Adding upstream version 255.4.upstream/255.4

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1463 insertions, 0 deletions

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+<?xml version='1.0'?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
+
+<refentry id="systemd"
+    xmlns:xi="http://www.w3.org/2001/XInclude">
+
+  <refentryinfo>
+    <title>systemd</title>
+    <productname>systemd</productname>
+  </refentryinfo>
+
+  <refmeta>
+    <refentrytitle>systemd</refentrytitle>
+    <manvolnum>1</manvolnum>
+  </refmeta>
+
+  <refnamediv>
+    <refname>systemd</refname>
+    <refname>init</refname>
+    <refpurpose>systemd system and service manager</refpurpose>
+  </refnamediv>
+
+  <refsynopsisdiv>
+    <cmdsynopsis>
+      <command>/usr/lib/systemd/systemd</command>
+      <arg choice="opt" rep="repeat">OPTIONS</arg>
+    </cmdsynopsis>
+    <cmdsynopsis>
+      <command>init</command>
+      <arg choice="opt" rep="repeat">OPTIONS</arg>
+      <arg choice="req">COMMAND</arg>
+    </cmdsynopsis>
+  </refsynopsisdiv>
+
+  <refsect1>
+    <title>Description</title>
+
+    <para>systemd is a system and service manager for Linux operating systems. When run as first process on
+    boot (as PID 1), it acts as init system that brings up and maintains userspace services. Separate
+    instances are started for logged-in users to start their services.</para>
+
+    <para><command>systemd</command> is usually not invoked directly by the user, but is installed as the
+    <filename>/sbin/init</filename> symlink and started during early boot. The user manager instances are
+    started automatically through the
+    <citerefentry><refentrytitle>user@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    service.</para>
+
+    <para>For compatibility with SysV, if the binary is called as <command>init</command> and is not the
+    first process on the machine (PID is not 1), it will execute <command>telinit</command> and pass all
+    command line arguments unmodified. That means <command>init</command> and <command>telinit</command> are
+    mostly equivalent when invoked from normal login sessions. See
+    <citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry> for more
+    information.</para>
+
+    <para>When run as a system instance, systemd interprets the
+    configuration file <filename>system.conf</filename> and the files
+    in <filename>system.conf.d</filename> directories; when run as a
+    user instance, systemd interprets the configuration file
+    <filename>user.conf</filename> and the files in
+    <filename>user.conf.d</filename> directories. See
+    <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    for more information.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Concepts</title>
+
+    <para>systemd provides a dependency system between various
+    entities called "units" of 11 different types. Units encapsulate
+    various objects that are relevant for system boot-up and
+    maintenance. The majority of units are configured in unit
+    configuration files, whose syntax and basic set of options is
+    described in
+    <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+    however some are created automatically from other configuration
+    files, dynamically from system state or programmatically at runtime.
+    Units may be "active" (meaning started, bound, plugged in, …,
+    depending on the unit type, see below), or "inactive" (meaning
+    stopped, unbound, unplugged, …), as well as in the process of
+    being activated or deactivated, i.e. between the two states (these
+    states are called "activating", "deactivating"). A special
+    "failed" state is available as well, which is very similar to
+    "inactive" and is entered when the service failed in some way
+    (process returned error code on exit, or crashed, an operation
+    timed out, or after too many restarts). If this state is entered,
+    the cause will be logged, for later reference. Note that the
+    various unit types may have a number of additional substates,
+    which are mapped to the five generalized unit states described
+    here.</para>
+
+    <para>The following unit types are available:</para>
+
+    <orderedlist>
+      <listitem><para>Service units, which start and control daemons
+      and the processes they consist of. For details, see
+      <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
+
+      <listitem><para>Socket units, which encapsulate local IPC or
+      network sockets in the system, useful for socket-based
+      activation. For details about socket units, see
+      <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      for details on socket-based activation and other forms of
+      activation, see
+      <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
+
+      <listitem><para>Target units are useful to group units, or
+      provide well-known synchronization points during boot-up, see
+      <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
+
+      <listitem><para>Device units expose kernel devices in systemd
+      and may be used to implement device-based activation. For
+      details, see
+      <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
+
+      <listitem><para>Mount units control mount points in the file
+      system, for details see
+      <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
+
+      <listitem><para>Automount units provide automount capabilities,
+      for on-demand mounting of file systems as well as parallelized
+      boot-up. See
+      <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
+
+      <listitem><para>Timer units are useful for triggering activation
+      of other units based on timers. You may find details in
+      <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
+
+      <listitem><para>Swap units are very similar to mount units and
+      encapsulate memory swap partitions or files of the operating
+      system. They are described in
+      <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
+
+      <listitem><para>Path units may be used to activate other
+      services when file system objects change or are modified. See
+      <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
+
+      <listitem><para>Slice units may be used to group units which
+      manage system processes (such as service and scope units) in a
+      hierarchical tree for resource management purposes. See
+      <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
+
+      <listitem><para>Scope units are similar to service units, but
+      manage foreign processes instead of starting them as well. See
+      <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
+
+    </orderedlist>
+
+    <para>Units are named as their configuration files. Some units
+    have special semantics. A detailed list is available in
+    <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
+
+    <para>systemd knows various kinds of dependencies, including
+    positive and negative requirement dependencies (i.e.
