I attempted to upgrade my Ubuntu 18.04 LTS to 20.04 this morning. After reboot, a symbol 'grub_file_filters' not found error was reported.

I googled and tried the two popular methods which I found, but none of them succeeded. The same error stuck every time I rebooted the system

The operations I applied are shown below, wish could help to find out the root cause and solution:

1. Repair by a livecd

My /boot is an independent partition so I mounted it as an extra step based on the solution what I found. The whole operations sequence is

% sudo su

 

% mount /dev/sdb3 /mnt

% mount --bind /dev /mnt/dev

% mount --bind /dev/pts /mnt/dev/pts

% mount --bind /proc /mnt/proc

% mount --bind /sys /mnt/sys

% mount /dev/sdb2 /mnt/boot

 

% chroot /mnt

% grub-install /dev/sdb

% update-grub



% exit

% umount /mnt/boot

% umount /mnt/dev/pts

% umount /mnt/dev

% umount /mnt/proc

% umount /mnt/sys

% umount /mnt

 

% reboot

2. Boot-repair

I doubt what this did is similar to the operation sequence in part 1. The whole log is a little bit long so I uploaded it to https://0bin.net/paste/aChHYcRK#h2E3oydL5mm6JxbVmBAOQgpKkax4nHHXuDCFgOm77qp

3. insmod

In the grub rescure console, I tried

grub rescure> insmod (hd1,2)/grub/i386-pc/linux.mod

error: symbol `grub_file_filters' not found.

grub rescure> ls (hd1,2)/grub/

./ ../ gfxblacklist.txt unicode.pf2 i386-pc/ locale/ fonts/ grubenv grub.cfg

Please kindly to help me, thank you!