Configuring Disk Quotas | Disk Quotas

 Disk Quotas:

Disk space can be restricted by implementing disk quotas which alert a system administrator before a user consumes too much disk space or a partition becomes full..

Disk quotas can be configured for individual users as well as user groups. This makes it possible to manage the space allocated for user-specific files (such as email) separately from the space allocated to the projects a user works on (assuming the projects are given their own groups).

In addition, quotas can be set not just to control the number of disk blocks consumed but to control the number of inodes (data structures that contain information about files in UNIX file systems).

Because inodes are used to contain file-related information, this allows control over the number of files that can be created.

The quota RPM must be installed to implement disk quotas. 

Configuring Disk Quotas

To implement disk quotas, use the following steps:

1. Enable quotas per file system by modifying the /etc/fstab file.
2. Remount the file system(s).
3. Create the quota database files and generate the disk usage table.
4. Assign quota policies.

Each of these steps is discussed in detail in the following sections.

Enabling Quotas

As root, using a text editor, edit the /etc/fstab file.

Edit /etc/fstab

For example, to use the text editor vim type the following:

# vim /etc/fstab

Add the usrquota and/or grpquota options to the file systems that require quotas:

Add quotas

/dev/VolGroup00/LogVol00 /         ext3    defaults        1 1 
LABEL=/boot              /boot     ext3    defaults        1 2 
none                     /dev/pts  devpts  gid=5,mode=620  0 0 
none                     /dev/shm  tmpfs   defaults        0 0 
none                     /proc     proc    defaults        0 0 
none                     /sys      sysfs   defaults        0 0 
/dev/VolGroup00/LogVol02 /home     ext3    defaults,usrquota,grpquota  1 2 
/dev/VolGroup00/LogVol01 swap      swap    defaults        0 0 . . .

In this example, the /home file system has both user and group quotas enabled.

Note

The following examples assume that a separate /home partition was created during the installation of Red Hat Enterprise Linux. The root (/) partition can be used for setting quota policies in the /etc/fstab file.

Remounting the File Systems

After adding the usrquota and/or grpquota options, remount each file system whose fstab entry has been modified. If the file system is not in use by any process, use one of the following methods:

• Issue the umount command followed by the mount command to remount the file system. Refer to the man page for both umount and mount for the specific syntax for mounting and unmounting various file system types.
• Issue the mount -o remount file-system command (where file-system is the name of the file system) to remount the file system. For example, to remount the /home file system, the command to issue is mount -o remount /home.

If the file system is currently in use, the easiest method for remounting the file system is to reboot the system.

Creating the Quota Database Files

After each quota-enabled file system is remounted run the quotacheck command.

The quotacheck command examines quota-enabled file systems and builds a table of the current disk usage per file system. The table is then used to update the operating system's copy of disk usage. In addition, the file system's disk quota files are updated.

To create the quota files (aquota.user and aquota.group) on the file system, use the -c option of the quotacheck command.

Create quota files

For example, if user and group quotas are enabled for the /home file system, create the files in the /home directory:

# quotacheck -cug /home

The -c option specifies that the quota files should be created for each file system with quotas enabled, the -u option specifies to check for user quotas, and the -g option specifies to check for group quotas.

If neither the -u or -g options are specified, only the user quota file is created. If only -g is specified, only the group quota file is created.

After the files are created, run the following command to generate the table of current disk usage per file system with quotas enabled:

# quotacheck -avug

The options used are as follows:

a

Check all quota-enabled, locally-mounted file systems

v

Display verbose status information as the quota check proceeds

u

Check user disk quota information

g

Check group disk quota information

After quotacheck has finished running, the quota files corresponding to the enabled quotas (user and/or group) are populated with data for each quota-enabled locally-mounted file system such as /home.

Assigning Quotas per User

The last step is assigning the disk quotas with the edquota command.

To configure the quota for a user, as root in a shell prompt, execute the command:

# edquota username 

Perform this step for each user who needs a quota. For example, if a quota is enabled in /etc/fstab for the /home partition (/dev/VolGroup00/LogVol02 in the example below) and the command edquota testuser is executed, the following is shown in the editor configured as the default for the system:

Disk quotas for user testuser (uid 501):   
Filesystem                blocks     soft     hard    inodes   soft   hard   
/dev/VolGroup00/LogVol02  440436        0        0     37418      0      0

Note

The text editor defined by the EDITOR environment variable is used by edquota. To change the editor, set the EDITOR environment variable in your ~/.bash_profile file to the full path of the editor of your choice.

The first column is the name of the file system that has a quota enabled for it. The second column shows how many blocks the user is currently using. The next two columns are used to set soft and hard block limits for the user on the file system. The inodes column shows how many inodes the user is currently using. The last two columns are used to set the soft and hard inode limits for the user on the file system.

The hard block limit is the absolute maximum amount of disk space that a user or group can use. Once this limit is reached, no further disk space can be used.

The soft block limit defines the maximum amount of disk space that can be used. However, unlike the hard limit, the soft limit can be exceeded for a certain amount of time.

That time is known as the grace period. The grace period can be expressed in seconds, minutes, hours, days, weeks, or months.

If any of the values are set to 0, that limit is not set. In the text editor, change the desired limits.

