Funtoo Filesystem Hierarchy
The Funtoo Filesystem Hierarchy is derived from the Filesystem Hierarchy Standard. It is updated to address deficiencies in the upstream standard, lack of Funtoo-specific descrepancies, and lack of Funtoo-specific coverage.
To be clear, this specification is modified from the upstream standard.
In accordance with the upstream documentation this statement is made:
Copyright © 1994-2004 Daniel Quinlan
Copyright © 2001-2004 Paul 'Rusty' Russell
Copyright © 2003-2004 Christopher Yeoh
Permission is granted to make and distribute verbatim copies of this standard provided the copyright and this permission notice are preserved on all copies.
Permission is granted to copy and distribute modified versions of this standard under the conditions for verbatim copying, provided also that the title page is labeled as modified including a reference to the original standard, provided that information on retrieving the original standard is included, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.
Permission is granted to copy and distribute translations of this standard into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the copyright holder.
This standard enables:
- Software to predict the location of installed files and directories, and
- Users to predict the location of installed files and directories.
We do this by:
- Specifying guiding principles for each area of the filesystem,
- Specifying the minimum files and directories required,
- Enumerating exceptions to the principles, and
- Enumerating specific cases where there has been historical conflict.
The FHS document is used by:
- Independent software suppliers to create applications which are FHS compliant, and work with distributions which are FHS complaint,
- OS creators to provide systems which are FHS compliant, and
- Users to understand and maintain the FHS compliance of a system.
The FHS document has a limited scope:
- Local placement of local files is a local issue, so FHS does not attempt to usurp system administrators.
- FHS addresses issues where file placements need to be coordinated between multiple parties such as local sites, distributions, applications, documentation, etc.
We recommend that you read a typeset version of this document rather than the plain text version. In the typeset version, the names of files and directories are displayed in a constant-width font.
Components of filenames that vary are represented by a description of the contents enclosed in "<" and ">" characters, <thus>. Electronic mail addresses are also enclosed in "<" and ">" but are shown in the usual typeface.
Optional components of filenames are enclosed in "[" and "]" characters and may be combined with the "<" and ">" convention. For example, if a filename is allowed to occur either with or without an extension, it might be represented by <filename>[.<extension>].
Variable substrings of directory names and filenames are indicated by "*".
The sections of the text marked as Rationale are explanatory and are non-normative.
This standard assumes that the operating system underlying an FHS-compliant file system supports the same basic security features found in most UNIX filesystems.
It is possible to define two independent distinctions among files: shareable vs. unshareable and variable vs. static. In general, files that differ in either of these respects should be located in different directories. This makes it easy to store files with different usage characteristics on different filesystems.
"Shareable" files are those that can be stored on one host and used on others. "Unshareable" files are those that are not shareable. For example, the files in user home directories are shareable whereas device lock files are not.
"Static" files include binaries, libraries, documentation files and other files that do not change without system administrator intervention. "Variable" files are files that are not static.
Shareable files can be stored on one host and used on several others. Typically, however, not all files in the filesystem hierarchy are shareable and so each system has local storage containing at least its unshareable files. It is convenient if all the files a system requires that are stored on a foreign host can be made available by mounting one or a few directories from the foreign host.
Static and variable files should be segregated because static files, unlike variable files, can be stored on read-only media and do not need to be backed up on the same schedule as variable files.
Historical UNIX-like filesystem hierarchies contained both static and variable files under both /usr and /etc. In order to realize the advantages mentioned above, the /var hierarchy was created and all variable files were transferred from /usr to /var. Consequently /usr can now be mounted read-only (if it is a separate filesystem). Variable files have been transferred from /etc to /var over a longer period as technology has permitted.
Here is an example of a FHS-compliant system. (Other FHS-compliant layouts are possible.)
The Root Filesystem
The contents of the root filesystem must be adequate to boot, restore, recover, and/or repair the system.
- To boot a system, enough must be present on the root partition to mount other filesystems. This includes utilities, configuration, boot loader information, and other essential start-up data. /usr, /opt, and /var are designed such that they may be located on other partitions or filesystems.
- To enable recovery and/or repair of a system, those utilities needed by an experienced maintainer to diagnose and reconstruct a damaged system must be present on the root filesystem.
- To restore a system, those utilities needed to restore from system backups (on floppy, tape, etc.) must be present on the root filesystem.
