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:
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 of the system is /usr/share/man . /usr/share/man contains manual information for commands and data under the / and /usr filesystems. [31]
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/ / , unless they are empty: [32]
The component 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 string is:
The 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 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. [33]
The field must represent the standard describing the character set. If the 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 of the profile may be placed after the 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 field, unless it is necessary.
Systems which use a unique language and code set for all manual pages may omit the substring and store all manual pages in . For example, systems which only have English manual pages coded with ASCII, may store manual pages (the man 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 field, but it is strongly recommended that it be included, especially for countries with several competing standards.
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 directory in the appropriate man directory; for example, a man page for the i386 ctrlaltdel(8) command might be placed in /usr/share/man/ /man8/i386/ctrlaltdel.8 .
Manual pages for commands and data under /usr/local are stored in /usr/local/man . Manual pages for X11R6 are stored in /usr/X11R6/man . It follows that all manual page hierarchies in the system must have the same structure as /usr/share/man .
The cat page sections ( cat ) containing formatted manual page entries are also found within subdirectories of / , 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 . .
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 and /usr/X11R6/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:
Other (application-specific) files may appear here, but a distributor may place them in /usr/lib at their discretion. [34]
/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:
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:
Source code may be place placed in this subdirectory, only for reference purposes. [35]
/var contains variable data files. This includes spool directories and files, administrative and logging data, and transient and temporary files.
Some portions of /var are not shareable between different systems. For instance, /var/log , /var/lock , and /var/run . Other portions may be shared, notably /var/mail , /var/cache/man , /var/cache/fonts , and /var/spool/news .
/var is specified here in order to make it possible to mount /usr read-only. Everything that once went into /usr that is written to during system operation (as opposed to installation and software maintenance) must be in /var .
If /var cannot be made a separate partition, it is often preferable to move /var out of the root partition and into the /usr partition. (This is sometimes done to reduce the size of the root partition or when space runs low in the root partition.) However, /var must not be linked to /usr because this makes separation of /usr and /var more difficult and is likely to create a naming conflict. Instead, link /var to /usr/var .
Applications must generally not add directories to the top level of /var . Such directories should only be added if they have some system-wide implication, and in consultation with the FHS mailing list.
The following directories, or symbolic links to directories, are required in /var .
Several directories are `reserved’ in the sense that they must not be used arbitrarily by some new application, since they would conflict with historical and/or local practice. They are:
/var/backups /var/cron /var/msgs /var/preserve
The following directories, or symbolic links to directories, must be in /var , if the corresponding subsystem is installed:
This directory holds the current active process accounting log and the composite process usage data (as used in some UNIX-like systems by lastcomm and sa ).
/var/cache is intended for cached data from applications. Such data is locally generated as a result of time-consuming I/O or calculation. The application must be able to regenerate or restore the data. Unlike /var/spool , the cached files can be deleted without data loss. The data must remain valid between invocations of the application and rebooting the system.
Files located under /var/cache may be expired in an application specific manner, by the system administrator, or both. The application must always be able to recover from manual deletion of these files (generally because of a disk space shortage). No other requirements are made on the data format of the cache directories.
| Rationale |
The existence of a separate directory for cached data allows system administrators to set different disk and backup policies from other directories in /var .
Package specific cache data (optional) |
The directory /var/cache/fonts should be used to store any dynamically-created fonts. In particular, all of the fonts which are automatically generated by mktexpk must be located in appropriately-named subdirectories of /var/cache/fonts . [36]
Other dynamically created fonts may also be placed in this tree, under appropriately-named subdirectories of /var/cache/fonts .
This directory provides a standard location for sites that provide a read-only /usr partition, but wish to allow caching of locally-formatted man pages. Sites that mount /usr as writable (e.g., single-user installations) may choose not to use /var/cache/man and may write formatted man pages into the cat directories in /usr/share/man directly. We recommend that most sites use one of the following options instead:
Preformat all manual pages alongside the unformatted versions.
