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System Management Concepts: Operating System and Devices

Disk Quota System Overview

Note: The information in this section is specific to POWER-based.

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

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:

The soft limit defines the number of 1 KB disk blocks or files below which the user must 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 is 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:

Implementing the Disk Quota System

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

If these conditions do not apply to your environment, you might 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: Do not establish disk quotas for the /tmp file system.

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