Linux Quota

Quota is used to limit the disk space used by a user or group on a particular file system, thus giving system administrators better control over their disk usage policies. The quota package helps implementing quota for Linux.

The first step in setting up quota is to enable quota for a file system partition. To do this, either remount the file system with appropriate mount options, or edit /etc/fstab to make the changes permanent.

Suppose your home partition is mounted on the file system /dev/hda5 and you want to enforce quota for users. Mount the file system with quota options,

/etc/fstab

/dev/hda5 /home ext3 defaults,usrquota,grpquota 0 0

usrquota : Enables per user quota
grpquota : Enables per group quota

Remount home partition
[root@LinuxBox1 ~]#mount -o remount /home
[root@LinuxBox1 ~]#mount|grep /home
/dev/hda5 on /home type ext3 (rw,usrquota,grpquota)

Quota information for a file system is stored in files aquota.user and aquota.group files under the root of the file system, in this case /home. This files will be owned and accessible only by root. You have to initialise these files first using quotacheck command.
[root@LinuxBox1 ~]#quotacheck -vgum /home
quotacheck: Scanning /dev/hda5 [/home] done
quotacheck: Checked 1708 directories and 8935 files
If you are using this command for the first time, you may see some errors about file not in correct format/missing. Its ok.
[root@LinuxBox1 ~]#ls -la /home/aquota*
-rw------- 1 root root 9216 Apr 10 04:44 /home/aquota.group
-rw------- 1 root root 8192 Apr 10 04:44 /home/aquota.user

Enable quota on /home partition with quotaon command
[root@LinuxBox1 ~]#quotaon /home
/dev/hda5 [/home]: group quotas turned on
/dev/hda5 [/home]: user quotas turned on

Now everything is set up correctly, we can set quota for user 'safeer' using edquota command. This will open a file in your default editor (most probably 'vi '). You have to change its values appropriately.
[root@LinuxBox1 ~]#edquota -f /home -u safeer
Disk quotas for user safeer (uid 507):
Filesystem blocks soft hard inodes soft hard
/dev/hda5 1020 0 0 14 0 0

blocks : Space in 1k blocks used by the user (Current usage is 1MB)
inodes : Number of files/folders created by user (14 files/folders in total)
soft : Warning limit of space used/number of files created by the user. User gets a warning when this limit is reached, but he can still create/modify files.
hard : Maximum of space used/number of files created by the user. User can't cross this limit.

Let us enforce a soft limit of 4 MB and hard limit of 5 MB on space usage.
[root@LinuxBox1 ~]#edquota -f /home -u safeer
Disk quotas for user safeer (uid 507):
Filesystem blocks soft hard inodes soft hard
/dev/hda5 1020 4096 5120 14 0 0
Note that we are not restricting the number of inodes

Let us check this by creating files as safeer
[root@LinuxBox1 ~]#su - safeer
[safeer@LinuxBox1 ~]$quota
Disk quotas for user safeer (uid 507):
Filesystem blocks quota limit grace files quota limit grace
/dev/hda5 1020 4096 5120 2 0 0
Users can use quota command to view his current quota usage and quota limits as above.
'safeer' is already using 1MB of disk space. Let us create a file of 2MB:
[safeer@LinuxBox1 ~]$dd if=/dev/zero of=./temp1 bs=1024 count=2048
2048+0 records in
2048+0 records out
2097152 bytes (2.1 MB) copied, 0.024208 seconds, 86.6 MB/s
This will work fine since user has not exceeded the quota limit.
Now create another file of 1.5MB, making the total disk usage 4.5 MB (exceeds softlimit of 4MB)
[safeer@LinuxBox1 ~]$dd if=/dev/zero of=./temp2 bs=1024 count=2560
hda5: warning, user block quota exceeded.
2048+0 records in
2048+0 records out
2097152 bytes (2.6 MB) copied, 0.024208 seconds, 86.6 MB/s
Again create another file of size 1MB, thus exceeding the hard limit:
[safeer@LinuxBox1 ~]$dd if=/dev/zero of=./temp3 bs=1024 count=1024
hda5: write failed, user block limit reached.
dd: writing `./temp3': Disk quota exceeded
497+0 records in
496+0 records out
507904 bytes (508 kB) copied, 0.007349 seconds, 69.1 MB/s
If you want to set quota based on inode or both inode & space in the same way.
You can also set quota for group using the command
[root@LinuxBox1 ~]#edquota -f /home -g developers
This will edit the quota for group 'developer'. One thing people often misunderstand is that group quota means total space/inodes used by all members of a group. But actually it is the size/inodes used by users who have this group as primary group.

Administrators will frequently need to check the status of user quotas.
To find out the quota usage of a particular user:
[root@LinuxBox1 ~]#quota -u safeer
Disk quotas for user safeer (uid 507):
Filesystem blocks quota limit grace files quota limit grace
/dev/hda5 5008* 4096 5010 6days 5 0 0

Similarly use -g option instead of -u to find the quota of a group
Instead of individual quota reports, you can get the quota report for the entire filesystem:
[root@LinuxBox1 ~]#repquota /home
*** Report for user quotas on device /dev/hda5
Block grace time: 7days; Inode grace time: 7days
Block limits File limits
User used soft hard grace used soft hard grace
----------------------------------------------------------------------
root -- 1172676 0 0 6109 0 0
vinu -- 239188 0 0 4347 0 0
safeer +- 5008 4096 5010 6days 5 0 0
nebu +- 5120 4096 5120 6days 4 0 0

This will list each users current usage as well as the limit for usage. Using repquota with -g option will give the group quota report. Use '-a' option to list quota of all patitions.

You can use the command warnquota to sent mail to all users who have exceeded quota. The message sent can be customeised by editing the file /etc/warnquota.conf. You should set an administrator for each group so that this administrators will be emailed when their groups exceed the quota (use command: warnquota -g). You can do this by editting /etc/quotagrpadmins, syntax of the file is group:admin_user.