Quotas are a feature of the filesystem; therefore, they require kernel support. The first thing you'll need to do is verify that you have quota support in your kernel. You can do this using grep:

# cd /usr/src/linux
# grep -i quota .config
CONFIG_QUOTA=y
CONFIG_XFS_QUOTA=y

If this command returns something less conclusive (such as CONFIG_QUOTA is not set) then you should rebuild your kernel to include quota support. This is not a difficult process, but is outside of the scope of this section of the tutorial. If you're unfamiliar with the steps to build and install a new kernel, you might consider referencing this tutorial.