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1

Ubuntu partition unknown, cannot mount or update grub

rated 0 times [ 1] [ 0] / answers: 1 / hits: 1320 / 2 Years ago, wed, december 22, 2021, 11:59:26

After a power failure, I had the following error:

error: unknown filesystem

grub rescue>

I ran the Ubuntu repair using a live usb. The log can be found here

After this grub disappeared (I cannot select which OS to boot) and by default I am booting windows now. I have an important application running on Linux but I cannot boot to Linux.

I then edited the grub file and tried to update-grub but it says:
```
 failed to get canonical path of /cow
```

The next option was to sudo mount /dev/sda5 /mnt But then I get the error:
```
 mount: you must specify the filesystem type
```

I do not know the filesystem type, since I did not do the installation on this particular machine.

I also tried cat /etc/fstab but it does not show sda5, neither can I see it using blkid command. From the GUI (since i have booted the system from live usb), I can see the partition 5 as having unknown type.

UPDATE: fsck -a -t ext4 /dev/sda5 immediately gives the following error:

fsck from util-linux 2.20.1 fsck.ext4: Bad magic number in super-block
while trying to open /dev/sda5 /dev/sda5: The superblock could not be
read or does not describe a valid ext2/ext3/ext4 filesystem.

If the
device is valid and it really contains an ext2/ext3/ext4 filesystem
(and not swap or ufs or something else), then the superblock is
corrupt, and you might try running e2fsck with an alternate
superblock: e2fsck -b 8193 or e2fsck -b 32768

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ugeeport

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3 Years ago

answered 2 Years ago tonhorn · Accepted Answer

Test this:

You must boot from a live-dvd/usb.

Open a terminal.

Run it:

sudo -i

fsck -a -t ext4 /dev/sda5

mount /dev/sda5 /mnt

mount --bind /dev /mnt/dev 

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

mount --bind /proc /mnt/proc

mount --bind /sys /mnt/sys

chroot /mnt

grub-install --root-directory=/mnt /dev/sda

update-grub

umount /mnt

reboot