Linux: Linux Standards

Chen Weixiang @ Dec 12, 2015 | TAG: Linux

This article introduces standards related to Linux: Filesystem Hierarchy Standard (FHS) and Linux Standard Base (LSB).

Filesystem Hierarchy Standard (FHS)

The Filesystem Hierarchy Standard (FHS) defines the directory structure and directory contents in Unix and Unix-like operating systems. It is maintained by the Linux Foundation. This page is the home of the Filesystem Hierarchy Standard (FHS). Currently, it is only used by Linux distributions. And the Linux Standard Base (LSB) refers to it as a standard, see section VI. Execution Environment 16. File System Hierarchy in Linux Standard Base (LSB) Core Specification 3.1.

History of FHS

FHS releases the following versions, which can be downloaded from here for FHS 1.0, and from Filesystem Hierarchy Standard Specifications Archive for FHS 2.3 and beyond.

Version Release Date Notes
1.0 1994-02-14 FSSTND (FileSystem STaNDard)
1.1 1994-10-09 FSSTND (FileSystem STaNDard)
1.2 1995-03-28 FSSTND (FileSystem STaNDard)
2.0 1997-10-26 FHS 2.0 is the direct successor for FSSTND 1.2. Name changed from FSSTND to FHS.
2.1 2000-04-12 FHS (Filesystem Hierarchy Standard)
2.2 2001-05-23 FHS (Filesystem Hierarchy Standard)
2.3 2004-01-29 FHS (Filesystem Hierarchy Standard)
3.0 2015-05-18 FHS (Filesystem Hierarchy Standard)

Directory Structure defined in FHS 3

The following table contains the directory structures defined in FHS 3.0. For more detail explanations and the files contained in the directories, refer to FHS 3.0.