Allow no caching of formatted man pages, and require formatting to be done each time a man page is brought up.
Allow local caching of formatted man pages in /var/cache/man .
The structure of /var/cache/man needs to reflect both the fact of multiple man page hierarchies and the possibility of multiple language support.
Given an unformatted manual page that normally appears in
/man/ /man , the directory to place formatted man pages in is /var/cache/man/ / /cat , where is derived from
by removing any leading usr and/or trailing share pathname components. (Note that the component may be missing.) [37]
Man pages written to /var/cache/man may eventually be transferred to the appropriate preformatted directories in the source man hierarchy or expired; likewise formatted man pages in the source man hierarchy may be expired if they are not accessed for a period of time.
If preformatted manual pages come with a system on read-only media (a CD-ROM, for instance), they must be installed in the source man hierarchy (e.g. /usr/share/man/cat ). /var/cache/man is reserved as a writable cache for formatted manual pages.
| Rationale |
Release 1.2 of the standard specified /var/catman for this hierarchy. The path has been moved under /var/cache to better reflect the dynamic nature of the formatted man pages. The directory name has been changed to man to allow for enhancing the hierarchy to include post-processed formats other than «cat», such as PostScript, HTML, or DVI.
This directory holds system crash dumps. As of the date of this release of the standard, system crash dumps were not supported under Linux but may be supported by other systems which may comply with the FHS.
Any variable data relating to games in /usr should be placed here. /var/games should hold the variable data previously found in /usr ; static data, such as help text, level descriptions, and so on, must remain elsewhere, such as /usr/share/games .
| Rationale |
/var/games has been given a hierarchy of its own, rather than leaving it merged in with the old /var/lib as in release 1.2. The separation allows local control of backup strategies, permissions, and disk usage, as well as allowing inter-host sharing and reducing clutter in /var/lib . Additionally, /var/games is the path traditionally used by BSD.
This hierarchy holds state information pertaining to an application or the system. State information is data that programs modify while they run, and that pertains to one specific host. Users must never need to modify files in /var/lib to configure a package’s operation.
State information is generally used to preserve the condition of an application (or a group of inter-related applications) between invocations and between different instances of the same application. State information should generally remain valid after a reboot, should not be logging output, and should not be spooled data.
An application (or a group of inter-related applications) must use a subdirectory of /var/lib for its data. There is one required subdirectory, /var/lib/misc , which is intended for state files that don’t need a subdirectory; the other subdirectories should only be present if the application in question is included in the distribution. [38]
/var/lib/ is the location that must be used for all distribution packaging support. Different distributions may use different names, of course.
The following directories, or symbolic links to directories, are required in /var/lib :
The following directories, or symbolic links to directories, must be in /var/lib , if the corresponding subsystem is installed:
Packaging support files (optional) |
| State data for packages and subsystems (optional) |
| hwclock | State directory for hwclock (optional) |
| xdm | X display manager variable data (optional) |
These directories contain saved files generated by any unexpected termination of an editor (e.g., elvis , jove , nvi ).
Other editors may not require a directory for crash-recovery files, but may require a well-defined place to store other information while the editor is running. This information should be stored in a subdirectory under /var/lib (for example, GNU Emacs would place lock files in /var/lib/emacs/lock ).
Future editors may require additional state information beyond crash-recovery files and lock files — this information should also be placed under /var/lib/ .
| Rationale |
Previous Linux releases, as well as all commercial vendors, use /var/preserve for vi or its clones. However, each editor uses its own format for these crash-recovery files, so a separate directory is needed for each editor.
Editor-specific lock files are usually quite different from the device or resource lock files that are stored in /var/lock and, hence, are stored under /var/lib .
This directory contains the file /var/lib/hwclock/adjtime .
| Rationale |
In FHS 2.1, this file was /etc/adjtime , but as hwclock updates it, that was obviously incorrect.
