The /usr Hierarchy
/usr is the second major section of the filesystem. /usr is shareable, read-only data. That means that /usr should be shareable between various FHS-compliant hosts and must not be written to. Any information that is host-specific or varies with time is stored elsewhere.
Large software packages must not use a direct subdirectory under the /usr hierarchy.
Requirements
The following directories, or symbolic links to directories, are required in /usr.
Directory Description bin Most user commands include Header files included by C programs lib Libraries local Local hierarchy (empty after main installation) sbin Non-vital system binaries share Architecture-independent data
Specific Options
Directory Description X11R6 XWindow System, version 11 release 6 (optional) games Games and educational binaries (optional) lib<qual> Alternate Format Libraries (optional) src Source code (optional)
An exception is made for the X Window System because of considerable precedent and widely-accepted practice.
The following symbolic links to directories may be present. This possibility is based on the need to preserve compatibility with older systems until all implementations can be assumed to use the /var hierarchy.
/usr/spool -> /var/spool /usr/tmp -> /var/tmp /usr/spool/locks -> /var/lock
Once a system no longer requires any one of the above symbolic links, the link may be removed, if desired.
/usr/X11R6 : X Window System, Version 11 Release 6 (optional)
This hierarchy is reserved for the X Window System, version 11 release 6, and related files.
To simplify matters and make XFree86 more compatible with the X Window System on other systems, the following symbolic links must be present if /usr/X11R6 exists:
/usr/bin/X11 -> /usr/X11R6/bin /usr/lib/X11 -> /usr/X11R6/lib/X11 /usr/include/X11 -> /usr/X11R6/include/X11
In general, software must not be installed or managed via the above symbolic links. They are intended for utilization by users only. The difficulty is related to the release version of the X Window System — in transitional periods, it is impossible to know what release of X11 is in use.
Specific Options
Host-specific data in /usr/X11R6/lib/X11 should be interpreted as a demonstration file. Applications requiring information about the current host must reference a configuration file in /etc/X11, which may be linked to a file in /usr/X11R6/lib. [1]
/usr/bin : Most user commands
This is the primary directory of executable commands on the system.
Specific Options
The following directories, or symbolic links to directories, must be in /usr/bin, if the corresponding subsystem is installed:
Directory Description mh Commands for the MH mail handling system (optional)
/usr/bin/X11 must be a symlink to /usr/X11R6/bin if the latter exists.
The following files, or symbolic links to files, must be in /usr/bin, if the corresponding subsystem is installed:
Command Description perl The Practical Extraction and Report Language (optional) python The Python interpreted language (optional) tclsh Simple shell containing Tcl interpreter (optional) wish Simple Tcl/Tk windowing shell (optional) expect Program for interactive dialog (optional)
Tip Rationale
Because shell script interpreters (invoked with #!<path> on the first line of a shell script) cannot rely on a path, it is advantageous to standardize their locations. The Bourne shell and C-shell interpreters are already fixed in /bin, but Perl, Python, and Tcl are often found in many different places. They may be symlinks to the physical location of the shell interpreters.
/usr/include : Directory for standard include files.
This is where all of the system's general-use include files for the C programming language should be placed.
Specific Options
The following directories, or symbolic links to directories, must be in /usr/include, if the corresponding subsystem is installed:
Directory Description bsd BSD compatibility include files (optional)
The symbolic link /usr/include/X11 must link to /usr/X11R6/include/X11 if the latter exists.
/usr/lib : Libraries for programming and packages
/usr/lib includes object files, libraries, and internal binaries that are not intended to be executed directly by users or shell scripts. [2]
Applications may use a single subdirectory under /usr/lib. If an application uses a subdirectory, all architecture-dependent data exclusively used by the application must be placed within that subdirectory. [3]
Specific Options
For historical reasons, /usr/lib/sendmail must be a symbolic link to /usr/sbin/sendmail if the latter exists. [4]
If /lib/X11 exists, /usr/lib/X11 must be a symbolic link to /lib/X11, or to whatever /lib/X11 is a symbolic link to. [5]
/usr/lib<qual> : Alternate format libraries (optional)
/usr/lib<qual> performs the same role as /usr/lib for an alternate binary format, except that the symbolic links /usr/lib<qual>/sendmail and /usr/lib<qual>/X11 are not required. [6]
/usr/local : Local hierarchy
The /usr/local hierarchy is for use by the system administrator when installing software manually, without using Portage. IIt may be used for programs and data that are shareable amongst a group of hosts, but not found in /usr.