Directory Requirement Description
/ Required Primary hierarchy root directory.
/bin Required Essential command binaries (for use by all users). Must be no subdirectories in /bin.
/boot Required Static files of the boot loader.
/dev Required Device files.
/dev/null Required Required for Linux. All data written to this device is discarded. A read from this device will return an EOF condition.
/dev/zero Required Required for Linux. 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.
/dev/tty Required Required for Linux. 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.
/etc Required Host-specific system configuration. Recommended that configuration files are stored in subdirectories of /etc rather than directly in /etc.
/etc/opt Required Configuration files for add-on software packages that are stored in /opt.
/etc/X11 Optional Configuration for the X Window system.
/etc/sgml Optional Configuration for SGML.
/etc/xml Optional Configuration for XML.
/home Optional User home directories. User configuration files are ~/.<file> or ~/.<subdir>/<files>
/lib Required Essential shared libraries and kernel modules.
/lib/modules Optional Loadable kernel modules.
/lib<qual> Optional Alternate format essential shared libraries.
/media Required Mount point for removable media (appeared in FHS 2.3), which contains subdirectories for different removable medias.
/media/cdrom Optional CD-ROM drive.
/media/cdrecorder Optional CD writer.
/media/floppy Optional Floppy drive.
/media/zip Optional Zip drive.
/mnt Required Mount point for a temporarily mounted filesystem.
/opt Required Add-on application software packages. A package to be installed in /opt must locate its static files in a separate directory /opt/<package> or /opt/<provider>.
/opt/<package> Optional Static package objects.
/opt/<package>/bin Optional Binaries of the software package.
/opt/<package>/share/man Optional UNIX manual pages of the software package. Has the same substructure as /usr/share/man.
/opt/<provider> Optional <provider> is LANANA registered provider name. Recommended that packages are installed in /opt/<provider>/<package> and follow a similar structure of /opt/<package>.
/opt/bin Reserved Reserved for local system administrator use.
/opt/doc Reserved Reserved for local system administrator use.
/opt/include Reserved Reserved for local system administrator use.
/opt/info Reserved Reserved for local system administrator use.
/opt/lib Reserved Reserved for local system administrator use.
/opt/man Reserved Reserved for local system administrator use.
/proc De-facto Kernel and process information virtual filesystem.
/root Optional Home directory for the root user.
/run Required Data relevant to running processes since system was booted. The purposes of this directory were once served by /var/run.
/run/<program-name>.pid Optional Process identifier (PID) files, which were originally placed in /etc, must be placed in /run. The file contains the process identifier in ASCII-encoded decimal, followed by a newline character.
/sbin Required Essential system binaries used for system administration (and other root-only commands) are stored in /sbin, /usr/sbin, and /usr/local/sbin. /sbin contains binaries essential for booting, restoring, recovering, and/or repairing the system in addition to the binaries in /bin. Must be no subdirectories in /sbin.
/srv Required Site-specific data for services provided by this system.
/sys Required Required for Linux. Kernel and system information virtual filesystem.
/tmp Required Temporary files. Often not preserved between system reboots, see /var/tmp.
/usr Required Secondary hierarchy for shareable, read-only user data.
/usr/bin Required Non-essential command binaries. This is the primary directory of executable commands on the system. Must be no subdirectories in /usr/bin.
/usr/games Optional Games and educational binaries.
/usr/include Optional Header files included by C programs.
/usr/include/bsd Optional BSD compatibility include files.
/usr/lib Required Libraries for the binaries in /usr/bin/ and /usr/sbin/. Applications may use a single subdirectory under /usr/lib.
/usr/lib/sendmail Optional Symbolic link to the sendmail-compatible command for historical reasons.
/usr/libexec Optional Binaries run by other programs. Applications may use a single subdirectory under /usr/libexec.
/usr/lib<qual> Optional Alternate format libraries, which performs the same role as /usr/lib. The symbolic links /usr/lib<qual>/sendmail and /usr/lib<qual>/X11 are not required.
/usr/local Required Tertiary hierarchy for local data, specific to this host.
/usr/local/bin Required Local binaries.
/usr/local/etc Required Host-specific system configuration for local binaries. /usr/local/etc may be a symbolic link to /etc/local. NOTE: /usr/etc is not allowed: programs in /usr should place configuration files in /etc.
/usr/local/games Required Local game binaries.
/usr/local/include Required Local C header files.
/usr/local/lib Required Local libraries.
/usr/local/lib<qual> Optional Exist only if /lib<qual> or /usr/lib<qual> exist.
/usr/local/man Required Local online manuals.
/usr/local/sbin Required Local system binaries.
/usr/local/share Required Local architecture-independent hierarchy. The requirements for the contents of this directory are the same as for /usr/share.
/usr/local/share/color Optional Exist only if /usr/share/color exists. It follows the same rules as /usr/share/color.
/usr/local/src Required Local source code.
/usr/sbin Required Non-essential standard system binaries. Must be no subdirectories in /usr/sbin.
/usr/share Required Shareable, read-only, architecture-independent data. Recommended that a subdirectory be used in /usr/share for any program or package. Applications using a single file may use /usr/share/misc.
/usr/share/color Optional Color management information. The top-level directory /usr/share/color must not contain any files; all files should be in subdirectories of /usr/share/color.
/usr/share/color/icc Optional ICC color profiles.
/usr/share/dict Optional Word lists.
/usr/share/dict/words Optional List of English words.
/usr/share/doc Optional Miscellaneous documentation.
/usr/share/games Optional Static data files for /usr/games. Any modifiable files, such as score files, game play logs, and so forth, should be placed in /var/games.
/usr/share/info Optional Primary directory for GNU Info system.