+    <varname>Requires=</varname> and <varname>Conflicts=</varname>) as
+    well as ordering dependencies (<varname>After=</varname> and
+    <varname>Before=</varname>). NB: ordering and requirement
+    dependencies are orthogonal. If only a requirement dependency
+    exists between two units (e.g. <filename>foo.service</filename>
+    requires <filename>bar.service</filename>), but no ordering
+    dependency (e.g. <filename>foo.service</filename> after
+    <filename>bar.service</filename>) and both are requested to start,
+    they will be started in parallel. It is a common pattern that both
+    requirement and ordering dependencies are placed between two
+    units. Also note that the majority of dependencies are implicitly
+    created and maintained by systemd. In most cases, it should be
+    unnecessary to declare additional dependencies manually, however
+    it is possible to do this.</para>
+
+    <para>Application programs and units (via dependencies) may
+    request state changes of units. In systemd, these requests are
+    encapsulated as 'jobs' and maintained in a job queue. Jobs may
+    succeed or can fail, their execution is ordered based on the
+    ordering dependencies of the units they have been scheduled
+    for.</para>
+
+    <para>On boot systemd activates the target unit
+    <filename>default.target</filename> whose job is to activate
+    on-boot services and other on-boot units by pulling them in via
+    dependencies. Usually, the unit name is just an alias (symlink) for
+    either <filename>graphical.target</filename> (for fully-featured
+    boots into the UI) or <filename>multi-user.target</filename> (for
+    limited console-only boots for use in embedded or server
+    environments, or similar; a subset of graphical.target). However,
+    it is at the discretion of the administrator to configure it as an
+    alias to any other target unit. See
+    <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+    for details about these target units.</para>
+
+    <para>On first boot, <command>systemd</command> will enable or disable units according to preset policy.
+    See <citerefentry><refentrytitle>systemd.preset</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    and "First Boot Semantics" in
+    <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
+
+    <para>systemd only keeps a minimal set of units loaded into memory. Specifically, the only units that are
+    kept loaded into memory are those for which at least one of the following conditions is true:</para>
+
+    <orderedlist>
+      <listitem><para>It is in an active, activating, deactivating or failed state (i.e. in any unit state except for <literal>inactive</literal>)</para></listitem>
+      <listitem><para>It has a job queued for it</para></listitem>
+      <listitem><para>It is a dependency of at least one other unit that is loaded into memory</para></listitem>
+      <listitem><para>It has some form of resource still allocated (e.g. a service unit that is inactive but for which
+      a process is still lingering that ignored the request to be terminated)</para></listitem>
+      <listitem><para>It has been pinned into memory programmatically by a D-Bus call</para></listitem>
+    </orderedlist>
+
+    <para>systemd will automatically and implicitly load units from disk — if they are not loaded yet — as soon as
+    operations are requested for them. Thus, in many respects, the fact whether a unit is loaded or not is invisible to
+    clients. Use <command>systemctl list-units --all</command> to comprehensively list all units currently loaded. Any
+    unit for which none of the conditions above applies is promptly unloaded. Note that when a unit is unloaded from
+    memory its accounting data is flushed out too. However, this data is generally not lost, as a journal log record
+    is generated declaring the consumed resources whenever a unit shuts down.</para>
+
+    <para>Processes systemd spawns are placed in individual Linux control groups named after the unit which
+    they belong to in the private systemd hierarchy. (see <ulink
+    url="https://docs.kernel.org/admin-guide/cgroup-v2.html">Control Groups v2</ulink> for more information
+    about control groups, or short "cgroups").  systemd uses this to effectively keep track of
+    processes. Control group information is maintained in the kernel, and is accessible via the file system
+    hierarchy (beneath <filename>/sys/fs/cgroup/</filename>), or in tools such as <citerefentry
+    project='man-pages'><refentrytitle>systemd-cgls</refentrytitle><manvolnum>1</manvolnum></citerefentry> or
+    <citerefentry
+    project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry> (<command>ps
+    xawf -eo pid,user,cgroup,args</command> is particularly useful to list all processes and the systemd
+    units they belong to.).</para>
+
+    <para>systemd is compatible with the SysV init system to a large
+    degree: SysV init scripts are supported and simply read as an
+    alternative (though limited) configuration file format. The SysV
+    <filename>/dev/initctl</filename> interface is provided, and
+    compatibility implementations of the various SysV client tools are
+    available. In addition to that, various established Unix
+    functionality such as <filename>/etc/fstab</filename> or the
+    <filename>utmp</filename> database are supported.</para>
+
+    <para>systemd has a minimal transaction system: if a unit is
+    requested to start up or shut down it will add it and all its
+    dependencies to a temporary transaction. Then, it will verify if
+    the transaction is consistent (i.e. whether the ordering of all
+    units is cycle-free). If it is not, systemd will try to fix it up,
