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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Filesystem Hierarchy Standard</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"><meta name="description" content="This standard consists of a set of requirements and guidelines for file and directory placement under UNIX-like operating systems. The guidelines are intended to support interoperability of applications, system administration tools, development tools, and scripts as well as greater uniformity of documentation for these systems."></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book"><div class="titlepage"><div><div><h1 class="title"><a name="idm236094246400"></a>Filesystem Hierarchy Standard</h1></div><div><h3 class="corpauthor">LSB Workgroup, The Linux Foundation</h3></div><div><p class="releaseinfo">Version 3.0</p></div><div><p class="copyright">Copyright © 2015 The Linux Foundation</p></div><div><p class="copyright">Copyright © 1994-2004 Daniel Quinlan</p></div><div><p class="copyright">Copyright © 2001-2004 Paul 'Rusty' Russell</p></div><div><p class="copyright">Copyright © 2003-2004 Christopher Yeoh</p></div><div><div class="legalnotice"><a name="idm236089089712"></a><p>All trademarks and copyrights are owned by their owners, unless
specifically noted otherwise.  Use of a term in this document should not
be regarded as affecting the validity of any trademark or service
mark.</p><p>Permission is granted to make and distribute verbatim copies of
this standard provided the copyright and this permission notice are
preserved on all copies.</p><p>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.</p><p>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.</p></div></div><div><p class="pubdate">March 19, 2015</p></div><div><div class="abstract"><p class="title"><b>Abstract</b></p><p>This standard consists of a set of requirements and guidelines for file
and directory placement under UNIX-like operating systems.  The
guidelines are intended to support interoperability of applications,
system administration tools, development tools, and scripts as well as
greater uniformity of documentation for these systems.</p></div></div></div><hr></div><div class="dedication"><div class="titlepage"><div><div><h1 class="title"><a name="idm236089710608"></a>Dedication</h1></div></div></div><p>This release is dedicated to the memory of Christopher Yeoh,
a long-time friend and colleague, and one of the original editors
of the FHS. Without his dedication this work would not have been possible.
</p></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="chapter"><a href="#introduction">1. Introduction</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose">1.1. Purpose</a></span></dt><dt><span class="section"><a href="#conventions">1.2. Conventions</a></span></dt></dl></dd><dt><span class="chapter"><a href="#thefilesystem">2. The Filesystem</a></span></dt><dt><span class="chapter"><a href="#theRootFilesystem">3. The Root Filesystem</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose2">3.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements">3.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions">3.3. Specific Options</a></span></dt><dt><span class="section"><a href="#binEssentialUserCommandBinaries">3.4. /bin : Essential user command binaries (for use by all users)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose3">3.4.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements2">3.4.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions2">3.4.3. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#bootStaticFilesOfTheBootLoader">3.5. /boot : Static files of the boot loader</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose4">3.5.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions3">3.5.2. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#devDeviceFiles">3.6. /dev : Device files</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose5">3.6.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions4">3.6.2. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#etcHostspecificSystemConfiguration">3.7. /etc : Host-specific system configuration</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose6">3.7.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements3">3.7.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions5">3.7.3. Specific Options</a></span></dt><dt><span class="section"><a href="#etcoptConfigurationFilesForOpt">3.7.4. /etc/opt : Configuration files for /opt</a></span></dt><dt><span class="section"><a href="#etcx11ConfigurationForTheXWindowS">3.7.5. /etc/X11 : Configuration for the X Window System (optional)</a></span></dt><dt><span class="section"><a href="#etcsgmlConfigurationFilesForSgmlAn">3.7.6. /etc/sgml : Configuration files for SGML (optional)</a></span></dt><dt><span class="section"><a href="#idm236088418512">3.7.7. /etc/xml : Configuration files for XML (optional)</a></span></dt></dl></dd><dt><span class="section"><a href="#homeUserHomeDirectories">3.8. /home : User home directories (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose10">3.8.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements4a">3.8.2. Requirements</a></span></dt><dt><span class="section"><a href="#homeReferences">3.8.3. Home Directory Specifications and Conventions</a></span></dt></dl></dd><dt><span class="section"><a href="#libEssentialSharedLibrariesAndKern">3.9. /lib : Essential shared libraries and kernel modules</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose11">3.9.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements5">3.9.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions7">3.9.3. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#libltqualgtAlternateFormatEssential">3.10. /lib<em class="replaceable"><code>&lt;qual&gt;</code></em> : Alternate format essential shared libraries (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose12">3.10.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements6">3.10.2. Requirements</a></span></dt></dl></dd><dt><span class="section"><a href="#mediaMountPoint">3.11. /media : Mount point for removable media</a></span></dt><dd><dl><dt><span class="section"><a href="#purposeMediaMountPoint">3.11.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptionsMediaMount">3.11.2. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#mntMountPointForATemporarilyMount">3.12. /mnt : Mount point for a temporarily mounted filesystem</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose13">3.12.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#optAddonApplicationSoftwarePackages">3.13. /opt : Add-on application software packages</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose14">3.13.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements7">3.13.2. Requirements</a></span></dt></dl></dd><dt><span class="section"><a href="#rootHomeDirectoryForTheRootUser">3.14. /root : Home directory for the root user (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose15">3.14.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#runRuntimeVariableData">3.15. /run : Run-time variable data</a></span></dt><dd><dl><dt><span class="section"><a href="#runPurpose">3.15.1. Purpose</a></span></dt><dt><span class="section"><a href="#runRequirements">3.15.2. Requirements</a></span></dt></dl></dd><dt><span class="section"><a href="#sbinSystemBinaries">3.16. /sbin : System binaries</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose16">3.16.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements8">3.16.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions8">3.16.3. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#srvDataForServicesProvidedBySystem">3.17. /srv : Data for services provided by this system</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose16a">3.17.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#tmpTemporaryFiles">3.18. /tmp : Temporary files</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose17">3.18.1. Purpose</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#theUsrHierarchy">4. The /usr Hierarchy</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose18">4.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements9">4.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions9">4.3. Specific Options</a></span></dt><dt><span class="section"><a href="#usrbinMostUserCommands">4.4. /usr/bin : Most user commands</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose20">4.4.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements9a">4.4.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions11">4.4.3. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#usrincludeDirectoryForStandardInclu">4.5. /usr/include : Directory for standard include files.</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose21">4.5.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions12">4.5.2. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#usrlibLibrariesForProgrammingAndPa">4.6. /usr/lib : Libraries for programming and packages</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose22">4.6.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions13">4.6.2. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#usrlibexec">4.7. /usr/libexec : Binaries run by other programs (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#usrlibexecPurpose">4.7.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#usrlibltqualgtAlternateFormatLibrari">4.8. /usr/lib<em class="replaceable"><code>&lt;qual&gt;</code></em> : Alternate format libraries (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose23">4.8.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#usrlocalLocalHierarchy">4.9. /usr/local : Local hierarchy</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose24">4.9.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements10">4.9.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions14">4.9.3. Specific Options</a></span></dt><dt><span class="section"><a href="#usrlocalshare1">4.9.4. /usr/local/share : Local architecture-independent hierarchy</a></span></dt></dl></dd><dt><span class="section"><a href="#usrsbinNonessentialStandardSystemBi">4.10. /usr/sbin : Non-essential standard system binaries</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose25">4.10.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements10a">4.10.2. Requirements</a></span></dt></dl></dd><dt><span class="section"><a href="#usrshareArchitectureindependentData">4.11. /usr/share : Architecture-independent data</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose26">4.11.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements11">4.11.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions15">4.11.3. Specific Options</a></span></dt><dt><span class="section"><a href="#usrsharecolorColorManagement">4.11.4. /usr/share/color : Color management information (optional)</a></span></dt><dt><span class="section"><a href="#usrsharedictWordLists">4.11.5. /usr/share/dict : Word lists (optional)</a></span></dt><dt><span class="section"><a href="#usrsharemanManualPages">4.11.6. /usr/share/man : Manual pages</a></span></dt><dt><span class="section"><a href="#usrsharemiscMiscellaneousArchitecture">4.11.7. /usr/share/misc : Miscellaneous architecture-independent data</a></span></dt><dt><span class="section"><a href="#usrshareppd">4.11.8. /usr/share/ppd : Printer definitions (optional)</a></span></dt><dt><span class="section"><a href="#usrsharesgmlSgmlAndXmlData">4.11.9. /usr/share/sgml : SGML data (optional)</a></span></dt><dt><span class="section"><a href="#idm236087237360">4.11.10. /usr/share/xml : XML data (optional)</a></span></dt></dl></dd><dt><span class="section"><a href="#usrsrcSourceCode">4.12. /usr/src : Source code (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose30">4.12.1. Purpose</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#theVarHierarchy">5. The /var Hierarchy</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose31">5.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements12">5.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions20">5.3. Specific Options</a></span></dt><dt><span class="section"><a href="#varaccountProcessAccountingLogs">5.4. /var/account : Process accounting logs (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose32">5.4.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#varcacheApplicationCacheData">5.5. /var/cache : Application cache data</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose33">5.5.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions21">5.5.2. Specific Options</a></span></dt><dt><span class="section"><a href="#varcachefontsLocallygeneratedFonts">5.5.3. /var/cache/fonts : Locally-generated fonts (optional)</a></span></dt><dt><span class="section"><a href="#varcachemanLocallyformattedManualPag">5.5.4. /var/cache/man : Locally-formatted manual pages (optional)</a></span></dt></dl></dd><dt><span class="section"><a href="#varcrashSystemCrashDumps">5.6. /var/crash : System crash dumps (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose36">5.6.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#vargamesVariableGameData">5.7. /var/games : Variable game data (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose37">5.7.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#varlibVariableStateInformation">5.8. /var/lib : Variable state information</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose38">5.8.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements13">5.8.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions23">5.8.3. Specific Options</a></span></dt><dt><span class="section"><a href="#varliblteditorgtEditorBackupFilesAn">5.8.4. /var/lib/&lt;editor&gt; : Editor backup files and state (optional)</a></span></dt><dt><span class="section"><a href="#varlibcolor">5.8.5. /var/lib/color : Color management information (optional)</a></span></dt><dt><span class="section"><a href="#varlibhwclockStateDirectoryForHwclo">5.8.6. /var/lib/hwclock : State directory for hwclock (optional)</a></span></dt><dt><span class="section"><a href="#varlibmiscMiscellaneousVariableData">5.8.7. /var/lib/misc : Miscellaneous variable data</a></span></dt></dl></dd><dt><span class="section"><a href="#varlockLockFiles">5.9. /var/lock : Lock files</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose42">5.9.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#varlogLogFilesAndDirectories">5.10. /var/log : Log files and directories</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose43">5.10.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions24">5.10.2. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#varmailUserMailboxFiles">5.11. /var/mail : User mailbox files (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose44">5.11.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#varoptVariableDataForOpt">5.12. /var/opt : Variable data for /opt</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose45">5.12.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#varrunRuntimeVariableData">5.13. /var/run : Run-time variable data</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose46">5.13.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements14">5.13.2. Requirements</a></span></dt></dl></dd><dt><span class="section"><a href="#varspoolApplicationSpoolData">5.14. /var/spool : Application spool data</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose47">5.14.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions25">5.14.2. Specific Options</a></span></dt><dt><span class="section"><a href="#varspoollpdLineprinterDaemonPrintQu">5.14.3. /var/spool/lpd : Line-printer daemon print queues (optional)</a></span></dt><dt><span class="section"><a href="#varspoolrwhoRwhodFiles">5.14.4. /var/spool/rwho : Rwhod files (optional)</a></span></dt></dl></dd><dt><span class="section"><a href="#vartmpTemporaryFilesPreservedBetwee">5.15. /var/tmp : Temporary files preserved between system reboots</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose50">5.15.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#varypNetworkInformationService">5.16. /var/yp : Network Information Service (NIS) database files (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose51">5.16.1. Purpose</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#operatingSystemSpecificAnnex">6. Operating System Specific Annex</a></span></dt><dd><dl><dt><span class="section"><a href="#linux">6.1. Linux</a></span></dt><dd><dl><dt><span class="section"><a href="#rootDirectory">6.1.1. / : Root directory</a></span></dt><dt><span class="section"><a href="#binEssentialUserCommandBinaries2">6.1.2. /bin : Essential user command binaries (for use by all users)</a></span></dt><dt><span class="section"><a href="#devDevicesAndSpecialFiles">6.1.3. /dev : Devices and special files</a></span></dt><dt><span class="section"><a href="#etcHostspecificSystemConfiguration2">6.1.4. /etc : Host-specific system configuration</a></span></dt><dt><span class="section"><a href="#procKernelAndProcessInformationVir">6.1.5. /proc : Kernel and process information virtual filesystem</a></span></dt><dt><span class="section"><a href="#sbinEssentialSystemBinaries">6.1.6. /sbin : Essential system binaries</a></span></dt><dt><span class="section"><a href="#sysKernelAndSystemInformation">6.1.7. /sys : Kernel and system information virtual filesystem</a></span></dt><dt><span class="section"><a href="#usrincludeHeaderFilesIncludedByCP">6.1.8. /usr/include : Header files included by C programs</a></span></dt><dt><span class="section"><a href="#usrsrcSourceCode2">6.1.9. /usr/src : Source code</a></span></dt><dt><span class="section"><a href="#varspoolcronCronAndAtJobs">6.1.10. /var/spool/cron : cron and at jobs</a></span></dt></dl></dd></dl></dd><dt><span class="chapter"><a href="#appendix">7. Appendix</a></span></dt><dd><dl><dt><span class="section"><a href="#theFhsMailingList">7.1. The FHS mailing list</a></span></dt><dt><span class="section"><a href="#backgroundOfTheFhs">7.2. Background of the FHS</a></span></dt><dt><span class="section"><a href="#generalGuidelines">7.3. General Guidelines</a></span></dt><dt><span class="section"><a href="#scope">7.4. Scope</a></span></dt><dt><span class="section"><a href="#acknowledgments">7.5. Acknowledgments</a></span></dt><dt><span class="section"><a href="#contributors">7.6. Contributors</a></span></dt></dl></dd></dl></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="introduction"></a>Chapter 1. Introduction</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#purpose">1.1. Purpose</a></span></dt><dt><span class="section"><a href="#conventions">1.2. Conventions</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="purpose"></a>1.1. Purpose</h2></div></div></div><p>This standard enables:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>Software to predict the location of installed files and
directories, and</p></li><li class="listitem"><p>Users to predict the location of installed files and
directories.</p></li></ul></div><p>We do this by:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>Specifying guiding principles for each area of the filesystem,</p></li><li class="listitem"><p>Specifying the minimum files and directories required,</p></li><li class="listitem"><p>Enumerating exceptions to the principles, and</p></li><li class="listitem"><p>Enumerating specific cases where there has been historical conflict.</p></li></ul></div><p>The FHS document is used by:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>Independent software suppliers to create applications which are FHS
compliant, and work with distributions which are FHS compliant,</p></li><li class="listitem"><p>OS creators to provide systems which are FHS compliant, and</p></li><li class="listitem"><p>Users to understand and maintain the FHS compliance of a system.</p></li></ul></div><p>The FHS document has a limited scope:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>Local placement of local files is a local issue, so FHS does not
attempt to usurp system administrators.</p></li><li class="listitem"><p>FHS addresses issues where file placements need to be coordinated
between multiple parties such as local sites, distributions,
applications, documentation, etc.</p></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="conventions"></a>1.2. Conventions</h2></div></div></div><p>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.</p><p>Components of filenames that vary are represented by a description
of the contents enclosed in "<em class="replaceable"><code>&lt;</code></em>" and
"<em class="replaceable"><code>&gt;</code></em>" characters, 
<em class="replaceable"><code>&lt;thus&gt;</code></em>.  Electronic mail addresses are also
enclosed in "&lt;" and "&gt;" but are shown in the usual
typeface.</p><p>Optional components of filenames are enclosed in
"<em class="replaceable"><code>[</code></em>" and "<em class="replaceable"><code>]</code></em>" characters and may
be combined with the "<em class="replaceable"><code>&lt;</code></em>" and
"<em class="replaceable"><code>&gt;</code></em>" convention.  For example, if a filename is
allowed to occur either with or without an extension, it might be
represented by
<em class="replaceable"><code>&lt;filename&gt;[.&lt;extension&gt;]</code></em>.</p><p>Variable substrings of directory names and filenames are indicated
by "<em class="replaceable"><code>*</code></em>".</p><p>The sections of the text marked as
<span class="emphasis"><em>Rationale</em></span> are explanatory and are
non-normative.</p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="thefilesystem"></a>Chapter 2. The Filesystem</h1></div></div></div><p>This standard assumes that the operating system underlying an
FHS-compliant file system supports the same basic security features
found in most UNIX filesystems.</p><p>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.</p><p>"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.</p><p>"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.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>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.</p><p>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.</p><p>Historical UNIX-like filesystem hierarchies contained both
static and variable files under both <code class="filename">/usr</code> and
<code class="filename">/etc</code>.  In order to realize the advantages
mentioned above, the <code class="filename">/var</code> hierarchy was
created and all variable files were transferred from
<code class="filename">/usr</code> to <code class="filename">/var</code>.
Consequently <code class="filename">/usr</code> can now be mounted read-only
(if it is a separate filesystem).  Variable files have been
transferred from <code class="filename">/etc</code> to
<code class="filename">/var</code> over a longer period as technology has
permitted.</p><p>Here is an example of a FHS-compliant system.
(Other FHS-compliant layouts are possible.)</p><div class="informaltable"><table border="1"><colgroup><col><col><col></colgroup><thead><tr><th align="left"><span class="emphasis"><em></em></span></th><th align="left">shareable</th><th align="left">unshareable</th></tr></thead><tbody><tr><td align="left">static</td><td align="left"><code class="filename">/usr</code></td><td align="left"><code class="filename">/etc</code></td></tr><tr><td align="left"> </td><td align="left"><code class="filename">/opt</code></td><td align="left"><code class="filename">/boot</code></td></tr><tr><td align="left">variable</td><td align="left"><code class="filename">/var/mail</code></td><td align="left"><code class="filename">/var/run</code></td></tr><tr><td align="left"> </td><td align="left"><code class="filename">/var/spool/news</code></td><td align="left"><code class="filename">/var/lock</code></td></tr></tbody></table></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="theRootFilesystem"></a>Chapter 3. The Root Filesystem</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#purpose2">3.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements">3.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions">3.3. Specific Options</a></span></dt><dt><span class="section"><a href="#binEssentialUserCommandBinaries">3.4. /bin : Essential user command binaries (for use by all users)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose3">3.4.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements2">3.4.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions2">3.4.3. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#bootStaticFilesOfTheBootLoader">3.5. /boot : Static files of the boot loader</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose4">3.5.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions3">3.5.2. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#devDeviceFiles">3.6. /dev : Device files</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose5">3.6.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions4">3.6.2. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#etcHostspecificSystemConfiguration">3.7. /etc : Host-specific system configuration</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose6">3.7.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements3">3.7.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions5">3.7.3. Specific Options</a></span></dt><dt><span class="section"><a href="#etcoptConfigurationFilesForOpt">3.7.4. /etc/opt : Configuration files for /opt</a></span></dt><dt><span class="section"><a href="#etcx11ConfigurationForTheXWindowS">3.7.5. /etc/X11 : Configuration for the X Window System (optional)</a></span></dt><dt><span class="section"><a href="#etcsgmlConfigurationFilesForSgmlAn">3.7.6. /etc/sgml : Configuration files for SGML (optional)</a></span></dt><dt><span class="section"><a href="#idm236088418512">3.7.7. /etc/xml : Configuration files for XML (optional)</a></span></dt></dl></dd><dt><span class="section"><a href="#homeUserHomeDirectories">3.8. /home : User home directories (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose10">3.8.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements4a">3.8.2. Requirements</a></span></dt><dt><span class="section"><a href="#homeReferences">3.8.3. Home Directory Specifications and Conventions</a></span></dt></dl></dd><dt><span class="section"><a href="#libEssentialSharedLibrariesAndKern">3.9. /lib : Essential shared libraries and kernel modules</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose11">3.9.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements5">3.9.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions7">3.9.3. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#libltqualgtAlternateFormatEssential">3.10. /lib<em class="replaceable"><code>&lt;qual&gt;</code></em> : Alternate format essential shared libraries (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose12">3.10.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements6">3.10.2. Requirements</a></span></dt></dl></dd><dt><span class="section"><a href="#mediaMountPoint">3.11. /media : Mount point for removable media</a></span></dt><dd><dl><dt><span class="section"><a href="#purposeMediaMountPoint">3.11.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptionsMediaMount">3.11.2. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#mntMountPointForATemporarilyMount">3.12. /mnt : Mount point for a temporarily mounted filesystem</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose13">3.12.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#optAddonApplicationSoftwarePackages">3.13. /opt : Add-on application software packages</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose14">3.13.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements7">3.13.2. Requirements</a></span></dt></dl></dd><dt><span class="section"><a href="#rootHomeDirectoryForTheRootUser">3.14. /root : Home directory for the root user (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose15">3.14.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#runRuntimeVariableData">3.15. /run : Run-time variable data</a></span></dt><dd><dl><dt><span class="section"><a href="#runPurpose">3.15.1. Purpose</a></span></dt><dt><span class="section"><a href="#runRequirements">3.15.2. Requirements</a></span></dt></dl></dd><dt><span class="section"><a href="#sbinSystemBinaries">3.16. /sbin : System binaries</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose16">3.16.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements8">3.16.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions8">3.16.3. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#srvDataForServicesProvidedBySystem">3.17. /srv : Data for services provided by this system</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose16a">3.17.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#tmpTemporaryFiles">3.18. /tmp : Temporary files</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose17">3.18.1. Purpose</a></span></dt></dl></dd></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="purpose2"></a>3.1. Purpose</h2></div></div></div><p>The contents of the root filesystem must be adequate to boot,
restore, recover, and/or repair the system.</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: bullet; "><li class="listitem" style="list-style-type: disc"><p>To boot a system, enough software and data must be present on the root partition
to mount other filesystems.  This includes utilities, configuration,
boot loader information, and other essential start-up data.
<code class="filename">/usr</code>, <code class="filename">/opt</code>, and
<code class="filename">/var</code> are designed such that they may be located
on other partitions or filesystems.</p></li><li class="listitem" style="list-style-type: disc"><p>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.</p></li><li class="listitem" style="list-style-type: disc"><p>To restore a system, those utilities needed to restore from
system backups (on floppy, tape, etc.) must be present on the root
filesystem.</p></li></ul></div><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>The minimum requirements for the root filesystem should be as
small as reasonably possible, but no smaller.  While many users may
not want the extra complexity of a partitioned system, the option to
keep the root small should be preserved for several reasons:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>It is occasionally mounted from very small media.</p></li><li class="listitem"><p>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.</p></li><li class="listitem"><p>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.</p></li><li class="listitem"><p>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.</p></li></ul></div><p>These considerations must be balanced against the need for a
minimally useful operating environment, for the sake of the boot
process as well as in failure recovery situations.</p></div><p>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.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>There are several reasons why creating a new subdirectory of
the root filesystem is prohibited:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: bullet; "><li class="listitem" style="list-style-type: disc"><p>It demands space on a root partition which the system
administrator may want kept small and simple for either performance or
security reasons.</p></li><li class="listitem" style="list-style-type: disc"><p>It evades whatever discipline the system administrator may have
set up for distributing standard file hierarchies across mountable
volumes.</p></li></ul></div><p>Distributions should not create new directories in the root
hierarchy without extremely careful consideration of the consequences
including for application portability.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="requirements"></a>3.2. Requirements</h2></div></div></div><p>The following directories, or symbolic links to directories, are
required in <code class="filename">/</code>.</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">bin</code></td><td align="left">Essential command binaries</td></tr><tr><td align="left"><code class="filename">boot</code></td><td align="left">Static files of the boot loader</td></tr><tr><td align="left"><code class="filename">dev</code></td><td align="left">Device files</td></tr><tr><td align="left"><code class="filename">etc</code></td><td align="left">Host-specific system configuration</td></tr><tr><td align="left"><code class="filename">lib</code></td><td align="left">Essential shared libraries and kernel modules</td></tr><tr><td align="left"><code class="filename">media</code></td><td align="left">Mount point for removable media</td></tr><tr><td align="left"><code class="filename">mnt</code></td><td align="left">Mount point for mounting a filesystem temporarily</td></tr><tr><td align="left"><code class="filename">opt</code></td><td align="left">Add-on application software packages</td></tr><tr><td align="left"><code class="filename">run</code></td><td align="left">Data relevant to running processes</td></tr><tr><td align="left"><code class="filename">sbin</code></td><td align="left">Essential system binaries</td></tr><tr><td align="left"><code class="filename">srv</code></td><td align="left">Data for services provided by this system</td></tr><tr><td align="left"><code class="filename">tmp</code></td><td align="left">Temporary files</td></tr><tr><td align="left"><code class="filename">usr</code></td><td align="left">Secondary hierarchy</td></tr><tr><td align="left"><code class="filename">var</code></td><td align="left">Variable data</td></tr></tbody></table></div><p>Each directory listed above is specified in detail in separate
subsections below.  <code class="filename">/usr</code> and
<code class="filename">/var</code> each has a complete section in this
document due to the complexity of those directories.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="specificOptions"></a>3.3. Specific Options</h2></div></div></div><p>The following directories, or symbolic links to directories,
must be in <code class="filename">/</code>, if the corresponding subsystem is
installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">home</code></td><td align="left">User home directories (optional)</td></tr><tr><td align="left"><code class="filename">lib<em class="replaceable"><code>&lt;qual&gt;</code></em></code></td><td align="left">Alternate format essential shared libraries (optional)</td></tr><tr><td align="left"><code class="filename">root</code></td><td align="left">Home directory for the root user (optional)</td></tr></tbody></table></div><p>Each directory listed above is specified in detail in separate
subsections below.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="binEssentialUserCommandBinaries"></a>3.4. /bin : Essential user command binaries (for use by all users)</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose3"></a>3.4.1. Purpose</h3></div></div></div><p><code class="filename">/bin</code> 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.