The primary concern used to balance these considerations, which favor placing many things on the root filesystem, is the goal of keeping root as small as reasonably possible. For several reasons, it is desirable to keep the root filesystem small:
- It is occasionally mounted from very small media.
- The root filesystem contains many system-specific configuration files. Possible examples include a kernel that is specific to the system, a specific hostname, etc. This means that the root filesystem isn't always shareable between networked systems. Keeping it small on servers in networked systems minimizes the amount of lost space for areas of unshareable files. It also allows workstations with smaller local hard drives.
- While you may have the root filesystem on a large partition, and may be able to fill it to your heart's content, there will be people with smaller partitions. If you have more files installed, you may find incompatibilities with other systems using root filesystems on smaller partitions. If you are a developer then you may be turning your assumption into a problem for a large number of users.
- Disk errors that corrupt data on the root filesystem are a greater problem than errors on any other partition. A small root filesystem is less prone to corruption as the result of a system crash.
Applications must never create or require special files or subdirectories in the root directory. Other locations in the FHS hierarchy provide more than enough flexibility for any package.
There are several reasons why creating a new subdirectory of the root filesystem is prohibited:
- It demands space on a root partition which the system administrator may want kept small and simple for either performance or security reasons.
- It evades whatever discipline the system administrator may have set up for distributing standard file hierarchies across mountable volumes.
Distributions should not create new directories in the root hierarchy without extremely careful consideration of the consequences including for application portability.
The following directories, or symbolic links to directories, are required in /.
|bin||Essential command binaries|
|boot||Static files of the boot loader|
|etc||Host-specific system configuration|
|lib||Essential shared libraries and kernel modules|
|media||Mount point for removeable media|
|mnt||Mount point for mounting a filesystem temporarily|
|opt||Add-on application software packages|
|sbin||Essential system binaries|
|srv||Data for services provided by this system|
Each directory listed above is specified in detail in separate subsections below. /usr and /var each have a complete section in this document due to the complexity of those directories.
The following directories, or symbolic links to directories, must be in /, if the corresponding subsystem is installed:
Directory Description home User home directories (optional) lib<qual> Alternate format essential shared libraries (optional) root Home directory for the root user (optional)
Each directory listed above is specified in detail in separate subsections below.
/bin : Essential user command binaries (for use by all users)
/bin contains commands that may be used by both the system administrator and by users, but which are required when no other filesystems are mounted (e.g. in single user mode). It may also contain commands which are used indirectly by scripts. 
There must be no subdirectories in /bin.
The following commands, or symbolic links to commands, are required in /bin.
Command Description cat Utility to concatenate files to standard output chgrp Utility to change file group ownership chmod Utility to change file access permissions chown Utility to change file owner and group cp Utility to copy files and directories date Utility to print or set the system data and time dd Utility to convert and copy a file df Utility to report filesystem disk space usage dmesg Utility to print or control the kernel message buffer echo Utility to display a line of text false Utility to do nothing, unsuccessfully hostname Utility to show or set the system's host name kill Utility to send signals to processes ln Utility to make links between files login Utility to begin a session on the system ls Utility to list directory contents mkdir Utility to make directories mknod Utility to make block or character special files more Utility to page through text mount Utility to mount a filesystem mv Utility to move/rename files ps Utility to report process status pwd Utility to print name of current working directory rm Utility to remove files or directories rmdir Utility to remove empty directories sed The `sed' stream editor sh The Bourne command shell stty Utility to change and print terminal line settings su Utility to change user ID sync Utility to flush filesystem buffers true Utility to do nothing, successfully umount Utility to unmount file systems uname Utility to print system information
If /bin/sh is not a true Bourne shell, it must be a hard or symbolic link to the real shell command.
The [ and test commands must be placed together in either /bin or /usr/bin.
For example bash behaves differently when called as sh or bash. The use of a symbolic link also allows users to easily see that /bin/sh is not a true Bourne shell.
The requirement for the [ and test commands to be included as binaries (even if implemented internally by the shell) is shared with the POSIX.2 standard.
The following programs, or symbolic links to programs, must be in /bin if the corresponding subsystem is installed:
Command Description csh The C shell (optional) ed The `ed' editor (optional) tar The tar archiving utility (optional) cpio The cpio archiving utility (optional) gzip The GNU compression utility (optional) gunzip The GNU uncompression utility (optional) zcat The GNU uncompression utility (optional) netstat The network statistics utility (optional) ping The ICMP network test utility (optional)
If the gunzip and zcat programs exist, they must be symbolic or hard links to gzip. /bin/csh may be a symbolic link to /bin/tcsh or /usr/bin/tcsh.
