quota

See redhat or linuxhelp

Install quota:
aptitude install quota quotatool

Add usrquota,grpquota to your /etc/fstab for some volume, eg.
/home /home ext3 defaults,usrquota,grpquota 1 2

Remount your volume
mount -o remount /home

Check quota
quotacheck -vagu

Turn quota on
quotaon -vagum

Set grace period
edquota -t

Modify user quota
edquota -u user

or by (200M is soft, 250 is hard limit for user new in /home):
quotatool -u new -bq 200M -l '250 Mb' /home

Copy user quota from old to new user
edquota -p old new

List of quotas on volume
repquota /home

List of all quotas
repquota -a