systemd startup on Debian GNU/Linux
|Original author(s)||Lennart Poettering, Kay Sievers, Harald Hoyer, Daniel Mack, Tom Gundersen and David Herrmann|
|Developer(s)||Lennart Poettering, Kay Sievers, Harald Hoyer, Daniel Mack, Tom Gundersen, David Herrmann, and others|
|Initial release||30 March 2010|
|Stable release||219 (February 16, 2015[±])|
|Preview release||228 (November 18, 2015[±])|
|License||GNU LGPL 2.1+|
systemd is an init system used by some Linux distributions to bootstrap the user space and manage all processes subsequently, in lieu of the UNIX System V and Berkeley Software Distribution (BSD) init systems. The name systemd adheres to the Unix convention of naming daemons by appending the letter d. It is published as free and open-source software under the terms of the GNU Lesser General Public License (LGPL) version 2.1 or later. One of systemd's main goals is to unify basic Linux configurations and service behaviors across all distributions.
As of 2015[update], many Linux distributions have adopted systemd as their default init system. The increasing adoption of systemd has been controversial, with critics arguing the software has violated the Unix philosophy by becoming increasingly complex, and that distributions have been forced to adopt it due to its tight coupling with various other software including, most notably, the GNOME 3 desktop environment.
Lennart Poettering and Kay Sievers, the software engineers working for Red Hat who initially developed systemd, sought to surpass the efficiency of the init daemon in several ways. They wanted to improve the software framework for expressing dependencies, to allow more processing to be done concurrently or in parallel during system booting, and to reduce the computational overhead of the shell.
Poettering describes systemd development as "never finished, never complete, but tracking progress of technology". In May 2014, Poettering further defined systemd as aiming to unify "pointless differences between distributions", by providing the following three general functions:
- A system and service manager (manages both the system, as by applying various configurations, and its services)
- A software platform (serves as a basis for developing other software)
- The glue between applications and the kernel (provides various interfaces that expose functionalities provided by the kernel)
systemd is not just the name of the init daemon but also refers to the entire software bundle around it, which, in addition to the systemd init daemon, includes the daemons journald, logind and networkd, and many other low-level components. In January 2013, Poettering described systemd not as one program, but rather a large software suite that includes 69 individual binaries. As an integrated software suite, systemd replaces the startup sequences and runlevels controlled by the traditional init daemon, along with the shell scripts executed under its control. systemd also integrates many other services that are common on Linux systems by handling user logins, the system console, device hotplugging (see udev), scheduled execution (replacing cron), logging, hostnames and locales.
Like the init daemon, systemd is a daemon that manages other daemons, which, including systemd itself, are background processes. systemd is the first daemon to start during booting and the last daemon to terminate during shutdown. The systemd daemon serves as the root of the user space's process tree; the first process (pid 1) has a special role on Unix systems, as it receives a SIGCHLD signal when a daemon process (which has detached from its parent) terminates. Therefore, the first process is particularly well suited for the purpose of monitoring daemons; systemd attempts to improve in that particular area over the traditional approach, which would usually not restart daemons automatically but only launch them once without further monitoring.
systemd executes elements of its startup sequence in parallel, which is faster than the traditional startup sequence's sequential approach. For inter-process communication (IPC), systemd makes Unix domain sockets and D-Bus available to the running daemons. The state of systemd itself can also be preserved in a snapshot for future recall.
systemd records initialization instructions for each daemon in a configuration file (referred to as a "unit file") that uses a declarative language, replacing the traditionally used per-daemon startup shell scripts. Unit file types include service, socket, device, mount, automount, swap, target, path, timer (which can be used as a cron-like job scheduler), snapshot, slice and scope.
Core components and libraries
Following its integrated approach, systemd also provides replacements for various daemons and utilities, including the startup shell scripts, pm-utils, inetd, acpid, syslog, watchdog, cron and atd. systemd's core components include the following:
- systemd is a system and service manager for Linux operating systems.
- systemctl may be used to introspect and control the state of the systemd system and service manager.
