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Filesystem Hierarchy Standard

Ted posted @ 2008年8月19日 21:50 in 未分类 with tags FHS , 2538 阅读

Edited by

Rusty Russell

Daniel Quinlan

Christopher Yeoh

 

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.

 

 

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.

Permission is granted to make and distribute verbatim copies of this standard provided the copyright and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this standard under the conditions for verbatim copying, provided also that the title page is labeled as modified including a reference to the original standard, provided that information on retrieving the original standard is included, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this standard into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the copyright holder.

 


Table of Contents
1. Introduction
Purpose
Conventions
2. The Filesystem
3. The Root Filesystem
Purpose
Requirements
Specific Options
/bin : Essential user command binaries (for use by all users)
Purpose
Requirements
Specific Options
/boot : Static files of the boot loader
Purpose
Specific Options
/dev : Device files
Purpose
Specific Options
/etc : Host-specific system configuration
Purpose
Requirements
Specific Options
/etc/opt : Configuration files for /opt
/etc/X11 : Configuration for the X Window System (optional)
/etc/sgml : Configuration files for SGML (optional)
/etc/xml : Configuration files for XML (optional)
/home : User home directories (optional)
Purpose
Requirements
/lib : Essential shared libraries and kernel modules
Purpose
Requirements
Specific Options
/lib<qual> : Alternate format essential shared libraries (optional)
Purpose
Requirements
/media : Mount point for removeable media
Purpose
Specific Options
/mnt : Mount point for a temporarily mounted filesystem
Purpose
/opt : Add-on application software packages
Purpose
Requirements
/root : Home directory for the root user (optional)
Purpose
/sbin : System binaries
Purpose
Requirements
Specific Options
/srv : Data for services provided by this system
Purpose
/tmp : Temporary files
Purpose
4. The /usr Hierarchy
Purpose
Requirements
Specific Options
/usr/X11R6 : X Window System, Version 11 Release 6 (optional)
Purpose
Specific Options
/usr/bin : Most user commands
Purpose
Specific Options
/usr/include : Directory for standard include files.
Purpose
Specific Options
/usr/lib : Libraries for programming and packages
Purpose
Specific Options
/usr/lib<qual> : Alternate format libraries (optional)
Purpose
/usr/local : Local hierarchy
/usr/local/share
/usr/sbin : Non-essential standard system binaries
Purpose
/usr/share : Architecture-independent data
Purpose
Requirements
Specific Options
/usr/share/dict : Word lists (optional)
/usr/share/man : Manual pages
/usr/share/misc : Miscellaneous architecture-independent data
/usr/share/sgml : SGML data (optional)
/usr/share/xml : XML data (optional)
/usr/src : Source code (optional)
Purpose
5. The /var Hierarchy
Purpose
Requirements
Specific Options
/var/account : Process accounting logs (optional)
Purpose
/var/cache : Application cache data
Purpose
Specific Options
/var/cache/fonts : Locally-generated fonts (optional)
/var/cache/man : Locally-formatted manual pages (optional)
/var/crash : System crash dumps (optional)
Purpose
/var/games : Variable game data (optional)
Purpose
/var/lib : Variable state information
Purpose
Requirements
Specific Options
/var/lib/<editor> : Editor backup files and state (optional)
/var/lib/hwclock : State directory for hwclock (optional)
/var/lib/misc : Miscellaneous variable data
/var/lock : Lock files
Purpose
/var/log : Log files and directories
Purpose
Specific Options
/var/mail : User mailbox files (optional)
Purpose
/var/opt : Variable data for /opt
Purpose
/var/run : Run-time variable data
Purpose
Requirements
/var/spool : Application spool data
Purpose
Specific Options
/var/spool/lpd : Line-printer daemon print queues (optional)
/var/spool/rwho : Rwhod files (optional)
/var/tmp : Temporary files preserved between system reboots
Purpose
/var/yp : Network Information Service (NIS) database files (optional)
Purpose
6. Operating System Specific Annex
Linux
/ : Root directory
/bin : Essential user command binaries (for use by all users)
/dev : Devices and special files
/etc : Host-specific system configuration
/lib64 and /lib32 : 64/32-bit libraries (architecture dependent)
/proc : Kernel and process information virtual filesystem
/sbin : Essential system binaries
/usr/include : Header files included by C programs
/usr/src : Source code
/var/spool/cron : cron and at jobs
7. Appendix
The FHS mailing list
Background of the FHS
General Guidelines
Scope
Acknowledgments
Contributors

Chapter 1. Introduction

Purpose

This standard enables:

 

  • Software to predict the location of installed files and directories, and

  • Users to predict the location of installed files and directories.

