Disk space can be restricted by implementing disk quotas which
alert a system administrator is alerted 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 kind of flexibility makes it possible to give
each user a small quota to handle "personal" files (such as email
and reports), while allowing the projects they work on to have more
sizable quotas (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.
To implement disk quotas, use the following steps:
-
Enable quotas per file system by modifying the /etc/fstab file.
-
Remount the file system(s).
-
Create the quota database files and generate the disk usage
table.
-
Assign quota policies.
Each of these steps is discussed in detail in the following
sections.
As root, using a text editor, edit the /etc/fstab file. Add the usrquota and/or grpquota
options to the file systems that require 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. Although not ideal, the root
(/) partition (the installation default
created partition) can be used for setting quota policies in the
/etc/fstab file.
|
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:
If the file system is currently in use, the easiest method for
remounting the file system is to reboot the system.
After each quota-enabled file system is remounted, the system is
capable of working with disk quotas. However, the file system
itself is not yet ready to support quotas. The next step is to 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. For example, if user and group
quotas are enabled for the /home file
system, create the files in the /home
directory:
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:
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.
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:
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) 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.
A hard 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 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. 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:
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:
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, save the file, and then configure the
quota.
To verify that the group quota has been set, use the
command:
To assign quotas based on each file system enabled for quotas,
use the command:
Like the other edquota commands, this
one opens the current quotas for the file system in the text
editor:
Grace period before enforcing soft limits for users:
Time units may be: days, hours, minutes, or seconds
Filesystem Block grace period Inode grace period
/dev/mapper/VolGroup00-LogVol02 7days 7days
|
Change the block grace period or inode grace period, save the
changes to the file, and exit the text editor.
