Du and df show different

[Michael Murphy_2]

Hello - I am having an issue where du and df show different sizes for the root FS - in the past there have been issues where a filesystem is mounted over some other large files in a dir (not sure if that case was root FS though) - is there a way to unmount root and check for this?

[Pete Randall]

The situation you're referring to, I believe, is where a file system under root gets unmounted and files get written underneath the mount point. For example, if /var was not mounted, log files would still be written to the directory called /var but they would actually take up space in the / file system. Then, when /var was remounted, the files would be invisible but the space under / would still be used. The easiest way to check for this would be to reboot in single user mode and do a simple ll against all the mount points: /var, /usr, /tmp, /opt, etc.

It is also quite common for du and bdf to report different totals, by the way, but that's a whole other subject.


Pete