<a href="#ftn.idm236088643344" class="footnote" name="idm236088643344"><sup class="footnote">[1]</sup></a>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="requirements2"></a>3.4.2. Requirements</h3></div></div></div><p>There must be no subdirectories in <code class="filename">/bin</code>.</p><p>The following commands, or symbolic links to commands, are
required in <code class="filename">/bin</code>:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Command</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><span class="command"><strong>cat</strong></span></td><td align="left">Utility to concatenate files to standard output</td></tr><tr><td align="left"><span class="command"><strong>chgrp</strong></span></td><td align="left">Utility to change file group ownership</td></tr><tr><td align="left"><span class="command"><strong>chmod</strong></span></td><td align="left">Utility to change file access permissions</td></tr><tr><td align="left"><span class="command"><strong>chown</strong></span></td><td align="left">Utility to change file owner and group</td></tr><tr><td align="left"><span class="command"><strong>cp</strong></span></td><td align="left">Utility to copy files and directories</td></tr><tr><td align="left"><span class="command"><strong>date</strong></span></td><td align="left">Utility to print or set the system data and time</td></tr><tr><td align="left"><span class="command"><strong>dd</strong></span></td><td align="left">Utility to convert and copy a file</td></tr><tr><td align="left"><span class="command"><strong>df</strong></span></td><td align="left">Utility to report filesystem disk space usage</td></tr><tr><td align="left"><span class="command"><strong>dmesg</strong></span></td><td align="left">Utility to print or control the kernel message buffer</td></tr><tr><td align="left"><span class="command"><strong>echo</strong></span></td><td align="left">Utility to display a line of text</td></tr><tr><td align="left"><span class="command"><strong>false</strong></span></td><td align="left">Utility to do nothing, unsuccessfully</td></tr><tr><td align="left"><span class="command"><strong>hostname</strong></span></td><td align="left">Utility to show or set the system's host name</td></tr><tr><td align="left"><span class="command"><strong>kill</strong></span></td><td align="left">Utility to send signals to processes</td></tr><tr><td align="left"><span class="command"><strong>ln</strong></span></td><td align="left">Utility to make links between files</td></tr><tr><td align="left"><span class="command"><strong>login</strong></span></td><td align="left">Utility to begin a session on the system</td></tr><tr><td align="left"><span class="command"><strong>ls</strong></span></td><td align="left">Utility to list directory contents</td></tr><tr><td align="left"><span class="command"><strong>mkdir</strong></span></td><td align="left">Utility to make directories</td></tr><tr><td align="left"><span class="command"><strong>mknod</strong></span></td><td align="left">Utility to make block or character special files</td></tr><tr><td align="left"><span class="command"><strong>more</strong></span></td><td align="left">Utility to page through text</td></tr><tr><td align="left"><span class="command"><strong>mount</strong></span></td><td align="left">Utility to mount a filesystem</td></tr><tr><td align="left"><span class="command"><strong>mv</strong></span></td><td align="left">Utility to move/rename files</td></tr><tr><td align="left"><span class="command"><strong>ps</strong></span></td><td align="left">Utility to report process status</td></tr><tr><td align="left"><span class="command"><strong>pwd</strong></span></td><td align="left">Utility to print name of current working directory</td></tr><tr><td align="left"><span class="command"><strong>rm</strong></span></td><td align="left">Utility to remove files or directories</td></tr><tr><td align="left"><span class="command"><strong>rmdir</strong></span></td><td align="left">Utility to remove empty directories</td></tr><tr><td align="left"><span class="command"><strong>sed</strong></span></td><td align="left">The `sed' stream editor</td></tr><tr><td align="left"><span class="command"><strong>sh</strong></span></td><td align="left">POSIX compatible command shell</td></tr><tr><td align="left"><span class="command"><strong>stty</strong></span></td><td align="left">Utility to change and print terminal line settings</td></tr><tr><td align="left"><span class="command"><strong>su</strong></span></td><td align="left">Utility to change user ID</td></tr><tr><td align="left"><span class="command"><strong>sync</strong></span></td><td align="left">Utility to flush filesystem buffers</td></tr><tr><td align="left"><span class="command"><strong>true</strong></span></td><td align="left">Utility to do nothing, successfully</td></tr><tr><td align="left"><span class="command"><strong>umount</strong></span></td><td align="left">Utility to unmount file systems</td></tr><tr><td align="left"><span class="command"><strong>uname</strong></span></td><td align="left">Utility to print system information</td></tr></tbody></table></div><p>If <span class="command"><strong>/bin/sh</strong></span> is not the POSIX compatible shell
command itself, it must be a hard or symbolic link to the real shell
command.</p><p>The <span class="command"><strong>[</strong></span> and <span class="command"><strong>test</strong></span>
commands must be placed together in either <code class="filename">/bin</code>
or <code class="filename">/usr/bin</code>.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>Various shells behave differently when called as
<span class="command"><strong>sh</strong></span>, so as to preserve POSIX compatibility while
allowing changes or extensions to POSIX when desired.</p><p>The requirement for the <span class="command"><strong>[</strong></span> and
<span class="command"><strong>test</strong></span> commands to be included as binaries (even if
implemented internally by the shell) is shared with the POSIX.1-2008
standard.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions2"></a>3.4.3. Specific Options</h3></div></div></div><p>The following programs, or symbolic links to programs, must be
in <code class="filename">/bin</code> if the corresponding subsystem is
installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Command</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><span class="command"><strong>csh</strong></span></td><td align="left">The C shell (optional)</td></tr><tr><td align="left"><span class="command"><strong>ed</strong></span></td><td align="left">The `ed' editor (optional)</td></tr><tr><td align="left"><span class="command"><strong>tar</strong></span></td><td align="left">The tar archiving utility (optional)</td></tr><tr><td align="left"><span class="command"><strong>cpio</strong></span></td><td align="left">The cpio archiving utility (optional)</td></tr><tr><td align="left"><span class="command"><strong>gzip</strong></span></td><td align="left">The GNU compression utility (optional)</td></tr><tr><td align="left"><span class="command"><strong>gunzip</strong></span></td><td align="left">The GNU uncompression utility (optional)</td></tr><tr><td align="left"><span class="command"><strong>zcat</strong></span></td><td align="left">The GNU uncompression utility (optional)</td></tr><tr><td align="left"><span class="command"><strong>netstat</strong></span></td><td align="left">The network statistics utility (optional)</td></tr><tr><td align="left"><span class="command"><strong>ping</strong></span></td><td align="left">The ICMP network test utility (optional)</td></tr></tbody></table></div><p><span class="command"><strong>/bin/csh</strong></span> may be a symbolic link to
<span class="command"><strong>/bin/tcsh</strong></span> or
<span class="command"><strong>/usr/bin/tcsh</strong></span>.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>The <span class="command"><strong>tar</strong></span>, <span class="command"><strong>gzip </strong></span>
and <span class="command"><strong>cpio</strong></span>
commands have been added to make restoration of a
system possible (provided that <code class="filename">/</code> is intact).</p><p>Conversely, if no restoration from the root partition is ever
expected, then these binaries might be omitted (e.g., a ROM chip root,
mounting <code class="filename">/usr</code> through NFS).  If restoration of a
system is planned through the network, then <span class="command"><strong>ftp</strong></span>
or <span class="command"><strong>tftp</strong></span> (along with everything necessary to get
an ftp connection) must be available on the root partition.</p></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="bootStaticFilesOfTheBootLoader"></a>3.5. /boot : Static files of the boot loader</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose4"></a>3.5.1. Purpose</h3></div></div></div><p>This directory contains everything required for the boot process
except configuration files not needed at boot time and the map
installer. Thus <code class="filename">/boot</code> stores data that is used
before the kernel begins executing user-mode programs.  This may
include saved master boot sectors and sector map files.</p><p> Programs necessary to arrange for the boot loader to be able to
boot a file must be placed in <code class="filename">/sbin</code>.
Configuration files for boot loaders that are not required at boot
time must be placed in <code class="filename">/etc</code>.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions3"></a>3.5.2. Specific Options</h3></div></div></div><p>The operating system kernel must be located in either
<code class="filename">/</code> or <code class="filename">/boot</code>.</p><p>Certain architectures may have other requirements for
<code class="filename">/boot</code> related to limitations or expectations
specific to that architecture.  These requirements are not enumerated
here; distributions are allowed to add requirements as needed to
enable system startup on these architectures.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="devDeviceFiles"></a>3.6. /dev : Device files</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose5"></a>3.6.1. Purpose</h3></div></div></div><p>The <code class="filename">/dev</code> directory is the location of
special or device files.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions4"></a>3.6.2. Specific Options</h3></div></div></div><p>If it is possible that devices in <code class="filename">/dev</code> will
need to be manually created, <code class="filename">/dev</code> must contain a
command named <code class="filename">MAKEDEV</code>, which can create devices
as needed.  It may also contain a <code class="filename">MAKEDEV.local</code>
for any local devices.</p><p>If required, <code class="filename">MAKEDEV</code> must have provisions
for creating any device that may be found on the system, not just
those that a particular distribution installs.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="etcHostspecificSystemConfiguration"></a>3.7. /etc : Host-specific system configuration</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose6"></a>3.7.1. Purpose</h3></div></div></div><p>The <code class="filename">/etc</code> 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.

<a href="#ftn.idm236088529392" class="footnote" name="idm236088529392"><sup class="footnote">[2]</sup></a>
</p><p>
It is recommended that files be stored in subdirectories of
<code class="filename">/etc</code> rather than directly in
<code class="filename">/etc</code>.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="requirements3"></a>3.7.2. Requirements</h3></div></div></div><p>No binaries may be located under
<code class="filename">/etc</code>.</p><p>The following directories, or symbolic links to directories are
required in <code class="filename">/etc</code>:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left">opt</td><td align="left">Configuration for /opt</td></tr></tbody></table></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions5"></a>3.7.3. Specific Options</h3></div></div></div><p>The following directories, or symbolic links to directories must
be in <code class="filename">/etc</code>, if the corresponding subsystem is
installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left">X11</td><td align="left">Configuration for the X Window system (optional)</td></tr><tr><td align="left">sgml</td><td align="left">Configuration for SGML (optional)</td></tr><tr><td align="left">xml</td><td align="left">Configuration for XML (optional)</td></tr></tbody></table></div><p>The following files, or symbolic links to files, must be in
<code class="filename">/etc</code> if the corresponding subsystem is
installed:

<a href="#ftn.idm236088507872" class="footnote" name="idm236088507872"><sup class="footnote">[3]</sup></a>
</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">File</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">csh.login</code></td><td align="left">Systemwide initialization file for C shell logins (optional)</td></tr><tr><td align="left"><code class="filename">exports</code></td><td align="left">NFS filesystem access control list (optional)</td></tr><tr><td align="left"><code class="filename">fstab</code></td><td align="left">Static information about filesystems (optional)</td></tr><tr><td align="left"><code class="filename">ftpusers</code></td><td align="left">FTP daemon user access control list (optional)</td></tr><tr><td align="left"><code class="filename">gateways</code></td><td align="left">File which lists gateways for routed (optional)</td></tr><tr><td align="left"><code class="filename">gettydefs</code></td><td align="left">Speed and terminal settings used by getty (optional)</td></tr><tr><td align="left"><code class="filename">group</code></td><td align="left">User group file (optional)</td></tr><tr><td align="left"><code class="filename">host.conf</code></td><td align="left">Resolver configuration file (optional)</td></tr><tr><td align="left"><code class="filename">hosts</code></td><td align="left">Static information about host names (optional)</td></tr><tr><td align="left"><code class="filename">hosts.allow</code></td><td align="left">Host access file for TCP wrappers (optional)</td></tr><tr><td align="left"><code class="filename">hosts.deny</code></td><td align="left">Host access file for TCP wrappers (optional)</td></tr><tr><td align="left"><code class="filename">hosts.equiv</code></td><td align="left">List of trusted hosts for rlogin, rsh, rcp (optional)</td></tr><tr><td align="left"><code class="filename">hosts.lpd</code></td><td align="left">List of trusted hosts for lpd (optional)</td></tr><tr><td align="left"><code class="filename">inetd.conf</code></td><td align="left">Configuration file for inetd (optional)</td></tr><tr><td align="left"><code class="filename">inittab</code></td><td align="left">Configuration file for init (optional)</td></tr><tr><td align="left"><code class="filename">issue</code></td><td align="left">Pre-login message and identification file (optional)</td></tr><tr><td align="left"><code class="filename">ld.so.conf</code></td><td align="left">List of extra directories to search for shared libraries (optional)</td></tr><tr><td align="left"><code class="filename">motd</code></td><td align="left">Post-login message of the day file (optional)</td></tr><tr><td align="left"><code class="filename">mtab</code></td><td align="left">Dynamic information about filesystems (optional)</td></tr><tr><td align="left"><code class="filename">mtools.conf</code></td><td align="left">Configuration file for mtools (optional)</td></tr><tr><td align="left"><code class="filename">networks</code></td><td align="left">Static information about network names (optional)</td></tr><tr><td align="left"><code class="filename">passwd</code></td><td align="left">The password file (optional)</td></tr><tr><td align="left"><code class="filename">printcap</code></td><td align="left">The lpd printer capability database (optional)</td></tr><tr><td align="left"><code class="filename">profile</code></td><td align="left">Systemwide initialization file for sh shell logins (optional)</td></tr><tr><td align="left"><code class="filename">protocols</code></td><td align="left">IP protocol listing (optional)</td></tr><tr><td align="left"><code class="filename">resolv.conf</code></td><td align="left">Resolver configuration file (optional)</td></tr><tr><td align="left"><code class="filename">rpc</code></td><td align="left">RPC protocol listing (optional)</td></tr><tr><td align="left"><code class="filename">securetty</code></td><td align="left">TTY access control for root login (optional)</td></tr><tr><td align="left"><code class="filename">services</code></td><td align="left">Port names for network services (optional)</td></tr><tr><td align="left"><code class="filename">shells</code></td><td align="left">Pathnames of valid login shells (optional)</td></tr><tr><td align="left"><code class="filename">syslog.conf</code></td><td align="left">Configuration file for syslogd (optional)</td></tr></tbody></table></div><p><code class="filename">mtab</code> does not fit the static nature of
<code class="filename">/etc</code>: it is excepted for historical reasons.

