Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Scaricare il pdf (Pagina 17)

Chapter 1.

File System Structure

1.1. Why Share a Common Structure?

An operating system’s ﬁle system structure is its most basic level of organization. Almost all of the

ways an operating system interacts with its users, applications, and security model are dependent upon

the way it stores its ﬁles on a primary storage device (normally a hard disk drive). It is crucial for a

variety of reasons that users, as well as programs at the time of installation and beyond, be able to

refer to a common guideline to know where to read and write their binary, conﬁguration, log, and

other necessary ﬁles.

A ﬁle system can be seen in terms of two different logical categories of ﬁles:

• Shareable vs. unshareable ﬁles

• Variable vs. static ﬁles

Shareable ﬁles are those that can be accessed by various hosts; unshareable ﬁles are not available

to any other hosts. Variable ﬁles can change at any time without system administrator intervention

(whether active or passive); static ﬁles, such as documentation and binaries, do not change without an

action from the system administrator or an agent that the system administrator has placed in motion

to accomplish that task.

The reason for looking at ﬁles in this way has to do with the type of permissions given to the directory

that holds them. The way in which the operating system and its users need to utilize the ﬁles deter-

mines the directory where those ﬁles should be placed, whether the directory is mounted read-only

or read-write, and the level of access allowed on each ﬁle. The top level of this organization is cru-

cial, as the access to the underlying directories can be restricted or security problems may manifest

themselves if the top level is left disorganized or without a widely-utilized structure.

However, simply having a structure does not mean very much unless it is a standard. Competing

structures can actually cause more problems than they ﬁx. Because of this, Red Hat has chosen the

the most widely-used ﬁle system structure and extended it only slightly to accommodate special ﬁles

used within Red Hat Linux.

1.2. Overview of File System Hierarchy Standard (FHS)

Red Hat is committed to the Filesystem Hierarchy Standard (FHS), a collaborative document that

deﬁnes the names and locations of many ﬁles and directories. We will continue to track and follow

the standard to keep Red Hat Linux FHS-compliant.

The current FHS document is the authoritative reference to any FHS-compliant ﬁle system, but the

standard leaves many areas undeﬁned or extensible. In this section, we provide an overview of the

standard and a description of the parts of the ﬁle system not covered by the standard.

The complete standard is available at:

http://www.pathname.com/fhs

Compliance with the standard means many things, but the two most important are compatibility with

other compliant systems and the ability to mount the /usr partition as read-only (because it contains

common executables and is not meant to be changed by users). Since /usr can be mounted read-only,

/usr can be mounted from the CD-ROM or from another machine via read-only NFS.

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 17