File system hierarchy standard

File system hierarchy standard
	; Example of a standard root directory
Basic data
Maintainer	Linux Foundation
developer	LSB working group
Current version	3 ; (June 2015)
operating system	Linux
German speaking	No
	refspecs.linuxfoundation.org/fhs

The Filesystem Hierarchy Standard ( FHS ) is a guideline for the directory structure under Unix-like operating systems .

The standard is aimed at software developers , system integrators and system administrators . Its purpose is to promote the interoperability of computer programs by making the location of directories and files predictable.

The development of this guideline began in August 1993 and was initially only related to Linux . In the meantime, some of the FreeBSD developers have helped create a comprehensive standard for all Unix-like systems. This collaboration was officially discontinued in May 2011 after the Linux Foundation took over the project. Currently, this standard is only used by Linux distributions . The first documentation of such a hierarchy appeared in AT&T UNIX Version 7.

File categories

The FHS differentiates files under two aspects:

"Static" or "variable"

“Static” are those files that do not change without the intervention of a system administrator. All other files are considered "variables".

"Shareable" or "unshareable"

"Shareable" are those files that can be used by other computers via a computer network. All other files are considered "unshareable".

Four categories of files result from these two aspects:

"Static shareable"
"Static unshareable"
"Variable shareable"
"Variable unshareable"

In order to make data backups and provision in the computer network more efficient, the FHS does not plan to save files of different categories in the same directory. Historically, this separation did not exist.

Root directory

The partition ( volume ) of the root directory must contain all the files that are necessary to start up the operating system and to integrate further partitions. In order to be able to repair a system, it must also contain the necessary tools.

In order to increase flexibility and reliability, the FHS recommends creating parts of the directory structure in other partitions. Additional partitions are transparent under Unix and similar operating systems .

Main directories

14 directories or symbolic links to directories are required in the root directory:

/ am	Basic command binaries	historical: "utility programs" (programs such as assembler and compiler )
/boat	static files of the boot loader	historical: -
/ dev	Device files	historical: "devices" (devices such as hard drives and system console )
/Etc	Host- specific system configuration	historically: "essential data and dangerous maintenance utilities" (essential data and dangerous maintenance programs such as init and passwd )
/ lib	basic dynamic libraries and kernel modules	historical: "object libraries and other stuff" (object libraries and other material)
/ media	Mount point for removable media	historical: -
/ mnt	for temporarily mounted file system	historical: -
/ opt	additional application programs	historical: -
/run	data relevant to ongoing processes	historical: -
/ sbin	essential binaries of the system	historical: -
/ srv	Data for services	historical: -
/ tmp	temporary data	historical: "temporary files" (temporary files, usually on a fast device)
/ usr	secondary hierarchy	historically: "general-purpose directory" (universal directory, usually the mount point of another file system)
/ var	variable data	historical: -

The directories / opt, / usr and / var are designed so that they do not have to be in the partition of the root directory.

Additional directories are required if appropriate subsystems are installed:

/ home	User directories
/ root	Directory of the root account
/ lib ...	alternative dynamic libraries, e.g. / lib32 and / lib64 for 32-bit and 64-bit

Other directories should not be created in the root directory. Application programs should not request or create files in the root directory.

/ bin - basic system commands (for all users)

/ bin contains all commands that can be called by both the administrator and the user and are also required when no other file systems are mounted, for example in single user mode. In addition, scripts that use such commands can also be stored there.

