The FHS offers a significant level of detail describing the exact locations of files, using rationale derived from the static/variable and sharable/nonsharable definitions. However, knowledge of the location of every file is not necessary or required for Exam 101. This section discusses the major portions of the FHS directory hierarchy overall, with specific example files offered as illustrations.
Although the FHS is a defining document for the Linux filesystem, it does not follow that all directories described in the FHS will be present in all Linux installations. Some directory locations cited in the FHS are package-dependent or open to customization by the vendor.
The root filesystem is located at the top of the entire directory hierarchy. The FHS defines these goals for the root filesystem:
It must contain utilities and files sufficient to boot the operating system, including the ability to mount other filesystems. This includes utilities, device files, configuration, boot loader information, and other essential start-up data.
It should contain the utilities needed by the system administrator to repair or restore a damaged system.
It should be relatively small. Small partitions are less likely to be corrupted due to a system crash or power failure than large ones are. In addition, the root partition should contain nonsharable data to maximize the remaining disk space for sharable data.
Software should not create files or directories in the root filesystem. ...