Init

This article is about the Unix process. For other uses, see INIT (disambiguation).
Version 7 Unix: /etc listing, showing init and rc
Version 7 Unix: contents of an /etc/rc Bourne shell script

In Unix-based computer operating systems, init (short for initialization) is the first process started during booting of the operating system. Init is a daemon process that continues running until the system is shut down. It is the direct or indirect ancestor of all other processes and automatically adopts all orphaned processes. Init is started by the kernel during the booting process; a kernel panic will occur if the kernel is unable to start it, or it should die for any reason. Init is typically assigned process identifier 1.

In Unix systems such as System III and System V, the design of init has diverged from the functionality provided by the init in Research Unix and its BSD derivatives. Up until the early 2010s,[1][failed verification] most Linux distributions employed a traditional init that was somewhat compatible with System V, while some distributions such as Slackware use BSD-style startup scripts, and other distributions such as Gentoo have their own customized versions.

Since then, several additional init implementations have been created, attempting to address design limitations in the traditional versions. These include launchd, the Service Management Facility, systemd, Runit and OpenRC.

Research Unix-style/BSD-style

Research Unix init runs the initialization shell script located at /etc/rc,[2] then launches getty on terminals under the control of /etc/ttys.[3] There are no runlevels; the /etc/rc file determines what programs are run by init. The advantage of this system is that it is simple and easy to edit manually. However, new software added to the system may require changes to existing files that risk producing an unbootable system.

BSD init was, prior to 4.3BSD, the same as Research UNIX's init;[4][5] in 4.3BSD, it added support for running a windowing system such as X on graphical terminals under the control of /etc/ttys.[6][7] To remove the requirement to edit /etc/rc, BSD variants have long supported a site-specific /etc/rc.local file that is run in a sub-shell near the end of the boot sequence.

A fully modular system was introduced with NetBSD 1.5 and ported to FreeBSD 5.0 and successors. This system executes scripts in the /etc/rc.d directory. Unlike System V's script ordering, which is derived from the filename of each script, this system uses explicit dependency tags placed within each script.[8] The order in which scripts are executed is determined by the rcorder utility based on the requirements stated in these tags.

SysV-style

sysv-rc-conf, a TUI utility that selects which SysV-style init scripts will be run in each runlevel

When compared to its predecessors, AT&T's UNIX System III introduced a new style of system startup configuration,[9] which survived (with modifications) into UNIX System V and is therefore called the "SysV-style init".

At any moment, a running System V is in one of the predetermined number of states, called runlevels. At least one runlevel is the normal operating state of the system; typically, other runlevels represent single-user mode (used for repairing a faulty system), system shutdown, and various other states. Switching from one runlevel to another causes a per-runlevel set of scripts to be run, which typically mount filesystems, start or stop daemons, start or stop the X Window System, shutdown the machine, etc.

Runlevels

Further information: Runlevel

The runlevels in System V describe certain states of a machine, characterized by the processes and daemons running in each of them. In general, there are seven runlevels, out of which three runlevels are considered "standard", as they are essential to the operation of a system:

  1. Turn off
  2. Single-user mode (also known as S or s)
  3. Reboot

Aside from these standard ones, Unix and Unix-like systems treat runlevels somewhat differently. The common denominator, the /etc/inittab file, defines what each configured runlevel does in a given system.

Default runlevels

Operating system Default runlevel
AIX 2
antiX 5
Gentoo Linux 3[10]
HP-UX 3 (console/server/multiuser) or 4 (graphical)
Linux From Scratch 3
Slackware Linux 3
Solaris / illumos 3[11]
UNIX System V Releases 3.x, 4.x 2
UnixWare 7.x 3

On Linux distributions defaulting to runlevel 5 in the table on the right, runlevel 5 invokes a multiuser graphical environment running the X Window System, usually with a display manager like GDM or KDM. However, the Solaris and illumos operating systems typically reserve runlevel 5 to shut down and automatically power off the machine.

On most systems, all users can check the current runlevel with either the runlevel or who -r command.[12] The root user typically changes the current runlevel by running the telinit or init commands. The /etc/inittab file sets the default runlevel with the :initdefault: entry.