We do this by:

 

  • Specifying guiding principles for each area of the filesystem,

  • Specifying the minimum files and directories required,

  • Enumerating exceptions to the principles, and

  • Enumerating specific cases where there has been historical conflict.

The FHS document is used by:

 

  • Independent software suppliers to create applications which are FHS compliant, and work with distributions which are FHS complaint,

  • OS creators to provide systems which are FHS compliant, and

  • Users to understand and maintain the FHS compliance of a system.

The FHS document has a limited scope:

 

  • Local placement of local files is a local issue, so FHS does not attempt to usurp system administrators.

  • FHS addresses issues where file placements need to be coordinated between multiple parties such as local sites, distributions, applications, documentation, etc.


Conventions

We recommend that you read a typeset version of this document rather than the plain text version. In the typeset version, the names of files and directories are displayed in a constant-width font.

Components of filenames that vary are represented by a description of the contents enclosed in "<" and ">" characters, <thus>. Electronic mail addresses are also enclosed in "<" and ">" but are shown in the usual typeface.

Optional components of filenames are enclosed in "[" and "]" characters and may be combined with the "<" and ">" convention. For example, if a filename is allowed to occur either with or without an extension, it might be represented by <filename>[.<extension>].

Variable substrings of directory names and filenames are indicated by "*".

The sections of the text marked as Rationale are explanatory and are non-normative.


Chapter 2. The Filesystem

This standard assumes that the operating system underlying an FHS-compliant file system supports the same basic security features found in most UNIX filesystems.

It is possible to define two independent distinctions among files: shareable vs. unshareable and variable vs. static. In general, files that differ in either of these respects should be located in different directories. This makes it easy to store files with different usage characteristics on different filesystems.

"Shareable" files are those that can be stored on one host and used on others. "Unshareable" files are those that are not shareable. For example, the files in user home directories are shareable whereas device lock files are not.

"Static" files include binaries, libraries, documentation files and other files that do not change without system administrator intervention. "Variable" files are files that are not static.

 

Tip Rationale
 

Shareable files can be stored on one host and used on several others. Typically, however, not all files in the filesystem hierarchy are shareable and so each system has local storage containing at least its unshareable files. It is convenient if all the files a system requires that are stored on a foreign host can be made available by mounting one or a few directories from the foreign host.

Static and variable files should be segregated because static files, unlike variable files, can be stored on read-only media and do not need to be backed up on the same schedule as variable files.

Historical UNIX-like filesystem hierarchies contained both static and variable files under both /usr and /etc. In order to realize the advantages mentioned above, the /var hierarchy was created and all variable files were transferred from /usr to /var. Consequently /usr can now be mounted read-only (if it is a separate filesystem). Variable files have been transferred from /etc to /var over a longer period as technology has permitted.

Here is an example of a FHS-compliant system. (Other FHS-compliant layouts are possible.)

 

  shareable unshareable
static /usr /etc
  /opt /boot
variable /var/mail /var/run
  /var/spool/news /var/lock

 


Chapter 3. The Root Filesystem

Purpose

The contents of the root filesystem must be adequate to boot, restore, recover, and/or repair the system.

 

  • To boot a system, enough must be present on the root partition to mount other filesystems. This includes utilities, configuration, boot loader information, and other essential start-up data. /usr, /opt, and /var are designed such that they may be located on other partitions or filesystems.

  • To enable recovery and/or repair of a system, those utilities needed by an experienced maintainer to diagnose and reconstruct a damaged system must be present on the root filesystem.

  • To restore a system, those utilities needed to restore from system backups (on floppy, tape, etc.) must be present on the root filesystem.

 

Tip Rationale
 

The primary concern used to balance these considerations, which favor placing many things on the root filesystem, is the goal of keeping root as small as reasonably possible. For several reasons, it is desirable to keep the root filesystem small:

 

  • It is occasionally mounted from very small media.

  • The root filesystem contains many system-specific configuration files. Possible examples include a kernel that is specific to the system, a specific hostname, etc. This means that the root filesystem isn't always shareable between networked systems. Keeping it small on servers in networked systems minimizes the amount of lost space for areas of unshareable files. It also allows workstations with smaller local hard drives.

