in run proc sys dev/pts dev; do sudo umount mnt/$i; done
Third, unmount the root file systems and delete the mount point:
$ sudo umount mnt $ sudo rmdir mnt
That's all. You can reboot the computer now! Hoping this will fix your problem.