On Unix systems, changing the runlevel is achieved by starting only the missing services (as each level defines only those that are started / stopped).[citation needed] For example, changing a system from runlevel 3 to 4 might only start the local X server. Going back to runlevel 3, it would be stopped again.

Other implementations

Traditionally, one of the major drawbacks of init is that it starts tasks serially, waiting for each to finish loading before moving on to the next. When startup processes end up Input/output (I/O) blocked, this can result in long delays during boot. Speeding up I/O, e.g. by using SSDs, may shorten the delays but it does not address the root cause.

Various efforts have been made to replace the traditional init daemons to address this and other design problems, including:

  • BootScripts in GoboLinux
  • busybox-init, suited to embedded operating systems, used by Alpine Linux (before being replaced with OpenRC), SliTaz 5 (Rolling), Tiny Core Linux, and VMware ESXi, and used by OpenWrt before it was replaced with procd
  • Dinit, a service manager and init system.[13]
  • Epoch, a single-threaded Linux init system focused on simplicity and service management[14]
  • ginitd, a software package that consists of an init system and a service management system[15]
  • Initng, a full replacement of init designed to start processes asynchronously
  • launchd, a replacement for init in Darwin/macOS/iOS/tvOS starting with Mac OS X v10.4 (it launches SystemStarter to run old-style 'rc.local' and SystemStarter processes)
  • OpenRC, a process spawner that utilizes system-provided init, while providing process isolation, parallelized startup, and service dependency; used by Alpine Linux, Gentoo and its derivatives, and available as an option in Devuan and Artix Linux.
  • runit, a cross-platform full replacement for init with parallel starting of services, used by default in Void Linux[16]
  • Sun Service Management Facility (SMF), a complete replacement/redesign of init from the ground up in illumos/Solaris starting with Solaris 10, but launched as the only service by the original System V-style init
  • Shepherd, the GNU service and daemon manager which provides asynchronous, dependency-based initialisation; written in Guile Scheme and meant to be interactively hackable during normal system operation[17]
  • s6, a software suite that includes an init system. [18][19]
  • systemd, a software suite, full replacement for init in Linux that includes an init daemon, with concurrent starting of services, service manager, and other features. Used by Debian (replaces SysV init), Ubuntu among other popular linux distributions.
  • SystemStarter, a process spawner started by the BSD-style init in Mac OS X prior to Mac OS X v10.4
  • Upstart, a full replacement of init designed to start processes asynchronously. Initiated by Ubuntu and used by them until 2014. It was also used in Fedora 9,[20][21] Red Hat Enterprise Linux 6[22] and Google's ChromeOS.[23]

As of February 2019, systemd has been adopted by most major Linux distributions.[24]

