In Ubuntu 12.04 I was used to run the 'Disk Utility' and choose 'Check Filesystem'; its subtitle showed also 'and repair'. In Ubuntu 16.04 I have only found the 'Disks' utility that looks similarly but has no 'Check Filesystem' option, even for the superuser.
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
fsckcommand if there were errors
If for some reason you can't do the above...
- boot to a Ubuntu Live DVD/USB
gpartedand determine which /dev/sdaX is your Ubuntu EXT4 partition
- open a
sudo fsck -f /dev/sdaX# replacing X with the number you found earlier
- repeat the fsck command if there were errors