Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
This tutorial walks you through implementing disk quotas for both users and groups on Linux, using a virtual filesystem, which is a filesystem created from a disk file. Since quotas work on a per-filesystem basis, this is a way to implement quotas on a sub-section, or even multiple subsections of your drive, without reformatting. This tutorial also covers quotactl, or quota's C interface, by way of an example program that can store disk usage in a SQLite database for monitoring data usage over time.
This tutorial was tested on Fedora Core 2, 3, and 4. I'm assuming you have the quota tools installed. If you're not sure, try the following test, which will return 3.12-6 or 3.12-5 depending on which version of Fedora Core you are using.
$ rpm -q quota
Sharing a Directory amoung Several Users
This step creates a group and implements group rights on a directory within the quota filesystem. Specifically, this step creates the group, "quotagrp" and adds the two existing users "chirico" and "sporkey" into this group. The direcory "/quota/share" is setup so that any files created in this directory by these two users will be sharable by default for members of this group. This is done by setting the setgid bit on the directory.