Full Generic System V ABI

File System Structure and ContentsThe file system on an ABI-conforming system is a tree-like structure. All ABIconformingsystems have a ‘‘root’’ (or /) directory that contains a / u s r directory,a / v a r directory, a / e t c directory, and a / o p t directory.The following are primary characteristics of the file system tree:/ This directory contains machine-specific files and executable filesrequired to boot the system, to check, and to repair file systems.It also contains other directories. No application may install filesin the / directory./ e t c This directory subtree contains machine-specific configurationfiles and some executable files, including one command usedduring application package installation. Application programsshould never execute applications in this directory subtree, andshould never access directly any data files in this subtree, exceptfor the files they install themselves in the / e t c / o p t directory./ o p t This subtree contains add-on software application packages. E/ t m p This directory contains temporary files created by system utili- Eties./ u s r This subtree contains only sharable files and executable files providedby the system./ v a r This subtree contains files that change.Applications should install or create files only in designated places within the tree,as noted below.This section describes those aspects of the root, user and var file systems thatapplication programs can rely on being present.Root subtreeThe / directory contains executable programs and other files necessary to boot thesystem, check and repair file systems, and files describing the identity of a particularmachine. The following components must be present in the root file system:File System Structure and Contents 9-3