See also

References

  1. ^ "Lennart Poettering on systemd's Tumultuous Ascendancy". The New Stack. 2018-11-08. Archived from the original on 2018-11-08. Retrieved 2024-01-30.
  2. ^ init(8) – Version 7 Unix Programmer's Manual
  3. ^ ttys(5) – Version 7 Unix Programmer's Manual
  4. ^ init(8) – 4.2BSD System Manager's Manual
  5. ^ ttys(5) – 4.2BSD File Formats Manual
  6. ^ init(8) – 4.3BSD System Manager's Manual
  7. ^ ttys(5) – 4.3BSD File Formats Manual
  8. ^ Andrew Smallshaw (7 December 2009). "Unix and Linux startup scripts, Part 2". Archived from the original on 18 December 2009. Retrieved 6 June 2011.
  9. ^ "init(8)". minnie.tuhs.org. Archived from the original on 2021-07-27. Retrieved 2015-09-12.
  10. ^ "Initscripts". Gentoo Linux Documentation. Gentoo.org. 2014-12-13. Archived from the original on 2020-12-03. Retrieved 2020-12-08.
  11. ^ "Run Levels". Oracle Solaris Administration: Common Tasks. Oracle. Archived from the original on 2016-04-10. Retrieved 2017-11-14.
  12. ^ "UNIX man pages : runlevel (8)". Unixhelp.ed.ac.uk. 1997-05-27. Archived from the original on 2014-07-14. Retrieved 2014-07-12.
  13. ^ "GitHub - davmac314/dinit: Service monitoring / "init" system". GitHub. Archived from the original on 2021-12-12. Retrieved 2021-12-12.
  14. ^ "Epoch Init System Homepage". Archived from the original on 2014-08-02. Retrieved 2014-07-31.
  15. ^ Wood-Mattheusson, S. M. (2024-12-16). "ginitd: det effektivaste init-systemet".
  16. ^ "Void Linux main page". Archived from the original on 2020-08-29. Retrieved 2020-08-31.
  17. ^ "The Shepherd - GNU Project". Free Software Foundation, Inc. Archived from the original on 2016-02-12. Retrieved 2016-01-16.
  18. ^ "s6: why another supervision suite". Archived from the original on 2021-09-13. Retrieved 2021-09-13.
  19. ^ "s6 init system". Archived from the original on 2021-09-13.
  20. ^ Fedora 14 Accepted Features, 2010-07-13, archived from the original on 2022-03-27, retrieved 2010-07-13
  21. ^ "Fedora defers systemd to F15". Linux Weekly News. 2010-09-14. Archived from the original on 2010-09-19. Retrieved 2010-09-17.
  22. ^ "Deployment". Red Hat Enterprise Linux 6: Technical Notes. Red Hat. Archived from the original on 2018-08-29. Retrieved 2013-12-31.
  23. ^ Software Architecture: Chromium OS design documents, archived from the original on 9 April 2022, retrieved 25 January 2014
  24. ^ See Systemd#Adoption

Read other articles:

Anne Northup

Anne Northup Anne Meagher Northup (lahir 22 Januari 1948) adalah politikus Partai Republik dan pengajar Amerika Serikat asal Persemakmuran Kentucky. Dari 1997 sampai 2007, ia menjadi anggota DPR Referensi Pranala luar Kongres Amerika Serikat. Anne Northup (id: N000143). Biographical Directory of the United States Congress.  Northup for Congress 2008 campaign website. Diarsipkan dari versi asli tanggal 2008-07-30. Diakses tanggal 2008-02-08.  Parameter |url-status= yang tidak di...

 

 

Sogo

Logo Sogo Department Store. Sogo Department Store di Kobe, Jepang. Sogo Co., Ltd. (Jepang: 株式会社そごう) merupakan sebuah toserba berantai yang mengoperasikan sebuah jaringan ekstensif atas cabang-cabangnya, yang berpusat di Jepang. Sogo memiliki toko-toko di berbagai lokasi di beberapa negara seperti di Jakarta, Tangerang, Bandung, Surabaya, Medan, Samarinda, dan Bali di Indonesia, Beijing dan Hong Kong di Republik Rakyat Tiongkok, Taipei di Taiwan, Kuala Lumpur di Malaysia, Sin...

 

 

KGBX-FM

Adult contemporary radio station in Nixa, Missouri KGBX-FMNixa, MissouriBroadcast areaSpringfield, MissouriFrequency105.9 MHzBranding105.9 KGBXProgrammingFormatAdult contemporaryAffiliationsPremiere NetworksOwnershipOwneriHeartMedia, Inc.(iHM Licenses, LLC)Sister stationsKGMY, KSWF, KTOZ-FM, KXUSHistoryFirst air dateApril 23, 1979 (1979-04-23) (as KBLR-FM)Former call signsKBLR-FM (1979-1979)KYOO-FM (1979-1989)Technical informationFacility ID63887ClassC2ERP38,000 wattsHAAT170 me...

WFLA (AM)

For the short-lived Boca Raton station of 1927, see WFLA (Boca Raton, Florida). Radio station in Tampa, Florida This article includes a list of general references, but it lacks sufficient corresponding inline citations. Please help to improve this article by introducing more precise citations. (November 2009) (Learn how and when to remove this template message) WFLATampa, FloridaBroadcast areaTampa-St. Petersburg-Clearwater and Sarasota-Bradenton, FloridaFrequency970 kHz25.87 MHz (Shortwave)B...

