Startup messages on Fedora 17, which uses systemd
|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||218 (December 10, 2014[±])|
|License||GNU LGPL 2.1+|
systemd is a suite of system management daemons, libraries, and utilities designed for Linux and programmed exclusively for the Linux API. Systemd authors characterize the software suite as a "basic building block" for an operating system.
In systems that use the systemd suite, systemd daemon is the init daemon, which is the first process executed in user space during the Linux startup process. Therefore, systemd daemon serves as the root of the user space's process tree. The name systemd adheres to the Unix convention of making daemons easier to distinguish by having the letter d as the last letter of the filename.
- 1 Overview
- 2 Components and libraries
- 3 Adoption
- 4 Criticism
- 5 Graphical frontends
- 6 Forks and alternative implementations
- 7 See also
- 8 Notes
- 9 References
- 10 External links
Before systemd, Linux distributions had their startup sequences and runlevels controlled by the traditional init daemon and a set of startup shell scripts executed under its control. As an integrated software suite, systemd replaces the traditional init daemon and startup scripts, and also integrates many other services that are common on Linux systems, such as user logins, handling of the system console, device and hot plugging management (replacing udev), hostname and locale handling, scheduled execution (replacing cron), and a unified system for logging various events. Systemd executes elements of its startup sequence in parallel, which is faster than the traditional startup sequence's sequential approach.
Systemd is not just the name of the init daemon but can also refer to the entire software bundle around systemd. This includes the daemons systemd, journald, logind and networkd, and many other low-level components such as libraries and utilities. In January 2013, systemd author Lennart Poettering described systemd not as one program, but rather a large software suite that includes 69 individual binaries.
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)
Components and libraries
The developers of systemd aimed to replace the Linux init system inherited from UNIX System V and Berkeley Software Distribution (BSD) operating systems. Like init, systemd is a daemon that manages other daemons; all daemons, including systemd, are background processes. Systemd is the first daemon to start during booting and the last daemon to terminate during shutdown. 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.
Lennart Poettering and Kay Sievers, software engineers that 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.
Systemd's initialization instructions for each daemon are recorded in a declarative configuration file, replacing the traditionally used per-daemon startup shell scripts. For inter-process communication (IPC), systemd makes Unix domain sockets and D-Bus available to the running daemons. Systemd is also capable of executing the elements of its startup sequence in parallel. The state of systemd itself can be preserved in a snapshot for future recall.
Among systemd's auxiliary features is a cron-like job scheduler called systemd Calendar Timers. 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.
- is a system and service manager for Linux operating systems.
- may be used to introspect and control the state of the systemd system and service manager.
- 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 and , two utility programs to facilitate the creation and management of software containers. Since version 205, systemd offers ControlGroupInterface, 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:
- In October 2014, the beginnings of consoled were integrated, providing a user console daemon, and handling Linux virtual terminal support. Consoled is meant to be included in systemd version 217.
- systemd-journald is a daemon doing 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.
- may be used to query the contents of the systemd(1) journal as written by systemd-journald.
- – configuration file for various parameters of the systemd journal service, such as rotation and compression.
- In version 30, systemd-logind was integrated, as a tiny daemon that manages user logins and seats in various ways. systemd-logind 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.
- may be used to introspect and control the state of the login manager systemd-logind.
- – configuration file for various parameters of the systemd login manager.
- In version 209, networkd was integrated, which provides abilities for systemd to perform various network configurations; as of version 209, support is 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.
- Since version 30, systemd includes systemd-timedated, as 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. systemd-timedated is accessible through D-Bus.
- In April 2012, the source tree for udev (a device manager for the Linux kernel, which handles the /dev directory and all user space actions when adding/removing devices, including firmware loading) was merged into the systemd source tree.
- The standard library for utilizing udev is now integrated into the systemd project. By linking against this library, third-party applications may query udev resources.
In May 2011, Fedora became the first major Linux distribution to enable systemd by default. As of August 2014[update], Slackware does not support or use systemd, but Slackware's lead Patrick Volkerding has not ruled out the possibility of switching to it. Some distributions allow other init systems to be used; only the default init system (for new installs) was changed to systemd. For such distributions, switching the init system is usually possible by installing the appropriate packages.
|Linux distribution||Date added to software repository[a]||Enabled by default?||Date released as default|
|Arch Linux||January 2012||Yes||October 2012|
|CoreOS||July 2013||Yes||October 2013 (v94.0.0)|
|Debian||April 2012||Planned for Debian 8 "Jessie"[b]||not yet released|
|Fedora||May 2011 (v15)||Yes||May 2011 (v15)|
|Mageia||May 2012 (v2.0)||Yes||May 2012 (v2.0)|
|openSUSE||March 2011 (v11.4)||Yes||September 2012 (v12.2)|
|Red Hat Enterprise Linux||June 2014 (v7.0)||Yes||June 2014 (v7.0)|
|SUSE Linux Enterprise Server||2014 (v12)||Yes||October 2014 (v12)|
|Ubuntu[e]||April 2013 (v13.04)||Planned||not yet released|
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 did provide a logind binary that is separate from the rest of systemd, but this became a de facto dependency of GNOME on systemd 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.
