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Unit 10: File System

notes

Note The /etc/exports file specifies which file systems NFS should export (sometimes
referred to as “share”).

10.1.4 Quota management

This feature of Linux allows the system administrator to allocate a maximum amount of disk
space a user or group may use. It allows to limit the amount of disk space and/or the number
of files a user can use. It can be flexible in its adherence to the rules assigned and is applied per
filesystem. The default Linux Kernel which comes with Redhat and Fedora Core comes with
quota support compiled in.
Disk quotas are implemented on a per-file system basis. In other words, it is possible to configure
quotas for /home (assuming /home is on its own file system), while leaving /tmp without any
quotas at all.

Quotas can be set on two levels:
1. For individual users
2. For individual groups
This kind of flexibility makes it possible to give each user a small quota to handle “personal”
file (such as email, reports, etc.), 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 also
to control the number of inodes. Because inodes are used to contain file-related information, this
allows control over the number of files that can be created.
But before we can implement quotas, we should have a better understanding of how they work.
The first step in this process is to understand the manner in which disk quotas are applied. There
are three major concepts that you should understand prior to implementing disk quotas:

Hard Limit

The hard limit defines 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.

soft Limit

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.

grace period

The grace period is the time during which the soft limit may be exceeded. The grace period can be
expressed in seconds, minutes, hours, days, weeks, or months, giving the system administrator a
great deal of freedom in determining how much time to give users to get their disk usage below
their soft limit.
The quota tools package usually needs to be installed, it contains the command line tools. The
quotas are not limited per default (set to 0). The limits are set with edquota/setquota for single
user. A quota can be also duplicated to many users.

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