Refer: https://askubuntu.com/questions/953728/how-to-check-a-filesystem-in-ubuntu-16-04/953750
To check the file system on your Ubuntu partition...
- boot to the GRUB menu
- choose Advanced Options
- choose Recovery mode
- choose Root access
- at the # prompt, type sudo fsck -f /
- repeat the fsck command if there were errors
- type reboot
If for some reason you can't do the above...
- boot to a Ubuntu Live DVD/USB
- start gparted and determine which /dev/sdaX is your Ubuntu EXT4 partition
- quit gparted
- open a terminal window
- type sudo fsck -f /dev/sdaX # replacing X with the number you found earlier
- repeat the fsck command if there were errors
- type reboot