This directory contains variable data not placed in a subdirectory in /var/lib . An attempt should be made to use relatively unique names in this directory to avoid namespace conflicts. [39]
Lock files should be stored within the /var/lock directory structure.
Lock files for devices and other resources shared by multiple applications, such as the serial device lock files that were originally found in either /usr/spool/locks or /usr/spool/uucp , must now be stored in /var/lock . The naming convention which must be used is «LCK..» followed by the base name of the device. For example, to lock /dev/ttyS0 the file «LCK..ttyS0» would be created. [40]
The format used for the contents of such lock files must be the HDB UUCP lock file format. The HDB format is to store the process identifier (PID) as a ten byte ASCII decimal number, with a trailing newline. For example, if process 1230 holds a lock file, it would contain the eleven characters: space, space, space, space, space, space, one, two, three, zero, and newline.
This directory contains miscellaneous log files. Most logs must be written to this directory or an appropriate subdirectory.
The following files, or symbolic links to files, must be in /var/log , if the corresponding subsystem is installed:
The mail spool must be accessible through /var/mail and the mail spool files must take the form . [41]
User mailbox files in this location must be stored in the standard UNIX mailbox format.
| Rationale |
The logical location for this directory was changed from /var/spool/mail in order to bring FHS in-line with nearly every UNIX implementation. This change is important for inter-operability since a single /var/mail is often shared between multiple hosts and multiple UNIX implementations (despite NFS locking issues).
It is important to note that there is no requirement to physically move the mail spool to this location. However, programs and header files must be changed to use /var/mail .
Variable data of the packages in /opt must be installed in /var/opt/ , where is the name of the subtree in /opt where the static data from an add-on software package is stored, except where superseded by another file in /etc . No structure is imposed on the internal arrangement of /var/opt/ .
| Rationale |
Refer to the rationale for /opt .
This directory contains system information data describing the system since it was booted. Files under this directory must be cleared (removed or truncated as appropriate) at the beginning of the boot process. Programs may have a subdirectory of /var/run ; this is encouraged for programs that use more than one run-time file. [42] Process identifier (PID) files, which were originally placed in /etc , must be placed in /var/run . The naming convention for PID files is
.pid . For example, the crond PID file is named /var/run/crond.pid .
The internal format of PID files remains unchanged. The file must consist of the process identifier in ASCII-encoded decimal, followed by a newline character. For example, if crond was process number 25, /var/run/crond.pid would contain three characters: two, five, and newline.
Programs that read PID files should be somewhat flexible in what they accept; i.e., they should ignore extra whitespace, leading zeroes, absence of the trailing newline, or additional lines in the PID file. Programs that create PID files should use the simple specification located in the above paragraph.
The utmp file, which stores information about who is currently using the system, is located in this directory.
System programs that maintain transient UNIX-domain sockets must place them in this directory.
/var/spool contains data which is awaiting some kind of later processing. Data in /var/spool represents work to be done in the future (by a program, user, or administrator); often data is deleted after it has been processed. [43]
The following directories, or symbolic links to directories, must be in /var/spool , if the corresponding subsystem is installed:
The lock file for lpd , lpd.lock , must be placed in /var/spool/lpd . It is suggested that the lock file for each printer be placed in the spool directory for that specific printer and named lock .
This directory holds the rwhod information for other systems on the local net.
| Rationale |
Some BSD releases use /var/rwho for this data; given its historical location in /var/spool on other systems and its approximate fit to the definition of `spooled’ data, this location was deemed more appropriate.
The /var/tmp directory is made available for programs that require temporary files or directories that are preserved between system reboots. Therefore, data stored in /var/tmp is more persistent than data in /tmp .
Files and directories located in /var/tmp must not be deleted when the system is booted. Although data stored in /var/tmp is typically deleted in a site-specific manner, it is recommended that deletions occur at a less frequent interval than /tmp .
