Systemd

Lennart Poettering and Kay Sievers, the software engineers then working for Red Hat who initially developed systemd, An April 2010 blog post from Poettering, titled "Rethinking PID 1", introduced an experimental version of what would later become systemd. They 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 processes to run concurrently or in parallel during system booting, and to reduce the computational overhead of the shell. In May 2011, Fedora Linux became the first major Linux distribution to enable systemd by default, replacing Upstart. The reasoning at the time was that systemd provided extensive parallelization during startup, better management of processes and overall a saner, dependency-based approach to control of the system. Developers had debated since August 2012 Some thought the criticism of systemd was not based on actual shortcomings of the software but rather personal dislike of Poettering and a general opposition to change. Several complaints about systemd—including its use of D-bus, C instead of bash, and an optional on-disk journal format—were instead described as advantages by the Arch maintainers. Between 2013 and 2014, the Debian Technical Committee engaged in a widely publicized debate on the mailing list about which init system to use as the default in Debian 8 before settling on systemd. In September 2016, a security bug was discovered that allowed any unprivileged user to perform a denial-of-service attack against systemd. Rich Felker, developer of musl, stated that this bug reveals a major "system development design flaw". In 2017 another security bug was discovered in systemd-resolved, , which "allows disruption of service" by a "malicious DNS server". Later in 2017, the Pwnie Awards gave author Lennart Poettering a "lamest vendor response" award due to his handling of the vulnerabilities. == Design ==

. Several systemd targets, including telephony, bootmode, dlog, and tizen service are from Tizen and are not components of systemd. Poettering describes systemd development as "never finished, never complete, but tracking progress of technology". In May 2014, Poettering further described systemd as unifying "pointless differences between distributions", by providing the following three general functions: and Inhibitor Locks. It is not just the name of the init daemon but also refers to the entire software bundle around it, which, in addition to the init daemon, includes the daemons , and , 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. networkctl may be used to review the state of the network links as seen by systemd-networkd. Configuration of new interfaces has to be added under the /lib/systemd/network/ as a new file ending with .network extension. ; : provides network name resolution to local applications ; : is a boot manager, formerly known as gummiboot. Kay Sievers merged it into systemd with rev 220. ; : is an error reporter used to generate Blue Screen of Death. ; : may be used to run a command or OS in a namespace container. ; : 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. : On 29 May 2014, support for firmware loading through udev was dropped from systemd, as it was decided that the kernel should be responsible for loading firmware. Configuration of systemd is configured exclusively via plain-text files although GUI tools such as systemd-manager are also available. 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. The syntax of the language is inspired by files. Unit-file types) • • • • • • (which can be used as a cron-like job scheduler) • (used to group worker processes, not intended to be configured via unit files) == Adoption ==

While many 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 called Devuan was developed to avoid systemd and has reached version 5.0 for stable usage. In December 2019, the Debian project voted in favour of retaining systemd as the default init system for the distribution, but with support for "exploring alternatives". 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 and ConsoleKit API, the former being provided at the time only by systemd. Ubuntu provided a separate binary, but systemd became a de facto dependency of GNOME for most Linux distributions, in particular since ConsoleKit is no longer actively maintained and upstream recommends the use of 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 . As of Mutter version 3.13.2, is a dependency for Wayland sessions. == Reception ==

The design of systemd has ignited controversy within the free-software community. Critics regard systemd as overly complex and suffering from continued feature creep, arguing that its architecture violates the Unix philosophy. 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 comes 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. In March 2014, Eric S. Raymond commented 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 regard to modifications to the Linux kernel submitted by Sievers. In late April 2014, a campaign to boycott systemd was launched, with a website listing various reasons against its adoption. 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 a September 2014 ZDNet interview, prominent Linux kernel developer 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. He cited 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 Sievers and his co-developer, Lennart Poettering, to that of GNOME's developers. == Forks and alternative implementations ==

Forks of systemd are closely tied to critiques of it outlined in the above section. Forks generally try to improve on at least one of portability (to other libcs and Unix-like systems), modularity, or size. A few forks have collaborated under the FreeInit banner. Forks of components eudev 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. elogind Elogind is the systemd project's "logind", extracted to be a standalone daemon. It integrates with PAM to know the set of users that are logged into 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 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. systembsd 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 did not provide an init replacement, but aimed to provide OpenBSD with compatible daemons for , , , and . The project did not create new systemd-like functionality, and was only meant to act as a wrapper over the native OpenBSD system. The developer aimed 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." It was forked by the Parabola GNU/Linux-libre developers to build packages with their development tools without the necessity of having systemd installed to run systemd-nspawn. Development ceased in July 2018. Fork including init system uselessd In 2014, uselessd was created as a lightweight fork of systemd. The project sought to remove features and programs deemed unnecessary for an init system, as well as address other perceived faults. uselessd supported the musl and μClibc libraries, so it may have been used on embedded systems, whereas systemd only supported glibc. The uselessd project had planned further improvements on cross-platform compatibility, as well as architectural overhauls and refactoring for the Linux build in the future. == All Systems Go! ==

All Systems Go! is the annual systemd conference, which is held in Berlin. The main topic is systemd but other Linux areas are covered as well, like TPM, DBus, desktop environment, containers, eBPF etc. == See also ==