</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="etcoptConfigurationFilesForOpt"></a>3.7.4. /etc/opt : Configuration files for /opt</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="purpose7"></a>3.7.4.1. Purpose</h4></div></div></div><p>Host-specific configuration files for add-on application
software packages must be installed within the directory
<code class="filename">/etc/opt/&lt;subdir&gt;</code>, where
<code class="filename">&lt;subdir&gt;</code> is the name of the subtree in
<code class="filename">/opt</code> where the static data from that package is
stored.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="requirements4"></a>3.7.4.2. Requirements</h4></div></div></div><p>No structure is imposed on the internal arrangement of
<code class="filename">/etc/opt/&lt;subdir&gt;</code>.</p><p>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
<code class="filename">/etc/opt/&lt;subdir&gt;</code>.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>Refer to the rationale for <code class="filename">/opt</code>.</p></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="etcx11ConfigurationForTheXWindowS"></a>3.7.5. /etc/X11 : Configuration for the X Window System (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="purpose8"></a>3.7.5.1. Purpose</h4></div></div></div><p><span class="emphasis"><em>/etc/X11</em></span> is the location for all X11
host-specific configuration.  This directory is necessary to allow
local control if <span class="emphasis"><em>/usr</em></span> is mounted read
only.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="specificOptions6"></a>3.7.5.2. Specific Options</h4></div></div></div><p>The following files, or symbolic links to files, must be in
<code class="filename">/etc/X11</code> if the corresponding subsystem is
installed:</p><div class="informaltable"><table border="0"><colgroup><col align="left" class="c1"><col align="left" class="c2"></colgroup><thead><tr><th align="left">File</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">xorg.conf</code></td><td align="left">The configuration file for X.org versions 7 and later (optional)</td></tr><tr><td align="left"><code class="filename">Xmodmap</code></td><td align="left">Global X11 keyboard modification file (optional)</td></tr></tbody></table></div><p>Subdirectories of <code class="filename">/etc/X11</code> may include
those for <code class="filename">xdm</code> and for any other programs (some
window managers, for example) that need them.

<a href="#ftn.idm236088427216" class="footnote" name="idm236088427216"><sup class="footnote">[5]</sup></a>
</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="etcsgmlConfigurationFilesForSgmlAn"></a>3.7.6. /etc/sgml : Configuration files for SGML (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="purpose9"></a>3.7.6.1. Purpose</h4></div></div></div><p>Generic configuration files defining high-level parameters of
the SGML systems are installed here.  Files with names
<code class="filename">*.conf</code> indicate generic configuration files.
File with names <code class="filename">*.cat</code> are the DTD-specific
centralized catalogs, containing references to all other catalogs
needed to use the given DTD.  The super catalog file
<code class="filename">catalog</code> references all the centralized
catalogs.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idm236088418512"></a>3.7.7. /etc/xml : Configuration files for XML (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idm236088417872"></a>3.7.7.1. Purpose</h4></div></div></div><p>Generic configuration files defining high-level parameters of
the XML systems are installed here.  Files with names
<code class="filename">*.conf</code> indicate generic configuration files.
The super catalog file
<code class="filename">catalog</code> references all the centralized
catalogs.</p></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="homeUserHomeDirectories"></a>3.8. /home : User home directories (optional)</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose10"></a>3.8.1. Purpose</h3></div></div></div><p><code class="filename">/home</code> is a fairly standard concept, but it
is clearly a site-specific filesystem.

<a href="#ftn.idm236088412656" class="footnote" name="idm236088412656"><sup class="footnote">[6]</sup></a>
The setup will differ from host to host.  Therefore, no program should
assume any specific location for a home directory, rather it
should query for it.
<a href="#ftn.idm236088405632" class="footnote" name="idm236088405632"><sup class="footnote">[7]</sup></a>

</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="requirements4a"></a>3.8.2. Requirements</h3></div></div></div><p>
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.
<a href="#ftn.idm236088400112" class="footnote" name="idm236088400112"><sup class="footnote">[8]</sup></a>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="homeReferences"></a>3.8.3. Home Directory Specifications and Conventions</h3></div></div></div><p>
A number of efforts have been made in the past to standardize 
the layout of home directories, 
including the XDG Base Directories specification
<a href="#ftn.idm236088397728" class="footnote" name="idm236088397728"><sup class="footnote">[9]</sup></a>
and the GLib conventions on user directory contents.
<a href="#ftn.idm236088395888" class="footnote" name="idm236088395888"><sup class="footnote">[10]</sup></a>
Additional efforts in this direction are possible in the future.
To accomodate software which makes use of these specifications and conventions,
distributions may create directory hierarchies which follow
the specifications and conventions. Those directory hierarchies may be located
underneath home directories.
</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="libEssentialSharedLibrariesAndKern"></a>3.9. /lib : Essential shared libraries and kernel modules</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose11"></a>3.9.1. Purpose</h3></div></div></div><p>The <code class="filename">/lib</code> directory contains those shared
library images needed to boot the system and run the commands in the
root filesystem, ie. by binaries in <code class="filename">/bin</code> and
<code class="filename">/sbin</code>.

<a href="#ftn.idm236088389760" class="footnote" name="idm236088389760"><sup class="footnote">[11]</sup></a>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="requirements5"></a>3.9.2. Requirements</h3></div></div></div><p>At least one of each of the following filename patterns are
required (they may be files, or symbolic links):</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">File</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">libc.so.*</code></td><td align="left">The dynamically-linked C library (optional)</td></tr><tr><td align="left"><code class="filename">ld*</code></td><td align="left">The execution time linker/loader (optional)</td></tr></tbody></table></div><p>If a C preprocessor is installed, <span class="emphasis"><em>/lib/cpp</em></span>
must be a reference to it, for historical reasons.

<a href="#ftn.idm236088374992" class="footnote" name="idm236088374992"><sup class="footnote">[12]</sup></a>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions7"></a>3.9.3. Specific Options</h3></div></div></div><p>The following directories, or symbolic links to directories,
must be in <code class="filename">/lib</code>, if the corresponding subsystem
is installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">modules</code></td><td align="left">Loadable kernel modules (optional)</td></tr></tbody></table></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="libltqualgtAlternateFormatEssential"></a>3.10. /lib<em class="replaceable"><code>&lt;qual&gt;</code></em> : Alternate format essential shared libraries (optional)</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose12"></a>3.10.1. Purpose</h3></div></div></div><p>There may be one or more variants of the
<code class="filename">/lib</code> directory on systems which support more than
one binary format requiring separate libraries.

<a href="#ftn.idm236088363216" class="footnote" name="idm236088363216"><sup class="footnote">[13]</sup></a>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="requirements6"></a>3.10.2. Requirements</h3></div></div></div><p>If one or more of these directories exist, the requirements for
their contents are the same as the normal <code class="filename">/lib</code>
directory, except that <code class="filename">/lib<em class="replaceable"><code>&lt;qual&gt;</code></em>/cpp</code> is
not required.

<a href="#ftn.idm236088357376" class="footnote" name="idm236088357376"><sup class="footnote">[14]</sup></a></p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="mediaMountPoint"></a>3.11. /media : Mount point for removable media</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purposeMediaMountPoint"></a>3.11.1. Purpose</h3></div></div></div><p>This directory contains subdirectories which are used as mount
points for removable media such as floppy disks, cdroms and zip
disks.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>Historically there have been a number of other different places
used to mount removable media such as <code class="filename">/cdrom</code>,
<code class="filename">/mnt</code> or <code class="filename">/mnt/cdrom</code>. Placing
the mount points for all removable media directly in the root
directory would potentially result in a large number of extra
directories in <code class="filename">/</code>. Although the use of
subdirectories in <code class="filename">/mnt</code> as a mount point has
recently been common, it conflicts with a much older tradition of
using <code class="filename">/mnt</code> directly as a temporary mount point.
</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptionsMediaMount"></a>3.11.2. Specific Options</h3></div></div></div><p>The following directories, or symbolic links to directories,
must be in <code class="filename">/media</code>, if the corresponding subsystem
is installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">floppy</code></td><td align="left">Floppy drive (optional)</td></tr><tr><td align="left"><code class="filename">cdrom</code></td><td align="left">CD-ROM drive (optional)</td></tr><tr><td align="left"><code class="filename">cdrecorder</code></td><td align="left">CD writer (optional)</td></tr><tr><td align="left"><code class="filename">zip</code></td><td align="left">Zip drive (optional)</td></tr></tbody></table></div><p>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.

</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="mntMountPointForATemporarilyMount"></a>3.12. /mnt : Mount point for a temporarily mounted filesystem</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose13"></a>3.12.1. Purpose</h3></div></div></div><p>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.</p><p>This directory must not be used by installation programs: a
suitable temporary directory not in use by the system must be used
instead.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="optAddonApplicationSoftwarePackages"></a>3.13. /opt : Add-on application software packages</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose14"></a>3.13.1. Purpose</h3></div></div></div><p><code class="filename">/opt</code> is reserved for the installation of
add-on application software packages.</p><p>A package to be installed in <code class="filename">/opt</code> must
locate its static files in a separate
<code class="filename">/opt/&lt;package&gt;</code> or
<code class="filename">/opt/&lt;provider&gt;</code> directory
tree, where <code class="filename">&lt;package&gt;</code> is a name that
describes the software package and
<code class="filename">&lt;provider&gt;</code> is the provider's LANANA
registered name.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="requirements7"></a>3.13.2. Requirements</h3></div></div></div><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left">&lt;package&gt;</td><td align="left">Static package objects</td></tr><tr><td align="left">&lt;provider&gt;</td><td align="left">LANANA registered provider name</td></tr></tbody></table></div><p>The directories <code class="filename">/opt/bin</code>,
<code class="filename">/opt/doc</code>, <code class="filename">/opt/include</code>,
<code class="filename">/opt/info</code>, <code class="filename">/opt/lib</code>, and
<code class="filename">/opt/man</code> 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.</p><p>Programs to be invoked by users must be located in the directory
<code class="filename">/opt/&lt;package&gt;/bin</code> or under the
<code class="filename">/opt/&lt;provider&gt;</code> hierarchy. If the package
includes UNIX manual pages, they must be located in
<code class="filename">/opt/&lt;package&gt;/share/man</code> or under the
<code class="filename">/opt/&lt;provider&gt;</code> hierarchy, and the same
substructure as <code class="filename">/usr/share/man</code> must be
used.</p><p>Package files that are variable (change in normal operation)
must be installed in <code class="filename">/var/opt</code>.  See the section
on <code class="filename">/var/opt</code> for more information.</p><p>Host-specific configuration files must be installed in
<code class="filename">/etc/opt</code>.  See the section on
<code class="filename">/etc</code> for more information.</p><p>No other package files may exist outside the
<code class="filename">/opt</code>, <code class="filename">/var/opt</code>, and
<code class="filename">/etc/opt</code> 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 <code class="filename">/var/lock</code> and devices must be
located in <code class="filename">/dev</code>.</p><p>Distributions may install and otherwise manage software in
<code class="filename">/opt</code> under an appropriately registered
subdirectory.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>The use of <code class="filename">/opt</code> for add-on software is a
well-established practice in the UNIX community.  The System V
Application Binary Interface [AT&amp;T 1990], based on the System V
Interface Definition (Third Edition), provides for an
<code class="filename">/opt</code> structure very similar to the one defined
here.</p><p>The Intel Binary Compatibility Standard v. 2 (iBCS2) also
provides a similar structure for <code class="filename">/opt</code>.</p><p>Generally, all data required to support a package on a system
must be present within <code class="filename">/opt/&lt;package&gt;</code>,
including files intended to be copied into
<code class="filename">/etc/opt/&lt;package&gt;</code> and
<code class="filename">/var/opt/&lt;package&gt;</code> as well as reserved
directories in <code class="filename">/opt</code>.</p><p>The minor restrictions on distributions using
<code class="filename">/opt</code> 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.</p><p>The structure of the directories below
<code class="filename">/opt/&lt;provider&gt;</code> is left up to the packager
of the software, though it is recommended that packages are installed
in <code class="filename">/opt/&lt;provider&gt;/&lt;package&gt;</code> and
follow a similar structure to the guidelines for
<code class="filename">/opt/&lt;package&gt;</code>. A valid reason for diverging from
this structure is for support packages which may have files installed
in <code class="filename">/opt/&lt;provider&gt;/lib</code> or
<code class="filename">/opt/&lt;provider&gt;/bin</code>.</p></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="rootHomeDirectoryForTheRootUser"></a>3.14. /root : Home directory for the root user (optional)</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose15"></a>3.14.1. Purpose</h3></div></div></div><p>The root account's home directory may be determined by developer
or local preference, but this is the recommended default
location.

<a href="#ftn.idm236088285600" class="footnote" name="idm236088285600"><sup class="footnote">[16]</sup></a>
</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="runRuntimeVariableData"></a>3.15. /run : Run-time variable data</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="runPurpose"></a>3.15.1. Purpose</h3></div></div></div><p>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.</p><p>The purposes of this directory were once served by
<code class="filename">/var/run</code>.  In general, programs may continue to
use <code class="filename">/var/run</code> to fulfill the requirements set out
for <code class="filename">/run</code> for the purposes of backwards
compatibility.  Programs which have migrated to use
<code class="filename">/run</code> should cease their usage of
<code class="filename">/var/run</code>, except as noted in the section on
<code class="filename">/var/run</code>.</p><p>Programs may have a subdirectory of
<code class="filename">/run</code>; this is encouraged for programs that
use more than one run-time file.  Users may also have a subdirectory
of <code class="filename">/run</code>, although care must be taken to
appropriately limit access rights to prevent unauthorized use of
<code class="filename">/run</code> itself and other subdirectories.

<a href="#ftn.idm236088274176" class="footnote" name="idm236088274176"><sup class="footnote">[17]</sup></a>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="runRequirements"></a>3.15.2. Requirements</h3></div></div></div><p>
Process identifier (PID) files, which were originally placed in
<code class="filename">/etc</code>, must be placed in
<code class="filename">/run</code>.  The naming convention for PID files is
<code class="filename">&lt;program-name&gt;.pid</code>.  For example, the
<span class="command"><strong>crond</strong></span> PID file is named
<code class="filename">/run/crond.pid</code>.</p><p>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
<span class="command"><strong>crond</strong></span> was process number 25,
<code class="filename">/run/crond.pid</code> would contain three characters:
two, five, and newline.</p><p>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.</p><p>System programs that maintain transient UNIX-domain sockets must
place them in this directory or an appropriate subdirectory as
outlined above.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="sbinSystemBinaries"></a>3.16. /sbin : System binaries</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose16"></a>3.16.1. Purpose</h3></div></div></div><p>Utilities used for system administration (and other root-only
commands) are stored in <code class="filename">/sbin</code>,
<code class="filename">/usr/sbin</code>, and
<code class="filename">/usr/local/sbin</code>.  <code class="filename">/sbin</code>
contains binaries essential for booting, restoring, recovering, and/or
repairing the system in addition to the binaries in
<code class="filename">/bin</code>.

Programs executed after
<code class="filename">/usr</code> is known to be mounted (when there are no
problems) are generally placed into <code class="filename">/usr/sbin</code>.
Locally-installed system administration programs should be placed into
<code class="filename">/usr/local/sbin</code>.

