I am going to discuss how to check the total disk space usage. I found that there is more than one way to answer this question.
The most traditional way to obtain this information is to open a terminal session and type the command: DF or DF - h.
Other DF variants that may be useful.
DF -a Use this to display all the DF information.
DF -h Use this to display the disk space usage in human readable form
I am using Gnome as my GUI. So I found that I can click on System then About this Computer and navigate to the File Systems tab. That gives me another place to check disk space usage. It gives general information about my Disk and Free Space.
Another GUI tool, Fine it by going to Application then System Tools, then selecting File Manager
The last GUI tool that I used was found: Application, then System Tools, then selecting Disk Utility
There are probably more add-on utilities to determine disk space, I have only mentioned some of the ones that are easily installed with the CentOS distribution with the Gnome GUI.