Disk quota system concept

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 (JFS and JFS2).

The disk quota system establishes limits based on the following parameters that can be changed with the edquota command for JFS file systems and the j2edlimit command for JFS2 file systems:

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

The soft limit defines the number of 1 KB disk blocks or files the user or group will be allowed to use during normal operations. 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.