<a href="#ftn.idm236088255488" class="footnote" name="idm236088255488"><sup class="footnote">[19]</sup></a></p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="requirements8"></a>3.16.2. Requirements</h3></div></div></div><p>There must be no subdirectories in <code class="filename">/sbin</code>.</p><p>The following commands, or symbolic links to commands, are
required in <code class="filename">/sbin</code>:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Command</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><span class="command"><strong>shutdown</strong></span></td><td align="left">Command to bring the system down.</td></tr></tbody></table></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions8"></a>3.16.3. Specific Options</h3></div></div></div><p>The following files, or symbolic links to files, must be in
<code class="filename">/sbin</code> if the corresponding subsystem is
installed:</p><div class="informaltable"><table border="0"><colgroup><col align="left" class="c1"><col align="left" class="c2"></colgroup><thead><tr><th align="left">Command</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">fastboot</code></td><td align="left">Reboot the system without checking the disks (optional)</td></tr><tr><td align="left"><code class="filename">fasthalt</code></td><td align="left">Stop the system without checking the disks (optional)</td></tr><tr><td align="left"><code class="filename">fdisk</code></td><td align="left">Partition table manipulator (optional)</td></tr><tr><td align="left"><code class="filename">fsck</code></td><td align="left">File system check and repair utility (optional)</td></tr><tr><td align="left"><code class="filename">fsck.*</code></td><td align="left">File system check and repair utility for a specific filesystem (optional)</td></tr><tr><td align="left"><code class="filename">getty</code></td><td align="left">The getty program (optional)</td></tr><tr><td align="left"><code class="filename">halt</code></td><td align="left">Command to stop the system (optional)</td></tr><tr><td align="left"><code class="filename">ifconfig</code></td><td align="left">Configure a network interface (optional)</td></tr><tr><td align="left"><code class="filename">init</code></td><td align="left">Initial process (optional)</td></tr><tr><td align="left"><code class="filename">mkfs</code></td><td align="left">Command to build a filesystem (optional)</td></tr><tr><td align="left"><code class="filename">mkfs.*</code></td><td align="left">Command to build a specific filesystem (optional)</td></tr><tr><td align="left"><code class="filename">mkswap</code></td><td align="left">Command to set up a swap area (optional)</td></tr><tr><td align="left"><code class="filename">reboot</code></td><td align="left">Command to reboot the system (optional)</td></tr><tr><td align="left"><code class="filename">route</code></td><td align="left">IP routing table utility (optional)</td></tr><tr><td align="left"><code class="filename">swapon</code></td><td align="left">Enable paging and swapping (optional)</td></tr><tr><td align="left"><code class="filename">swapoff</code></td><td align="left">Disable paging and swapping (optional)</td></tr><tr><td align="left"><code class="filename">update</code></td><td align="left">Daemon to periodically flush filesystem buffers (optional)</td></tr></tbody></table></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="srvDataForServicesProvidedBySystem"></a>3.17. /srv : Data for services provided by this system</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose16a"></a>3.17.1. Purpose</h3></div></div></div><p><code class="filename">/srv</code> contains site-specific data which is
served by this system.

</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>
This main purpose of specifying this is so that users may find the
location of the data files for a 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.  If the directory and file structure of the data is not 
exposed to consumers, it should go in <code class="filename">/var/lib</code>.
</p><p>
The methodology used to name subdirectories of
<code class="filename">/srv</code> is unspecified as there is currently no
consensus on how this should be done.  One method for structuring data
under <code class="filename">/srv</code> is by protocol,
eg. <code class="filename">ftp</code>, <code class="filename">rsync</code>,
<code class="filename">www</code>, and <code class="filename">cvs</code>. On large
systems it can be useful to structure <code class="filename">/srv</code> by
administrative context, such as <code class="filename">/srv/physics/www</code>,
<code class="filename">/srv/compsci/cvs</code>, etc. This setup will differ
from host to host. Therefore, no program should rely on a specific
subdirectory structure of <code class="filename">/srv</code> existing or data
necessarily being stored in <code class="filename">/srv</code>.  However
<code class="filename">/srv</code> should always exist on FHS compliant systems
and should be used as the default location for such data.
</p><p>
Distributions must take care not to remove locally placed files in
these directories without administrator permission.
<a href="#ftn.idm236088192752" class="footnote" name="idm236088192752"><sup class="footnote">[20]</sup></a>
</p></div><p>
</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="tmpTemporaryFiles"></a>3.18. /tmp : Temporary files</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose17"></a>3.18.1. Purpose</h3></div></div></div><p>The <code class="filename">/tmp</code> directory must be made available
for programs that require temporary files.</p><p>Programs must not assume that any files or directories in
<code class="filename">/tmp</code> are preserved between invocations of the
program.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>IEEE standard POSIX.1-2008 lists requirements 
similar to the above section.</p><p>Although data stored in <code class="filename">/tmp</code> may be deleted
in a site-specific manner, it is recommended that files and
directories located in <code class="filename">/tmp</code> be deleted whenever
the system is booted.</p><p>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.</p></div></div></div><div class="footnotes"><br><hr style="width:100; text-align:left;margin-left: 0"><div id="ftn.idm236088643344" class="footnote"><p><a href="#idm236088643344" class="para"><sup class="para">[1] </sup></a>
Command binaries that are not essential enough to place into
<code class="filename">/bin</code> must be placed in
<code class="filename">/usr/bin</code>, instead.  Items that are required only
by non-root users (the X Window System, <code class="filename">chsh</code>,
etc.) are generally not essential enough to be placed into the root
partition.
</p></div><div id="ftn.idm236088529392" class="footnote"><p><a href="#idm236088529392" class="para"><sup class="para">[2] </sup></a>
To be clear, <code class="filename">/etc</code> may contain executable scripts,
such as the command scripts commonly called by
<code class="filename">init</code> to start and shut down the system and start
daemon processes.  "Executable binary" in this context refers to
direct machine code or pseudocode not in a human-readable format, such
as native ELF executables.
</p></div><div id="ftn.idm236088507872" class="footnote"><p><a href="#idm236088507872" class="para"><sup class="para">[3] </sup></a>
Systems that use the shadow password suite will have additional
configuration files in <code class="filename">/etc</code>
(<code class="filename">/etc/shadow</code> and others) and programs in
<code class="filename">/usr/sbin</code> (<span class="command"><strong>useradd</strong></span>,
<span class="command"><strong>usermod</strong></span>, and others).
</p></div><div id="ftn.idm236088451984" class="footnote"><p><a href="#idm236088451984" class="para"><sup class="para">[4] </sup></a>
On some Linux systems, this may be a symbolic link to
<code class="filename">/proc/mounts</code>, in which case this exception is not
required.
</p></div><div id="ftn.idm236088427216" class="footnote"><p><a href="#idm236088427216" class="para"><sup class="para">[5] </sup></a>
<code class="filename">/etc/X11/xdm</code> holds the configuration files for
<code class="filename">xdm</code>.  These are most of the files previously
found in <code class="filename">/usr/lib/X11/xdm</code>.  Some local variable
data for <code class="filename">xdm</code> is stored in
<code class="filename">/var/lib/xdm</code>.
</p></div><div id="ftn.idm236088412656" class="footnote"><p><a href="#idm236088412656" class="para"><sup class="para">[6] </sup></a>
Different people prefer to place user accounts in a variety of places.
This section describes only a suggested placement for user home
directories; nevertheless we recommend that all FHS-compliant
distributions use this as the default location for user home
directories. Non-login accounts created for administrative
purposes often have their home directories elsewhere.</p><p>On smaller systems, each user's home directory is typically implemented
as a subdirectory directly under <code class="filename">/home</code>, for example
<code class="filename">/home/smith</code>, <code class="filename">/home/torvalds</code>,
<code class="filename">/home/operator</code>, etc.  On large systems
(especially when the <code class="filename">/home</code> directories are shared
amongst many hosts using NFS) it is useful to subdivide user home
directories.  Subdivision may be accomplished by using subdirectories
such as <code class="filename">/home/staff</code>,
<code class="filename">/home/guests</code>,
<code class="filename">/home/students</code>, etc.
</p></div><div id="ftn.idm236088405632" class="footnote"><p><a href="#idm236088405632" class="para"><sup class="para">[7] </sup></a>
To find a user's home directory, use a library function such
as <code class="function">getpwent</code>,
<code class="function">getpwent_r</code> of
<code class="function">fgetpwent</code> rather than relying
on <code class="filename">/etc/passwd</code> because user information may be
stored remotely using systems such as NIS.
</p></div><div id="ftn.idm236088400112" class="footnote"><p><a href="#idm236088400112" class="para"><sup class="para">[8] </sup></a>
It is recommended that, apart from autosave and lock files, programs
should refrain from creating non dot files or directories in a home
directory without user consent.
</p></div><div id="ftn.idm236088397728" class="footnote"><p><a href="#idm236088397728" class="para"><sup class="para">[9] </sup></a>Found at
<a class="ulink" href="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html" target="_top">http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html</a>
and
<a class="ulink" href="http://www.freedesktop.org/wiki/Software/xdg-user-dirs" target="_top">http://www.freedesktop.org/wiki/Software/xdg-user-dirs</a>.
</p></div><div id="ftn.idm236088395888" class="footnote"><p><a href="#idm236088395888" class="para"><sup class="para">[10] </sup></a>A description of GLib's conventions can be found in the
documentation for GUserDirectory, at
<a class="ulink" href="http://developer.gnome.org/glib/unstable/glib-Miscellaneous-Utility-Functions.html#GUserDirectory" target="_top">http://developer.gnome.org/glib/unstable/glib-Miscellaneous-Utility-Functions.html#GUserDirectory</a>.
</p></div><div id="ftn.idm236088389760" class="footnote"><p><a href="#idm236088389760" class="para"><sup class="para">[11] </sup></a>
Shared libraries that are only necessary for binaries in
<code class="filename">/usr</code> (such as any X Window binaries) must not be
in <code class="filename">/lib</code>. Only the shared libraries required to
run binaries in <code class="filename">/bin</code> and
<code class="filename">/sbin</code> may be here.  In particular, the library
<code class="filename">libm.so.*</code> may also be placed in
<code class="filename">/usr/lib</code> if it is not required by anything in
<code class="filename">/bin</code> or <code class="filename">/sbin</code>.
</p></div><div id="ftn.idm236088374992" class="footnote"><p><a href="#idm236088374992" class="para"><sup class="para">[12] </sup></a>
The usual placement of this binary is <code class="filename">/usr/bin/cpp</code>.
</p></div><div id="ftn.idm236088363216" class="footnote"><p><a href="#idm236088363216" class="para"><sup class="para">[13] </sup></a>
This is commonly used for 64-bit or 32-bit support on
systems which support multiple binary formats, but require libraries
of the same name.  In this case, <code class="filename">/lib32</code> and
<code class="filename">/lib64</code> might be the library directories, and
<code class="filename">/lib</code> a symlink to one of them.
</p></div><div id="ftn.idm236088357376" class="footnote"><p><a href="#idm236088357376" class="para"><sup class="para">[14] </sup></a>
<code class="filename">/lib<em class="replaceable"><code>&lt;qual&gt;</code></em>/cpp</code> is still permitted: this
allows the case where <code class="filename">/lib</code> and
<code class="filename">/lib<em class="replaceable"><code>&lt;qual&gt;</code></em></code> are the same (one is a symbolic
link to the other). </p></div><div id="ftn.idm236088334544" class="footnote"><p><a href="#idm236088334544" class="para"><sup class="para">[15] </sup></a>
A compliant distribution with two CDROM drives might have
<code class="filename">/media/cdrom0</code> and
<code class="filename">/media/cdrom1</code> with
<code class="filename">/media/cdrom</code> a symlink to either of these.
</p></div><div id="ftn.idm236088285600" class="footnote"><p><a href="#idm236088285600" class="para"><sup class="para">[16] </sup></a>If the home directory of the root account is not
stored on the root partition it will be necessary to make certain it
will default to <code class="filename">/</code> if it cannot be
located.</p><p>We recommend against using the root account for tasks that can be
performed as an unprivileged user, and that it be used solely for system
administration.  For this reason, we recommend that subdirectories for
mail and other applications not appear in the root account's home
directory, and that mail for administration roles such as root,
postmaster, and webmaster be forwarded to an appropriate user.
</p></div><div id="ftn.idm236088274176" class="footnote"><p><a href="#idm236088274176" class="para"><sup class="para">[17] </sup></a>
<code class="filename">/run</code> should not be writable for unprivileged
users; it is a major security problem if any user can write in this
directory.  User-specific subdirectories should be writable only by
each directory's owner.
</p></div><div id="ftn.idm236088259440" class="footnote"><p><a href="#idm236088259440" class="para"><sup class="para">[18] </sup></a>
Originally, <code class="filename">/sbin</code> binaries were kept in
<code class="filename">/etc</code>.  
</p></div><div id="ftn.idm236088255488" class="footnote"><p><a href="#idm236088255488" class="para"><sup class="para">[19] </sup></a>Deciding what things go into
<span class="emphasis"><em>"sbin"</em></span> directories is simple: if a normal (not a
system administrator) user will ever run it directly, then it must be
placed in one of the <span class="emphasis"><em>"bin"</em></span> directories.  Ordinary
users should not have to place any of the <code class="filename">sbin</code>
directories in their path.</p><p>For example, files such as <span class="command"><strong>chfn</strong></span> which users
only occasionally use must still be placed in
<code class="filename">/usr/bin</code>.  <span class="command"><strong>ping</strong></span>, although it
is absolutely necessary for root (network recovery and diagnosis) is
often used by users and must live in <code class="filename">/bin</code> for
that reason.</p><p>We recommend that users have read and execute permission for
everything in <code class="filename">/sbin</code> except, perhaps, certain
setuid and setgid programs.  The division between
<code class="filename">/bin</code> and <code class="filename">/sbin</code> was not
created for security reasons or to prevent users from seeing the
operating system, but to provide a good partition between binaries
that everyone uses and ones that are primarily used for administration
tasks.  There is no inherent security advantage in making
<code class="filename">/sbin</code> off-limits for users.
</p></div><div id="ftn.idm236088192752" class="footnote"><p><a href="#idm236088192752" class="para"><sup class="para">[20] </sup></a>
This is particularly important as these areas will often contain both
files initially installed by the distributor, and those added by the
administrator.
</p></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="theUsrHierarchy"></a>Chapter 4. The /usr Hierarchy</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#purpose18">4.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements9">4.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions9">4.3. Specific Options</a></span></dt><dt><span class="section"><a href="#usrbinMostUserCommands">4.4. /usr/bin : Most user commands</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose20">4.4.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements9a">4.4.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions11">4.4.3. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#usrincludeDirectoryForStandardInclu">4.5. /usr/include : Directory for standard include files.</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose21">4.5.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions12">4.5.2. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#usrlibLibrariesForProgrammingAndPa">4.6. /usr/lib : Libraries for programming and packages</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose22">4.6.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions13">4.6.2. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#usrlibexec">4.7. /usr/libexec : Binaries run by other programs (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#usrlibexecPurpose">4.7.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#usrlibltqualgtAlternateFormatLibrari">4.8. /usr/lib<em class="replaceable"><code>&lt;qual&gt;</code></em> : Alternate format libraries (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose23">4.8.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#usrlocalLocalHierarchy">4.9. /usr/local : Local hierarchy</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose24">4.9.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements10">4.9.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions14">4.9.3. Specific Options</a></span></dt><dt><span class="section"><a href="#usrlocalshare1">4.9.4. /usr/local/share : Local architecture-independent hierarchy</a></span></dt></dl></dd><dt><span class="section"><a href="#usrsbinNonessentialStandardSystemBi">4.10. /usr/sbin : Non-essential standard system binaries</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose25">4.10.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements10a">4.10.2. Requirements</a></span></dt></dl></dd><dt><span class="section"><a href="#usrshareArchitectureindependentData">4.11. /usr/share : Architecture-independent data</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose26">4.11.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements11">4.11.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions15">4.11.3. Specific Options</a></span></dt><dt><span class="section"><a href="#usrsharecolorColorManagement">4.11.4. /usr/share/color : Color management information (optional)</a></span></dt><dt><span class="section"><a href="#usrsharedictWordLists">4.11.5. /usr/share/dict : Word lists (optional)</a></span></dt><dt><span class="section"><a href="#usrsharemanManualPages">4.11.6. /usr/share/man : Manual pages</a></span></dt><dt><span class="section"><a href="#usrsharemiscMiscellaneousArchitecture">4.11.7. /usr/share/misc : Miscellaneous architecture-independent data</a></span></dt><dt><span class="section"><a href="#usrshareppd">4.11.8. /usr/share/ppd : Printer definitions (optional)</a></span></dt><dt><span class="section"><a href="#usrsharesgmlSgmlAndXmlData">4.11.9. /usr/share/sgml : SGML data (optional)</a></span></dt><dt><span class="section"><a href="#idm236087237360">4.11.10. /usr/share/xml : XML data (optional)</a></span></dt></dl></dd><dt><span class="section"><a href="#usrsrcSourceCode">4.12. /usr/src : Source code (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose30">4.12.1. Purpose</a></span></dt></dl></dd></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="purpose18"></a>4.1. Purpose</h2></div></div></div><p><code class="filename">/usr</code> is the second major section of the
filesystem.  <code class="filename">/usr</code> is shareable, read-only data.
That means that <code class="filename">/usr</code> 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.</p><p>Large software packages must not use a direct subdirectory under
the <code class="filename">/usr</code> hierarchy.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="requirements9"></a>4.2. Requirements</h2></div></div></div><p>The following directories, or symbolic links to directories, are
required in <code class="filename">/usr</code>.</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">bin</code></td><td align="left">Most user commands</td></tr><tr><td align="left"><code class="filename">lib</code></td><td align="left">Libraries</td></tr><tr><td align="left"><code class="filename">local</code></td><td align="left">Local hierarchy (empty after main installation)</td></tr><tr><td align="left"><code class="filename">sbin</code></td><td align="left">Non-vital system binaries</td></tr><tr><td align="left"><code class="filename">share</code></td><td align="left">Architecture-independent data</td></tr></tbody></table></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="specificOptions9"></a>4.3. Specific Options</h2></div></div></div><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">games</code></td><td align="left">Games and educational binaries (optional)</td></tr><tr><td align="left"><code class="filename">include</code></td><td align="left">Header files included by C programs</td></tr><tr><td align="left"><code class="filename">libexec</code></td><td align="left">Binaries run by other programs (optional)</td></tr><tr><td align="left"><code class="filename">lib<em class="replaceable"><code>&lt;qual&gt;</code></em></code></td><td align="left">Alternate Format Libraries (optional)</td></tr><tr><td align="left"><code class="filename">src</code></td><td align="left">Source code (optional)</td></tr></tbody></table></div><p>An exception is made for the X Window System because of
considerable precedent and widely-accepted practice.</p><p>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
<code class="filename">/var</code> hierarchy.</p><pre class="screen">
    /usr/spool -&gt; /var/spool
    /usr/tmp -&gt; /var/tmp
    /usr/spool/locks -&gt; /var/lock
</pre><p>Once a system no longer requires any one of the above symbolic links,
the link may be removed, if desired.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="usrbinMostUserCommands"></a>4.4. /usr/bin : Most user commands</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose20"></a>4.4.1. Purpose</h3></div></div></div><p>This is the primary directory of executable commands on the
system.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="requirements9a"></a>4.4.2. Requirements</h3></div></div></div><p>There must be no subdirectories in <code class="filename">/usr/bin</code>.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions11"></a>4.4.3. Specific Options</h3></div></div></div><p>The following files, or symbolic links to files, must be in
<code class="filename">/usr/bin</code>, if the corresponding subsystem is
installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Command</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><span class="command"><strong>perl</strong></span></td><td align="left">The Practical Extraction and Report Language (optional)</td></tr><tr><td align="left"><span class="command"><strong>python</strong></span></td><td align="left">The Python interpreted language (optional)</td></tr><tr><td align="left"><span class="command"><strong>tclsh</strong></span></td><td align="left">Simple shell containing Tcl interpreter (optional)</td></tr><tr><td align="left"><span class="command"><strong>wish</strong></span></td><td align="left">Simple Tcl/Tk windowing shell (optional)</td></tr><tr><td align="left"><span class="command"><strong>expect</strong></span></td><td align="left">Program for interactive dialog (optional)</td></tr></tbody></table></div><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>In many executable scripts, the interpreter to be invoked to
execute the script is specified using 
<code class="filename">#!<em class="replaceable"><code>path_to_interpreter</code></em></code> 
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 <code class="filename">/bin</code> 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.
</p></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="usrincludeDirectoryForStandardInclu"></a>4.5. /usr/include : Directory for standard include files.</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose21"></a>4.5.1. Purpose</h3></div></div></div><p>This is where all of the system's general-use include files for the C
programming language should be placed.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions12"></a>4.5.2. Specific Options</h3></div></div></div><p>The following directories, or symbolic links to directories,
must be in <code class="filename">/usr/include</code>, if the corresponding
subsystem is installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left">bsd</td><td align="left">BSD compatibility include files (optional)</td></tr></tbody></table></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="usrlibLibrariesForProgrammingAndPa"></a>4.6. /usr/lib : Libraries for programming and packages</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose22"></a>4.6.1. Purpose</h3></div></div></div><p><code class="filename">/usr/lib</code> includes object files and libraries.
<a href="#ftn.idm236087593904" class="footnote" name="idm236087593904"><sup class="footnote">[21]</sup></a>
On some systems, it may also include internal binaries that are not
intended to be executed directly by users or shell scripts.
<a href="#ftn.idm236087592496" class="footnote" name="idm236087592496"><sup class="footnote">[22]</sup></a>
</p><p>Applications may use a single subdirectory under
<code class="filename">/usr/lib</code>.  If an application uses a subdirectory,
all architecture-dependent data exclusively used by the application
must be placed within that subdirectory.