/usr/share/locale Optional Locale information. Refer to man locale for locale-specific information. Also refer to How to add localization support to your bash scripts.
/usr/share/man Required Manual pages for commands and data under the / and /usr filesystems. This is the primary <mandir> of the system. Manual pages are stored in <mandir>/<locale>/man<section>.
/usr/share/man/man1 Optional User programs.
/usr/share/man/man2 Optional System calls.
/usr/share/man/man3 Optional Library calls.
/usr/share/man/man4 Optional Special files.
/usr/share/man/man5 Optional File formats.
/usr/share/man/man6 Optional Games.
/usr/share/man/man7 Optional Miscellaneous.
/usr/share/man/man8 Optional System administration.
/usr/share/man/<locale>/
man<section>		 Optional Manual pages for specific <locale> and <section>. The <locale> is based on Appendix E of the POSIX 1003.1 standard and has format
<lang>[_<terr>][.<char-set>][,<ver>]
/usr/share/misc Required Miscellaneous architecture-independent data.
/usr/share/misc/ascii Optional ASCII character set table.
/usr/share/misc/termcap Optional Terminal capability database.
/usr/share/misc/termcap.db Optional Terminal capability database.
/usr/share/nls Optional Message catalogs for Native language support.
/usr/share/ppd Optional Printer definitions, that’s PostScript Printer Definition (PPD) files.
/usr/share/sgml Optional SGML data.
/usr/share/sgml/docbook Optional docbook DTD.
/usr/share/sgml/tei Optional tei DTD.
/usr/share/sgml/html Optional html DTD.
/usr/share/sgml/mathml Optional mathml DTD.
/usr/share/terminfo Optional Directories for terminfo database.
/usr/share/tmac Optional troff macros not distributed with groff.
/usr/share/xml Optional XML data.
/usr/share/xml/docbook Optional docbook XML DTD.
/usr/share/xml/xhtml Optional XHTML DTD.
/usr/share/xml/mathml Optional MathML DTD.
/usr/share/zoneinfo Optional Timezone information and configuration.
/usr/src Optional Source code only for reference purposes. e.g., kernel source code with its header files. Generally, source should not be built within this hierarchy.
/usr/src/linux Optional It contains Linux kernel source code, or may be a symbolic link to a kernel source code tree.
/usr/X11R6 Optional X Window System, Version 11, Release 6 (up to FHS-2.3).
/usr/spool Optional Symbolic links to /var/spool for backwards compatibility.
/usr/spool/locks Optional Symbolic links to /var/lock for backwards compatibility.
/usr/tmp Optional Symbolic links to /var/tmp for backwards compatibility.
/var Required Variable files. /var is specified in order to make it possible to mount /usr read-only. Some portions of /var are not shareable between different systems, such as /var/log, /var/lock and /var/run. Other portions may be shared, such as /var/mail and /var/cache/man.
/var/account Optional Current active process accounting logs.
/var/backups Reserved Reserved to prevent conflict with historical and/or local practice.
/var/cache Required Application cache data. The data must remain valid between invocations of the application and rebooting the system, and may be expired in an application specific manner, by the system administrator, or both.
/var/cache/fonts Optional Locally-generated fonts.
/var/cache/man Optional Locally-formatted manual pages.
/var/cache/www Optional WWW proxy or cache data.
/var/cache/<package> Optional Package specific cache data.
/var/crash Optional System crash dumps.
/var/cron Reserved Reserved to prevent conflict with historical and/or local practice.
/var/games Optional Variable game data relating to games in /usr.
/var/lib Required Variable state information pertaining to an application or the system. State information should generally remain valid after a reboot, should not be logging output, and should not be spooled data. An application must use a subdirectory of /var/lib for its data.
/var/lib/<editor> Optional Editor backup files and state.
/var/lib/<pkgtool> Optional Packaging support files.
/var/lib/<package> Optional State data for packages and subsystems.
/var/lib/color Optional Color management information. This directory shall be laid out using the same rules as the /usr/share/color directory.
/var/lib/hwclock Optional State directory for hwclock.
/var/lib/misc Required Miscellaneous variable data, which is intended for state files that don’t need a subdirectory.
/var/lib/xdm Optional X display manager variable data.
/var/local Required Variable data for /usr/local.
/var/lock Required Lock files keeping track of resources currently in use. The naming convention which must be used is “LCK..” followed by the base name of the device.
/var/log Required Log files and directories.
/var/log/lastlog Optional Record of last login of each user.
/var/log/messages Optional System messages from syslogd.
/var/log/wtmp Optional Record of all logins and logouts.
/var/mail Optional User mailbox files, which must be stored in the standard UNIX mailbox format. Note that /var/mail may be a symbolic link to another directory.
/var/msgs Reserved Reserved to prevent conflict with historical and/or local practice.
/var/opt Required Variable data from add-on software packages that are stored in /opt/.
/var/opt/<subdir> Optional Variable data of the add-on software package in /opt/<subdir> must be installed in /var/opt/<subdir>.
/var/preserve Reserved Reserved to prevent conflict with historical and/or local practice.
/var/run Required Data relevant to running processes. The /var/run is used for the purposes of backwards compatibility. Migration to use /run is recommended. It’s valid to implement /var/run as a symlink to /run.
/var/spool Required Application spool data, which is awaiting some kind of later processing.
/var/spool/cron Required Required for Linux. Contain the variable data for the cron and at programs.
/var/spool/lpd Optional Printer spool directory.
/var/spool/lpd/printer Optional Spools for a specific printer.
/var/spool/mqueue Optional Outgoing mail queue.
/var/spool/news Optional News spool directory.
/var/spool/rwho Optional Rwhod files, which hold the rwhod information for other systems on the local net.
/var/spool/uucp Optional Spool directory for UUCP.
/var/tmp Required Temporary files to be preserved between reboots.
/var/yp Optional Network Information Service (NIS) database files. Formerly known as the Sun Yellow Pages (YP).

