How to configure disk qouta in rhel5 linux /centos5

Quota is used for limiting the disk usage for users or groups.

###To verify that the quota is enabled in the kernel###
#grep CONFIG_QUOTA /boot/config-`uname -r`

CONFIG_QUOTA=y -enables limit on usage
CONFIQ_QUOTACTL=y -associated with disk quota manipulation.

If you have custom or upgraded kernel
#make menuconfig
#make gconfig
#make xconfig

###The quota package###
#rpm -q quota

For using Quotas the partition we are using for quota [quota can only be used per partition.] should be mounted with quota options. For that go to /etc/fstab and edit the partition mount options.

#vi /etc/fstab
LABEL=home /home ext3 defaults,usrquota,grpquota 1 1
:wq

If the partition is already mounted remount it for affecting changes in mount options.
#mount -o remount /home

Check the filesystem is mounted with changed options. If not, you may have to umount and mount again or u've to restart the system.
#mount -to check

###Create quota database###
#quotacheck -mcug /home
[ If you are using quotacheck -cug, it will throw an error that it cannot remount the filesystem mounted on m_point so counted values might not be right. Please stop all the programs writing to filesystem or use -m flag to force checking. This will happen when we use the filesystems like "/". Many processes are writing into "/" that time. Thats why it is throwing this error.] 

-c option specifies that the quota files should be created for each file system with quotas enabled.
-u option specifies to check for user quotas.
-g option specifies to check for group quotas.
If not, those files will be created.

quotacheck -mcug /home -will create following files in /home
aquota.group
aquota.user
###Assign quota policies for user###
#edquota username
#quota username -shows the quota for set for that user

###Assign quota policies for group###
#edquota -g groupname -think a user should exist with that group
#quota -g groupname -shows the quota for set for that group

###Defining prototypical users###
edquota -p user1 user2

###To see all user qoutas###
#repquota -a

###To see the user quotas in /home###
#repquota -u /home

###To see the group quotas in /home###
#repquota -g /home

###To see the quotas in appropriate size###
#repquota -s /home -shows used space and hard limit in MB

###To check the quota is on or not###
#quotaon -v /home

###To update the usage###
#quotacheck -mavug -execute this often for knowing latest usage info. Put it in cronjob. may need -f option.
[This will check all the files and directories in all partitions which is mounted with quota options.]
-a Check all mounted non-NFS filesystems in /etc/mtab
-v Verbose. Displays the information as it proceeds.
-u Checks for the user quotas.
-g Checks for the group quotas.

###Setting grace period###
#edquota -t
10days not 10 days.

###To enable and disable the qoutas###
#quotaon -vaug with -m if needed. For only one partition; quotaon -vug /home
#quotaon -vaug -will turn on all the quotas [group and user]
#quotaoff -vaug -will turn off all the quotas [gruop and user]