<a href="#ftn.idm236087588928" class="footnote" name="idm236087588928"><sup class="footnote">[23]</sup></a></p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions13"></a>4.6.2. Specific Options</h3></div></div></div><p>For historical reasons, <span class="command"><strong>/usr/lib/sendmail</strong></span>
must be a symbolic link which resolves to the
<span class="emphasis"><em>sendmail</em></span>-compatible command provided by the
system's mail transfer agent, if the latter exists.

<a href="#ftn.idm236087578304" class="footnote" name="idm236087578304"><sup class="footnote">[25]</sup></a></p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="usrlibexec"></a>4.7. /usr/libexec : Binaries run by other programs (optional)</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="usrlibexecPurpose"></a>4.7.1. Purpose</h3></div></div></div><p><code class="filename">/usr/libexec</code> includes internal binaries
that are not intended to be executed directly by users or shell
scripts.  Applications may use a single subdirectory under
<code class="filename">/usr/libexec</code>.</p><p>Applications which use <code class="filename">/usr/libexec</code> in this
way must not also use <code class="filename">/usr/lib</code> to store internal
binaries, though they may use <code class="filename">/usr/lib</code> for the
other purposes documented here.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>Some previous versions of this document did not support
<code class="filename">/usr/libexec</code>, despite it being standard practice
in a number of environments.
<a href="#ftn.idm236087566784" class="footnote" name="idm236087566784"><sup class="footnote">[26]</sup></a>
To accomodate this restriction, it became common practice to use
<code class="filename">/usr/lib</code> instead.  Either practice is now
acceptable, but each application must choose one way or the other to
organize itself.
</p></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="usrlibltqualgtAlternateFormatLibrari"></a>4.8. /usr/lib<em class="replaceable"><code>&lt;qual&gt;</code></em> : Alternate format libraries (optional)</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose23"></a>4.8.1. Purpose</h3></div></div></div><p><code class="filename">/usr/lib<em class="replaceable"><code>&lt;qual&gt;</code></em></code> performs the same role as <code class="filename">/usr/lib</code> for an
alternate binary format, except that the symbolic links
<code class="filename">/usr/lib<em class="replaceable"><code>&lt;qual&gt;</code></em>/sendmail</code> and <code class="filename">/usr/lib<em class="replaceable"><code>&lt;qual&gt;</code></em>/X11</code> are not required.

<a href="#ftn.idm236087558816" class="footnote" name="idm236087558816"><sup class="footnote">[27]</sup></a></p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="usrlocalLocalHierarchy"></a>4.9. /usr/local : Local hierarchy</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose24"></a>4.9.1. Purpose</h3></div></div></div><p>The <code class="filename">/usr/local</code> 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 <code class="filename">/usr</code>.</p><p>Locally installed software must be placed within
<code class="filename">/usr/local</code> rather than <code class="filename">/usr</code>
unless it is being installed to replace or upgrade software in
<code class="filename">/usr</code>.

<a href="#ftn.idm236087550400" class="footnote" name="idm236087550400"><sup class="footnote">[28]</sup></a>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="requirements10"></a>4.9.2. Requirements</h3></div></div></div><p>The following directories, or symbolic links to directories,
must be in <code class="filename">/usr/local</code></p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">bin</code></td><td align="left">Local binaries</td></tr><tr><td align="left"><code class="filename">etc</code></td><td align="left">Host-specific system configuration for local binaries</td></tr><tr><td align="left"><code class="filename">games</code></td><td align="left">Local game binaries</td></tr><tr><td align="left"><code class="filename">include</code></td><td align="left">Local C header files</td></tr><tr><td align="left"><code class="filename">lib</code></td><td align="left">Local libraries</td></tr><tr><td align="left"><code class="filename">man</code></td><td align="left">Local online manuals</td></tr><tr><td align="left"><code class="filename">sbin</code></td><td align="left">Local system binaries</td></tr><tr><td align="left"><code class="filename">share</code></td><td align="left">Local architecture-independent hierarchy</td></tr><tr><td align="left"><code class="filename">src</code></td><td align="left">Local source code</td></tr></tbody></table></div><p>No other directories, except those listed below, may be in
<code class="filename">/usr/local</code> after first installing a FHS-compliant
system.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions14"></a>4.9.3. Specific Options</h3></div></div></div><p>If directories <code class="filename">/lib<em class="replaceable"><code>&lt;qual&gt;</code></em></code> or
<code class="filename">/usr/lib<em class="replaceable"><code>&lt;qual&gt;</code></em></code> exist, the equivalent
directories must also exist in <code class="filename">/usr/local</code>.</p><p><code class="filename">/usr/local/etc</code> may be a symbolic link to
<code class="filename">/etc/local</code>.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>The consistency of <code class="filename">/usr/local/etc</code> is
beneficial to installers, and is already used in other systems.  As
all of <code class="filename">/usr/local</code> needs to be backed up to
reproduce a system, it introduces no additional maintenance overhead,
but a symlink to <code class="filename">/etc/local</code> is suitable if
systems want all their configuration under one hierarchy.
</p><p>
Note that <code class="filename">/usr/etc</code> is still not allowed: programs
in <code class="filename">/usr</code> should place configuration files in
<code class="filename">/etc</code>.
</p></div><p>If the directory <code class="filename">/usr/share/color</code> exists as
specified in this document, then the directory
<code class="filename">/usr/local/share/color</code> must also exist, governed
by the same rules as <code class="filename">/usr/share/color</code>.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>This usage allows the sysadmin a place to install color profiles
manually when necessary.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="usrlocalshare1"></a>4.9.4. /usr/local/share : Local architecture-independent hierarchy</h3></div></div></div><p>The requirements for the contents of this directory are the same
as for <code class="filename">/usr/share</code>.

</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="usrsbinNonessentialStandardSystemBi"></a>4.10. /usr/sbin : Non-essential standard system binaries</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose25"></a>4.10.1. Purpose</h3></div></div></div><p>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 <code class="filename">/usr</code>, or other essential functions must
be placed in <code class="filename">/sbin</code> instead.

<a href="#ftn.idm236087505920" class="footnote" name="idm236087505920"><sup class="footnote">[29]</sup></a></p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="requirements10a"></a>4.10.2. Requirements</h3></div></div></div><p>There must be no subdirectories in <code class="filename">/usr/sbin</code>.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="usrshareArchitectureindependentData"></a>4.11. /usr/share : Architecture-independent data</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose26"></a>4.11.1. Purpose</h3></div></div></div><p>The <code class="filename">/usr/share</code> hierarchy is for all
read-only architecture independent data files.

</p><p>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
<code class="filename">/usr/share</code> directory that is centrally-mounted.
Note, however, that <code class="filename">/usr/share</code> is generally not
intended to be shared by different OSes or by different releases of
the same OS.</p><p>Any program or package which contains or requires data that
doesn't need to be modified should store that data in
<code class="filename">/usr/share</code> (or
<code class="filename">/usr/local/share</code>, if installed locally).  It is
recommended that a subdirectory be used in
<code class="filename">/usr/share</code> for this purpose. Applications using
a single file may use <code class="filename">/usr/share/misc</code>.</p><p>Game data stored in <code class="filename">/usr/share/games</code> must
be purely static data.  Any modifiable files, such as score files,
game play logs, and so forth, should be placed in
<code class="filename">/var/games</code>.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="requirements11"></a>4.11.2. Requirements</h3></div></div></div><p>The following directories, or symbolic links to directories,
must be in <code class="filename">/usr/share</code></p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">man</code></td><td align="left">Online manuals</td></tr><tr><td align="left"><code class="filename">misc</code></td><td align="left">Miscellaneous architecture-independent data</td></tr></tbody></table></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions15"></a>4.11.3. Specific Options</h3></div></div></div><p>The following directories, or symbolic links to directories, must be in <code class="filename">/usr/share</code>, if the corresponding
subsystem is installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">color</code></td><td align="left">Color management information (optional)</td></tr><tr><td align="left"><code class="filename">dict</code></td><td align="left">Word lists (optional)</td></tr><tr><td align="left"><code class="filename">doc</code></td><td align="left">Miscellaneous documentation (optional)</td></tr><tr><td align="left"><code class="filename">games</code></td><td align="left">Static data files for /usr/games (optional)</td></tr><tr><td align="left"><code class="filename">info</code></td><td align="left">Primary directory for GNU Info system (optional)</td></tr><tr><td align="left"><code class="filename">locale</code></td><td align="left">Locale information (optional)</td></tr><tr><td align="left"><code class="filename">nls</code></td><td align="left">Message catalogs for Native language support (optional)</td></tr><tr><td align="left"><code class="filename">ppd</code></td><td align="left">Printer definitions (optional)</td></tr><tr><td align="left"><code class="filename">sgml</code></td><td align="left">SGML data (optional)</td></tr><tr><td align="left"><code class="filename">terminfo</code></td><td align="left">Directories for terminfo database (optional)</td></tr><tr><td align="left"><code class="filename">tmac</code></td><td align="left">troff macros not distributed with groff (optional)</td></tr><tr><td align="left"><code class="filename">xml</code></td><td align="left">XML data (optional)</td></tr><tr><td align="left"><code class="filename">zoneinfo</code></td><td align="left">Timezone information and configuration (optional)</td></tr></tbody></table></div><p>It is recommended that application-specific,
architecture-independent directories be placed here.  Such directories
include <span class="command"><strong>groff</strong></span>, <span class="command"><strong>perl</strong></span>,
<span class="command"><strong>ghostscript</strong></span>, <span class="command"><strong>texmf</strong></span>, and
<span class="command"><strong>kbd</strong></span> (Linux) or <span class="command"><strong>syscons</strong></span>
(BSD).  They may, however, be placed in <code class="filename">/usr/lib</code>
for backwards compatibility, at the distributor's discretion.
Similarly, a <code class="filename">/usr/lib/games</code> hierarchy may be used
in addition to the <code class="filename">/usr/share/games</code> hierarchy if
the distributor wishes to place some game data there.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="usrsharecolorColorManagement"></a>4.11.4. /usr/share/color : Color management information (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="colorManagementPurpose"></a>4.11.4.1. Purpose</h4></div></div></div><p>This directory is the home for ICC color management files
installed by the system.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="colorManagementSpecificOptions"></a>4.11.4.2. Specific
Options</h4></div></div></div><p>The following directories must be in
<code class="filename">/usr/share/color</code>, if the corresponding subsystem
is installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left"><code class="filename">Directory</code></th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">icc</code></td><td align="left">ICC color profiles (optional)</td></tr></tbody></table></div><p>The top-level directory <code class="filename">/usr/share/color</code>
must not contain any files; all files should be in subdirectories of
<code class="filename">/usr/share/color</code>.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="usrsharedictWordLists"></a>4.11.5. /usr/share/dict : Word lists (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="purpose27"></a>4.11.5.1. Purpose</h4></div></div></div><p>This directory is the home for word lists on the system;
Traditionally this directory contains only the English
<code class="filename">words</code> file, which is used by
<span class="command"><strong>look(1)</strong></span> and various spelling programs.
<code class="filename">words</code> may use either American or British
spelling.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>The reason that only word lists are located here is that they
are the only files common to all spell checkers.</p></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="specificOptions16"></a>4.11.5.2. Specific Options</h4></div></div></div><p>The following files, or symbolic links to files, must be in
<code class="filename">/usr/share/dict</code>, if the corresponding subsystem
is installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left"><code class="filename">File</code></th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">words</code></td><td align="left">List of English words (optional)</td></tr></tbody></table></div><p>Sites that require both American and British spelling may link
<code class="filename">words</code> to
<code class="filename">/usr/share/dict/american-english</code> or
<code class="filename">/usr/share/dict/british-english</code>.</p><p>Word lists for other languages may be added using the English
name for that language, e.g.,
<code class="filename">/usr/share/dict/french</code>,
<code class="filename">/usr/share/dict/danish</code>, etc.  These should, if
possible, use a character set based on Unicode, with the UTF-8
character set being the preferred option.</p><p>Other word lists must be included here, if present.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="usrsharemanManualPages"></a>4.11.6. /usr/share/man : Manual pages</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="purpose28"></a>4.11.6.1. Purpose</h4></div></div></div><p>This section details the organization for manual pages
throughout the system, including <code class="filename">/usr/share/man</code>.
Also refer to the section on
<code class="filename">/var/cache/man</code>.</p><p>The primary <code class="filename">&lt;mandir&gt;</code> of the system is
<code class="filename">/usr/share/man</code>.
<code class="filename">/usr/share/man</code> contains manual information for
commands and data under the <code class="filename">/</code> and
<code class="filename">/usr</code> filesystems.

<a href="#ftn.idm236087409888" class="footnote" name="idm236087409888"><sup class="footnote">[31]</sup></a></p><p>Manual pages are stored in
<code class="filename">&lt;mandir&gt;/&lt;locale&gt;/man&lt;section&gt;/&lt;arch&gt;</code>.
An explanation of <code class="filename">&lt;mandir&gt;</code>,
<code class="filename">&lt;locale&gt;</code>,
<code class="filename">&lt;section&gt;</code>, and
<code class="filename">&lt;arch&gt;</code> is given below.</p><p>A description of each section follows:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: bullet; "><li class="listitem" style="list-style-type: disc"><p><code class="filename">man1</code>: 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.</p></li><li class="listitem" style="list-style-type: disc"><p><code class="filename">man2</code>: System calls

This section describes all of the system calls (requests for the
kernel to perform operations).</p></li><li class="listitem" style="list-style-type: disc"><p><code class="filename">man3</code>: 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.</p></li><li class="listitem" style="list-style-type: disc"><p><code class="filename">man4</code>: 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 <code class="filename">/dev</code> and the kernel interface to
networking protocol support.</p></li><li class="listitem" style="list-style-type: disc"><p><code class="filename">man5</code>: 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.</p></li><li class="listitem" style="list-style-type: disc"><p><code class="filename">man6</code>: Games

This chapter documents games, demos, and generally trivial programs.
Different people have various notions about how essential this is.</p></li><li class="listitem" style="list-style-type: disc"><p><code class="filename">man7</code>: 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.</p></li><li class="listitem" style="list-style-type: disc"><p><code class="filename">man8</code>: 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.</p></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="specificOptions17"></a>4.11.6.2. Specific Options</h4></div></div></div><p>The following directories, or symbolic links to directories,
must be in
<code class="filename">/usr/share/&lt;mandir&gt;/&lt;locale&gt;</code>, unless
they are empty:

<a href="#ftn.idm236087387344" class="footnote" name="idm236087387344"><sup class="footnote">[32]</sup></a></p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">man1</code></td><td align="left">User programs (optional)</td></tr><tr><td align="left"><code class="filename">man2</code></td><td align="left">System calls (optional)</td></tr><tr><td align="left"><code class="filename">man3</code></td><td align="left">Library calls (optional)</td></tr><tr><td align="left"><code class="filename">man4</code></td><td align="left">Special files (optional)</td></tr><tr><td align="left"><code class="filename">man5</code></td><td align="left">File formats (optional)</td></tr><tr><td align="left"><code class="filename">man6</code></td><td align="left">Games (optional)</td></tr><tr><td align="left"><code class="filename">man7</code></td><td align="left">Miscellaneous (optional)</td></tr><tr><td align="left"><code class="filename">man8</code></td><td align="left">System administration (optional)</td></tr></tbody></table></div><p>The component <code class="filename">&lt;section&gt;</code> describes the
manual section.</p><p>Provisions must be made in the structure of
<code class="filename">/usr/share/man</code> 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.</p><p>This naming of language subdirectories of
<code class="filename">/usr/share/man</code> 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 <code class="filename">&lt;locale&gt;</code> string
is:</p><p><code class="filename">&lt;language&gt;[_&lt;territory&gt;][.&lt;character-set&gt;][,&lt;version&gt;]</code></p><p>The <code class="filename">&lt;language&gt;</code> 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.</p><p>The <code class="filename">&lt;territory&gt;</code> 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 href="#ftn.idm236087362160" class="footnote" name="idm236087362160"><sup class="footnote">[33]</sup></a></p><p>The <code class="filename">&lt;character-set&gt;</code> field must
represent the standard describing the character set.  If the
<code class="filename">&lt;character-set&gt;</code> 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.</p><p>A parameter specifying a <code class="filename">&lt;version&gt;</code> of
the profile may be placed after the
<code class="filename">&lt;character-set&gt;</code> 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
<code class="filename">&lt;version&gt;</code> field, unless it is
necessary.</p><p>Systems which use a unique language and code set for all manual
pages may omit the <code class="filename">&lt;locale&gt;</code> substring and
store all manual pages in <code class="filename">&lt;mandir&gt;</code>.  For
example, systems which only have English manual pages coded with
ASCII, may store manual pages (the
<code class="filename">man&lt;section&gt;</code> directories) directly in
<code class="filename">/usr/share/man</code>.  (That is the traditional
circumstance and arrangement, in fact.)</p><p>Countries for which there is a well-accepted standard character
code set may omit the <code class="filename">&lt;character-set&gt;</code>
field, but it is strongly recommended that it be included, especially
for countries with several competing standards.</p><p>Various examples:</p><div class="informaltable"><table border="0"><colgroup><col align="center" class="c1"><col align="center" class="c2"><col align="center" class="c3"><col align="center" class="c4"></colgroup><thead><tr><th align="left">Language</th><th align="left">Territory</th><th align="left">Character Set</th><th align="left">Directory</th></tr></thead><tbody><tr><td align="left">English</td><td align="left">—</td><td align="left">ASCII</td><td align="left">/usr/share/man/en</td></tr><tr><td align="left">English</td><td align="left">United Kingdom</td><td align="left">Unicode UTF-8</td><td align="left">/usr/share/man/en_GB.10646</td></tr><tr><td align="left">English</td><td align="left">United States</td><td align="left">ASCII</td><td align="left">/usr/share/man/en_US</td></tr><tr><td align="left">French</td><td align="left">Canada</td><td align="left">ISO 8859-1</td><td align="left">/usr/share/man/fr_CA.88591</td></tr><tr><td align="left">French</td><td align="left">France</td><td align="left">ISO 8859-1</td><td align="left">/usr/share/man/fr_FR.88591</td></tr><tr><td align="left">German</td><td align="left">Germany</td><td align="left">ISO 646</td><td align="left">/usr/share/man/de_DE.646</td></tr><tr><td align="left">German</td><td align="left">Germany</td><td align="left">ISO 6937</td><td align="left">/usr/share/man/de_DE.6937</td></tr><tr><td align="left">German</td><td align="left">Germany</td><td align="left">ISO 8859-1</td><td align="left">/usr/share/man/de_DE.88591</td></tr><tr><td align="left">German</td><td align="left">Switzerland</td><td align="left">ISO 646</td><td align="left">/usr/share/man/de_CH.646</td></tr><tr><td align="left">Japanese</td><td align="left">Japan</td><td align="left">JIS</td><td align="left">/usr/share/man/ja_JP.jis</td></tr><tr><td align="left">Japanese</td><td align="left">Japan</td><td align="left">SJIS</td><td align="left">/usr/share/man/ja_JP.sjis</td></tr><tr><td align="left">Japanese</td><td align="left">Japan</td><td align="left">UJIS (or EUC-J)</td><td align="left">/usr/share/man/ja_JP.ujis</td></tr><tr><td align="left">Japanese</td><td align="left">Japan</td><td align="left">Unicode UTF-16</td><td align="left">/usr/share/man/ja_JP.10646</td></tr></tbody></table></div><p>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 <code class="filename">&lt;arch&gt;</code> directory in the appropriate
<code class="filename">man&lt;section&gt;</code> directory; for example, a man
page for the i386 ctrlaltdel(8) command might be placed in
<code class="filename">/usr/share/man/&lt;locale&gt;/man8/i386/ctrlaltdel.8</code>.
</p><p>Manual pages for commands and data under
<code class="filename">/usr/local</code> are stored in
<code class="filename">/usr/local/man</code> or
<code class="filename">/usr/local/share/man</code>.
All manual page hierarchies in the system must have the same structure as
<code class="filename">/usr/share/man</code>, as this structure is expected
by commands which consume manual page content.
<a href="#ftn.idm236087300336" class="footnote" name="idm236087300336"><sup class="footnote">[34]</sup></a>
</p><p>The cat page sections (<code class="filename">cat&lt;section&gt;</code>)
containing formatted manual page entries are also found within
subdirectories of <code class="filename">&lt;mandir&gt;/&lt;locale&gt;</code>,
but are not required nor may they be distributed in lieu of nroff
source manual pages.</p><p>The numbered sections "1" through "8" are traditionally defined.
In general, the file name for manual pages located within a particular
section end with <code class="filename">.&lt;section&gt;</code>.</p><p>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
<code class="filename">mh</code> appended to all MH manuals.  All X Window
System manual pages must have an <code class="filename">x</code> appended to
the filename.</p><p>The practice of placing various language manual pages in
appropriate subdirectories of <code class="filename">/usr/share/man</code> also
applies to the other manual page hierarchies, such as
<code class="filename">/usr/local/man</code>.  (This portion of the standard
also applies later in the section on the optional
<code class="filename">/var/cache/man</code> structure.)</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="usrsharemiscMiscellaneousArchitecture"></a>4.11.7. /usr/share/misc : Miscellaneous architecture-independent data</h3></div></div></div><p>This directory contains miscellaneous architecture-independent
files which don't require a separate subdirectory under
<code class="filename">/usr/share</code>.</p><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="specificOptions18"></a>4.11.7.1. Specific Options</h4></div></div></div><p>The following files, or symbolic links to files, must be in
<code class="filename">/usr/share/misc</code>, if the corresponding subsystem
is installed:</p><div class="informaltable"><table border="0"><colgroup><col align="left" class="c1"><col align="left" class="c2"></colgroup><thead><tr><th align="left">File</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">ascii</code></td><td align="left">ASCII character set table (optional)</td></tr><tr><td align="left"><code class="filename">termcap</code></td><td align="left">Terminal capability database (optional)</td></tr><tr><td align="left"><code class="filename">termcap.db</code></td><td align="left">Terminal capability database (optional)</td></tr></tbody></table></div><p>Other (application-specific) files may appear here, but a distributor
may place them in <code class="filename">/usr/lib</code> at their discretion.
<a href="#ftn.idm236087277008" class="footnote" name="idm236087277008"><sup class="footnote">[35]</sup></a>
<a href="#ftn.idm236087260144" class="footnote" name="idm236087260144"><sup class="footnote">[36]</sup></a>
</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="usrshareppd"></a>4.11.8. /usr/share/ppd : Printer definitions (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="usrshareppdPurpose"></a>4.11.8.1. Purpose</h4></div></div></div><p><code class="filename">/usr/share/ppd</code> 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.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="usrsharesgmlSgmlAndXmlData"></a>4.11.9. /usr/share/sgml : SGML data (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="purpose29"></a>4.11.9.1. Purpose</h4></div></div></div><p><code class="filename">/usr/share/sgml</code> contains
architecture-independent files used by SGML applications, such
as ordinary catalogs (not the centralized ones, see
<code class="filename">/etc/sgml</code>), DTDs, entities, or style
sheets.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="specificOptions19"></a>4.11.9.2. Specific Options</h4></div></div></div><p>The following directories, or symbolic links to directories,
must be in <code class="filename">/usr/share/sgml</code>, if the corresponding
subsystem is installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">docbook</code></td><td align="left">docbook DTD (optional)</td></tr><tr><td align="left"><code class="filename">tei</code></td><td align="left">tei DTD (optional)</td></tr><tr><td align="left"><code class="filename">html</code></td><td align="left">html DTD (optional)</td></tr><tr><td align="left"><code class="filename">mathml</code></td><td align="left">mathml DTD (optional)</td></tr></tbody></table></div><p>Other files that are not specific to a given DTD may reside in
their own subdirectory.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idm236087237360"></a>4.11.10. /usr/share/xml : XML data (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idm236087236720"></a>4.11.10.1. Purpose</h4></div></div></div><p><code class="filename">/usr/share/xml</code> contains
architecture-independent files used by XML applications, such
as ordinary catalogs (not the centralized ones, see
<code class="filename">/etc/sgml</code>), DTDs, entities, or style
sheets.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="idm236087234432"></a>4.11.10.2. Specific Options</h4></div></div></div><p>The following directories, or symbolic links to directories,
must be in <code class="filename">/usr/share/xml</code>, if the corresponding
subsystem is installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">docbook</code></td><td align="left">docbook XML DTD (optional)</td></tr><tr><td align="left"><code class="filename">xhtml</code></td><td align="left">XHTML DTD (optional)</td></tr><tr><td align="left"><code class="filename">mathml</code></td><td align="left">MathML DTD (optional)</td></tr></tbody></table></div></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="usrsrcSourceCode"></a>4.12. /usr/src : Source code (optional)</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose30"></a>4.12.1. Purpose</h3></div></div></div><p>Source code may be placed in this
subdirectory, only for reference purposes.

<a href="#ftn.idm236087222480" class="footnote" name="idm236087222480"><sup class="footnote">[37]</sup></a>
</p></div></div><div class="footnotes"><br><hr style="width:100; text-align:left;margin-left: 0"><div id="ftn.idm236087593904" class="footnote"><p><a href="#idm236087593904" class="para"><sup class="para">[21] </sup></a> Miscellaneous
architecture-independent application-specific static files and
subdirectories must be placed in <code class="filename">/usr/share</code>.
</p></div><div id="ftn.idm236087592496" class="footnote"><p><a href="#idm236087592496" class="para"><sup class="para">[22] </sup></a>See below, in the <code class="filename">/usr/libexec</code>
section, for a discussion of <code class="filename">/usr/lib</code>
vs. <code class="filename">/usr/libexec</code> for executable binaries.
</p></div><div id="ftn.idm236087588928" class="footnote"><p><a href="#idm236087588928" class="para"><sup class="para">[23] </sup></a> For example, the <code class="filename">perl5</code> subdirectory for
Perl 5 modules and libraries.</p></div><div id="ftn.idm236087585280" class="footnote"><p><a href="#idm236087585280" class="para"><sup class="para">[24] </sup></a>
Some executable commands such as <span class="command"><strong>makewhatis</strong></span> and
<span class="command"><strong>sendmail</strong></span> have also been traditionally placed in
<code class="filename">/usr/lib</code>.  <span class="command"><strong>makewhatis</strong></span> is an
internal binary and must be placed in a binary directory; users access
only <span class="command"><strong>catman</strong></span>.  Newer <span class="command"><strong>sendmail</strong></span>
binaries are now placed by default in <code class="filename">/usr/sbin</code>.
Additionally, systems using a <span class="emphasis"><em>sendmail</em></span>-compatible
mail transfer agent must provide <span class="command"><strong>/usr/sbin/sendmail</strong></span>
as the <span class="command"><strong>sendmail</strong></span> command, either as the executable
itself or as a symlink to the appropriate executable. </p></div><div id="ftn.idm236087578304" class="footnote"><p><a href="#idm236087578304" class="para"><sup class="para">[25] </sup></a>
Host-specific data for the X Window System must not be stored in
<code class="filename">/usr/lib/X11</code>.  Host-specific configuration files
such as <code class="filename">xorg.conf</code> must be stored in
<code class="filename">/etc/X11</code>.  This includes configuration data such
as <code class="filename">system.twmrc</code> even if it is only made a
symbolic link to a more global configuration file (probably in
<code class="filename">/usr/lib/X11</code>).
</p></div><div id="ftn.idm236087566784" class="footnote"><p><a href="#idm236087566784" class="para"><sup class="para">[26] </sup></a>See, for example, the "GNU Coding Standards" from
the Free Software Foundation.</p></div><div id="ftn.idm236087558816" class="footnote"><p><a href="#idm236087558816" class="para"><sup class="para">[27] </sup></a>
The case where <code class="filename">/usr/lib</code> and <code class="filename">/usr/lib<em class="replaceable"><code>&lt;qual&gt;</code></em></code> are the
same (one is a symbolic link to the other) these files and the
per-application subdirectories will exist.
</p></div><div id="ftn.idm236087550400" class="footnote"><p><a href="#idm236087550400" class="para"><sup class="para">[28] </sup></a>
Software placed in <code class="filename">/</code> or
<code class="filename">/usr</code> may be overwritten by system upgrades
(though we recommend that distributions do not overwrite data in
<code class="filename">/etc</code> under these circumstances).  For this
reason, local software must not be placed outside of
<code class="filename">/usr/local</code> without good reason.
</p></div><div id="ftn.idm236087505920" class="footnote"><p><a href="#idm236087505920" class="para"><sup class="para">[29] </sup></a>
Locally installed system administration programs should be placed in
<code class="filename">/usr/local/sbin</code>.
</p></div><div id="ftn.idm236087499712" class="footnote"><p><a href="#idm236087499712" class="para"><sup class="para">[30] </sup></a>
Much of this data originally lived in <code class="filename">/usr</code>
(<code class="filename">man</code>, <code class="filename">doc</code>) or
<code class="filename">/usr/lib</code> (<code class="filename">dict</code>,
<code class="filename">terminfo</code>, <code class="filename">zoneinfo</code>).
</p></div><div id="ftn.idm236087409888" class="footnote"><p><a href="#idm236087409888" class="para"><sup class="para">[31] </sup></a>Obviously, there are no manual pages in <code class="filename">/</code>
because they are not required at boot time nor are they required in
emergencies. Really.</p></div><div id="ftn.idm236087387344" class="footnote"><p><a href="#idm236087387344" class="para"><sup class="para">[32] </sup></a>For example, if <code class="filename">/usr/share/man</code>
has no manual pages in section 4 (Devices), then
<code class="filename">/usr/share/man/man4</code> may be omitted.</p></div><div id="ftn.idm236087362160" class="footnote"><p><a href="#idm236087362160" class="para"><sup class="para">[33] </sup></a> A major exception to this rule is the
United Kingdom, which is `GB' in the ISO 3166, but `UK' for most email
addresses.</p></div><div id="ftn.idm236087300336" class="footnote"><p><a href="#idm236087300336" class="para"><sup class="para">[34] </sup></a>
<code class="filename">/usr/local/man</code> is deprecated and may be
dropped in a future version of this specification.
</p></div><div id="ftn.idm236087277008" class="footnote"><p><a href="#idm236087277008" class="para"><sup class="para">[35] </sup></a>
Some such files include:

<code class="filename">airport</code>, <code class="filename">birthtoken</code>,
<code class="filename">eqnchar</code>, <code class="filename">getopt</code>,
<code class="filename">gprof.callg</code>, <code class="filename">gprof.flat</code>,
<code class="filename">inter.phone</code>, <code class="filename">ipfw.samp.filters</code>,
<code class="filename">ipfw.samp.scripts</code>, <code class="filename">keycap.pcvt</code>,
<code class="filename">mail.help</code>, <code class="filename">mail.tildehelp</code>,
<code class="filename">man.template</code>, <code class="filename">map3270</code>,
<code class="filename">mdoc.template</code>, <code class="filename">more.help</code>,
<code class="filename">na.phone</code>, <code class="filename">nslookup.help</code>,
<code class="filename">operator</code>, <code class="filename">scsi_modes</code>,
<code class="filename">sendmail.hf</code>, <code class="filename">style</code>,
<code class="filename">units.lib</code>, <code class="filename">vgrindefs</code>,
<code class="filename">vgrindefs.db</code>, <code class="filename">zipcodes</code>.

</p></div><div id="ftn.idm236087260144" class="footnote"><p><a href="#idm236087260144" class="para"><sup class="para">[36] </sup></a>
Historically, the <code class="filename">magic</code> file was placed in
<code class="filename">/usr/share/misc</code>, but modern variants of the file
command use several files and place them in
<code class="filename">/usr/share/file</code>. For compatibility,
distribution may create a symlink at
<code class="filename">/usr/share/misc/magic</code>, pointing to
<code class="filename">/usr/share/file/magic</code>.
</p></div><div id="ftn.idm236087222480" class="footnote"><p><a href="#idm236087222480" class="para"><sup class="para">[37] </sup></a>
Generally, source should not be built within this hierarchy.
</p></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="theVarHierarchy"></a>Chapter 5. The /var Hierarchy</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#purpose31">5.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements12">5.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions20">5.3. Specific Options</a></span></dt><dt><span class="section"><a href="#varaccountProcessAccountingLogs">5.4. /var/account : Process accounting logs (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose32">5.4.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#varcacheApplicationCacheData">5.5. /var/cache : Application cache data</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose33">5.5.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions21">5.5.2. Specific Options</a></span></dt><dt><span class="section"><a href="#varcachefontsLocallygeneratedFonts">5.5.3. /var/cache/fonts : Locally-generated fonts (optional)</a></span></dt><dt><span class="section"><a href="#varcachemanLocallyformattedManualPag">5.5.4. /var/cache/man : Locally-formatted manual pages (optional)</a></span></dt></dl></dd><dt><span class="section"><a href="#varcrashSystemCrashDumps">5.6. /var/crash : System crash dumps (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose36">5.6.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#vargamesVariableGameData">5.7. /var/games : Variable game data (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose37">5.7.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#varlibVariableStateInformation">5.8. /var/lib : Variable state information</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose38">5.8.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements13">5.8.2. Requirements</a></span></dt><dt><span class="section"><a href="#specificOptions23">5.8.3. Specific Options</a></span></dt><dt><span class="section"><a href="#varliblteditorgtEditorBackupFilesAn">5.8.4. /var/lib/&lt;editor&gt; : Editor backup files and state (optional)</a></span></dt><dt><span class="section"><a href="#varlibcolor">5.8.5. /var/lib/color : Color management information (optional)</a></span></dt><dt><span class="section"><a href="#varlibhwclockStateDirectoryForHwclo">5.8.6. /var/lib/hwclock : State directory for hwclock (optional)</a></span></dt><dt><span class="section"><a href="#varlibmiscMiscellaneousVariableData">5.8.7. /var/lib/misc : Miscellaneous variable data</a></span></dt></dl></dd><dt><span class="section"><a href="#varlockLockFiles">5.9. /var/lock : Lock files</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose42">5.9.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#varlogLogFilesAndDirectories">5.10. /var/log : Log files and directories</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose43">5.10.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions24">5.10.2. Specific Options</a></span></dt></dl></dd><dt><span class="section"><a href="#varmailUserMailboxFiles">5.11. /var/mail : User mailbox files (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose44">5.11.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#varoptVariableDataForOpt">5.12. /var/opt : Variable data for /opt</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose45">5.12.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#varrunRuntimeVariableData">5.13. /var/run : Run-time variable data</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose46">5.13.1. Purpose</a></span></dt><dt><span class="section"><a href="#requirements14">5.13.2. Requirements</a></span></dt></dl></dd><dt><span class="section"><a href="#varspoolApplicationSpoolData">5.14. /var/spool : Application spool data</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose47">5.14.1. Purpose</a></span></dt><dt><span class="section"><a href="#specificOptions25">5.14.2. Specific Options</a></span></dt><dt><span class="section"><a href="#varspoollpdLineprinterDaemonPrintQu">5.14.3. /var/spool/lpd : Line-printer daemon print queues (optional)</a></span></dt><dt><span class="section"><a href="#varspoolrwhoRwhodFiles">5.14.4. /var/spool/rwho : Rwhod files (optional)</a></span></dt></dl></dd><dt><span class="section"><a href="#vartmpTemporaryFilesPreservedBetwee">5.15. /var/tmp : Temporary files preserved between system reboots</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose50">5.15.1. Purpose</a></span></dt></dl></dd><dt><span class="section"><a href="#varypNetworkInformationService">5.16. /var/yp : Network Information Service (NIS) database files (optional)</a></span></dt><dd><dl><dt><span class="section"><a href="#purpose51">5.16.1. Purpose</a></span></dt></dl></dd></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="purpose31"></a>5.1. Purpose</h2></div></div></div><p><code class="filename">/var</code> contains variable data files.  This
includes spool directories and files, administrative and logging data,
and transient and temporary files.</p><p>Some portions of <code class="filename">/var</code> are not shareable
between different systems.  For instance,
<code class="filename">/var/log</code>, <code class="filename">/var/lock</code>, and
<code class="filename">/var/run</code>.  Other portions may be shared, notably
<code class="filename">/var/mail</code>, <code class="filename">/var/cache/man</code>,
<code class="filename">/var/cache/fonts</code>, and
<code class="filename">/var/spool/news</code>.</p><p><code class="filename">/var</code> is specified here in order to make it
possible to mount <code class="filename">/usr</code> read-only.  Everything
that once went into <code class="filename">/usr</code> that is written to
during system operation (as opposed to installation and software
maintenance) must be in <code class="filename">/var</code>.</p><p>If <code class="filename">/var</code> cannot be made a separate
partition, it is often preferable to move <code class="filename">/var</code>
out of the root partition and into the <code class="filename">/usr</code>
partition.  (This is sometimes done to reduce the size of the root
partition or when space runs low in the root partition.)  However,
<code class="filename">/var</code> must not be linked to
<code class="filename">/usr</code> because this makes separation of
<code class="filename">/usr</code> and <code class="filename">/var</code> more difficult
and is likely to create a naming conflict.  Instead, link
<code class="filename">/var</code> to <code class="filename">/usr/var</code>.</p><p>Applications must generally not add directories to the top level
of <code class="filename">/var</code>.  Such directories should only be added
if they have some system-wide implication, and in consultation with
the FHS mailing list.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="requirements12"></a>5.2. Requirements</h2></div></div></div><p>The following directories, or symbolic links to directories, are
required in <code class="filename">/var</code>:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">cache</code></td><td align="left">Application cache data</td></tr><tr><td align="left"><code class="filename">lib</code></td><td align="left">Variable state information</td></tr><tr><td align="left"><code class="filename">local</code></td><td align="left">Variable data for /usr/local</td></tr><tr><td align="left"><code class="filename">lock</code></td><td align="left">Lock files</td></tr><tr><td align="left"><code class="filename">log</code></td><td align="left">Log files and directories</td></tr><tr><td align="left"><code class="filename">opt</code></td><td align="left">Variable data for /opt</td></tr><tr><td align="left"><code class="filename">run</code></td><td align="left">Data relevant to running processes</td></tr><tr><td align="left"><code class="filename">spool</code></td><td align="left">Application spool data</td></tr><tr><td align="left"><code class="filename">tmp</code></td><td align="left">Temporary files preserved between system reboots</td></tr></tbody></table></div><p>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:</p><pre class="screen">
    /var/backups
    /var/cron
    /var/msgs
    /var/preserve
</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="specificOptions20"></a>5.3. Specific Options</h2></div></div></div><p>The following directories, or symbolic links to directories,
must be in <code class="filename">/var</code>, if the corresponding subsystem
is installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">account</code></td><td align="left">Process accounting logs (optional)</td></tr><tr><td align="left"><code class="filename">crash</code></td><td align="left">System crash dumps (optional)</td></tr><tr><td align="left"><code class="filename">games</code></td><td align="left">Variable game data (optional)</td></tr><tr><td align="left"><code class="filename">mail</code></td><td align="left">User mailbox files (optional)</td></tr><tr><td align="left"><code class="filename">yp</code></td><td align="left">Network Information Service (NIS) database files (optional)
       </td></tr></tbody></table></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="varaccountProcessAccountingLogs"></a>5.4. /var/account : Process accounting logs (optional)</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose32"></a>5.4.1. Purpose</h3></div></div></div><p>This directory holds the current active process accounting log
and the composite process usage data (as used in some UNIX-like
systems by <span class="command"><strong>lastcomm</strong></span> and
<span class="command"><strong>sa</strong></span>).</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="varcacheApplicationCacheData"></a>5.5. /var/cache : Application cache data</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose33"></a>5.5.1. Purpose</h3></div></div></div><p><code class="filename">/var/cache</code> 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
<code class="filename">/var/spool</code>, the cached files can be deleted
without data loss.  The data must remain valid between invocations of
the application and rebooting the system.</p><p>Files located under <code class="filename">/var/cache</code> 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.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>The existence of a separate directory for cached data allows
system administrators to set different disk and backup policies from
other directories in <code class="filename">/var</code>.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions21"></a>5.5.2. Specific Options</h3></div></div></div><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">fonts</code></td><td align="left">Locally-generated fonts (optional)</td></tr><tr><td align="left"><code class="filename">man</code></td><td align="left">Locally-formatted manual pages (optional)</td></tr><tr><td align="left"><code class="filename">www</code></td><td align="left">WWW proxy or cache data (optional)</td></tr><tr><td align="left"><code class="filename">&lt;package&gt;</code></td><td align="left">Package specific cache data (optional)</td></tr></tbody></table></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="varcachefontsLocallygeneratedFonts"></a>5.5.3. /var/cache/fonts : Locally-generated fonts (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="purpose34"></a>5.5.3.1. Purpose</h4></div></div></div><p>The directory <code class="filename">/var/cache/fonts</code> should be used to store any
dynamically-created fonts.  In particular, all of the fonts which are
automatically generated by <span class="command"><strong>mktexpk</strong></span> must be located in
appropriately-named subdirectories of <code class="filename">/var/cache/fonts</code>.