Linux Standard Base (LSB)

The Linux Standard Base (LSB) was created to lower the overall costs of supporting the Linux platform. By reducing the differences between individual Linux distributions, the LSB greatly reduces the costs involved with porting applications to different distributions, as well as lowers the cost and effort involved in after-market support of those applications.

The picture below represents the key LSB deliverables for application and distribution developers: LSB Specifications and Tools

LSB Specifications

The official home of the LSB specification is the Linux Foundation’s Reference Specifications Archive. The following LSB specifications are released:

  • LSB 1.0 was released on June 29, 2001.

    LSB 1.0 supports Filesystem Hierarchy Standard (FHS) 2.2.

  • LSB 1.1 was released on January 22, 2002.

    LSB 1.1 supports Filesystem Hierarchy Standard (FHS) 2.2.

  • LSB 1.2 was released on June 28, 2002.

    LSB 1.2 supports Filesystem Hierarchy Standard (FHS) 2.2.

  • LSB 1.3 was released on December 17, 2002.

    LSB 1.3 supports Filesystem Hierarchy Standard (FHS) 2.2.

  • LSB 2.0 was released on August 31, 2004. The release omitted the PPC32 and S390 architectures.

    LSB 2.0 supports Filesystem Hierarchy Standard (FHS) 2.3.

  • LSB 2.0.1 was released on October 21, 2004.

    LSB 2.0.1 supports Filesystem Hierarchy Standard (FHS) 2.3.

  • LSB 2.1 was released on March 11, 2005.

    LSB 3.0 supports Filesystem Hierarchy Standard (FHS) 2.3.

  • LSB 3.0 was released on July 6, 2005.

    LSB 3.0 supports Filesystem Hierarchy Standard (FHS) 2.3.

  • LSB 3.1 Core was released on October 27, 2005; LSB 3.1 C++ and Desktop were released April 24, 2006.