- systemd-analyze may be used to determine system boot-up performance statistics and retrieve other state and tracing information from the system and service manager.
systemd tracks processes using the Linux kernel's cgroups subsystem instead of by using process identifiers (PIDs); thus, daemons cannot "escape" systemd, not even by double-forking. systemd not only uses cgroups, but also augments them with systemd-nspawn and machinectl, two utility programs that facilitate the creation and management of software containers. Since version 205, systemd also offers ControlGroupInterface, which is an API to the Linux kernel cgroups. The Linux kernel cgroups are adapted to support kernfs, and are being modified to support a unified hierarchy.
Beside its primary purpose of providing a replacement Linux init system, systemd suite provides additional functionality, including its following components:
- systemd-consoled provides a user console daemon, intending to replace the Linux kernel's virtual terminal support with a more capable userspace component. Its preview version was released in October 2014, as part of systemd version 217.
- systemd-journald is a daemon responsible for event logging, with append-only binary files serving as its logfiles. The system administrator may choose whether to log system events with systemd-journald, syslog-ng or rsyslog. The corruption and obfuscation of the binary format has led to much heated debate.
- systemd-logind is a daemon that manages user logins and seats in various ways. It is an integrated login manager that offers multiseat improvements and replaces ConsoleKit, which is no longer maintained. For X11 display managers the switch to logind requires a minimal amount of porting. It was integrated in systemd version 30.
- networkd is a daemon to handle the configuration of the network interfaces; in version 209, when it was first integrated, support was limited to statically assigned addresses and basic support for bridging configuration. In July 2014, systemd version 215 was released, adding new features such as a DHCP server for IPv4 hosts, and VXLAN support.
- systemd-timedated is a daemon that can be used to control time-related settings, such as the system time, system time zone, or selection between UTC and local time zone system clock. It is accessible through D-Bus. It was integrated in systemd version 30.
- udev is a device manager for the Linux kernel, which handles the /dev directory and all user space actions when adding/removing devices, including firmware loading. In April 2012, the source tree for udev was merged into the systemd source tree.
- It is the standard library for utilizing udev, which allows third-party applications to query udev resources.
A few graphical frontends are available, including:
- Also known as systemadm, it is a simple GTK+-based graphical front-end for systemd. It provides a simple user interface to manage services and a graphical agent to request passwords from the user. As of 2014[update] the systemadm program has received little development or maintenance in the last few years, because development focus has shifted to command-line tools like systemctl and systemd-analyze.
- Provides a graphical systemd frontend for the KDE Plasma 5 desktop. It integrates into the system settings window and allows monitoring and controlling of systemd units and logind sessions, as well as graphical editing of configuration files.
Adoption and reception
While most distributions boot systemd by default, some allow other init systems to be used; in this case switching the init system is possible by installing the appropriate packages. A fork of Debian has been proposed to avoid systemd.
|Linux distribution||Date added to software repository[a]||Enabled by default?||Can run without?||Date released as default|
|Arch Linux||January 2012||Yes||Yes, but unsupported||October 2012|
|CoreOS||July 2013||Yes||?||October 2013 (v94.0.0)|
|Debian||April 2012||Yes||Yes||April 2015 (v8)|
|Fedora||November 2010 (v14)||Yes||No||May 2011 (v15)|
|Gentoo Linux[b]||July 2011||No||Yes||N/A|
|Mageia||January 2011 (v1.0)||Yes||?||May 2012 (v2.0)|
|openSUSE||March 2011 (v11.4)||Yes||?||September 2012 (v12.2)|
|Red Hat Enterprise Linux||June 2014 (v7.0)||Yes||No||June 2014 (v7.0)|
|Slackware||N/A (not in repository)||N/A||Yes||N/A|
|SUSE Linux Enterprise Server||October 2014 (v12)||Yes||No||October 2014 (v12)|
|Ubuntu||April 2013 (v13.04)||Yes||?||April 2015 (v15.04)|
Integration with other software
In the interest of enhancing the interoperability between systemd and the GNOME desktop environment, systemd coauthor Lennart Poettering asked the GNOME Project to consider making systemd an external dependency of GNOME 3.2.
In November 2012, the GNOME Project concluded that basic GNOME functionality should not rely on systemd. However, GNOME 3.8 introduced a compile-time choice between the logind and ConsoleKit API, the former being provided at the time only by systemd. Ubuntu provided a separate logind binary but systemd became a de facto dependency of GNOME for most Linux distributions, in particular since ConsoleKit is not actively maintained anymore and upstream recommends the use of systemd-logind instead. The developers of Gentoo Linux also attempted to adapt these changes in OpenRC, but the implementation contained too many bugs, causing the distribution to mark systemd as a dependency of GNOME.