<a href="#ftn.idm236086662944" class="footnote" name="idm236086662944"><sup class="footnote">[38]</sup></a></p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="specificOptions22"></a>5.5.3.2. Specific Options</h4></div></div></div><p>Other dynamically created fonts may also be placed in this tree,
under appropriately-named subdirectories of
<code class="filename">/var/cache/fonts</code>.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="varcachemanLocallyformattedManualPag"></a>5.5.4. /var/cache/man : Locally-formatted manual pages (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="purpose35"></a>5.5.4.1. Purpose</h4></div></div></div><p>This directory provides a standard location for sites that provide a
read-only <code class="filename">/usr</code> partition, but wish to allow caching of
locally-formatted man pages.  Sites that mount <code class="filename">/usr</code> as writable
(e.g., single-user installations) may choose not to use
<code class="filename">/var/cache/man</code> and may write formatted man pages into the
<code class="filename">cat&lt;section&gt;</code> directories in <code class="filename">/usr/share/man</code> directly.  We
recommend that most sites use one of the following options instead:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: bullet; "><li class="listitem" style="list-style-type: disc"><p>Preformat all manual pages alongside the unformatted versions.</p></li><li class="listitem" style="list-style-type: disc"><p>Allow no caching of formatted man pages, and require formatting to be
done each time a man page is brought up.</p></li><li class="listitem" style="list-style-type: disc"><p>Allow local caching of formatted man pages in <code class="filename">/var/cache/man</code>.</p></li></ul></div><p>The structure of <code class="filename">/var/cache/man</code> needs to
reflect both the fact of multiple man page hierarchies and the
possibility of multiple language support.</p><p>Given an unformatted manual page that normally appears in
<code class="filename">&lt;path&gt;/man/&lt;locale&gt;/man&lt;section&gt;</code>,
the directory to place formatted man pages in is
<code class="filename">/var/cache/man/&lt;catpath&gt;/&lt;locale&gt;/cat&lt;section&gt;</code>,
where <code class="filename">&lt;catpath&gt;</code> is derived from
<code class="filename">&lt;path&gt;</code> by removing any leading
<code class="filename">usr</code> and/or trailing <code class="filename">share</code>
pathname components.  (Note that the
<code class="filename">&lt;locale&gt;</code> component may be missing.)

<a href="#ftn.idm236086641360" class="footnote" name="idm236086641360"><sup class="footnote">[39]</sup></a></p><p>Man pages written to <code class="filename">/var/cache/man</code> may
eventually be transferred to the appropriate preformatted directories
in the source <code class="filename">man</code> hierarchy or expired; likewise
formatted man pages in the source <code class="filename">man</code> hierarchy
may be expired if they are not accessed for a period of time.</p><p>If preformatted manual pages come with a system on read-only
media (a CD-ROM, for instance), they must be installed in the source
<code class="filename">man</code> hierarchy
(e.g. <code class="filename">/usr/share/man/cat&lt;section&gt;</code>).
<code class="filename">/var/cache/man</code> is reserved as a writable cache
for formatted manual pages.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>Release 1.2 of this standard specified
<code class="filename">/var/catman</code> for this hierarchy.  The path has
been moved under <code class="filename">/var/cache</code> to better reflect the
dynamic nature of the formatted man pages.  The directory name has
been changed to <code class="filename">man</code> to allow for enhancing the
hierarchy to include post-processed formats other than "cat", such as
PostScript, HTML, or DVI.</p></div></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="varcrashSystemCrashDumps"></a>5.6. /var/crash : System crash dumps (optional)</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose36"></a>5.6.1. Purpose</h3></div></div></div><p>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.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="vargamesVariableGameData"></a>5.7. /var/games : Variable game data (optional)</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose37"></a>5.7.1. Purpose</h3></div></div></div><p>Any variable data relating to games in <code class="filename">/usr</code>
should be placed here.  <code class="filename">/var/games</code> should hold
the variable data previously found in <code class="filename">/usr</code>;
static data, such as help text, level descriptions, and so on, must
remain elsewhere, such as
<code class="filename">/usr/share/games</code>.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p><code class="filename">/var/games</code> has been given a hierarchy of
its own, rather than leaving it underneath
<code class="filename">/var/lib</code> as in release 1.2 of this standard.
The separation
allows local control of backup strategies, permissions, and disk
usage, as well as allowing inter-host sharing and reducing clutter in
<code class="filename">/var/lib</code>.  Additionally,
<code class="filename">/var/games</code> is the path traditionally used by BSD.</p></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="varlibVariableStateInformation"></a>5.8. /var/lib : Variable state information</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose38"></a>5.8.1. Purpose</h3></div></div></div><p>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 <code class="filename">/var/lib</code> to
configure a package's operation, and the specific file hierarchy
used to store the data must not be exposed to regular users.

<a href="#ftn.idm236086612224" class="footnote" name="idm236086612224"><sup class="footnote">[40]</sup></a>
</p><p>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.</p><p>An application (or a group of inter-related applications) must
use a subdirectory of <code class="filename">/var/lib</code> for its data.
There is one required subdirectory,
<code class="filename">/var/lib/misc</code>, 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.

<a href="#ftn.idm236086608112" class="footnote" name="idm236086608112"><sup class="footnote">[41]</sup></a></p><p><code class="filename">/var/lib/&lt;name&gt;</code> is the location that
must be used for all distribution packaging support.  Different
distributions may use different names, of course.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="requirements13"></a>5.8.2. Requirements</h3></div></div></div><p>The following directories, or symbolic links to directories, are
required in <code class="filename">/var/lib</code>:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">misc</code></td><td align="left">Miscellaneous state data</td></tr></tbody></table></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions23"></a>5.8.3. Specific Options</h3></div></div></div><p>The following directories, or symbolic links to directories, must be in <code class="filename">/var/lib</code>, if the
corresponding subsystem is installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left">&lt;editor&gt;</td><td align="left">Editor backup files and state (optional)</td></tr><tr><td align="left">&lt;pkgtool&gt;</td><td align="left">Packaging support files (optional)</td></tr><tr><td align="left">&lt;package&gt;</td><td align="left">State data for packages and subsystems (optional)</td></tr><tr><td align="left"><code class="filename">color</code></td><td align="left">Color management information (optional)</td></tr><tr><td align="left"><span class="command"><strong>hwclock</strong></span></td><td align="left">State directory for hwclock (optional)</td></tr><tr><td align="left"><span class="command"><strong>xdm</strong></span></td><td align="left">X display manager variable data (optional)</td></tr></tbody></table></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="varliblteditorgtEditorBackupFilesAn"></a>5.8.4. /var/lib/&lt;editor&gt; : Editor backup files and state (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="purpose39"></a>5.8.4.1. Purpose</h4></div></div></div><p>These directories contain saved files generated by any
unexpected termination of an editor (e.g., <span class="command"><strong>elvis</strong></span>,
<span class="command"><strong>jove</strong></span>, <span class="command"><strong>nvi</strong></span>).</p><p>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 <code class="filename">/var/lib</code> (for example, GNU
Emacs would place lock files in
<code class="filename">/var/lib/emacs/lock</code>).</p><p>Future editors may require additional state information beyond
crash-recovery files and lock files — this information should
also be placed under
<code class="filename">/var/lib/&lt;editor&gt;</code>.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>Previous Linux releases, as well as all commercial vendors, use
<code class="filename">/var/preserve</code> 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.</p><p>Editor-specific lock files are usually quite different from the
device or resource lock files that are stored in
<code class="filename">/var/lock</code> and, hence, are stored under
<code class="filename">/var/lib</code>.</p></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="varlibcolor"></a>5.8.5. /var/lib/color : Color management information (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="varlibcolorPurpose"></a>5.8.5.1. Purpose</h4></div></div></div><p>This directory is the home for ICC color management files
installed dynamically.  This directory shall be laid out using the
same rules as the <code class="filename">/usr/share/color</code>
directory.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="varlibhwclockStateDirectoryForHwclo"></a>5.8.6. /var/lib/hwclock : State directory for hwclock (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="purpose40"></a>5.8.6.1. Purpose</h4></div></div></div><p>This directory contains the file
<code class="filename">/var/lib/hwclock/adjtime</code>.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>In FHS 2.1, this file was <code class="filename">/etc/adjtime</code>, but
as <span class="command"><strong>hwclock</strong></span> updates it, that was obviously
incorrect.</p></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="varlibmiscMiscellaneousVariableData"></a>5.8.7. /var/lib/misc : Miscellaneous variable data</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="purpose41"></a>5.8.7.1. Purpose</h4></div></div></div><p>This directory contains variable data not placed in a
subdirectory in <code class="filename">/var/lib</code>.  An attempt should be
made to use relatively unique names in this directory to avoid
namespace conflicts.

<a href="#ftn.idm236086558032" class="footnote" name="idm236086558032"><sup class="footnote">[42]</sup></a></p></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="varlockLockFiles"></a>5.9. /var/lock : Lock files</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose42"></a>5.9.1. Purpose</h3></div></div></div><p>Lock files should be stored within the
<code class="filename">/var/lock</code> directory structure.</p><p>Lock files for devices and other resources shared by multiple
applications, such as the serial device lock files that were
originally found in either <code class="filename">/usr/spool/locks</code> or
<code class="filename">/usr/spool/uucp</code>, must now be stored in
<code class="filename">/var/lock</code>.  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.

<a href="#ftn.idm236086548848" class="footnote" name="idm236086548848"><sup class="footnote">[43]</sup></a></p><p>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.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="varlogLogFilesAndDirectories"></a>5.10. /var/log : Log files and directories</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose43"></a>5.10.1. Purpose</h3></div></div></div><p>This directory contains miscellaneous log files.  Most logs must
be written to this directory or an appropriate subdirectory.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions24"></a>5.10.2. Specific Options</h3></div></div></div><p>The following files, or symbolic links to files, must be in
<code class="filename">/var/log</code>, if the corresponding subsystem is
installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">File</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">lastlog</code></td><td align="left">record of last login of each user</td></tr><tr><td align="left"><code class="filename">messages</code></td><td align="left">system messages from <span class="command"><strong>syslogd</strong></span></td></tr><tr><td align="left"><code class="filename">wtmp</code></td><td align="left">record of all logins and logouts</td></tr></tbody></table></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="varmailUserMailboxFiles"></a>5.11. /var/mail : User mailbox files (optional)</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose44"></a>5.11.1. Purpose</h3></div></div></div><p>The mail spool must be accessible through
<code class="filename">/var/mail</code> and the mail spool files must take the
form <code class="filename">&lt;username&gt;</code>.
<a href="#ftn.idm236086527232" class="footnote" name="idm236086527232"><sup class="footnote">[44]</sup></a></p><p>User mailbox files in this location must be stored in the standard
UNIX mailbox format.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>The logical location for this directory was changed from
<code class="filename">/var/spool/mail</code> in order to bring FHS in-line
with nearly every UNIX distribution.  This change is important for
inter-operability since a single <code class="filename">/var/mail</code> is
often shared between multiple hosts and multiple UNIX distribution
(despite NFS locking issues).</p><p>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
<code class="filename">/var/mail</code>.</p></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="varoptVariableDataForOpt"></a>5.12. /var/opt : Variable data for /opt</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose45"></a>5.12.1. Purpose</h3></div></div></div><p>Variable data of the packages in <code class="filename">/opt</code> must
be installed in <code class="filename">/var/opt/&lt;subdir&gt;</code>, where
<code class="filename">&lt;subdir&gt;</code> is the name of the subtree in
<code class="filename">/opt</code> where the static data from an add-on
software package is stored, except where superseded by another file in
<code class="filename">/etc</code>.  No structure is imposed on the internal
arrangement of <code class="filename">/var/opt/&lt;subdir&gt;</code>.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>Refer to the rationale for <code class="filename">/opt</code>.</p></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="varrunRuntimeVariableData"></a>5.13. /var/run : Run-time variable data</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose46"></a>5.13.1. Purpose</h3></div></div></div><p>This directory was once intended for system information data
describing the system since it was booted.  These functions have been
moved to <code class="filename">/run</code>; this directory exists to ensure
compatibility with systems and software using an older version of this
specification.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="requirements14"></a>5.13.2. Requirements</h3></div></div></div><p>In general, the requirements for <code class="filename">/run</code> shall
also apply to <code class="filename">/var/run</code>.  It is valid to implement
<code class="filename">/var/run</code> as a symlink to
<code class="filename">/run</code>.</p><p>The <code class="filename">utmp</code> file, which stores information
about who is currently using the system, is located in this
directory.</p><p>Programs should not access both <code class="filename">/var/run</code>
and <code class="filename">/run</code> directly, except to access
<code class="filename">/var/run/utmp</code>.

</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="varspoolApplicationSpoolData"></a>5.14. /var/spool : Application spool data</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose47"></a>5.14.1. Purpose</h3></div></div></div><p><code class="filename">/var/spool</code> contains data which is awaiting
some kind of later processing.  Data in
<code class="filename">/var/spool</code> represents work to be done in the
future (by a program, user, or administrator); often data is deleted
after it has been processed.

