Check to make sure the quota package is installed, else run:
# yum install quota
Edit "/etc/fstab" and add "usrquota,grpquota" to the / partition:
LABEL=/ / ext3 defaults,usrquota,grpquota 1 1
Then run:
# mount -o remount /
# quotacheck -avugm
# quotaon -avugm
To check quotas for all users:
# repquota -a
To edit quota for a particular user:
# edquota -u <user>
Alternately use setquota:
# setquota <softlimit> <hardlimit> 0 0 <user>