The tar, gzip and cpio commands have been added to make restoration of a system possible (provided that / is intact).
Conversely, if no restoration from the root partition is ever expected, then these binaries might be omitted (e.g., a ROM chip root, mounting /usr through NFS). If restoration of a system is planned through the network, then ftp or tftp (along with everything necessary to get an ftp connection) must be available on the root partition.
/boot : Static files of the boot loader
This directory contains everything required for the boot process except configuration files not needed at boot time and the map installer. Thus /boot stores data that is used before the kernel begins executing user-mode programs. This may include saved master boot sectors and sector map files. 
The operating system kernel must be located in either / or /boot. 
/dev : Device files
The /dev directory is the location of special or device files.
If it is possible that devices in /dev will need to be manually created, /dev must contain a command named MAKEDEV, which can create devices as needed. It may also contain a MAKEDEV.local for any local devices.
If required, MAKEDEV must have provisions for creating any device that may be found on the system, not just those that a particular implementation installs.
/etc : Host-specific system configuration
The /etc hierarchy contains configuration files. A "configuration file" is a local file used to control the operation of a program; it must be static and cannot be an executable binary. 
No binaries may be located under /etc. 
The following directories, or symbolic links to directories are required in /etc:
Directory Description opt Configuration for /opt X11 Configuration for the X Window system (optional) sgml Configuration for SGML (optional) xml Configuration for XML (optional)
The following directories, or symbolic links to directories must be in /etc, if the corresponding subsystem is installed:
Directory Description opt Configuration for /opt
The following files, or symbolic links to files, must be in /etc if the corresponding subsystem is installed: 
File Description csh.login Systemwide initialization file for C shell logins (optional) exports NFS filesystem access control list (optional) fstab Static information about filesystems (optional) ftpusers FTP daemon user access control list (optional) gateways File which lists gateways for routed (optional) gettydefs Speed and terminal settings used by getty (optional) group User group file (optional) host.conf Resolver configuration file (optional) hosts Static information about host names (optional) hosts.allow Host access file for TCP wrappers (optional) hosts.deny Host access file for TCP wrappers (optional) hosts.equiv List of trusted hosts for rlogin, rsh, rcp (optional) hosts.lpd List of trusted hosts for lpd (optional) inetd.conf Configuration file for inetd (optional) inittab Configuration file for init (optional) issue Pre-login message and identification file (optional) ld.so.conf List of extra directories to search for shared libraries (optional) motd Post-login message of the day file (optional) mtab Dynamic information about filesystems (optional) mtools.conf Configuration file for mtools (optional) networks Static information about network names (optional) passwd The password file (optional) printcap The lpd printer capability database (optional) profile Systemwide initialization file for sh shell logins (optional) protocols IP protocol listing (optional) resolv.conf Resolver configuration file (optional) rpc RPC protocol listing (optional) securetty TTY access control for root login (optional) services Port names for network services (optional) shells Pathnames of valid login shells (optional) syslog.conf Configuration file for syslogd (optional)
mtab does not fit the static nature of /etc: it is excepted for historical reasons. 
/etc/opt : Configuration files for /opt
Host-specific configuration files for add-on application software packages must be installed within the directory /etc/opt/<subdir>, where <subdir> is the name of the subtree in /opt where the static data from that package is stored.
No structure is imposed on the internal arrangement of /etc/opt/<subdir>.
If a configuration file must reside in a different location in order for the package or system to function properly, it may be placed in a location other than /etc/opt/<subdir>.
Refer to the rationale for /opt.
/etc/X11 : Configuration for the X Window System (optional)
/etc/X11 is the location for all X11 host-specific configuration. This directory is necessary to allow local control if /usr is mounted read only.
The following files, or symbolic links to files, must be in /etc/X11 if the corresponding subsystem is installed:
File Description Xconfig The configuration file for early versions of XFree86 (optional) XF86Config The configuration file for XFree86 versions 3 and 4 (optional) Xmodmap Global X11 keyboard modification file (optional)
Subdirectories of /etc/X11 may include those for xdm and for any other programs (some window managers, for example) that need them.  We recommend that window managers with only one configuration file which is a default .*wmrc file must name it system.*wmrc (unless there is a widely-accepted alternative name) and not use a subdirectory. Any window manager subdirectories must be identically named to the actual window manager binary.
