/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.

The following directories, or symbolic links to directories, are required in /usr. Directory Description bin Most user commands lib Libraries local Local hierarchy (empty after main installation) sbin Non-vital system binaries share Architecture-independent data

DirectoryDescription games Games and educational binaries (optional) include Header files included by C programs libexec Binaries run by other programs (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 distribution 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.

This is the primary directory of executable commands on the system.

There must be no subdirectories in /usr/bin.

The following files, or symbolic links to files, must be in /usr/bin, if the corresponding subsystem is installed: CommandDescription 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) In many executable scripts, the interpreter to be invoked to execute the script is specified using #!path_to_interpreter on the first line of a script. To make such scripts portable among different systems, it is advantageous to standardize the interpreter locations. The shell interpreter is already fixed in /bin by this specification, but interpreters for Perl, Python, Tcl and expect may be installed in various places. The locations specified here may be implemented as symbolic links to the physical location of the interpreters.

This is where all of the system's general-use include files for the C programming language should be placed.

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)

/usr/lib includes object files and libraries. Miscellaneous architecture-independent application-specific static files and subdirectories must be placed in /usr/share. On some systems, it may also include internal binaries that are not intended to be executed directly by users or shell scripts. See below, in the /usr/libexec section, for a discussion of /usr/lib vs. /usr/libexec for executable binaries. 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. For example, the perl5 subdirectory for Perl 5 modules and libraries.

For historical reasons, /usr/lib/sendmail must be a symbolic link which resolves to the sendmail-compatible command provided by the system's mail transfer agent, if the latter exists. Some executable commands such as makewhatis and sendmail have also been traditionally placed in /usr/lib. makewhatis is an internal binary and must be placed in a binary directory; users access only catman. Newer sendmail binaries are now placed by default in /usr/sbin. Additionally, systems using a sendmail-compatible mail transfer agent must provide /usr/sbin/sendmail as the sendmail command, either as the executable itself or as a symlink to the appropriate executable. Host-specific data for the X Window System must not be stored in /usr/lib/X11. Host-specific configuration files such as xorg.conf must be stored in /etc/X11. This includes configuration data such as system.twmrc even if it is only made a symbolic link to a more global configuration file (probably in /usr/lib/X11).

/usr/libexec includes internal binaries that are not intended to be executed directly by users or shell scripts. Applications may use a single subdirectory under /usr/libexec. Applications which use /usr/libexec in this way must not also use /usr/lib to store internal binaries, though they may use /usr/lib for the other purposes documented here. Some previous versions of this document did not support /usr/libexec, despite it being standard practice in a number of environments. See, for example, the "GNU Coding Standards" from the Free Software Foundation. To accomodate this restriction, it became common practice to use /usr/lib instead. Either practice is now acceptable, but each application must choose one way or the other to organize itself.

/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. The case where /usr/lib and /usr/lib<qual> are the same (one is a symbolic link to the other) these files and the per-application subdirectories will exist.

The /usr/local hierarchy is for use by the system administrator when installing software locally. It needs to be safe from being overwritten when the system software is updated. It 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. Software placed in / or /usr may be overwritten by system upgrades (though we recommend that distributions do not overwrite data in /etc under these circumstances). For this reason, local software must not be placed outside of /usr/local without good reason.

The following directories, or symbolic links to directories, must be in /usr/local Directory Description 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.

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. 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 all their configuration under one hierarchy. Note that /usr/etc is still not allowed: programs in /usr should place configuration files in /etc. If the directory /usr/share/color exists as specified in this document, then the directory /usr/local/share/color must also exist, governed by the same rules as /usr/share/color. This usage allows the sysadmin a place to install color profiles manually when necessary.

The requirements for the contents of this directory are the same as for /usr/share.

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. Locally installed system administration programs should be placed in /usr/local/sbin.

There must be no subdirectories in /usr/sbin.

The /usr/share hierarchy is for all read-only architecture independent data files. Much of this data originally lived in /usr (man, doc) or /usr/lib (dict, terminfo, zoneinfo). 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. Applications using a single file may use /usr/share/misc. 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.

