In Windows, sfc /scannow will check the system files with those available in OS disk and replace faulty, missing files. Is there anything similar available for Ubuntu 16.04 ?
There are two things to do to replicate
sudo debsums -s(
sudo apt install debsumsto install it) will list system files that have been changed or corrupted as well as what packages they come from. If none are listed, all system files are fine.
sudo debsums -sato check configuration files as well.
sudo apt install --reinstall [package]will reinstall the package, reinstalling the file.
I found a guide pretty easily with google search: https://help.ubuntu.com/community/FilesystemTroubleshooting
Have you seen that guide?