 

 

Шаблон:Мифология

МифологияРитуально-мифологическийкомплекс Система ценностей Сакральное Миф Мономиф Теория основного мифа Ритуал Обряд Праздник Жречество Мифологическое сознание Магическое мышление Низшая мифология Модель мира Цикличность Сотворение мира Мировое яйцо Мифическое �...

 

 

1942 North Dakota gubernatorial election

Election for the governor of North Dakota For related races, see 1942 United States gubernatorial elections. 1942 North Dakota gubernatorial election ← 1940 November 3, 1942 1944 →   Nominee John Moses Oscar W. Hagen Party Democratic Republican Popular vote 101,390 74,577 Percentage 57.62% 42.38% County resultsMoses:      50–60%      60–70%      70–80% Hagen:    ...

2007 Arena Football League season

Sports season2007 Arena Football League seasonLeagueArena Football LeagueSportArena footballDurationMarch 1, 2007 – July 29, 2007Regular seasonSeason championsDallas DesperadosAFL PlayoffsNational Conference championsColumbus Destroyers  National Conference runners-upGeorgia ForceAmerican Conference championsSan Jose SaberCats  American Conference runners-upChicago RushArenaBowl XXIChampionsSan Jose SaberCats  Runners-upColumbus DestroyersFinals MVPMark Grieb, ...

 

 

112 (numéro d'appel d'urgence)

Pour les articles homonymes, voir 112 (homonymie). Si ce bandeau n'est plus pertinent, retirez-le. Cliquez ici pour en savoir plus. Cet article doit être actualisé (août 2019). Des passages de cet article ne sont plus d’actualité ou annoncent des événements désormais passés. Améliorez-le ou discutez-en. Vous pouvez également préciser les sections à actualiser en utilisant {{section à actualiser}}. 112 (numéro d'appel d'urgence) Centre de régulation des appels d'urgen...

 

 

Erdwärmesonde

Bohrung einer Erdwärmesonde (links im Vordergrund aufgerollt die eigentliche Sonde) Der U-förmige Sondenfuß, das untere Ende einer Erdwärmesonde. Die Anschlußrohre wurden durchtrennt. Die Rohre einer Erdwärmesonde ragen aus dem Erdboden, sind rot markiert und müssen noch an den Wärmeträgerkreislauf angeschlossen werden. Eine Erdwärmesonde (EWS) ist ein Erdwärmeübertrager, in dem eine Wärmeträgerflüssigkeit zirkuliert. Im Gegensatz zum horizontal verlegten Erdwärmekollektor wir...

Castaways of the Flying Dutchman

2001 novel by Brian Jacques Castaways of the Flying Dutchman AuthorBrian JacquesIllustratorIan SchoenherrCover artistMichael KoelschLanguageEnglishSeriesCastawaysGenreFantasy novelPublisherPuffin BooksPublication date2001Publication placeUnited StatesMedia typePrint (paperback)Pages336ISBN978-0-399-23601-3OCLC45058678Dewey Decimal[Fic] 21LC ClassPZ7.J15317 Cas 2001Followed byThe Angel's Command  Castaways of the Flying Dutchman is the first novel in the Castaways seri...

 

 

Bucine

Bucinecomune Bucine – Veduta LocalizzazioneStato Italia Regione Toscana Provincia Arezzo AmministrazioneSindacoNicola Benini (centro-sinistra) dal 27-5-2019 TerritorioCoordinate43°28′39″N 11°36′57″E43°28′39″N, 11°36′57″E (Bucine) Altitudine250 m s.l.m. Superficie131,11 km² Abitanti9 955[2] (31-8-2022) Densità75,93 ab./km² FrazioniAmbra, Badia Agnano, Badia a Roti, Capannole, Cennina, Duddova, Levane, Mercatale-Tor...

 

 

مجزرة مدرسة الفاخورة

  لمعانٍ أخرى، طالع مجزرة مدرسة الفاخورة (توضيح). مجزرة الفاخورة المعلومات الموقع بالقرب من مدرسة الفاخورة، مخيم جباليا للاجئين، قطاع غزة الإحداثيات 31°32′16″N 34°29′53″E / 31.5377°N 34.498°E / 31.5377; 34.498   التاريخ 6 يناير 2009 نوع الهجوم قذائف المدفعية الخسائر الوفيات ...