GNOME has further integrated logind. As of Mutter version 3.13.2, logind is a dependency for Wayland sessions. There are plans to replace gnome-session with systemd, but systemd would not be running as PID 1 and gnome-session would remain available on non-Linux systems. Since systemd supports only Linux and cannot be easily ported to other operating systems due to the heavy use of Linux kernel APIs, there is a need to offer compatible APIs on other operating systems such as OpenBSD.
In a September 2014 ZDNet interview, Theodore Ts'o expressed his opinion that the dispute over systemd's centralized design philosophy, more than technical concerns, indicates a dangerous general trend toward uniformizing the Linux ecosystem, alienating and marginalizing parts of the open-source community, and leaving little room for alternative projects. In this he found similarities with the attitude he found in the GNOME project toward non-standard configurations. On social media, Ts'o also later compared the attitudes of two key developers to that of GNOME's developers.
History and controversy
||This article's Criticism or Controversy section may compromise the article's neutral point of view of the subject. (November 2015)|
The design of systemd has ignited controversy within the free software community. Critics argue that systemd is overly complex and suffers continued feature creep, and that its architecture violates the design principles of Unix-like operating systems. There is also concern that it forms a system of interlocked dependencies, thereby giving distribution maintainers little choice but to adopt systemd as more user-space software come to depend on its components.
In a 2012 interview, Slackware's lead Patrick Volkerding expressed reservations about the systemd architecture, stating his belief that its design was contrary to the Unix philosophy of interconnected utilities with narrowly defined functionalities. As of August 2014[update], Slackware does not support or use systemd, but Volkerding has not ruled out the possibility of switching to it.
Between October 2013 and February 2014, a long debate among the Debian Technical Committee occurred on the Debian mailing list, discussing which init system to use as the default in Debian 8 "jessie", and culminating in a decision in favor of systemd. The debate was widely publicized and in the wake of the decision the debate continues on the Debian mailing list.
In January 2013, Lennart Poettering attempted to address concerns about systemd in a blog post called The Biggest Myths. After continued controversy over systemd, in October 2014, Poettering complained that the "Open Source community is full of assholes, and I probably more than most others am one of their most favourite targets." Poettering went on to blame Linus Torvalds and other kernel developers for the state of the community.
In February 2014, after Debian's decision was made, Mark Shuttleworth announced on his blog that Ubuntu would be following through as well in implementing systemd, despite his earlier comments in October 2013 that described systemd as "hugely invasive and hardly justified".
In March 2014, Eric S. Raymond opined that systemd's design goals were prone to mission creep and software bloat. In April 2014, Linus Torvalds expressed reservations about the attitude of Kay Sievers, a key systemd developer, toward users and bug reports in regards to modifications sent to the linux kernel itself by Kay Sievers.
In an August 2014 article published in InfoWorld, Paul Venezia wrote about the systemd controversy, and attributed the controversy to violation of the Unix philosophy, and to "enormous egos who firmly believe they can do no wrong". The article also characterizes the architecture of systemd as similar to that of svchost.exe, a critical system component in Microsoft Windows with a broad functional scope.
In November 2014, Debian maintainers and Technical Committee members Joey Hess, Russ Allbery, Ian Jackson and systemd package maintainer Tollef Fog Heen resigned from their positions. All four justified their decision on the public Debian mailing list and in personal blogs with their exposure to extraordinary stress levels related to ongoing disputes on systemd integration within the Debian and open source community that rendered regular maintenance virtually impossible.
In December 2014, a fork of Debian, called Devuan, was announced by a group calling themselves the "Veteran Unix Admins". Its intention is to provide a Debian variant without systemd installed by default.
In August 2015, systemd now provides a login shell, callable via machinectl shell.
In October 2015, an article titled "Structural and semantic deficiencies in the systemd architecture for real-world service management" was published, which criticized systemd in several areas, including its design as an object system with too many layers of indirection that make it prone to ordering-related failure cases, a difficult to predict execution model, its non-deterministic boot order, implicit state in unit file configurations and its general inadequacy at providing a uniform external abstraction for unit types.
