Editing Init (section)

== {{Anchor|S6}}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:
* [[GoboLinux#Boot system|BootScripts]] in [[GoboLinux]]
* [[Busybox|busybox-init]], suited to [[embedded operating system]]s, 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 [[OpenWrt#procd|procd]]
* Dinit, a service manager and init system.<ref>{{cite web |url=https://github.com/davmac314/dinit |title=GitHub - davmac314/dinit: Service monitoring / "init" system |website=[[GitHub]] |access-date=2021-12-12 |archive-date=2021-12-12 |archive-url=https://web.archive.org/web/20211212163253/https://github.com/davmac314/dinit |url-status=live }}</ref>
* [[Epoch (init system)|Epoch]], a single-threaded Linux init system focused on simplicity and service management<ref>{{cite web |url=http://universe2.us/epoch.html |title=Epoch Init System Homepage |access-date=2014-07-31 |archive-date=2014-08-02 |archive-url=https://web.archive.org/web/20140802142947/http://universe2.us/epoch.html |url-status=live }}</ref>
* [[ginitd]], a software package that consists of an init system and a service management system<ref>{{Cite web |last=Wood-Mattheusson |first=S. M. |date=2024-12-16 |title=ginitd: det effektivaste init-systemet |url=https://ylur.me/gershwin/ginitd }}</ref>
* [[Initng]], a full replacement of init designed to start processes asynchronously
* [[launchd]], a replacement for init in [[Darwin (operating system)|Darwin]]/[[macOS]]/[[iOS]]/[[tvOS]] starting with [[Mac&nbsp;OS&nbsp;X v10.4]] (it launches SystemStarter to run old-style <nowiki>'rc.local'</nowiki> 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 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]]<ref>{{Cite web |url=http://voidlinux.org/ |title=Void Linux main page |access-date=2020-08-31 |archive-date=2020-08-29 |archive-url=https://web.archive.org/web/20200829154800/https://voidlinux.org/ |url-status=live }}</ref>
* Sun [[Service Management Facility]] (SMF), a complete replacement/redesign of init from the ground up in [[illumos]]/[[Solaris (operating system)|Solaris]] starting with Solaris 10, but launched as the only service by the original System&nbsp;V-style init
* [[GNU Guix System#GNU Shepherd init system|Shepherd]], the [[GNU]] service and daemon manager which provides asynchronous, dependency-based initialisation; written in [[Guile (programming language)|Guile Scheme]] and meant to be interactively hackable during normal system operation<ref>{{cite web |url=https://www.gnu.org/software/shepherd/ |title=The Shepherd - GNU Project |publisher=Free Software Foundation, Inc. |access-date=2016-01-16 |archive-date=2016-02-12 |archive-url=https://web.archive.org/web/20160212224150/https://www.gnu.org/software/shepherd/ |url-status=live }}</ref>
* [[S6 (software)|s6]], a software suite that includes an init system. <ref>{{cite web |url=https://www.skarnet.org/software/s6/why.html |title=s6: why another supervision suite |access-date=2021-09-13 |archive-date=2021-09-13 |archive-url=https://web.archive.org/web/20210913201711/https://skarnet.org/software/s6/why.html |url-status=live }}</ref><ref>{{cite web |url=https://www.linuxquestions.org/questions/slackware-14/s6-init-system-4175658553/ |url-status=dead |archive-url=https://web.archive.org/web/20210913201707/https://www.linuxquestions.org/questions/slackware-14/s6-init-system-4175658553/ |archive-date=2021-09-13 |title=s6 init system}}</ref>
* [[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) and [[Ubuntu]], among other popular Linux distributions.
* [[SystemStarter]], a process spawner started by the BSD-style init in [[Mac&nbsp;OS&nbsp;X]] prior to Mac&nbsp;OS&nbsp;X v10.4
* [[Upstart (software)|Upstart]], a full replacement of init designed to start processes asynchronously. Initiated by [[Ubuntu (operating system)|Ubuntu]] and used by them until 2014. It was also used in Fedora 9,<ref>{{citation |url=https://fedoraproject.org/wiki/Releases/14/FeatureList |title=Fedora 14 Accepted Features |date=2010-07-13 |access-date=2010-07-13 |archive-date=2022-03-27 |archive-url=https://web.archive.org/web/20220327191742/https://fedoraproject.org/wiki/Releases/14/FeatureList |url-status=live }}</ref><ref>{{cite web |url=https://lwn.net/Articles/405100/ |title=Fedora defers systemd to F15 |date=2010-09-14 |access-date=2010-09-17 |publisher=Linux Weekly News |archive-date=2010-09-19 |archive-url=https://web.archive.org/web/20100919142259/http://lwn.net/Articles/405100/ |url-status=live }}</ref>  Red Hat Enterprise Linux 6<ref>{{cite web |url=https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/6.0_technical_notes/deployment |publisher=[[Red Hat]] |title=Deployment |work=Red Hat Enterprise Linux 6: Technical Notes |access-date=2013-12-31 |archive-date=2018-08-29 |archive-url=https://web.archive.org/web/20180829175441/https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/6.0_technical_notes/deployment |url-status=live }}</ref> and [[Google]]'s [[ChromeOS]].<ref name="chrome-os">{{citation |url=https://sites.google.com/a/chromium.org/dev/chromium-os/chromiumos-design-docs/software-architecture |title=Software Architecture: Chromium OS design documents |access-date=25 January 2014 |archive-date=9 April 2022 |archive-url=https://web.archive.org/web/20220409203000/https://sites.google.com/a/chromium.org/dev/chromium-os/chromiumos-design-docs/software-architecture |url-status=live }}</ref>

{{As of|2019|2}}, systemd has been [[Systemd#Adoption|adopted]] by most major Linux distributions.<ref>See [[Systemd#Adoption]]</ref>