Thanks for you guys' replies. I read the RedHat customization manual and here's their procedure of enabling quota management:
1. Add the "usrquota" and/or "grpquota" to the /etc/fstab file.
2. Remount the file system by "umount" followed by "mount" or reboot the system.
3. Create the "aquota.user" and "aquota.group" file typing
quotacheck -acug /path_to_filesystem
at a shell prompt.
4. Generate the table of current disk usage per file system with quotas by
5. Use "edquota username" to assing the disk quotas.
I tried to do the above steps for my /boot partition and they did generate the "aquota.user" file. However, when I did the same thing to the root(/) partition, it displayed an error message and did not generate the "aquota.user" file. So, my question is: does RedHat prohibit the user from enabling quota management on the root(/) partition? Thanks a lot!