    Note that the Core module specification of LSB 3.1 is the document submitted for publication by ISO/IEC as IS 23360:1996. The following are the main parts of it and can be downloaded from Publicly Available Standards:

    ISO/IEC 23360-1:2006 Linux Standard Base (LSB) core specification 3.1 – Part 1: Generic specification ISO/IEC 23360-2:2006 Linux Standard Base (LSB) core specification 3.1 – Part 2: Specification for IA-32 architecture ISO/IEC 23360-3:2006 Linux Standard Base (LSB) core specification 3.1 – Part 3: Specification for IA-64 architecture ISO/IEC 23360-4:2006 Linux Standard Base (LSB) core specification 3.1 – Part 4: Specification for AMD64 architecture ISO/IEC 23360-5:2006 Linux Standard Base (LSB) core specification 3.1 – Part 5: Specification for PPC32 architecture ISO/IEC 23360-6:2006 Linux Standard Base (LSB) core specification 3.1 – Part 6: Specification for PPC64 architecture ISO/IEC 23360-7:2006 Linux Standard Base (LSB) core specification 3.1 – Part 7: Specification for S390 architecture ISO/IEC 23360-8:2006 Linux Standard Base (LSB) core specification 3.1 – Part 8: Specification for S390X architecture

    There is also ISO/IEC TR 24715:2006 which identifies areas of conflict between ISO/IEC 23360 (the Linux Standard Base 3.1 specification) and the ISO/IEC 9945:2003 (POSIX) International Standard. The ISO/IEC TR 24715:2006 can be downloaded from Publicly Available Standards.

    LSB 3.1 supports Filesystem Hierarchy Standard (FHS) 2.3.

  • LSB 3.2 was released on January 25, 2008

    Note that the LSB 3.2 Core specification is an evolution of the ISO/IEC International Standard 23360, which corresponded to LSB 3.1. This edition is not to be considered an ISO standard.

    LSB 3.2 supports Filesystem Hierarchy Standard (FHS) 2.3.

  • LSB 4.0 was released on May 1, 2009

    Note that the LSB 4.0 Core specification is an evolution of the ISO/IEC International Standard 23360, which corresponded to LSB 3.1. This edition is not to be considered an ISO standard.

    LSB 4.0 supports Filesystem Hierarchy Standard (FHS) 2.3.

  • LSB 4.1 was released on February 16, 2011

    Note that the LSB 4.1 Core specification is an evolution of the ISO/IEC International Standard 23360, which corresponded to LSB 3.1. This edition is not to be considered an ISO standard.

    LSB 4.1 supports Filesystem Hierarchy Standard (FHS) 2.3.

  • LSB 5.0 was released on June 3, 2015

    Note that the LSB 5.0 Core specification set is an evolution of the ISO/IEC International Standard 23360, which corresponded to LSB 3.1. This edition is not to be considered an ISO standard. LSB 5.0 contains two major changes to the specification: (1) the first major release to break 100% compatibility with earlier versions. It is compatible with LSB 3.0, and mostly compatible with LSB 3.1 and later, with one exception (Qt 3 Removed); (2) LSB 5.0 supports seven architectures: IA32, IA64, PPC32, PPC64, S390, S390X, and X86_64.

    LSB 5.0 supports Filesystem Hierarchy Standard (FHS) 3.0.

The Linux Standard Base (LSB) specifications are made available in two parts: an architecture independent (generic) part and an architecture dependent part. For LSB 5.0, the architecture independent part is comprised of five modules: Common, Core, Desktop, Runtime Languages and Imaging. The architecture dependent part is comprised of two modules: Core and Desktop.

Also, there are mandatory and trial use modules in the specification. The former impose mandatory requirements on LSB compliant distributions and applications may safely rely on the functionality described in mandatory modules. Functionality in trial use modules is not required in LSB compliant distributions and applications should take this into consideration. Meanwhile, trial use modules represent candidates for inclusion in the next versions of LSB.

LSB Navigator

LSB Database is a central place for storing information about the LSB standard and about the surrounding Linux ecosystem. LSB Navigator represents web based interface over all these information. It can be used by Linux developers, Linux distribution vendors and LSB workgroup to browse, query, analyze and submit various information.

LSB Elements

There are four Top Level Entities of LSB specifiction: Modules, ELF Elements, RPM Tags and Interpreted Languages. And the Modules contains ABI (Libraries) and Commands. The ELF Elements and RPM Tags belong to LSB_Core module only. The Interpreted Languages contains Java, Perl and Python languages.