The / bin directory must not contain any subdirectories. The following programs or symbolic links to the Unix commands are at least required in / bin:

cat: Append files together ( English: con cat enate ) and write to standard output (stdout)

chgrp : change group membership ( English: ch ange gr ou p )

chmod : Change the file access rights ( English: ch ange mod e )

chown : change owner and group membership ( English: ch ange own ership )

cp : Copying files or directories ( English: c o p y )

date: Show or set the system date and time

dd : converting or copying data ( English: d ump d ata )

df: Show the free disk space ( in English: d isk f rees pace )

dmesg: Show or configure the ring buffer of the kernel ( English: d isplay mes sa g es )

echo : Play a line of text

false : Generating an error status code

hostname : Show or set the current computer name

kill : kill a process
ln : setting links between files ( English: l i n k )
login: check user identity and start user interface
ls : show directory contents ( English: l i s t )
mkdir: creating a directory ( English: m a k e dir ectory )
mknod: creating special device files ( English: m a k e nod e )
more : show data scrolling page by page
mount: mounting of file systems
mv : moving or renaming files ( English: m o v e )
ps : show process status ( English: p rocess s tatus )

pwd : Show the name of the current directory ( English: p rint w orking d irectory )

rm : deleting files or directories ( English: r e m ove )

rmdir: delete empty directories ( English: r e m ove you ectory )

sed : Editing of data without interaction ( English: s tream ed itor )

sh : Unix shell ( command line interpreter , English: sh ell ). If sh is not the original Bourne shell , sh must bea hard or soft link to the shell used.

stty: Show or set settings of a data terminal device ( English: s et t ele ty per )

su : starts a user interface with a new user identity ( English: s ubstitute u ser )

sync: Writing the contents of data buffers to the data carrier ( English: sync hronize )

true : Generate a success status code

umount: Unmount filesystems ( English: u n mount )

uname : Show various system information ( English: U NIX name )

If required, the following commands (or links to them) must also be installed in the / bin directory:

csh : C -like command line interpreter ( English: c -like sh ell )

ed : Editing of text ( English: ed it )

tar : Management of file archives ( English: t ape ar chiver )

cpio : Copying files to or from archives ( English: c o p y i nput / o utput )

gzip : Compression of data ( English: G NU zip )

gunzip : Decompress data (mostly as a link to gzip)

zcat: decompress and display data ( English: z ipped con cat enation )

netstat : Show network status information ( English: net work stat us )

ping : Sending and receiving data packets via ICMP

All other commands that are required for recovery, such as ftp , tftp or various archiving programs , also have their place here.

/ boot - static files of the boot loader

This directory contains all files required by the boot loader for the boot process. This includes e.g. B. also saved master boot records . The operating system kernel must also be stored either in this directory or in the root directory.

/ dev - device files

The dev contains special files directory / (special file) or device files (device file) . Some of the device files have to be created manually. In this case, the directory must contain the command MAKEDEV or MAKEDEV.local, which can create these device files using the existing hardware.
Worth mentioning are / dev / null , which can be written to but everything is discarded, / dev / zero , from which zero bytes can be read in any amount, and / dev / random (or / dev / urandom), which is used as hardware -Random generator is used.

udev has replaced devfs since Kernel 2.6 and now uses configuration files (by default in / etc / udev ) in the user space to automatically create the devices in / dev.

/ etc - specific configuration files

/ etc originally stood for "everything else" (lat. et cetera ). However, it has then established itself as a configuration directory and is therefore often interpreted as an "editable text configuration". The / etc directory and its subdirectories contain all kinds of configuration files . These files must be static files (see above). There must be no binary files in this directory.

The following subdirectories can be: a. exist in / etc:

/ etc / opt

In general, the configurations of individual services are located in / etc / <service name> / and / or /etc/<service name>.conf (the LDAP under the Debian derivative Ubuntu, for example, does both without a clear file name). With daemons the final d is often missing , the NTP server z. B. has the process ntpd , but the configuration file /etc/ntp.conf .

The following configuration files definitely belong in / etc (if available):

csh.login: system-wide initialization file for the C-like command interpreter
exports: Access rights for NFS shares
fstab: Table with static information about mountable file systems
ftpusers: Contains the names of the users to be excluded from the ftp call
gateways

/ home - home directories, optional

This directory structure is used to hold the user-specific data of the individual users of the system. The FHS only lists this directory as optional, although it is established as a quasi-standard. All user-specific configuration files are stored in hidden files and directories (which have a dot as the first character of the file name) under / home / $ USER / . These hidden files and directories in the user directory are often called "dot files".

