Disk Quota System Overview

The disk quota system allows system administrators to control the number of files and data blocks that can be allocated to users or groups. The following sections provide further information about the disk quota system, its implementation, and use:

• Understanding the Disk Quota System
• Recovering from Over-Quota Conditions
• Implementing the Disk Quota System

Understanding the Disk Quota System

The disk quota system, based on the Berkeley Disk Quota System, provides an effective way to control the use of disk space. The quota system can be defined for individual users or groups, and is maintained for each journaled file system.

The disk quota system establishes limits based on three parameters that can be changed with the edquota command:

• User's or group's soft limits
• User's or group's hard limits
• Quota grace period

The soft limit defines the number of 1KB disk blocks or files below which the user should remain. The hard limit defines the maximum amount of disk blocks or files the user can accumulate under the established disk quotas. The quota grace period allows the user to exceed the soft limit for a short period of time (the default value is one week). If the user fails to reduce usage below the soft limit during the specified time, the system will interpret the soft limit as the maximum allocation allowed, and no further storage will be allocated to the user. The user can reset this condition by removing enough files to reduce usage below the soft limit.

The disk quota system tracks user and group quotas in the quota.user and quota.group files that reside in the root directories of file systems enabled with quotas. These files are created with the quotacheck and edquota commands and are readable with the quota commands.

Recovering from Over-Quota Conditions

There are several methods available to reduce file system usage when you have exceeded quota limits:

• Abort the current process that caused the file system to reach its limit, remove surplus files to bring the limit below quota, and retry the failed program.
• If you are running an editor such as vi, use the shell escape sequence to check your file space, remove surplus files, and return without losing your edited file. Alternatively, if you are using the C or Korn shells, you can suspend the editor with the Ctrl-Z key sequence, issue the file system commands, and then return with the fg (foreground) command.
• Temporarily write the file to a file system where quota limits have not been exceeded, delete surplus files, and then return the file to the correct file system.

Implementing the Disk Quota System

You should consider implementing the disk quota system under the following conditions:

• Your system has limited disk space.
• You require more file system security.
• Your disk-usage levels are large, such as at many universities.

If these conditions do not apply to your environment, you may not want to create disk-usage limits by implementing the disk quota system.

Typically, only those file systems that contain user home directories and files require disk quotas. The disk quota system works only with the journaled file system.

Note: It is recommended that disk quotas not be established for the /tmp file system.