Change desired limits

For example:

Disk quotas for user testuser (uid 501):   
Filesystem                blocks     soft     hard   inodes   soft   hard   
/dev/VolGroup00/LogVol02  440436   500000   550000    37418      0      0

To verify that the quota for the user has been set, use the command:

# quota username
Disk quotas for user username (uid 501): 
   Filesystem  blocks   quota   limit   grace   files   quota   limit   grace
     /dev/sdb    1000*   1000    1000               0       0       0

Assigning Quotas per Group

Quotas can also be assigned on a per-group basis. For example, to set a group quota for the devel group (the group must exist prior to setting the group quota), use the command:

# edquota -g devel

This command displays the existing quota for the group in the text editor:

Disk quotas for group devel (gid 505):   
Filesystem                blocks    soft     hard    inodes    soft    hard   
/dev/VolGroup00/LogVol02  440400       0        0     37418       0       0

Modify the limits, then save the file.

To verify that the group quota has been set, use the command:

# quota -g devel

Setting the Grace Period for Soft Limits

If a given quota has soft limits, you can edit the grace period (i.e. the amount of time a soft limit can be exceeded) with the following command:

# edquota -t

This command works on quotas for inodes or blocks, for either users or groups.

Important

While other edquota commands operate on quotas for a particular user or group, the -t option operates on every file system with quotas enabled. 

Managing Disk Quotas

If quotas are implemented, they need some maintenance — mostly in the form of watching to see if the quotas are exceeded and making sure the quotas are accurate.

Of course, if users repeatedly exceed their quotas or consistently reach their soft limits, a system administrator has a few choices to make depending on what type of users they are and how much disk space impacts their work. The administrator can either help the user determine how to use less disk space or increase the user's disk quota.

Enabling and Disabling

It is possible to disable quotas without setting them to 0. To turn all user and group quotas off, use the following command:

# quotaoff -vaug 

If neither the -u or -g options are specified, only the user quotas are disabled. If only -g is specified, only group quotas are disabled. The -v switch causes verbose status information to display as the command executes.

To enable quotas again, use the quotaon command with the same options.

For example, to enable user and group quotas for all file systems, use the following command:

# quotaon -vaug 

To enable quotas for a specific file system, such as /home, use the following command:

# quotaon -vug /home 

If neither the -u or -g options are specified, only the user quotas are enabled. If only -g is specified, only group quotas are enabled. 

 Reporting on Disk Quotas

Creating a disk usage report entails running the repquota utility.

Output of repquota command

For example, the command repquota /home produces this output:

*** Report for user quotas on device /dev/mapper/VolGroup00-LogVol02 
Block grace time: 7days; Inode grace time: 7days
   Block limits   File limits  
User  used soft hard grace used soft hard grace 
---------------------------------------------------------------------- 
root      --      36       0       0              4     0     0 
kristin   --     540       0       0            125     0     0 
testuser  --  440400  500000  550000          37418     0     0

To view the disk usage report for all (option -a) quota-enabled file systems, use the command:

# repquota -a 

While the report is easy to read, a few points should be explained. The -- displayed after each user is a quick way to determine whether the block or inode limits have been exceeded. If either soft limit is exceeded, a + appears in place of the corresponding -; the first - represents the block limit, and the second represents the inode limit.

The grace columns are normally blank. If a soft limit has been exceeded, the column contains a time specification equal to the amount of time remaining on the grace period. If the grace period has expired, none appears in its place. 

Keeping Quotas Accurate

When a file system fails to unmount cleanly (due to a system crash, for example), it is necessary to run quotacheck. However, quotacheck can be run on a regular basis, even if the system has not crashed. Safe methods for periodically running quotacheck include:

Ensuring quotacheck runs on next reboot

 

Note: Best method for most systems

This method works best for (busy) multiuser systems which are periodically rebooted.

As root, place a shell script into the /etc/cron.daily/ or /etc/cron.weekly/ directory—or schedule one using the crontab -e command—that contains the touch /forcequotacheck command.

This creates an empty forcequotacheck file in the root directory, which the system init script looks for at boot time. If it is found, the init script runs quotacheck. Afterward, the init script removes the /forcequotacheck file; thus, scheduling this file to be created periodically with cron ensures that quotacheck is run during the next reboot.

For more information about cron, refer to man cron. 

Running quotacheck in single user mode

An alternative way to safely run quotacheck is to boot the system into single-user mode to prevent the possibility of data corruption in quota files and run the following commands:

# quotaoff -vaug /file_system

# quotacheck -vaug /file_system

# quotaon -vaug /file_system

Running quotacheck on a running system

If necessary, it is possible to run quotacheck on a machine during a time when no users are logged in, and thus have no open files on the file system being checked. Run the command quotacheck -vaug file_system ;

this command will fail if quotacheck cannot remount the given file_system as read-only. Note that, following the check, the file system will be remounted read-write.

Warning

Running quotacheck on a live file system mounted read-write is not recommended due to the possibility of quota file corruption.

Refer to man cron for more information about configuring cron. 

References

For more information on disk quotas, refer to the man pages of the following commands:

• quotacheck
• edquota
• repquota
• quota
• quotaon
• quotaoff