Forks and alternative implementations
- In 2012, the Gentoo Linux project created a fork of udev in order to avoid dependency on the systemd architecture. The resulting fork is called eudev and it makes udev functionality available without systemd. A stated goal of the project is to keep eudev independent of any Linux distribution or init system.
- Elogind is the systemd project's "logind", extracted out to be a standalone daemon. It integrates with PAM to know the set of users that are logged in to a system and whether they are logged in graphically, on the console, or remotely. Elogind exposes this information via the standard org.freedesktop.login1 D-Bus interface, as well as through the file system using systemd's standard /run/systemd layout. Elogind also provides "libelogind", which is a subset of the facilities offered by "libsystemd". There is a "libelogind.pc" pkg-config file as well.
- In 2014, uselessd was created as a lightweight fork of systemd. The project seeks to remove features and programs deemed unnecessary for an init system, increase implementation modularity, improve portability across platforms, as well as address other perceived faults.
- uselessd supports the musl and µClibc libraries, so it may be used on embedded systems, whereas systemd only supports glibc. uselessd is attempting initial support for non-Linux platforms (so far only build time being ready), whereas the systemd project does not attempt any compatibility with BSD systems. The uselessd project plans further improvements on cross-platform compatibility, as well as architectural overhauls and refactoring for the Linux build in the future.
- In 2014, a Google Summer of Code project named "systembsd" was started in order to provide alternative implementations of these APIs for OpenBSD. The original project developer began it in order to ease his transition from Linux to OpenBSD.
- The systembsd project will not provide an init replacement, but aims at providing OpenBSD with compatible daemons for hostnamed, timedated, localed, and logind in particular. The project does not create new systemd-like functionality, and is only meant to act as a wrapper over the native OpenBSD system. The developer aims for systembsd to be installable as part of the ports collection, not as part of a base system, stating that, "systemd and *BSD differ fundamentally in terms of philosophy and development practices."
- ConsoleKit was forked in October 2014 by Xfce developers wanting its features to still be maintained and available on operating systems other than Linux. While not ruling out the possibility of reviving the original repository in the long term, the main developer considers ConsoleKit2 a temporary necessity until systembsd matures.
- LoginKit is an attempt to implement a logind (systemd-logind) shim, which allows packages that depend on it to work, without dependency on a specific init system.
- "systemd README", freedesktop.org, retrieved 2012-09-09
- "[systemd-devel] [ANNOUNCE] systemd v219". freedesktop.org. 2015-02-16. Retrieved 2015-02-16.
- "[systemd-devel] [ANNOUNCE] systemd v228". freedesktop.org. 2015-11-18. Retrieved 2015-11-20.
- systemd Analysis Summary, Ohloh, retrieved 2011-06-16
- Lennart Poettering (2012-04-21), systemd Status Update, retrieved 2012-04-28
- Lennart Poettering, Kay Sievers, Thorsten Leemhuis (2012-05-08), Control Centre: The systemd Linux init system, The H, archived from the original on 14 October 2012, retrieved 2012-09-09
- "InterfaceStabilityPromise". freedesktop.org.
- Saunders, Mike (2015-11-11). "Linux 101: Get the most out of systemd". Linux Voice. Retrieved 2016-01-28.
- Gundersen, Tom E. (2014-09-25). "The End of Linux". Retrieved 2014-10-25.
It certainly is not something that comes with systemd from upstream.
- "The New Control Group Interfaces". Freedesktop.org. 2015-08-28. Retrieved 2016-02-06.
- Poettering, Lennart (May 2014). "A Perspective for systemd: What Has Been Achieved, and What Lies Ahead" (PDF). Retrieved 2014-11-30.
- Poettering, Lennart (2013-01-26). "The Biggest Myths".
- "Debate/initsystem/systemd – Debian Documentation". Debian. 2014-01-02. Retrieved 2014-12-04.
- "systemd Dreams Up New Feature, Makes It Like Cron". Phoronix. 2013-01-28. Retrieved 2014-01-22.
- "systemd.unit man page". freedesktop.org.
- Jake Edge (2013-11-07). "Creating containers with systemd-nspawn". LWN.net. Retrieved 2014-07-30.