  • While you may have the root filesystem on a large partition, and may be able to fill it to your heart's content, there will be people with smaller partitions. If you have more files installed, you may find incompatibilities with other systems using root filesystems on smaller partitions. If you are a developer then you may be turning your assumption into a problem for a large number of users.

  • Disk errors that corrupt data on the root filesystem are a greater problem than errors on any other partition. A small root filesystem is less prone to corruption as the result of a system crash.

Applications must never create or require special files or subdirectories in the root directory. Other locations in the FHS hierarchy provide more than enough flexibility for any package.

 

Tip Rationale
 

There are several reasons why creating a new subdirectory of the root filesystem is prohibited:

 

  • It demands space on a root partition which the system administrator may want kept small and simple for either performance or security reasons.

  • It evades whatever discipline the system administrator may have set up for distributing standard file hierarchies across mountable volumes.

Distributions should not create new directories in the root hierarchy without extremely careful consideration of the consequences including for application portability.


Requirements

The following directories, or symbolic links to directories, are required in /.

 

Directory Description
bin Essential command binaries
boot Static files of the boot loader
dev Device files
etc Host-specific system configuration
lib Essential shared libraries and kernel modules
media Mount point for removeable media
mnt Mount point for mounting a filesystem temporarily
opt Add-on application software packages
sbin Essential system binaries
srv Data for services provided by this system
tmp Temporary files
usr Secondary hierarchy
var Variable data

 

Each directory listed above is specified in detail in separate subsections below. /usr and /var each have a complete section in this document due to the complexity of those directories.


Specific Options

The following directories, or symbolic links to directories, must be in /, if the corresponding subsystem is installed:

 

Directory Description
home User home directories (optional)
lib<qual> Alternate format essential shared libraries (optional)
root Home directory for the root user (optional)

 

Each directory listed above is specified in detail in separate subsections below.


/bin : Essential user command binaries (for use by all users)

Purpose

/bin contains commands that may be used by both the system administrator and by users, but which are required when no other filesystems are mounted (e.g. in single user mode). It may also contain commands which are used indirectly by scripts. [1]


Requirements

There must be no subdirectories in /bin.

The following commands, or symbolic links to commands, are required in /bin.

 

Command Description
cat Utility to concatenate files to standard output
chgrp Utility to change file group ownership
chmod Utility to change file access permissions
chown Utility to change file owner and group
cp Utility to copy files and directories
date Utility to print or set the system data and time
dd Utility to convert and copy a file
df Utility to report filesystem disk space usage
dmesg Utility to print or control the kernel message buffer
echo Utility to display a line of text
false Utility to do nothing, unsuccessfully
hostname Utility to show or set the system's host name
kill Utility to send signals to processes
ln Utility to make links between files
login Utility to begin a session on the system
ls Utility to list directory contents
mkdir Utility to make directories
mknod Utility to make block or character special files
more Utility to page through text
mount Utility to mount a filesystem
mv Utility to move/rename files
ps Utility to report process status
pwd Utility to print name of current working directory
rm Utility to remove files or directories
rmdir Utility to remove empty directories
sed The `sed' stream editor
sh The Bourne command shell
stty Utility to change and print terminal line settings
su Utility to change user ID
sync Utility to flush filesystem buffers
true Utility to do nothing, successfully
umount Utility to unmount file systems
uname Utility to print system information

 

If /bin/sh is not a true Bourne shell, it must be a hard or symbolic link to the real shell command.

The [ and test commands must be placed together in either /bin or /usr/bin.

 

Tip Rationale
 

For example bash behaves differently when called as sh or bash. The use of a symbolic link also allows users to easily see that /bin/sh is not a true Bourne shell.

The requirement for the [ and test commands to be included as binaries (even if implemented internally by the shell) is shared with the POSIX.2 standard.


Specific Options

The following programs, or symbolic links to programs, must be in /bin if the corresponding subsystem is installed:

 

Command Description
csh The C shell (optional)
ed The `ed' editor (optional)
tar The tar archiving utility (optional)
cpio The cpio archiving utility (optional)
gzip The GNU compression utility (optional)
gunzip The GNU uncompression utility (optional)
zcat The GNU uncompression utility (optional)
netstat The network statistics utility (optional)
ping The ICMP network test utility (optional)

 

If the gunzip and zcat programs exist, they must be symbolic or hard links to gzip. /bin/csh may be a symbolic link to /bin/tcsh or /usr/bin/tcsh.