Top Level Schema of LSB Elements

LSB Certification

This part of the LSB Certification System represents central place for managing certification workflow and status. In that website, you can track the industry picture of LSB certification in Product Directory area. For instance, a list of Linux distributions and applications certified for compliance with the LSB standard can be found here.

Additional Requirements for FHS in LSB 3.1

An LSB conforming application shall conform to the Filesystem Hierarchy Standard (FHS).

An LSB conforming implementation shall provide the mandatory portions of the file system hierarchy specified in the Filesystem Hierarchy Standard (FHS), together with following additional requirements made in LSB specification 3.1.

Directory Requirement Description
/dev Required Device files.
/dev/null Required An infinite data source and data sink. Data written to this device shall be discarded. Reads from this device shall always return end-of-file (EOF).
/dev/zero Required An infinite data source and data sink.
/dev/null Required This device is a source of zeroed out data. All data written to this device shall be discarded. A read from this device shall always return the requested number of bytes, each initialized to the value \0.
/dev/tty Required In each process, a synonym for the controlling terminal associated with the process group of that process, if any. All reads and writes to this device shall behave as if the actual controlling terminal device had been opened.
/etc Required Host-specific system configuration. Recommended that configuration files are stored in subdirectories of /etc rather than directly in /etc.
/etc/cron.d Required A directory containing extended crontab files, refer to Cron Jobs.
/etc/cron.daily Required A directory containing shell scripts to be executed once a day.
/etc/cron.hourly Required A directory containing shell scripts to be executed once per hour.
/etc/cron.monthly Required A directory containing shell scripts to be executed once per month.
/etc/cron.weekly Required A directory containing shell scripts to be executed once a week.
/etc/init.d Required A directory containing system initialization scripts.
/etc/profile.d Required A directory containing shell scripts. Script names should follow the same conventions as specified for cron jobs, but should have the suffix .sh. The behavior is unspecified if a script is installed in this directory that does not have the suffix .sh.

Content of LSB 5

Commands and Utilities

According to Linux Standard Base (LSB) 5.0, an LSB conforming implementation shall provide the commands and utilities as described in following table, with at least the behavior described as mandatory in the referenced underlying specification, with the following exceptions:

  • If any operand (except one which follows --) starts with a hyphen, the behavior is unspecified.

    Rationale (Informative): Applications should place options before operands, or use --, as needed. This text is needed because, by default, GNU option parsing differs from POSIX, unless the environment variable POSIXLY_CORRECT is set. For example, ls . -a in GNU ls means to list the current directory, showing all files (that is, . is an operand and -a is an option). In POSIX, . and -a are both operands, and the command means to list the current directory, and also the file named -a. Suggesting that applications rely on the setting of the POSIXLY_CORRECT environment variable, or try to set it, seems worse than just asking the applications to invoke commands in ways which work with either the POSIX or GNU behaviors.