- "ControlGroupInterface". freedesktop.org. Retrieved 9 November 2014.
- Tejun Heo (2014-01-28). "cgroup: convert to kernfs". linux-kernel (Mailing list).
- Tejun Heo (2014-03-13). "cgroup: prepare for the default unified hierarchy". linux-kernel (Mailing list).
- Michael Larabel (2014-10-07). "systemd 217 Will Introduce Its New "Consoled" User Console Daemon". Retrieved 2015-01-24.
- Lennart Poettering (2014-10-28). "[systemd-devel] [ANNOUNCE] systemd 217". systemd-devel (Mailing list). Retrieved 2015-01-23.
- "systemd's binary logs and corruption". Retrieved Jan 21, 2016.
- "systemd-logind.service". freedesktop.org. Retrieved 2014-02-17.
- "ConsoleKit official website". freedesktop.org. Retrieved 9 November 2014.
- "How to hook up your favorite X11 display manager with systemd". freedesktop.org.
- "Networking in +systemd - 1. Background". 2013-11-27. Retrieved 2014-02-22.
- "Networking in +systemd - 2. libsystemd-rtnl". 2013-11-27. Retrieved 2014-02-22.
- "Networking in +systemd - 3. udev". 2013-11-27. Retrieved 2014-02-22.
- "Networking in +systemd - 4. networkd". 2013-11-27. Retrieved 2014-02-22.
- "Networking in +systemd - 5. the immediate future". 2013-11-27. Retrieved 2014-02-22.
- Michael Larabel (2014-07-04). "systemd 215 Works On Factory Reset, DHCPv4 Server Support". Retrieved 2014-11-08.
- Pavel Šimerda (3 February 2013). "Can Linux network configuration suck less?".
- "timedated". freedesktop.org. Retrieved 9 November 2014.
- Sievers, Kay. "The future of the udev source tree". linux-hotplug (Mailing list). Retrieved 2013-05-22.
- Sievers, Kay, "Commit importing udev into systemd", freedesktop.org, retrieved 25 May 2012
- "Details of package systemd-ui in Debian "Jessie" 8". Debian. Retrieved 2014-07-31.
- "Systemd-kcm 1.2.0 released". 2015-07-06.
- "Meet Devuan, the Debian fork born from a bitter systemd revolt".
- "Git clone of the 'packages' repository". Web interface to the Arch Linux git repositories. 2012-01-12.
- "Init". Arch Wiki. 2015-10-13. Retrieved 2015-11-07.
- "systemd is now the default on new installations". Arch Linux.
- "coreos/manifest: Releases: v94.0.0". github.com. October 3, 2013. Retrieved September 22, 2014.
- "CoreOS's init system", coreos.com, retrieved 2014-02-14
- "systemd". debian.org. Retrieved 2014-11-19.
- Bdale Garbee (2014-02-11). "Bug#727708: call for votes on default Linux init system for jessie". debian-ctte (Mailing list).
- "Fedora 14 talking points".
- "systemd", wiki.gentoo.org, retrieved 2012-08-26
- "Installing the Gentoo Base System § Optional: Using systemd".
- "Comment #210 (bug #318365)", gentoo.org, retrieved 2011-07-05
- "systemd", gentoo.org, retrieved 2011-07-05
- ChangeLog of Mageia's systemd package
- Fabian Scherschel (2012-05-23), Mageia 2 arrives with GNOME 3 and systemd, The H, archived from the original on 8 December 2013, retrieved 2012-08-22
- Directory view of the 11.4 i586 installation showing presence of the systemd v18 installables, 2011-02-23, retrieved 2013-09-24
- "OpenSUSE: Not Everyone Likes systemd". Phoronix.
The recently released openSUSE 12.2 does migrate from SysVinit to systemd
- Red Hat Unveils Red Hat Enterprise Linux 7, 2014-06-10
- Lennart Poettering (2011-05-18). "systemd as an external dependency". desktop-devel (Mailing list) (GNOME). Retrieved 2011-05-26.
- Frederic Peters (2011-11-04). "20121104 meeting minutes". GNOME release-team (Mailing list). Retrieved 2013-01-14.
- "ConsoleKit". Retrieved 15 November 2014.