Variable data for the Network Information Service (NIS), formerly known as the Sun Yellow Pages (YP), must be placed in this directory.
| Rationale |
/var/yp is the standard directory for NIS (YP) data and is almost exclusively used in NIS documentation and systems. [44]
This section is for additional requirements and recommendations that only apply to a specific operating system. The material in this section should never conflict with the base standard.
This is the annex for the Linux operating system.
On Linux systems, if the kernel is located in / , we recommend using the names vmlinux or vmlinuz , which have been used in recent Linux kernel source packages.
Linux systems which require them place these additional files into /bin :
The following devices must exist under /dev.
All data written to this device is discarded. A read from this device will return an EOF condition.
This device is a source of zeroed out data. All data written to this device is discarded. A read from this device will return as many bytes containing the value zero as was requested.
This device is a synonym for the controlling terminal of a process. Once this device is opened, all reads and writes will behave as if the actual controlling terminal device had been opened.
| Rationale |
Previous versions of the FHS had stricter requirements for /dev . Other devices may also exist in /dev. Device names may exist as symbolic links to other device nodes located in /dev or subdirectories of /dev. There is no requirement concerning major/minor number values.
Linux systems which require them place these additional files into /etc .
The 64-bit architectures PPC64, s390x, sparc64 and AMD64 must place 64-bit libraries in /lib64 , and 32-bit (or 31-bit on s390) libraries in /lib .
The 64-bit architecture IA64 must place 64-bit libraries in /lib .
| Rationale |
This is a refinement of the general rules for /lib and /usr/lib . The architectures PPC64, s390x, sparc64 and AMD64 support support both 32-bit (for s390 more precise 31-bit) and 64-bit programs. Using lib for 32-bit binaries allows existing binaries from the 32-bit systems to work without any changes: such binaries are expected to be numerous. IA-64 uses a different scheme, reflecting the deprecation of 32-bit binaries (and hence libraries) on that architecture.
The proc filesystem is the de-facto standard Linux method for handling process and system information, rather than /dev/kmem and other similar methods. We strongly encourage this for the storage and retrieval of process information as well as other kernel and memory information.
Linux systems place these additional files into /sbin .
Second extended filesystem commands (optional):
Boot-loader map installer (optional):
Optional files for /sbin:
Static ln ( sln ) and static sync ( ssync ) are useful when things go wrong. The primary use of sln (to repair incorrect symlinks in /lib after a poorly orchestrated upgrade) is no longer a major concern now that the ldconfig program (usually located in /usr/sbin ) exists and can act as a guiding hand in upgrading the dynamic libraries. Static sync is useful in some emergency situations. Note that these need not be statically linked versions of the standard ln and sync , but may be.
The ldconfig binary is optional for /sbin since a site may choose to run ldconfig at boot time, rather than only when upgrading the shared libraries. (It’s not clear whether or not it is advantageous to run ldconfig on each boot.) Even so, some people like ldconfig around for the following (all too common) situation:
I’ve just removed /lib/ .
I can’t find out the name of the library because ls is dynamically linked, I’m using a shell that doesn’t have ls built-in, and I don’t know about using » echo * » as a replacement.
I have a static sln , but I don’t know what to call the link.
So as to cope with the fact that some keyboards come up with such a high repeat rate as to be unusable, kbdrate may be installed in /sbin on some systems.
Since the default action in the kernel for the Ctrl-Alt-Del key combination is an instant hard reboot, it is generally advisable to disable the behavior before mounting the root filesystem in read-write mode. Some init suites are able to disable Ctrl-Alt-Del, but others may require the ctrlaltdel program, which may be installed in /sbin on those systems.
These symbolic links are required if a C or C++ compiler is installed and only for systems not based on glibc.
For systems based on glibc, there are no specific guidelines for this directory. For systems based on Linux libc revisions prior to glibc, the following guidelines and rationale apply:
The only source code that should be placed in a specific location is the Linux kernel source code. It is located in /usr/src/linux .