The following directories, or symbolic links to directories, must be in /usr/share Directory Description man Online manuals misc Miscellaneous architecture-independent data

The following directories, or symbolic links to directories, must be in /usr/share, if the corresponding subsystem is installed: Directory Description color Color management information (optional) dict Word lists (optional) doc Miscellaneous documentation (optional) games Static data files for /usr/games (optional) info Primary directory for GNU Info system (optional) locale Locale information (optional) nls Message catalogs for Native language support (optional) ppd Printer definitions (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 ICC color management files installed by the system.

The following directories must be in /usr/share/color, if the corresponding subsystem is installed: Directory Description icc ICC color profiles (optional) The top-level directory /usr/share/color must not contain any files; all files should be in subdirectories of /usr/share/color.

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. The reason that only word lists are located here is that they are the only files common to all spell checkers.

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 a character set based on Unicode, with the UTF-8 character set being the preferred option. 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. Obviously, there are no manual pages in / because they are not required at boot time nor are they required in emergencies. Really. Manual pages are stored in <mandir>/<locale>/man<section>/<arch>. An explanation of <mandir>, <locale>, <section>, and <arch> is given below. A description of each section follows: man1: User programs Manual pages that describe publicly accessible commands are contained in this chapter. Most program documentation that a user will need to use is located here. man2: System calls This section describes all of the system calls (requests for the kernel to perform operations). man3: Library functions and subroutines Section 3 describes program library routines that are not direct calls to kernel services. This and chapter 2 are only really of interest to programmers. man4: Special files Section 4 describes the special files, related driver functions, and networking support available in the system. Typically, this includes the device files found in /dev and the kernel interface to networking protocol support. man5: File formats The formats for many data files are documented in the section 5. This includes various include files, program output files, and system files. man6: Games This chapter documents games, demos, and generally trivial programs. Different people have various notions about how essential this is. man7: Miscellaneous Manual pages that are difficult to classify are designated as being section 7. The troff and other text processing macro packages are found here. man8: System administration Programs used by system administrators for system operation and maintenance are documented here. Some of these programs are also occasionally useful for normal users.

The following directories, or symbolic links to directories, must be in /usr/share/<mandir>/<locale>, unless they are empty: For example, if /usr/share/man has no manual pages in section 4 (Devices), then /usr/share/man/man4 may be omitted. Directory Description man1 User programs (optional) man2 System calls (optional) man3 Library calls (optional) man4 Special files (optional) man5 File formats (optional) man6 Games (optional) man7 Miscellaneous (optional) man8 System administration (optional) The component <section> describes the manual section. Provisions must be made in the structure of /usr/share/man to support manual pages which are written in different (or multiple) languages. These provisions must take into account the storage and reference of these manual pages. Relevant factors include language (including geographical-based differences), and character code set. This naming of language subdirectories of /usr/share/man is based on Appendix E of the POSIX 1003.1 standard which describes the locale identification string — the most well-accepted method to describe a cultural environment. The <locale> string is: <language>[_<territory>][.<character-set>][,<version>] The <language> field must be taken from ISO 639 (a code for the representation of names of languages). It must be two characters wide and specified with lowercase letters only. The <territory> field must be the two-letter code of ISO 3166 (a specification of representations of countries), if possible. (Most people are familiar with the two-letter codes used for the country codes in email addresses.) It must be two characters wide and specified with uppercase letters only. A major exception to this rule is the United Kingdom, which is `GB' in the ISO 3166, but `UK' for most email addresses. The <character-set> field must represent the standard describing the character set. If the ­<character-set> field is just a numeric specification, the number represents the number of the international standard describing the character set. It is recommended that this be a numeric representation if possible (ISO standards, especially), not include additional punctuation symbols, and that any letters be in lowercase. A parameter specifying a <version> of the profile may be placed after the ­<character-set> field, delimited by a comma. This may be used to discriminate between different cultural needs; for instance, dictionary order versus a more systems-oriented collating order. This standard recommends not using the <version> field, unless it is necessary. Systems which use a unique language and code set for all manual pages may omit the <locale> substring and store all manual pages in <mandir>. For example, systems which only have English manual pages coded with ASCII, may store manual pages (the man<section> directories) directly in /usr/share/man. (That is the traditional circumstance and arrangement, in fact.) Countries for which there is a well-accepted standard character code set may omit the ­<character-set> field, but it is strongly recommended that it be included, especially for countries with several competing standards. Various examples: Language Territory Character Set Directory English — ASCII /usr/share/man/en English United Kingdom Unicode UTF-8 /usr/share/man/en_GB.10646 English United States ASCII /usr/share/man/en_US French Canada ISO 8859-1 /usr/share/man/fr_CA.88591 French France ISO 8859-1 /usr/share/man/fr_FR.88591 German Germany ISO 646 /usr/share/man/de_DE.646 German Germany ISO 6937 /usr/share/man/de_DE.6937 German Germany ISO 8859-1 /usr/share/man/de_DE.88591 German Switzerland ISO 646 /usr/share/man/de_CH.646 Japanese Japan JIS /usr/share/man/ja_JP.jis Japanese Japan SJIS /usr/share/man/ja_JP.sjis Japanese Japan UJIS (or EUC-J) /usr/share/man/ja_JP.ujis Japanese Japan Unicode UTF-16 /usr/share/man/ja_JP.10646 Similarly, provision must be made for manual pages which are architecture-dependent, such as documentation on device-drivers or low-level system administration commands. These must be placed under an <arch> directory in the appropriate man<section> directory; for example, a man page for the i386 ctrlaltdel(8) command might be placed in /usr/share/man/<locale>/man8/i386/ctrlaltdel.8. Manual pages for commands and data under /usr/local are stored in /usr/local/man or /usr/local/share/man. All manual page hierarchies in the system must have the same structure as /usr/share/man, as this structure is expected by commands which consume manual page content. /usr/local/man is deprecated and may be dropped in a future version of this specification. The cat page sections (cat<section>) containing formatted manual page entries are also found within subdirectories of <mandir>/<locale>, but are not required nor may they be distributed in lieu of nroff source manual pages. The numbered sections "1" through "8" are traditionally defined. In general, the file name for manual pages located within a particular section end with .<section>. In addition, some large sets of application-specific manual pages have an additional suffix appended to the manual page filename. For example, the MH mail handling system manual pages must have mh appended to all MH manuals. All X Window System manual pages must have an x appended to the filename. The practice of placing various language manual pages in appropriate subdirectories of /usr/share/man also applies to the other manual page hierarchies, such as /usr/local/man. (This portion of the standard also applies later in the section on the optional /var/cache/man structure.)