ConsoleKit is currently not actively maintained. The focus has shifted to the built-in seat/user/session management of Software/systemd called systemd-logind!
- Vitters, Olav. "GNOME and logind+systemd thoughts". Retrieved 24 April 2014.
- "GNOME 3.10 arrives with experimental Wayland support". ZDNet. Retrieved 24 April 2014.
- "GNOME initiatives: systemd". Retrieved 2014-05-01.
- "Mutter 3.13.2: launcher: Replace mutter-launch with logind integration". 2014-05-19. Retrieved 2014-05-28.
- "Linus Torvalds and others on Linux's systemd". Retrieved 2014-11-21.
- "A realization that I recently came to while discussing the whole systemd...". 31 March 2014. Retrieved 8 July 2014.
- Vaughan-Nichols, Steven. "Linus Torvalds and others on Linux's systemd".
- "F15 one page release notes", fedoraproject.org, 2001-05-24
- "Interview with Patrick Volkerding of Slackware". linuxquestions.org. 2012-06-07. Retrieved 2014-03-19.
- "I'm back after a break from Slackware: sharing thoughts and seeing whats new!". linuxquestions.org. Retrieved 2014-03-14.
- "#727708 - tech-ctte: Decide which init system to default to in Debian.". 2013-10-25. Retrieved 2014-09-14.
- "Which init system for Debian?". 2013-11-05. Retrieved 2014-09-14.
- "Debian Still Debating systemd Vs. Upstart Init System". Phoronix. 2013-12-30. Retrieved 2014-09-14.
- Steven J. Vaughan-Nichols (2014-10-06). "Lennart Poettering's Linus Torvalds rant". ZDNet. Retrieved 2014-10-31.
- "Losing graciously". 2014-02-14. Retrieved 2014-09-14.
- "Quantal, raring, saucy...". 2013-10-18. Retrieved 2014-09-14.
- "Interviews: ESR Answers Your Questions". Slashdot.org. 2014-03-10. Retrieved 2014-03-19.
- Linus Torvalds (2014-04-02). "Re: [RFC PATCH] cmdline: Hide "debug" from /proc/cmdline". linux-kernel (Mailing list). Retrieved 2014-07-08.
- "Is systemd as bad as boycott systemd is trying to make it?". LinuxToday. Retrieved 2014-09-22.
- "Boycott systemd.org". Archived from the original on 2014-12-06. Retrieved 2015-07-15.
- Paul Venezia (2014-08-18). "systemd: Harbinger of the Linux apocalypse". Retrieved 2014-09-20.
- Joey Hess. "on leaving". Retrieved 2015-07-15.
- Russ Allbery (2014-11-16). "Resigning from the Technical Committee". debian-ctte (Mailing list). Retrieved 2015-07-15.
- Ian Jackson (2014-11-19). "Resignation". debian-ctte (Mailing list). Retrieved 2015-07-15.
- Tollef Fog Heen (2014-11-16). "Resignation from the pkg-systemd maintainer team". pkg-systemd-maintainers (Mailing list). Retrieved 2015-07-15.
- "The "Devuan" Debian fork". LWN.net. Retrieved 2014-12-08.
- Paul Carroty (August 28, 2015). "Lennart Poettering merged "su" command replacement into systemd: Test Drive on Fedora Rawhide".
- V.R. (October 11, 2015). "Structural and semantic deficiencies in the systemd architecture for real-world service management".
- "eudev/README". Retrieved 2015-06-01.
- "Gentoo eudev project". Retrieved 2015-06-01.
- "elogind/README". Retrieved 2015-09-02.
- Michael Larabel (2014-09-21). "Uselessd: A Stripped Down Version Of systemd". Phoronix. Retrieved 2014-10-26.
- "uselessd :: information system". uselessd.darknedgy.net. Retrieved 2014-10-26.
- "GSoC 2014: systemd replacement utilities (systembsd)". OpenBSD Journal. Retrieved 28 November 2014.
- Koegel, Eric (2014-10-20). "ConsoleKit2". Retrieved 2015-03-07.
- "loginkit/README". Retrieved 2014-12-04.
- Official website
- Systemd on GitHub
- Rethinking PID 1
- The road forward for systemd (LWN.net)
- Init systems comparison: part 1 and part 2 (LWN.net)