Shut down my Pi today and thought to make a copy of files in its SD card. This is what
mount /dev/sdf2 /mnt had to say:
mount: wrong fs type, bad option, bad superblock on /dev/sdf2, missing codepage or helper program, or other error In some cases useful info is found in syslog - try dmesg | tail or so
Great. After trying
fsck, it became apparent that for some reason, the root partition is marked as being 1 block longer than the physical card. Must be a bug with Raspbian partition expansion or something.
Thankfully, I found this gold nugget which suggested using
resize2fs to fix it. Turns out I had to run e2fsck first (and say “y” a couple of times):
sudo e2fsck /dev/sdf2 sudo resize2fs /dev/sdf2 mount /dev/sdf2 /mnt
Voilá! Fully functioning filesystem again.