While the reception of systemd has been sufficiently positive for most major Linux distributions to adopt it and enable it by default, there has also been much heated debate, and many respected developers have and continue to criticise systemd.
Concerning the architecture
Concerning systemd, I do like the idea of a faster boot time (obviously), but I also like controlling the startup of the system with shell scripts that are readable, and I'm guessing that's what most Slackware users prefer too. I don't spend all day rebooting my machine, and having looked at systemd config files it seems to me a very foreign way of controlling a system to me, and attempting to control services, sockets, devices, mounts, etc., all within one daemon flies in the face of the UNIX concept of doing one thing and doing it well.
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.
A long debate among the Debian Technical Committee occurred on the Debian mailing list between October 2013 and February 2014 concerning what init system to use as the default in Debian 8 "jessie", 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.
Shortly after Debian's decision, Mark Shuttleworth announced on his blog that Ubuntu would be following through as well, despite earlier comments describing systemd as "hugely invasive and hardly justified".
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 more similar to that of Microsoft Windows software:
While systemd has succeeded in its original goals, it's not stopping there. systemd is becoming the Svchost of Linux – which I don't think most Linux folks want. You see, systemd is growing, like wildfire, well outside the bounds of enhancing the Linux boot experience. systemd wants to control most, if not all, of the fundamental functional aspects of a Linux system – from authentication to mounting shares to network configuration to syslog to cron.
Theodore Ts'o expressed his opinion in a ZDNet interview in September 2014, that more than technical concerns the dispute over systemd's centralized design philosophy indicates a dangerous general trend towards uniformizing the Linux ecosystem, alienating and marginalizing parts of the open-source community, leaving little room for alternative projects:
Systemd problems might not have mattered that much, except that GNOME has a similar attitude; they only care for a small subset of the Linux desktop users, and they have historically abandoned some ways of interacting the Desktop in the interest of supporting touchscreen devices and to try to attract less technically sophisticated users. If you don't fall in the demographic of what GNOME supports, you're sadly out of luck. (Or you become a second class citizen, being told that you have to rely on GNOME extensions that may break on every single new version of GNOME.) [...] As a result, many traditional GNOME users have moved over to Cinnamon, XFCE, KDE, etc. But as systemd starts subsuming new functions, components like network-manager will only work on systemd or other components that are forced to be used due to a network of interlocking dependencies; and it may simply not be possible for these alternate desktops to continue to function, because there is [no] viable alternative to systemd supported by more and more distributions.
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 three 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.
Concerning the developer team
Linus Torvalds has expressed reservations about the attitude of a key systemd developer towards users and bug reports. Theodore Ts'o has also had reservations about the systemd philosophy and the attitudes of two key developers.
Forks and boycotts
In late April 2014, a campaign to boycott systemd was launched; their website http://boycottsystemd.org lists various reasons against its adoption. Various forks have also been launched, both forks of systemd (see below) and even a fork of Debian, called Devuan, to provide Debian without systemd installed by default.
A few graphical frontends are available, including the following:
- Systemd-ui, also known as
systemadm, 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
- Kcmsystemd is a graphical systemd frontend for the KDE desktop environment. It integrates into the KDE's system settings window, allowing monitoring and controlling of systemd services, as well as graphical editing of configuration files.
Forks and alternative implementations
In 2012, the Gentoo Linux project created a fork of systemd-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. The Gentoo project describes eudev as follows:
eudev is a fork of system-udev with the goal of obtaining better compatibility with existing software such as OpenRC and Upstart, older kernels, various toolchains and anything else required by users and various distributions.
In 2014, uselessd, a lightweight fork of systemd was created. 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.
An increasing number of projects (in particular GNOME) relies on functionality provided by systemd, for example for multi-seat management (via logind). 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 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:
I took this project because I was fed up with what systemd was doing to my then-main computer running Arch Linux. I figured this would be a great way to make the move to OpenBSD and I couldn't be happier.
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."
- Dates are for the general availability release.
- The Debian Technical Committee voted to make systemd the default system management daemon for Linux in the "jessie" release.
- systemd is supported in Gentoo as an alternative to OpenRC, the default init system for those who "want to use systemd instead, or are planning to use Gnome 3.8 and later (which requires systemd)"
- As of 2014, Gentoo requires systemd when selecting the GNOME profile or installing GNOME 3.
- Ubuntu's development documentation offers instructions on how to use systemd as an experimental option.
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It certainly is not something that comes with systemd from upstream.
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ConsoleKit is currently not actively maintained. The focus has shifted to the built-in seat/user/session management of Software/systemd called systemd-logind!
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- Official website
- Boycott systemd. A site that lists various reasons against its adoption
- Rethinking PID 1
- systemd: System and Session Manager
- The road forward for systemd (LWN.net)
- systemd's git repository browser
- Interface Portability And Stability Chart
- Init systems comparison: part 1 and part 2 (LWN.net)
- SysVinit to Systemd Cheatsheet
- eudev project
- uselessd homepage