/etc/sgml : Configuration files for SGML (optional)
Generic configuration files defining high-level parameters of the SGML systems are installed here. Files with names *.conf indicate generic configuration files. File with names *.cat are the DTD-specific centralized catalogs, containing references to all other catalogs needed to use the given DTD. The super catalog file catalog references all the centralized catalogs. /etc/xml : Configuration files for XML (optional) Purpose
Generic configuration files defining high-level parameters of the XML systems are installed here. Files with names *.conf indicate generic configuration files. The super catalog file catalog references all the centralized catalogs.
/home : User home directories (optional)
/home is a fairly standard concept, but it is clearly a site-specific filesystem.  The setup will differ from host to host. Therefore, no program should rely on this location. 
User specific configuration files for applications are stored in the user's home directory in a file that starts with the '.' character (a "dot file"). If an application needs to create more than one dot file then they should be placed in a subdirectory with a name starting with a '.' character, (a "dot directory"). In this case the configuration files should not start with the '.' character. 
The /lib directory contains those shared library images needed to boot the system and run the commands in the root filesystem, ie. by binaries in /bin and /sbin. 
At least one of each of the following filename patterns are required (they may be files, or symbolic links):
File Description libc.so.* The dynamically-linked C library (optional) ld* The execution time linker/loader (optional)
If a C preprocessor is installed, /lib/cpp must be a reference to it, for historical reasons. 
The following directories, or symbolic links to directories, must be in /lib, if the corresponding subsystem is installed:
Directory Description modules Loadable kernel modules (optional)
There may be one or more variants of the /lib directory on systems which support more than one binary format requiring separate libraries. 
If one or more of these directories exist, the requirements for their contents are the same as the normal /lib directory, except that /lib<qual>/cpp is not required. 
/media : Mount point for removeable media
This directory contains subdirectories which are used as mount points for removeable media such as floppy disks, cdroms and zip disks.
Historically there have been a number of other different places used to mount removeable media such as /cdrom, /mnt or /mnt/cdrom. Placing the mount points for all removeable media directly in the root directory would potentially result in a large number of extra directories in /. Although the use of subdirectories in /mnt as a mount point has recently been common, it conflicts with a much older tradition of using /mnt directly as a temporary mount point.
The following directories, or symbolic links to directories, must be in /media, if the corresponding subsystem is installed:
Directory Description floppy Floppy drive (optional) cdrom CD-ROM drive (optional) cdrecorder CD writer (optional) zip Zip drive (optional)
On systems where more than one device exists for mounting a certain type of media, mount directories can be created by appending a digit to the name of those available above starting with '0', but the unqualified name must also exist. 
/mnt : Mount point for a temporarily mounted filesystem
This directory is provided so that the system administrator may temporarily mount a filesystem as needed. The content of this directory is a local issue and should not affect the manner in which any program is run.
This directory must not be used by installation programs: a suitable temporary directory not in use by the system must be used instead.
/opt : Add-on application software packages
/opt is reserved for the installation of add-on application software packages.
A package to be installed in /opt must locate its static files in a separate /opt/<package> or /opt/<provider> directory tree, where <package> is a name that describes the software package and <provider> is the provider's LANANA registered name.
Directory Description <package> Static package objects <provider> LANANA registered provider name
The directories /opt/bin, /opt/doc, /opt/include, /opt/info, /opt/lib, and /opt/man are reserved for local system administrator use. Packages may provide "front-end" files intended to be placed in (by linking or copying) these reserved directories by the local system administrator, but must function normally in the absence of these reserved directories.
Programs to be invoked by users must be located in the directory /opt/<package>/bin or under the /opt/<provider> hierarchy. If the package includes UNIX manual pages, they must be located in /opt/<package>/share/man or under the /opt/<provider> hierarchy, and the same substructure as /usr/share/man must be used.
Package files that are variable (change in normal operation) must be installed in /var/opt. See the section on /var/opt for more information.
Host-specific configuration files must be installed in /etc/opt. See the section on /etc for more information.
No other package files may exist outside the /opt, /var/opt, and /etc/opt hierarchies except for those package files that must reside in specific locations within the filesystem tree in order to function properly. For example, device lock files must be placed in /var/lock and devices must be located in /dev.