Commands Reference Implementations Note
[ [1] GNU coreutils check file types and compare values. Also see test
ar [2] GNU Binutils create and maintain library archives (DEPRECATED)
at [2] Debian, Ubuntu examine or delete jobs for later execution
awk [2] GNU Awk pattern scanning and processing language
basename [1] GNU coreutils strip directory and suffix from a file name
batch [2] GNU batch schedule commands to be executed in a batch queue
bc [2] GNU bc an arbitrary precision calculator language
cat [1] GNU coreutils concatenate files and print on the standard output
chfn [2] shadow-utils change user name and information
chgrp [1] GNU coreutils change group ownership
chmod [1] GNU coreutils change file mode bits
chown [1] GNU coreutils change file owner and group
chsh [2] shadow-utils change login shell
cksum [1] GNU coreutils checksum and count the bytes in a file
cmp [1] GNU diffutils compare two files byte by byte
col [2] BSD col filter reverse line feeds from input
comm [1] GNU coreutils compare two sorted files line by line
cp [1] GNU coreutils copy files and directories
cpio [2] GNU cpio copy file archives in and out
crontab [2] BSD crontab maintain crontab files for individual users
csplit [1] GNU coreutils split a file into sections determined by context lines. Also refer to split
cut [1] GNU coreutils remove sections from each line of files
date [1] GNU coreutils print or set the system date and time
dd [1] GNU coreutils convert and copy a file
df [2] GNU coreutils report file system disk space usage
diff [1] GNU diffutils compare files line by line
dirname [1] GNU coreutils strip last component from file name
dmesg [2] util-linux print or control the system message buffer
du [2] GNU coreutils estimate file space usage
echo [2] GNU coreutils write arguments to standard output
ed [1] GNU ed line-oriented text editor
egrep [2] GNU grep search a file with an Extended Regular Expression pattern
env [1] GNU coreutils run a program in a modified environment
expand [1] GNU coreutils convert tabs to spaces. Also see unexpand
expr [1] GNU coreutils evaluate expressions
false [1] GNU coreutils do nothing, unsuccessfully. Also see true
fgrep [2] GNU grep search a file with a fixed pattern
find [1] GNU findutils search for files in a directory hierarchy
file [2] File determine file type
fold [1] GNU coreutils wrap each input line to fit in specified width
fuser [2] PSmisc identify processes using files or sockets
gencat [1] BSD gencat generate a formatted message catalog
getconf [1] BSD getconf get configuration values
gettext [2] GNU gettext-tools retrieve text string from message catalog
grep [2] GNU grep print lines matching a pattern
groupadd [2] shadow-utils create a new group
groupdel [2] shadow-utils delete a group
groupmod [2] shadow-utils modify a group
groups [2] GNU coreutils display a group
gunzip [2] GNU Gzip uncompress files
gzip [2] GNU Gzip compress or expand files
head [1] GNU coreutils output the first part of files. Also see tail
hostname [2] net-tools show or set the system’s host name
iconv [1] BSD iconv convert encoding of given files from one encoding to another
id [1] GNU coreutils print real and effective user and group IDs
infocmp [3] GNU ncurses compare or print out terminfo descriptions
install [2] GNU coreutils copy files and set attributes
install_initd [2] initd-tools activate an init script
ipcrm [2] util-linux remove IPC Resources
ipcs [2] util-linux provide information on ipc facilities
join [1] GNU coreutils join lines of two files on a common field
kill [1] procps-ng send a signal to a process
killall [2] PSmisc kill processes by name
ln [1] GNU coreutils link files
locale [1] BSD locale get locale-specific information
localedef [1] BSD locale define locale environment
logger [1] util-linux a shell command interface to the syslog(3) system log module
logname [1] GNU coreutils print user’s login name
lp [1] Apple lp send files to a printer
lpr [2] Apple lpr off line print
ls [2] GNU coreutils list directory contents
lsb_release [2] lsb_release print distribution specific information
m4 [2] GNU M4 macro processor
mailx [1] Heirloom mailx process messages
make [1] GNU Make GNU make utility to maintain groups of programs
man [1] man on wikipedia format and display the on-line manual pages
md5sum [2] GNU coreutils generate or check MD5 message digests
mkdir [1] GNU coreutils make directories
mkfifo [1] GNU coreutils make FIFOs (named pipes)
mknod [2] GNU coreutils make special files
mktemp [2] GNU coreutils make temporary file name (unique)
more [2] util-linux display files on a page-by-page basis
mount [2] util-linux mount a file system
msgfmt [2] GNU gettext-tools create a message object from a message file
mv [1] GNU coreutils move (rename) files
newgrp [2] shadow-utils change group ID
nice [1] GNU coreutils run a program with modified scheduling priority
nl [1] GNU coreutils number lines of files
nohup [1] GNU coreutils run a command immune to hangups, with output to a non-tty
od [2] GNU coreutils dump files in octal and other formats
passwd [2] shadow-utils change user password
paste [1] GNU coreutils merge lines of files
patch [2] GNU patch apply a diff file to an original
pathchk [1] GNU coreutils check whether file names are valid or portable
pax [1] MirBSD read and write file archives and copy directory hierarchies
pidof [2] pidof find the process ID of a running program
pr [1] GNU coreutils convert text files for printing
printf [1] GNU coreutils format and print data
ps [1] procps-ng report a snapshot of the current processes
pwd [1] GNU coreutils print name of current/working directory
remove_initd [2] initd-tools clean up init script system modifications introduced by install_initd
renice [2] util-linux alter priority of running processes
rm [1] GNU coreutils remove files or directories
rmdir [1] GNU coreutils remove empty directories
sed [2] GNU sed stream editor
sendmail [2] sendmail an electronic mail transport agent
seq [2] GNU coreutils generate a sequence of numbers
sh [2] GNU Bash shell, the standard command language interpreter
shutdown [2] upstart shut the system down
sleep [1] GNU coreutils delay for a specified amount of time
sort [1] GNU coreutils sort lines of text files
split [1] GNU coreutils split a file into pieces. Also see csplit
strings [1] GNU Binutils print the strings of printable characters in files
strip [1] GNU Binutils discard symbols from object files
su [2] shadow-utils change user ID
stty [1] GNU coreutils change and print terminal line settings. Also see tty
sync [2] GNU coreutils flush file system buffers
tail [1] GNU coreutils output the last part of files. Also see head
tar [2] GNU tar file archiver
tee [1] GNU coreutils read from standard input and write to standard output and files
test [1] GNU coreutils check file types and compare values. Also see [
tic [3] GNU ncurses the terminfo entry-description compiler
time [1] time run programs and summarize system resource usage
touch [1] GNU coreutils change file timestamps
tput [3] GNU ncurses initialize a terminal or query terminfo database
tr [1] GNU coreutils translate or delete characters
true [1] GNU coreutils do nothing, successfully. Also see false
tsort [1] GNU coreutils perform topological sort. Also see sort
tty [1] GNU coreutils print the file name of the terminal connected to standard input. Also see stty
umount [2] util-linux unmount file systems
uname [1] GNU coreutils print system information
unexpand [1] GNU coreutils convert spaces to tabs. Also see expand
uniq [1] GNU coreutils report or omit repeated lines
useradd [2] shadow-utils create a new user or update default new user information
userdel [2] shadow-utils delete a user account and related files
usermod [2] shadow-utils modify a user account
wc [1] GNU coreutils print newline, word, and byte counts for each file
xargs [2] GNU findutils build and execute command lines from standard input
zcat [2] GNU Gzip uncompress files to standard output