This directory contains miscellaneous architecture-independent files which don't require a separate subdirectory under /usr/share.

The following files, or symbolic links to files, must be in /usr/share/misc, if the corresponding subsystem is installed: File Description ascii ASCII character set table (optional) termcap Terminal capability database (optional) termcap.db Terminal capability database (optional) Other (application-specific) files may appear here, but a distributor may place them in /usr/lib at their discretion. Some such files include: airport, birthtoken, eqnchar, getopt, gprof.callg, gprof.flat, inter.phone, ipfw.samp.filters, ipfw.samp.scripts, keycap.pcvt, mail.help, mail.tildehelp, man.template, map3270, mdoc.template, more.help, na.phone, nslookup.help, operator, scsi_modes, sendmail.hf, style, units.lib, vgrindefs, vgrindefs.db, zipcodes. Historically, the magic file was placed in /usr/share/misc, but modern variants of the file command use several files and place them in /usr/share/file. For compatibility, distribution may create a symlink at /usr/share/misc/magic, pointing to /usr/share/file/magic.

/usr/share/ppd contains PostScript Printer Definition (PPD) files, which are used as descriptions of printer drivers by many print systems. PPD files may be placed in this directory, or in a subdirectory.

/usr/share/sgml contains architecture-independent files used by SGML applications, such as ordinary catalogs (not the centralized ones, see /etc/sgml), DTDs, entities, or style sheets.

The following directories, or symbolic links to directories, must be in /usr/share/sgml, if the corresponding subsystem is installed: Directory Description docbook docbook DTD (optional) tei tei DTD (optional) html html DTD (optional) mathml mathml DTD (optional) Other files that are not specific to a given DTD may reside in their own subdirectory.

/usr/share/xml contains architecture-independent files used by XML applications, such as ordinary catalogs (not the centralized ones, see /etc/sgml), DTDs, entities, or style sheets.

The following directories, or symbolic links to directories, must be in /usr/share/xml, if the corresponding subsystem is installed: Directory Description docbook docbook XML DTD (optional) xhtml XHTML DTD (optional) mathml MathML DTD (optional)

Source code may be placed in this subdirectory, only for reference purposes. Generally, source should not be built within this hierarchy.