Distributions may install software in /opt, but must not modify or delete software installed by the local system administrator without the assent of the local system administrator.
The use of /opt for add-on software is a well-established practice in the UNIX community. The System V Application Binary Interface [AT&T 1990], based on the System V Interface Definition (Third Edition), provides for an /opt structure very similar to the one defined here.
The Intel Binary Compatibility Standard v. 2 (iBCS2) also provides a similar structure for /opt.
Generally, all data required to support a package on a system must be present within /opt/<package>, including files intended to be copied into /etc/opt/<package> and /var/opt/<package> as well as reserved directories in /opt.
The minor restrictions on distributions using /opt are necessary because conflicts are possible between distribution-installed and locally-installed software, especially in the case of fixed pathnames found in some binary software.
The structure of the directories below /opt/<provider> is left up to the packager of the software, though it is recommended that packages are installed in /opt/<provider>/<package> and follow a similar structure to the guidelines for /opt/package. A valid reason for diverging from this structure is for support packages which may have files installed in /opt/<provider>/lib or /opt/<provider>/bin.
/root : Home directory for the root user (optional)
The root account's home directory may be determined by developer or local preference, but this is the recommended default location. 
/sbin : System binaries
Utilities used for system administration (and other root-only commands) are stored in /sbin, /usr/sbin, and /usr/local/sbin. /sbin contains binaries essential for booting, restoring, recovering, and/or repairing the system in addition to the binaries in /bin.  Programs executed after /usr is known to be mounted (when there are no problems) are generally placed into /usr/sbin. Locally-installed system administration programs should be placed into /usr/local/sbin. 
The following commands, or symbolic links to commands, are required in /sbin.
Command Description shutdown Command to bring the system down.
The following files, or symbolic links to files, must be in /sbin if the corresponding subsystem is installed:
Command Description fastboot Reboot the system without checking the disks (optional) fasthalt Stop the system without checking the disks (optional) fdisk Partition table manipulator (optional) fsck File system check and repair utility (optional) fsck.* File system check and repair utility for a specific filesystem (optional) getty The getty program (optional) halt Command to stop the system (optional) ifconfig Configure a network interface (optional) init Initial process (optional) mkfs Command to build a filesystem (optional) mkfs.* Command to build a specific filesystem (optional) mkswap Command to set up a swap area (optional) reboot Command to reboot the system (optional) route IP routing table utility (optional) swapon Enable paging and swapping (optional) swapoff Disable paging and swapping (optional) update Daemon to periodically flush filesystem buffers (optional)
/srv : Data for services provided by this system
/srv contains site-specific data which is served by this system.
This main purpose of specifying this is so that users may find the location of the data files for particular service, and so that services which require a single tree for readonly data, writable data and scripts (such as cgi scripts) can be reasonably placed. Data that is only of interest to a specific user should go in that users' home directory.
The methodology used to name subdirectories of /srv is unspecified as there is currently no consensus on how this should be done. One method for structuring data under /srv is by protocol, eg. ftp, rsync, www, and cvs. On large systems it can be useful to structure /srv by administrative context, such as /srv/physics/www, /srv/compsci/cvs, etc. This setup will differ from host to host. Therefore, no program should rely on a specific subdirectory structure of /srv existing or data necessarily being stored in /srv. However /srv should always exist on FHS compliant systems and should be used as the default location for such data.
Distributions must take care not to remove locally placed files in these directories without administrator permission. 
/tmp : Temporary files
The /tmp directory must be made available for programs that require temporary files.
Programs must not assume that any files or directories in /tmp are preserved between invocations of the program.
IEEE standard P1003.2 (POSIX, part 2) makes requirements that are similar to the above section.
Although data stored in /tmp may be deleted in a site-specific manner, it is recommended that files and directories located in /tmp be deleted whenever the system is booted.
FHS added this recommendation on the basis of historical precedent and common practice, but did not make it a requirement because system administration is not within the scope of this standard.
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.
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
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.
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. 
/usr/bin : Most user commands
This is the primary directory of executable commands on the system.
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)
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.
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. 
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 historical reasons, /usr/lib/sendmail must be a symbolic link to /usr/sbin/sendmail if the latter exists. 
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. 
/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. 
/usr/local : Local hierarchy
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. 
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 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). 
/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. 
The /usr/share hierarchy is for all read-only architecture independent data files. 
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.
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 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.
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 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. 
Manual pages are stored in <mandir>/<locale>/man