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.
