To enable user quota support on a file system, add "usrquota" to the fourth field containing the word "defaults" (man fstab for details).

/dev/hda1       /       ext2    defaults        1       1
/dev/hda2       /usr    ext2    defaults,usrquota       1       1
/dev/hdb5      /export  ext2    defaults,usrquota  1 2

Replace "usrquota" with "grpquota", should you need group quota support on a file system.

Both quota record files, quota.user and quota.group, should be owned by root, and read-write permission for root and none for anybody else.

Login as root. Go to the root of the partition you wish to enable quota, then create quota.user and quota.group.

touch /export/quota.user
touch /export/quota.group
chmod 600 /export/quota.user
chmod 600 /export/quota.group

% quotaon -avug
quotaon: using /export/quota.user on /dev/hdb5: No such file or directory

% quotacheck -avug
Scanning /dev/hdb5 [/export] done
Checked 6982 directories and 88226 files
Using quotafile /export/quota.user

% /sbin/quotaon -avug
/dev/hdb5: user quotas turned on

-a     All  file  systems in /etc/fstab marked read-write with quotas
       will have their quotas turned on.  This is  normally  used  at
       boot time to enable quotas.

-v     Display a message for each file system where quotas are turned
       on.

-u     Manupulate user quotas. This is the default.

-g     Manupulate group quotas.

make it into system init script (see howto).

reboot!