<a href="#ftn.idm236086493728" class="footnote" name="idm236086493728"><sup class="footnote">[46]</sup></a></p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="specificOptions25"></a>5.14.2. Specific Options</h3></div></div></div><p>The following directories, or symbolic links to directories,
must be in <code class="filename">/var/spool</code>, if the corresponding
subsystem is installed:</p><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">lpd</code></td><td align="left">Printer spool directory (optional)</td></tr><tr><td align="left"><code class="filename">mqueue</code></td><td align="left">Outgoing mail queue (optional)</td></tr><tr><td align="left"><code class="filename">news</code></td><td align="left">News spool directory (optional)</td></tr><tr><td align="left"><code class="filename">rwho</code></td><td align="left">Rwhod files (optional)</td></tr><tr><td align="left"><code class="filename">uucp</code></td><td align="left">Spool directory for UUCP (optional)</td></tr></tbody></table></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="varspoollpdLineprinterDaemonPrintQu"></a>5.14.3. /var/spool/lpd : Line-printer daemon print queues (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="purpose48"></a>5.14.3.1. Purpose</h4></div></div></div><p>The lock file for <span class="command"><strong>lpd</strong></span>,
<code class="filename">lpd.lock</code>, must be placed in
<code class="filename">/var/spool/lpd</code>.  It is suggested that the lock
file for each printer be placed in the spool directory for that
specific printer and named <code class="filename">lock</code>.</p></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="specificOptions26"></a>5.14.3.2. Specific Options</h4></div></div></div><div class="informaltable"><table border="0"><colgroup><col><col></colgroup><thead><tr><th align="left">Directory</th><th align="left">Description</th></tr></thead><tbody><tr><td align="left"><code class="filename">printer</code></td><td align="left">Spools for a specific printer (optional)</td></tr></tbody></table></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="varspoolrwhoRwhodFiles"></a>5.14.4. /var/spool/rwho : Rwhod files (optional)</h3></div></div></div><div class="section"><div class="titlepage"><div><div><h4 class="title"><a name="purpose49"></a>5.14.4.1. Purpose</h4></div></div></div><p>This directory holds the <span class="command"><strong>rwhod</strong></span> information
for other systems on the local net.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>Some BSD releases use <code class="filename">/var/rwho</code> for this
data; given its historical location in <code class="filename">/var/spool</code>
on other systems and its approximate fit to the definition of
`spooled' data, this location was deemed more appropriate.</p></div></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="vartmpTemporaryFilesPreservedBetwee"></a>5.15. /var/tmp : Temporary files preserved between system reboots</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose50"></a>5.15.1. Purpose</h3></div></div></div><p>The <code class="filename">/var/tmp</code> directory is made available
for programs that require temporary files or directories that are
preserved between system reboots.  Therefore, data stored in
<code class="filename">/var/tmp</code> is more persistent than data in
<code class="filename">/tmp</code>.</p><p>Files and directories located in <code class="filename">/var/tmp</code>
must not be deleted when the system is booted.  Although data stored
in <code class="filename">/var/tmp</code> is typically deleted in a
site-specific manner, it is recommended that deletions occur at a less
frequent interval than <code class="filename">/tmp</code>.</p></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="varypNetworkInformationService"></a>5.16. /var/yp : Network Information Service (NIS) database files (optional)</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="purpose51"></a>5.16.1. Purpose</h3></div></div></div><p>Variable data for the Network Information Service (NIS),
formerly known as the Sun Yellow Pages (YP), must be placed in this
directory.</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p><code class="filename">/var/yp</code> is the standard directory for NIS
(YP) data and is almost exclusively used in NIS documentation and
systems.

<a href="#ftn.idm236086446848" class="footnote" name="idm236086446848"><sup class="footnote">[47]</sup></a></p></div></div></div><div class="footnotes"><br><hr style="width:100; text-align:left;margin-left: 0"><div id="ftn.idm236086662944" class="footnote"><p><a href="#idm236086662944" class="para"><sup class="para">[38] </sup></a>
This standard does not currently incorporate the TeX Directory
Structure (a document that describes the layout TeX files and
directories), but it may be useful reading.  It is located at
<a class="ulink" href="ftp://ctan.tug.org/tex/" target="_top">ftp://ctan.tug.org/tex/</a></p></div><div id="ftn.idm236086641360" class="footnote"><p><a href="#idm236086641360" class="para"><sup class="para">[39] </sup></a>
For example, <code class="filename">/usr/share/man/man1/ls.1</code> is
formatted into <code class="filename">/var/cache/man/cat1/ls.1</code>, and
<code class="filename">/usr/X11R6/man/&lt;locale&gt;/man3/XtClass.3x</code> into
<code class="filename">/var/cache/man/X11R6/&lt;locale&gt;/cat3/XtClass.3x</code>.
</p></div><div id="ftn.idm236086612224" class="footnote"><p><a href="#idm236086612224" class="para"><sup class="para">[40] </sup></a>
Data with exposed filesystem structure should be stored in
<code class="filename">/srv</code>.
</p></div><div id="ftn.idm236086608112" class="footnote"><p><a href="#idm236086608112" class="para"><sup class="para">[41] </sup></a>
An important difference between this version of this standard and
previous ones is that applications are now required to use a
subdirectory of <code class="filename">/var/lib</code>.  
</p></div><div id="ftn.idm236086558032" class="footnote"><p><a href="#idm236086558032" class="para"><sup class="para">[42] </sup></a>This hierarchy should contain files stored in
<code class="filename">/var/db</code> in current BSD releases.  These include
<code class="filename">locate.database</code> and
<code class="filename">mountdtab</code>, and the kernel symbol database(s).
</p></div><div id="ftn.idm236086548848" class="footnote"><p><a href="#idm236086548848" class="para"><sup class="para">[43] </sup></a>Then, anything wishing to use <code class="filename">/dev/ttyS0</code>
can read the lock file and act accordingly (all locks in
<code class="filename">/var/lock</code> should be world-readable).
</p></div><div id="ftn.idm236086527232" class="footnote"><p><a href="#idm236086527232" class="para"><sup class="para">[44] </sup></a>Note that <code class="filename">/var/mail</code> may be a symbolic link to
another directory.</p></div><div id="ftn.idm236086500304" class="footnote"><p><a href="#idm236086500304" class="para"><sup class="para">[45] </sup></a>This is to prevent confusion about where transient files are
located.  In general, a program should use either
<code class="filename">/var/run</code> or <code class="filename">/run</code> to access
these files, not both.</p></div><div id="ftn.idm236086493728" class="footnote"><p><a href="#idm236086493728" class="para"><sup class="para">[46] </sup></a>
UUCP lock files must be placed in <code class="filename">/var/lock</code>.  See
the above section on <code class="filename">/var/lock</code>.  </p></div><div id="ftn.idm236086446848" class="footnote"><p><a href="#idm236086446848" class="para"><sup class="para">[47] </sup></a>
NIS should not be confused with Sun NIS+, which uses a different
directory, <code class="filename">/var/nis</code>.
</p></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="operatingSystemSpecificAnnex"></a>Chapter 6. Operating System Specific Annex</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#linux">6.1. Linux</a></span></dt><dd><dl><dt><span class="section"><a href="#rootDirectory">6.1.1. / : Root directory</a></span></dt><dt><span class="section"><a href="#binEssentialUserCommandBinaries2">6.1.2. /bin : Essential user command binaries (for use by all users)</a></span></dt><dt><span class="section"><a href="#devDevicesAndSpecialFiles">6.1.3. /dev : Devices and special files</a></span></dt><dt><span class="section"><a href="#etcHostspecificSystemConfiguration2">6.1.4. /etc : Host-specific system configuration</a></span></dt><dt><span class="section"><a href="#procKernelAndProcessInformationVir">6.1.5. /proc : Kernel and process information virtual filesystem</a></span></dt><dt><span class="section"><a href="#sbinEssentialSystemBinaries">6.1.6. /sbin : Essential system binaries</a></span></dt><dt><span class="section"><a href="#sysKernelAndSystemInformation">6.1.7. /sys : Kernel and system information virtual filesystem</a></span></dt><dt><span class="section"><a href="#usrincludeHeaderFilesIncludedByCP">6.1.8. /usr/include : Header files included by C programs</a></span></dt><dt><span class="section"><a href="#usrsrcSourceCode2">6.1.9. /usr/src : Source code</a></span></dt><dt><span class="section"><a href="#varspoolcronCronAndAtJobs">6.1.10. /var/spool/cron : cron and at jobs</a></span></dt></dl></dd></dl></div><p>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.</p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="linux"></a>6.1. Linux</h2></div></div></div><p>This is the annex for the Linux operating system.</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="rootDirectory"></a>6.1.1. / : Root directory</h3></div></div></div><p>On Linux systems, if the kernel is located in
<code class="filename">/</code>, we recommend using the names
<code class="filename">vmlinux</code> or <code class="filename">vmlinuz</code>, which
have been used in recent Linux kernel source packages.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="binEssentialUserCommandBinaries2"></a>6.1.2. /bin : Essential user command binaries (for use by all users)</h3></div></div></div><p>Linux systems which require them place these additional files into
<code class="filename">/bin</code>:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><span class="command"><strong>setserial</strong></span></p></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="devDevicesAndSpecialFiles"></a>6.1.3. /dev : Devices and special files</h3></div></div></div><p>The following devices must exist under 
<code class="filename">/dev</code>.

</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="filename">/dev/null</code></span></dt><dd><p>
All data written to this device is discarded. A read from this device
will return an EOF condition.
</p></dd><dt><span class="term"><code class="filename">/dev/zero</code></span></dt><dd><p>
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.
</p></dd><dt><span class="term"><code class="filename">/dev/tty</code></span></dt><dd><p>
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.
</p></dd></dl></div><p>

</p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>Previous versions of the FHS had stricter requirements for
<code class="filename">/dev</code>. 
Other devices may also exist in <code class="filename">/dev</code>.
Device names may exist as symbolic links to other device nodes
located in <code class="filename">/dev</code> 
or subdirectories of <code class="filename">/dev</code>. 
There is no requirement
concerning major/minor number values.</p></div><p>
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="etcHostspecificSystemConfiguration2"></a>6.1.4. /etc : Host-specific system configuration</h3></div></div></div><p>Linux systems which require them place these additional files into
<code class="filename">/etc</code>.</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><code class="filename">lilo.conf</code></p></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="procKernelAndProcessInformationVir"></a>6.1.5. /proc : Kernel and process information virtual filesystem</h3></div></div></div><p>The <code class="systemitem">proc</code> filesystem 
is the de-facto
standard Linux method for handling process and system information,
rather than <code class="filename">/dev/kmem</code> 
and other similar methods.
We strongly encourage this for the storage and retrieval of process
information as well as other kernel and memory information.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sbinEssentialSystemBinaries"></a>6.1.6. /sbin : Essential system binaries</h3></div></div></div><p>Linux systems place commands relating to filesystem maintenance and
boot loader management into <code class="filename">/sbin</code>.
</p><p>Optional files for <code class="filename">/sbin</code>:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: bullet; "><li class="listitem" style="list-style-type: disc"><p>Static binaries:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><span class="command"><strong>ldconfig</strong></span></p></li><li class="listitem"><p><span class="command"><strong>sln</strong></span></p></li><li class="listitem"><p><span class="command"><strong>ssync</strong></span></p></li></ul></div><p>Static <span class="command"><strong>ln</strong></span> (<span class="command"><strong>sln</strong></span>) and
static <span class="command"><strong>sync</strong></span> (<span class="command"><strong>ssync</strong></span>) are
useful when things go wrong.  The primary use of
<span class="command"><strong>sln</strong></span> (to repair incorrect symlinks in
<code class="filename">/lib</code> after a poorly orchestrated upgrade) is no
longer a major concern now that the <span class="command"><strong>ldconfig</strong></span>
program (usually located in <code class="filename">/usr/sbin</code>) 
exists and
can act as a guiding hand in upgrading the dynamic libraries.  Static
<span class="command"><strong>sync</strong></span> is useful in some emergency situations.
Note that these need not be statically linked versions of the standard
<span class="command"><strong>ln</strong></span> and <span class="command"><strong>sync</strong></span>, but may
be.</p><p>The <span class="command"><strong>ldconfig</strong></span> binary is optional for
<code class="filename">/sbin</code> since a site may choose to run
<span class="command"><strong>ldconfig</strong></span> at boot time, rather than only when
upgrading the shared libraries.  (It's not clear whether or not it is
advantageous to run <span class="command"><strong>ldconfig</strong></span> on each boot.)  Even
so, some people like <span class="command"><strong>ldconfig</strong></span> around for the
following (all too common) situation:</p><div class="orderedlist"><ol class="orderedlist" type="1"><li class="listitem"><p>I've just removed <code class="filename">/lib/&lt;file&gt;</code>.</p></li><li class="listitem"><p>I can't find out the name of the library because <span class="command"><strong>ls</strong></span> is
dynamically linked, I'm using a shell that doesn't have <span class="command"><strong>ls</strong></span>
built-in, and I don't know about using "<span class="command"><strong>echo *</strong></span>" as a
replacement.</p></li><li class="listitem"><p>I have a static <span class="command"><strong>sln</strong></span>, but I don't know what to call the link.</p></li></ol></div></li><li class="listitem" style="list-style-type: disc"><p>Miscellaneous:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p><span class="command"><strong>ctrlaltdel</strong></span></p></li><li class="listitem"><p><span class="command"><strong>kbdrate</strong></span></p></li></ul></div><p>So as to cope with the fact that some keyboards come up with
such a high repeat rate as to be unusable,
<span class="command"><strong>kbdrate</strong></span> may be installed in
<code class="filename">/sbin</code> on some systems.</p><p>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 <span class="command"><strong>init</strong></span> suites are able to disable
Ctrl-Alt-Del, but others may require the
<span class="command"><strong>ctrlaltdel</strong></span> program, which may be installed in
<code class="filename">/sbin</code> on those systems.</p></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="sysKernelAndSystemInformation"></a>6.1.7. /sys : Kernel and system information virtual filesystem</h3></div></div></div><p>The <code class="systemitem">sys</code> filesystem 
is the location where
information about devices, drivers, and some kernel features is
exposed.  Its underlying structure is determined by the particular
Linux kernel being used at the moment, and is otherwise
unspecified.</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="usrincludeHeaderFilesIncludedByCP"></a>6.1.8. /usr/include : Header files included by C programs</h3></div></div></div><p>These symbolic links are required if a C or C++ compiler is
installed and only for systems not based on glibc.</p><pre class="screen">
    /usr/include/asm -&gt; /usr/src/linux/include/asm-&lt;arch&gt;
    /usr/include/linux -&gt; /usr/src/linux/include/linux
</pre></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="usrsrcSourceCode2"></a>6.1.9. /usr/src : Source code</h3></div></div></div><p>For systems based on 
<code class="systemitem">glibc</code>, 
there are no specific guidelines for
this directory.  For systems based on Linux 
<code class="systemitem">libc</code> revisions prior to
<code class="systemitem">glibc</code>, 
the following guidelines and rationale apply:</p><p>The only source code that should be placed in a specific
location is the Linux kernel source code.  It is located in
<code class="filename">/usr/src/linux</code>.</p><p>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:</p><pre class="screen">
    /usr/src/linux/include/asm-&lt;arch&gt;
    /usr/src/linux/include/linux
</pre><p><code class="filename">&lt;arch&gt;</code> is the name of the system
architecture.</p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Note</h3><p><code class="filename">/usr/src/linux</code>
may be a symbolic link to a kernel source code tree.</p></div><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><h3 class="title">Rationale</h3><p>It is important that the kernel include files be located in
<code class="filename">/usr/src/linux</code> and not in
<code class="filename">/usr/include</code> 
so there are no problems when system
administrators upgrade their kernel version for the first time.</p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="varspoolcronCronAndAtJobs"></a>6.1.10. /var/spool/cron : cron and at jobs</h3></div></div></div><p>This directory contains the variable data for the
<span class="command"><strong>cron</strong></span> and <span class="command"><strong>at</strong></span> programs.</p></div></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="appendix"></a>Chapter 7. Appendix</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#theFhsMailingList">7.1. The FHS mailing list</a></span></dt><dt><span class="section"><a href="#backgroundOfTheFhs">7.2. Background of the FHS</a></span></dt><dt><span class="section"><a href="#generalGuidelines">7.3. General Guidelines</a></span></dt><dt><span class="section"><a href="#scope">7.4. Scope</a></span></dt><dt><span class="section"><a href="#acknowledgments">7.5. Acknowledgments</a></span></dt><dt><span class="section"><a href="#contributors">7.6. Contributors</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="theFhsMailingList"></a>7.1. The FHS mailing list</h2></div></div></div><p>The FHS mailing list is located at
<code class="email">&lt;<a class="email" href="mailto:fhs-discuss@lists.linuxfoundation.org">fhs-discuss@lists.linuxfoundation.org</a>&gt;</code> 
(subscription required as a spam limitation measure). Mailing
list subscription information, archives, etc. are at

<a class="ulink" href="https://lists.linux-foundation.org/mailman/listinfo/fhs-discuss" target="_top">
https://lists.linux-foundation.org/mailman/listinfo/fhs-discuss</a>
</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="backgroundOfTheFhs"></a>7.2. Background of the FHS</h2></div></div></div><p>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.</p><p>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.</p><p>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.</p><p>Thanks to Network Operations at the University of California at
San Diego, and later to SourceForge, who allowed us to use their 
excellent mailing list servers during earlier phases of development.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="generalGuidelines"></a>7.3. General Guidelines</h2></div></div></div><p>Here are some of the guidelines that have been used in the development
of this standard:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: bullet; "><li class="listitem" style="list-style-type: disc"><p>Solve technical problems while limiting transitional difficulties.</p></li><li class="listitem" style="list-style-type: disc"><p>Make the specification reasonably stable.</p></li><li class="listitem" style="list-style-type: disc"><p>Gain the approval of distributors, developers, and other decision-makers
in relevant development groups and encourage their participation.</p></li><li class="listitem" style="list-style-type: disc"><p>Provide a standard that is attractive to the implementors of different
UNIX-like systems.</p></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="scope"></a>7.4. Scope</h2></div></div></div><p>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.</p><p>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.</p><p>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.</p><p>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.</p><p>Comments related to this standard are welcome.  Any comments or
suggestions for changes may be directed to the 
FHS mailing list, or filed as bugs, or both.  
Typographical or grammatical comments should be filed as bugs.
The bugtracker is at

<a class="ulink" href="http://bugs.linuxfoundation.org" target="_top">http://bugs.linuxfoundation.org</a>
- use the category FHS.
</p><p>Before sending mail to the mailing list it is requested that you
first glance at the mailing list archives to avoid excessive re-discussion
of old topics.</p><p>Questions about how to interpret items in this document may
occasionally arise.  If you have need for a clarification, please
contact the FHS mailing list.  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.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="acknowledgments"></a>7.5. Acknowledgments</h2></div></div></div><p>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.</p><p>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.</p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="contributors"></a>7.6. Contributors</h2></div></div></div><div class="informaltable"><table border="0"><colgroup><col align="center" class="c1"><col align="center" class="c2"><col align="center" class="c3"></colgroup><tbody><tr><td align="left">Brandon S. Allbery</td><td align="left">John A. Martin</td><td align="left">Mike Sangrey</td></tr><tr><td align="left">Keith Bostic</td><td align="left">Ian McCloghrie</td><td align="left">David H. Silber</td></tr><tr><td align="left">Drew Eckhardt</td><td align="left">Chris Metcalf</td><td align="left">Thomas Sippel-Dau</td></tr><tr><td align="left">Rik Faith</td><td align="left">Ian Murdock</td><td align="left">Theodore Ts'o</td></tr><tr><td align="left">Karl Goetz</td><td align="left">David C. Niemi</td><td align="left">Stephen Tweedie</td></tr><tr><td align="left">Stephen Harris</td><td align="left">Lennart Poettering</td><td align="left">Fred N. van Kempen</td></tr><tr><td align="left">Ian Jackson</td><td align="left">Daniel Quinlan</td><td align="left">Bernd Warken</td></tr><tr><td align="left">Andreas Jaeger</td><td align="left">Eric S. Raymond</td><td align="left">Mats Wichmann</td></tr><tr><td align="left"><span class="personname"><span class="firstname">Jeff</span> <span class="surname">Licquia</span></span></td><td align="left"><span class="personname"><span class="firstname">Rusty</span> <span class="surname">Russell</span></span></td><td align="left"><span class="personname"><span class="firstname">Christopher</span> <span class="surname">Yeoh</span></span></td></tr></tbody></table></div></div></div></div></body></html>

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