سلالة أوان

لوحة تعود لسلالة آوان في متحف اللوفر سلالة أوان وهي أول سلالة عيلامية، لكن غير معروف متى ظهروا بالتحديد، العيلاميون ذكروا في النقوش السومرية منذ فجر التاريخ وظهروا كخصوم لهم إذ كانوا مجاورين لهم، وأول مرة تم ذكرهم من قبل الملك إين مي باراكي سي ملك كيش، حيث قام هذا الملك بمه...

 

 

Mine (Bazzi song)

2017 single by BazziMineSingle by Bazzifrom the album Cosmic ReleasedOctober 12, 2017GenreR&BLength2:11LabeliamcosmicAtlanticSongwriter(s)Andrew BazziProducer(s)BazziRice N' PeasBazzi singles chronology Beautiful (2017) Mine (2017) Why? (2018) Music videoMine on YouTube Mine is a song by American singer-songwriter Bazzi.[1] The song was self-released digitally on October 12, 2017.[2] The song made its chart debut on February 3, 2018, after becoming an internet meme.[3&...

 

 

Histoire de l’Azerbaïdjan pendant la Seconde Guerre mondiale

Bataillon envoyé au front sur la route de la gare de Biləcəri en 1942. La République socialiste soviétique d'Azerbaïdjan entre dans la Seconde Guerre mondiale après l'invasion allemande de l'Union soviétique le 22 juin 1941. Les champs pétrolifères azerbaïdjanais attiraient les Allemands en raison de la forte dépendance de l'URSS vis-à-vis du pétrole du Caucase – préparant le terrain pour les campagnes allemandes tentant de capturer et de s'emparer des champs pétrolifères d...

1985 Brisbane City Council election

Australian local election 1985 Brisbane City Council election ← 1982 30 March 1985 1988 →   First party Second party   Candidate Sallyanne Atkinson Roy Harvey Party Liberal Labor Lord Mayor before election Roy Harvey Labor Subsequent Lord Mayor Sallyanne Atkinson Liberal All 26 wards on the City Council13 wards needed for a majority Party Leader % Seats +/– Liberal Sallyanne Atkinson 52.0 15 Labor Roy Harvey This lists parties that won seats. See the complete...

 

 

Mana Endō

Questa voce sull'argomento tennisti giapponesi è solo un abbozzo. Contribuisci a migliorarla secondo le convenzioni di Wikipedia. Mana EndōNazionalità Giappone Altezza160 cm Tennis Termine carriera1998 1 Dati relativi al circuito maggiore professionistico.   Modifica dati su Wikidata · Manuale Mana Endō (遠藤 愛?, Endō Mana; Hiroshima, 6 febbraio 1971) è un'ex tennista giapponese. Biografia Ha impugnato la prima racchetta a 7 anni grazie a suo padre Hiroshi, che...

 

 

CRC Concise Encyclopedia of Mathematics

Book by Eric W. Weisstein This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these template messages) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed.Find sources: CRC Concise Encyclopedia of Mathematics – news · newspapers · books · scholar · J...

Venezuela

Disambiguazione – Se stai cercando altri significati, vedi Venezuela (disambigua). Venezuela (dettagli) (dettagli) (ES) Dios y Federación(IT) Dio e Federazione Venezuela - LocalizzazioneIn verde scuro i territori controllati dal Venezuela, in verde chiaro la Guayana Esequiba, territorio rivendicato ma non controllato. Dati amministrativiNome completoRepubblica Bolivariana del Venezuela Nome ufficiale(ES) República Bolivariana de Venezuela Lingue ufficialiSpagnolo Altre lingueLingue arawa...

 

 

井筒部屋

井筒部屋（いづつべや）は、かつて存在した日本相撲協会所属の相撲部屋。本項では14代（鶴ヶ嶺）が運営していた君ヶ浜部屋についても記す。 歴史 創設から高砂一門時代 歴史上最初に確認できる井筒部屋は、1884年（明治17年）に引退した6代井筒の幕内・井筒菊治郎が興した。6代井筒は二枚鑑札で井筒部屋を運営していたが、1887年（明治20年）に死去して部屋は閉鎖...