Referenced Specification(s) in above table:

Shell built-in Utilities

According to Linux Standard Base (LSB) 5.0, an LSB conforming implementation shall provide the shell built in utilities as described in following table, with at least the behavior described as mandatory in the referenced underlying specification, with the following exceptions:

  • The built in commands and utilities shall be provided by the sh utility itself, and need not be implemented in a manner so that they can be accessed via the exec family of functions as defined in POSIX 1003.1-2008 (ISO/IEC 9945-2009) and should not be invoked directly by those standard utilities that execute other utilities, that’s env, find, nice, nohup, time, xargs.

    Rationale (Informative): Since the built in utilities must affect the environment of the calling process, they have no effect when executed as a file.

LSB_Commands Reference Note
alias [1] Define or display aliases.
bg [1] Run jobs in the background.
cd [1] Change the working directory.
command [1] Execute a simple command.
fc [1] Process the command history list.
fg [1] Run jobs in the foreground.
getopts [1] Parse utility options.
hash [1] Remember or report utility locations.
jobs [1] Display status of jobs in the current session.
read [1] Read a line from standard input.
type [1] Write a description of command type.
ulimit [1] Set or report file size limit.
umask [1] Get or set the file mode creation mask.
unalias [1] Remove alias definitions.
wait [1] Await process completion.

Referenced Specification(s) in above table: [1] POSIX 1003.1-2008 (ISO/IEC 9945-2009)

References