If a C or C++ compiler is installed, but the complete Linux kernel source code is not installed, then the include files from the kernel source code must be located in these directories:
/usr/src/linux may be a symbolic link to a kernel source code tree.
| Rationale |
It is important that the kernel include files be located in /usr/src/linux and not in /usr/include so there are no problems when system administrators upgrade their kernel version for the first time.
This directory contains the variable data for the cron and at programs.
The FHS mailing list is located at . You can subscribe to the mailing list at this page http://sourceforge.net/projects/freestandards/ .
Thanks to Network Operations at the University of California at San Diego who allowed us to use their excellent mailing list server.
As noted in the introduction, please do not send mail to the mailing list without first contacting the FHS editor or a listed contributor.
The process of developing a standard filesystem hierarchy began in August 1993 with an effort to restructure the file and directory structure of Linux. The FSSTND, a filesystem hierarchy standard specific to the Linux operating system, was released on February 14, 1994. Subsequent revisions were released on October 9, 1994 and March 28, 1995.
In early 1995, the goal of developing a more comprehensive version of FSSTND to address not only Linux, but other UNIX-like systems was adopted with the help of members of the BSD development community. As a result, a concerted effort was made to focus on issues that were general to UNIX-like systems. In recognition of this widening of scope, the name of the standard was changed to Filesystem Hierarchy Standard or FHS for short.
Volunteers who have contributed extensively to this standard are listed at the end of this document. This standard represents a consensus view of those and other contributors.
Here are some of the guidelines that have been used in the development of this standard:
Solve technical problems while limiting transitional difficulties.
Make the specification reasonably stable.
Gain the approval of distributors, developers, and other decision-makers in relevant development groups and encourage their participation.
Provide a standard that is attractive to the implementors of different UNIX-like systems.
This document specifies a standard filesystem hierarchy for FHS filesystems by specifying the location of files and directories, and the contents of some system files.
This standard has been designed to be used by system integrators, package developers, and system administrators in the construction and maintenance of FHS compliant filesystems. It is primarily intended to be a reference and is not a tutorial on how to manage a conforming filesystem hierarchy.
The FHS grew out of earlier work on FSSTND, a filesystem organization standard for the Linux operating system. It builds on FSSTND to address interoperability issues not just in the Linux community but in a wider arena including 4.4BSD-based operating systems. It incorporates lessons learned in the BSD world and elsewhere about multi-architecture support and the demands of heterogeneous networking.
Although this standard is more comprehensive than previous attempts at filesystem hierarchy standardization, periodic updates may become necessary as requirements change in relation to emerging technology. It is also possible that better solutions to the problems addressed here will be discovered so that our solutions will no longer be the best possible solutions. Supplementary drafts may be released in addition to periodic updates to this document. However, a specific goal is backwards compatibility from one release of this document to the next.
Comments related to this standard are welcome. Any comments or suggestions for changes may be directed to the FHS editor (Daniel Quinlan ) or the FHS mailing list. Typographical or grammatical comments should be directed to the FHS editor.
Before sending mail to the mailing list it is requested that you first contact the FHS editor in order to avoid excessive re-discussion of old topics.
Questions about how to interpret items in this document may occasionally arise. If you have need for a clarification, please contact the FHS editor. Since this standard represents a consensus of many participants, it is important to make certain that any interpretation also represents their collective opinion. For this reason it may not be possible to provide an immediate response unless the inquiry has been the subject of previous discussion.
The developers of the FHS wish to thank the developers, system administrators, and users whose input was essential to this standard. We wish to thank each of the contributors who helped to write, compile, and compose this standard.
The FHS Group also wishes to thank those Linux developers who supported the FSSTND, the predecessor to this standard. If they hadn’t demonstrated that the FSSTND was beneficial, the FHS could never have evolved.
Notes
