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Installation

First, control of the user's consumption of disk space. If /home is contained

on the root partition the user disk consumption can consume all but 5% of the

available disk space choking off all disk use except by the root account. This

5% is set aside for root privilege specifically so this event would not kill system

activity. Root can then remove the offending files and return the machine to

usefulness. Placing /home on another partition allows that partition to contain

only the space you wish to give to user activity, rather than the complete root

partition. This means that even when users have exhausted their disk space

the rest of the system has plenty to continue servicing other processes needs.

The system continues happily along, oblivious of the plight of the poor user.

This is, of course, very useful when the same platform is supporting both user

activity and serving web pages. Having users plug up the web server is highly

undesirable. There are also other solutions to this problem, such as the quota

package, found in the admin section but, this is a complete hardware solution

requiring no additional software or configuration management.

Second, control over the contents of /usr. Many systems do this by making

/usr read only. The simplest way to accomplish this is to put /usr on its own

partition and mount it read only. When the system administrator wants to

add something to /usr the partition gets re mounted read write, the changes

get made and the partition gets re mounted read only. This partition could

just as easily be on a CD ROM which would guarantee the read only nature

of the file system. Of course any changes to /usr would require re mastering

the CD.

Similar arguments can be made for placing /var, /tmp, and possibly others on

their own partition. Controlling use of these areas by limiting their disk space

to a specific partition size is a common way to manage disk resources. Let's

see if this can be made clearer with a couple of examples. These examples will

all be based on a 2 GB IDE hard disk, but the principles translate to SCSI and

other disk devices as well. The first example is very simple, while the second

is much more complex.