/ lib - kernel modules and dynamic libraries

The / lib directory contains the installed dynamic libraries and kernel modules that are required to start the system and for the programs in / bin and / sbin. The dynamic C standard library libc.so. * and the linker library ld * are also located here . The modules subdirectory contains the above-mentioned kernel modules if they are installed.

/ lib <nr> - Alternative kernel modules and dynamic libraries

Some systems support multiple binary formats (for different processor architectures or modes), each with its own version of the same library. Then there are, for example, / lib32 and / lib64 for the two operating modes (32-bit and 64-bit) of the x86 processor.

/ media - mount points for removable media

The individual subdirectories in / media serve as a mount point for every type of removable medium. Earlier portable media was / mnt either directly in the root directory or in mounted . In order to streamline the root directory, the directories were moved to the / media folder. The standard provides the following optional subdirectories:

/ media / floppy: diskette
/ media / cdrom: CD-ROM
/ media / cdrecorder: CD burner
/ media / zip: Zip drive

If a device is present several times, appending a number to the device type is suggested.

/ mnt - temporary mount points for file systems

The directory is used for temporary mounting of foreign file systems of all kinds. Installation programs are expressly prohibited from using the / mnt directory for temporary files.

/ opt - additional software packages

The directory is for all optional, i. H. additionally installed software provided that does not come from the package sources belonging to the distribution. The packages must be in a subdirectory named/ opt / <package> or / opt / <manufacturer> be installed, where <package> is a descriptive package name and <manufacturer>is the name of the manufacturer registered with LANANA . The subdirectories/ opt / bin, / opt / doc, / opt / include, / opt / info, / opt / lib, and / opt / manare reserved for the local system administrator. Software package binaries are usually found only in/ opt / <package> / bin

/ root - user directory for user root, optional

The directory can form the user directory for the user root. This directory is only a recommendation by the FHS.

/ run directory

At the end of March 2011, the developers of the Linux distribution Fedora announced that future Fedora versions would contain the directory / run. Its function is to replace the / var / run directory and solve the problem that under certain circumstances / var / run is not yet available during the boot process, but is required for booting. Several Linux distributions have given their support. / run is now also required by the file system hierarchy standard.

/ sbin - important system commands

The directory contains commands for system administration and other tasks that only the root user can perform. These are essentially all commands that could have been placed in the / bin directory, but e.g. B. for reasons of storage space not there. Programs expected in / sbin: shutdown, fastboot, fasthalt, fdisk, fsck, fsck. *, Getty, halt, ifconfig, init, mkfs, mkfs. *, Mkswap, reboot, route, swapon, swapoff, update

/ srv - data offered by services

The data on the services offered should be stored in this directory. At the moment there are no regulations on how the directory structure in / srv should look. One suggested option is to name the subdirectories after the service, e.g. B. www, ftp, mysql, etc. Another possibility is to organize according to administrative units such as student councils at universities. This is currently only done by SuSE and Arch Linux. For example, the directory / var / www exists under Debian, whereas SuSE uses / srv / www (Arch: / srv / http).

/ tmp - temporary files

This directory must exist because there are programs that save their temporary files in this directory. This directory was included in the FHS primarily because of its historical significance. The directory is approved for writing by all users and must have a sticky bit .

/ usr directory structure

/ usr ( U nix S ystem R esources, originally: US e R ) is the second important level of the file system. This area can be used jointly by several computers (shareable) and accordingly does not contain any content that is dependent on the local computer or that varies over time. These are stored in other places in the file system.