 

Tip Rationale
 

The tar, gzip and cpio commands have been added to make restoration of a system possible (provided that / is intact).

Conversely, if no restoration from the root partition is ever expected, then these binaries might be omitted (e.g., a ROM chip root, mounting /usr through NFS). If restoration of a system is planned through the network, then ftp or tftp (along with everything necessary to get an ftp connection) must be available on the root partition.


/boot : Static files of the boot loader

Purpose

This directory contains everything required for the boot process except configuration files not needed at boot time and the map installer. Thus /boot stores data that is used before the kernel begins executing user-mode programs. This may include saved master boot sectors and sector map files. [2]


Specific Options

The operating system kernel must be located in either / or /boot. [3]


/dev : Device files

Purpose

The /dev directory is the location of special or device files.


Specific Options

If it is possible that devices in /dev will need to be manually created, /dev must contain a command named MAKEDEV, which can create devices as needed. It may also contain a MAKEDEV.local for any local devices.

If required, MAKEDEV must have provisions for creating any device that may be found on the system, not just those that a particular implementation installs.


/etc : Host-specific system configuration

Purpose

The /etc hierarchy contains configuration files. A "configuration file" is a local file used to control the operation of a program; it must be static and cannot be an executable binary. [4]


Requirements

No binaries may be located under /etc. [5]

The following directories, or symbolic links to directories are required in /etc:

 

Directory Description
opt Configuration for /opt
X11 Configuration for the X Window system (optional)
sgml Configuration for SGML (optional)
xml Configuration for XML (optional)

 


Specific Options

The following directories, or symbolic links to directories must be in /etc, if the corresponding subsystem is installed:

 

Directory Description
opt Configuration for /opt

 

The following files, or symbolic links to files, must be in /etc if the corresponding subsystem is installed: [6]

 

File Description
csh.login Systemwide initialization file for C shell logins (optional)
exports NFS filesystem access control list (optional)
fstab Static information about filesystems (optional)
ftpusers FTP daemon user access control list (optional)
gateways File which lists gateways for routed (optional)
gettydefs Speed and terminal settings used by getty (optional)
group User group file (optional)
host.conf Resolver configuration file (optional)
hosts Static information about host names (optional)
hosts.allow Host access file for TCP wrappers (optional)
hosts.deny Host access file for TCP wrappers (optional)
hosts.equiv List of trusted hosts for rlogin, rsh, rcp (optional)
hosts.lpd List of trusted hosts for lpd (optional)
inetd.conf Configuration file for inetd (optional)
inittab Configuration file for init (optional)
issue Pre-login message and identification file (optional)
ld.so.conf List of extra directories to search for shared libraries (optional)
motd Post-login message of the day file (optional)
mtab Dynamic information about filesystems (optional)
mtools.conf Configuration file for mtools (optional)
networks Static information about network names (optional)
passwd The password file (optional)
printcap The lpd printer capability database (optional)
profile Systemwide initialization file for sh shell logins (optional)
protocols IP protocol listing (optional)
resolv.conf Resolver configuration file (optional)
rpc RPC protocol listing (optional)
securetty TTY access control for root login (optional)
services Port names for network services (optional)
shells Pathnames of valid login shells (optional)
syslog.conf Configuration file for syslogd (optional)

 

mtab does not fit the static nature of /etc: it is excepted for historical reasons. [7]


/etc/opt : Configuration files for /opt

Purpose

Host-specific configuration files for add-on application software packages must be installed within the directory /etc/opt/<subdir>, where <subdir> is the name of the subtree in /opt where the static data from that package is stored.


Requirements

No structure is imposed on the internal arrangement of /etc/opt/<subdir>.

If a configuration file must reside in a different location in order for the package or system to function properly, it may be placed in a location other than /etc/opt/<subdir>.

 

Tip Rationale
 

Refer to the rationale for /opt.


/etc/X11 : Configuration for the X Window System (optional)

Purpose

/etc/X11 is the location for all X11 host-specific configuration. This directory is necessary to allow local control if /usr is mounted read only.


Specific Options

The following files, or symbolic links to files, must be in /etc/X11 if the corresponding subsystem is installed:

 

File Description
Xconfig
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