disk usage checking

["Hailong Li" <hailong li jsums edu>]

Hi there,
Recently, my server's disk usage grows very fast, do you know how to check the
users' file system size? Under /home directory, there are 20 subdirectories,
over 5,000 user accounts are assigned to those subdirectories. How to check
the user's filesystem size quickly so that I can ask users to delete some of
their files? The Operating System is RedHat 7.2.
Thanks alot!
Hailong Li