The following directories must exist in / usr:

/ usr / bin: many user commands; This is the primary directory for the system's executable files.
/ usr / include: Header files are integrated by programs; The header files contain the various include files with prototype definitions.
/ usr / lib: Libraries; Modular program code that is shared by different programs.
/ usr / local: Distribution-independent local hierarchy. The local system administration can and should store programs and data here that have been installed independently of the corresponding distribution of the respective system, such as self-compiled programs and files or programs and files downloaded independently of the distribution. The installation mechanisms of the distribution in question are expressly prohibited from touching this directory structure. The design of the internal structure of / usr / local is the responsibility of the local system administration and is not specified by the FHS.
/ usr / sbin: further, not mandatory system commands; In contrast to / sbin, these system commands are not used by the administrator during the boot process.
/ usr / share (architecture independent data)

In addition, the following directories can optionally exist:

/ usr / X11R6: X Window System , Version 11 Release 6
/ usr / games: Games
/ usr / lib <nr>: alternative versions of dynamic libraries
/ usr / src: Source code

To ensure compatibility with older systems, symbolic links can be created for the following directories:

/ usr / spool → / var / spool
/ usr / tmp → / var / tmp
/ usr / spool / locks → / var / lock

/ var directory structure

The / var directory (English var iable ) contains variable data that arise in the course of processing. The following directories, or symbolic links to directories, are expected in / var:

/ var / cache: data cached by application programs
/ var / lib: variable status information
/ var / local: variable data related to / usr / local
/ var / lock: Directory for lock files for process synchronization
/ var / log: Directory for log files
/ var / opt: variable data in connection with / opt
/ var / run: Data that are important for running processes (/ run now fulfills the function; the directory exists to ensure compatibility with systems and software that use an older version of the FHS specification and can be implemented as a symbolic link on / run)
/ var / spool: Directory for queues to be processed (print jobs, e-mail dispatch jobs ...)
/ var / tmp: temporary files that are retained after a restart

For "historical" reasons, the following directories still exist if required:

/ var / backups
/ var / cron (nowadays found under / var / spool / cron)
/ var / msgs
/ var / preserve

If the corresponding applications are installed, the following directories are also used:

/ var / account: Process accounting data
/ var / crash: System dumps in the event of a computer crash
/ var / games: variable game dates
/ var / mail: User mailbox files (often as a symlink to / var / spool / mail)
/ var / yp: Network Information Service database files

Web links

Individual evidence

^ Background of the FHS . In: Filesystem Hierarchy Standard 2.3 . Retrieved January 11, 2011.
↑ Filesystem Hierarchy Standard (FHS) and FreeBSD . freebsd.org. May 10, 2011. Retrieved February 27, 2016.
↑ Re: Filesystem Hierarchy Standard (FHS) and NetBSD . netbsd.org. May 10, 2011. Retrieved February 27, 2016.
↑ Filesystem Hierarchy Standard (FHS) and OpenBSD . nabble.com. May 10, 2011. Retrieved February 27, 2016.
↑ here - layout of file systems . In: FreeBSD Man Pages . FreeBSD Foundation . Retrieved October 3, 2016.
^ The File System . In: Filesystem Hierarchy Standard 2.3 . Retrieved January 11, 2011.
↑ Requirements . In: Filesystem Hierarchy Standard . Retrieved October 3, 2016.
↑ ^a ^b ^c ^d ^e ^f here - file system hierarchy . In: FreeBSD Man Pages - Unix Seventh Edition . FreeBSD Foundation. Retrieved October 3, 2016.
↑ Specific Options . In: Filesystem Hierarchy Standard 2.3 . Retrieved January 11, 2011.
↑ What's this / run directory doing on my system and where does it come from? . fedoraproject.org. March 30, 2011. Retrieved February 27, 2016.
↑ Distributions introduce new directory / run . In: Pro-Linux . March 31, 2011. Accessed February 27, 2016.

File system hierarchy standard
Example of a standard root directory
Basic data
Maintainer	Linux Foundation
developer	LSB working group
Current version	3 (June 2015)
operating system	Linux
German speaking	No
refspecs.linuxfoundation.org/fhs