Raspberry Pi Pod and micro:bit base

Introduction

This guide is for ext4 , though I’ll explain how other filesystems can be cured along the way. The easiest way to carry all this out, seeing as your computer probably won’t boot at this stage, is to download and burn a copy of Parted Magic. Boot from that, and you’ll get access to a number of useful tools.

The procedure

First, figure out what partition we’re dealing with.

sudo fdisk -l

The above will list all the partitions on all the drives in your computer. To recover a lost partition, you’re going to need Testdisk. Testdisk is included in Parted Magic, and there’s a great guide on their site. For this though, we just need the partition number, such as /dev/sda3 or /dev/hdb1.

Now, make sure your superblock is the problem, by starting a filesystem check, replacing xxx with your partition name. Here, you can change ext4 to ext3, or ext2 to suit the filesystem.

sudo fsck.ext4 -v /dev/xxx

If your superblock is corrupt, the output will look like this

fsck /dev/sda5
fsck 1.41.4 (27-Jan-2009)
e2fsck 1.41.4 (27-Jan-2009)
fsck.ext4: Group descriptors look bad... trying backup blocks...
fsck.ext4: Bad magic number in super-block while trying to open /dev/sda5
The superblock could not be read or does not describe a correct ext4
filesystem. If the device is valid and it really contains an 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 <device>

Now lets find where your superblock backups are kept.

sudo mke2fs -n /dev/xxx


Down at the bottom of this output, should be a list of the backups:

Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208


You’re almost there. Finally, restore the superblock from the backup, again replacing the x’s with your partition name, and block_number with the first backup superblock.

sudo e2fsck -b block_number /dev/xxx

Now reboot, and your superblock should be fixed. If it’s not, repeat the steps, but restore a different backup superblock

Checking your file system as a precaution

If you want to check your Pi file system because you feel it might be having a problem, try the following:

First of all, shut down your Pi using the following which will make the Pi check it’s own file system on reboot:

sudo shutdown -F -r now

Once the Pi comes up again, check the results of the scan by looking at the following file:

/var/log/fsck/