Locally installed software must be placed within /usr/local rather than /usr unless it is being installed to replace or upgrade software in /usr. [7]
Requirements
The following directories, or symbolic links to directories, must be in /usr/local:
- bin
- Local binaries
- etc
- Host-specific system configuration for local binaries
- games
- Local game binaries
- include
- Local C header files
- lib
- Local libraries
- man
- Local online manuals
- sbin
- Local system binaries
- share
- Local architecture-independent hierarchy
- src
- Local source code
No other directories, except those listed below, may be in /usr/local after first installing a FHS-compliant system.
Specific Options
If directories /lib<qual> or /usr/lib<qual> exist, the equivalent directories must also exist in /usr/local.
/usr/local/etc may be a symbolic link to /etc/local.
Tip Rationale
The consistency of /usr/local/etc is beneficial to installers, and is already used in other systems. As all of /usr/local needs to be backed up to reproduce a system, it introduces no additional maintenance overhead, but a symlink to /etc/local is suitable if systems want alltheir configuration under one hierarchy.
Note that /usr/etc is still not allowed: programs in /usr should place configuration files in /etc.
The requirements for the contents of this directory are the same as /usr/share. The only additional constraint is that /usr/local/share/man and /usr/local/man directories must be synonomous (usually this means that one of them must be a symbolic link). [8]
/usr/sbin : Non-essential standard system binaries
This directory contains any non-essential binaries used exclusively by the system administrator. System administration programs that are required for system repair, system recovery, mounting /usr, or other essential functions must be placed in /sbin instead. [9]
The /usr/share hierarchy is for all read-only architecture independent data files. [10]
This hierarchy is intended to be shareable among all architecture platforms of a given OS; thus, for example, a site with i386, Alpha, and PPC platforms might maintain a single /usr/share directory that is centrally-mounted. Note, however, that /usr/share is generally not intended to be shared by different OSes or by different releases of the same OS.
Any program or package which contains or requires data that doesn't need to be modified should store that data in /usr/share (or /usr/local/share, if installed locally). It is recommended that a subdirectory be used in /usr/share for this purpose.
Game data stored in /usr/share/games must be purely static data. Any modifiable files, such as score files, game play logs, and so forth, should be placed in /var/games.
Requirements
The following directories, or symbolic links to directories, must be in /usr/share
Directory Description man Online manuals misc Miscellaneous architecture-independent data
Specific Options
The following directories, or symbolic links to directories, must be in /usr/share, if the corresponding subsystem is installed:
Directory Description dict Word lists (optional) doc Miscellaneous documentation (optional) games Static data files for /usr/games (optional) info GNU Info system s primary directory (optional) locale Locale information (optional) nls Message catalogs for Native language support (optional) sgml SGML data (optional) terminfo Directories for terminfo database (optional) tmac troff macros not distributed with groff (optional) xml XML data (optional) zoneinfo Timezone information and configuration (optional)
It is recommended that application-specific, architecture-independent directories be placed here. Such directories include groff, perl, ghostscript, texmf, and kbd (Linux) or syscons (BSD). They may, however, be placed in /usr/lib for backwards compatibility, at the distributor's discretion. Similarly, a /usr/lib/games hierarchy may be used in addition to the /usr/share/games hierarchy if the distributor wishes to place some game data there.
This directory is the home for word lists on the system; Traditionally this directory contains only the English words file, which is used by look(1) and various spelling programs. words may use either American or British spelling.
Tip Rationale
The reason that only word lists are located here is that they are the only files common to all spell checkers.
Specific Options
The following files, or symbolic links to files, must be in /usr/share/dict, if the corresponding subsystem is installed:
File Description words List of English words (optional)
Sites that require both American and British spelling may link words to /usr/share/dict/american-english or /usr/share/dict/british-english.
Word lists for other languages may be added using the English name for that language, e.g., /usr/share/dict/french, /usr/share/dict/danish, etc. These should, if possible, use an ISO 8859 character set which is appropriate for the language in question; if possible the Latin1 (ISO 8859-1) character set should be used (this is often not possible).
Other word lists must be included here, if present.
This section details the organization for manual pages throughout the system, including /usr/share/man. Also refer to the section on /var/cache/man.
The primary <mandir> of the system is /usr/share/man. /usr/share/man contains manual information for commands and data under the / and /usr filesystems. [11]
Manual pages are stored in <mandir>/<locale>/man
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