Obtain a rescue CD.
Hopefully the machine is still up and running, or can get to that point, so do the following:
and note the device your problematic mount is located on.
devtmpfs 1.9G 0 1.9G 0% /dev tmpfs 1.9G 0 1.9G 0% /dev/shm /dev/sda3 96G 4.8G 91G 5% / /dev/sda1 1014M 224M 791M 23% /boot
For example, let's assume it is /dev/sda3
Now follow steps in https://www.golinuxcloud.com/e2fsck-repair-filesystem-in-rescue-mode-ext4/
This did not work…had to reinstall operating system.