+    and removes non-essential jobs from the transaction that might
+    remove the loop. Also, systemd tries to suppress non-essential
+    jobs in the transaction that would stop a running service. Finally
+    it is checked whether the jobs of the transaction contradict jobs
+    that have already been queued, and optionally the transaction is
+    aborted then. If all worked out and the transaction is consistent
+    and minimized in its impact it is merged with all already
+    outstanding jobs and added to the run queue. Effectively this
+    means that before executing a requested operation, systemd will
+    verify that it makes sense, fixing it if possible, and only
+    failing if it really cannot work.</para>
+
+    <para>Note that transactions are generated independently of a unit's
+    state at runtime, hence, for example, if a start job is requested on an
+    already started unit, it will still generate a transaction and wake up any
+    inactive dependencies (and cause propagation of other jobs as per the
+    defined relationships). This is because the enqueued job is at the time of
+    execution compared to the target unit's state and is marked successful and
+    complete when both satisfy. However, this job also pulls in other
+    dependencies due to the defined relationships and thus leads to, in our
+    example, start jobs for any of those inactive units getting queued as
+    well.</para>
+
+    <para>systemd contains native implementations of various tasks
+    that need to be executed as part of the boot process. For example,
+    it sets the hostname or configures the loopback network device. It
+    also sets up and mounts various API file systems, such as
+    <filename>/sys/</filename> or <filename>/proc/</filename>.</para>
+
+    <para>For more information about the concepts and
+    ideas behind systemd, please refer to the
+    <ulink url="https://0pointer.de/blog/projects/systemd.html">Original Design Document</ulink>.</para>
+
+    <para>Note that some but not all interfaces provided by systemd are covered by the
+    <ulink url="https://systemd.io/PORTABILITY_AND_STABILITY/">Interface Portability and Stability Promise</ulink>.</para>
+
+    <para>Units may be generated dynamically at boot and system
+    manager reload time, for example based on other configuration
+    files or parameters passed on the kernel command line. For details, see
+    <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
+
+    <para>The D-Bus API of <command>systemd</command> is described in
+    <citerefentry><refentrytitle>org.freedesktop.systemd1</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    and
+    <citerefentry><refentrytitle>org.freedesktop.LogControl1</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+    </para>
+
+    <para>Systems which invoke systemd in a container or initrd environment should implement the <ulink
+    url="https://systemd.io/CONTAINER_INTERFACE">Container Interface</ulink> or
+    <ulink url="https://systemd.io/INITRD_INTERFACE/">initrd Interface</ulink>
+    specifications, respectively.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Directories</title>
+
+    <variablelist>
+      <varlistentry>
+        <term>System unit directories</term>
+
+        <listitem><para>The systemd system manager reads unit
+        configuration from various directories. Packages that want to
+        install unit files shall place them in the directory returned
+        by <command>pkg-config systemd
+        --variable=systemdsystemunitdir</command>. Other directories
+        checked are <filename>/usr/local/lib/systemd/system</filename>
+        and <filename>/usr/lib/systemd/system</filename>. User
+        configuration always takes precedence. <command>pkg-config
+        systemd --variable=systemdsystemconfdir</command> returns the
+        path of the system configuration directory. Packages should
+        alter the content of these directories only with the
+        <command>enable</command> and <command>disable</command>
+        commands of the
+        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+        tool. Full list of directories is provided in
+        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+        </para></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <variablelist>
+      <varlistentry>
+        <term>User unit directories</term>
+
+        <listitem><para>Similar rules apply for the user unit
+        directories. However, here the
+        <ulink url="https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
+        Base Directory specification</ulink> is followed to find
+        units. Applications should place their unit files in the
+        directory returned by <command>pkg-config systemd
+        --variable=systemduserunitdir</command>. Global configuration
+        is done in the directory reported by <command>pkg-config
+        systemd --variable=systemduserconfdir</command>. The
+        <command>enable</command> and <command>disable</command>
+        commands of the
+        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+        tool can handle both global (i.e. for all users) and private
+        (for one user) enabling/disabling of units. Full list of
+        directories is provided in
+        <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+        </para></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <variablelist>
+      <varlistentry>
+        <term>SysV init scripts directory</term>
+
+        <listitem><para>The location of the SysV init script directory
+        varies between distributions. If systemd cannot find a native
+        unit file for a requested service, it will look for a SysV
+        init script of the same name (with the
+        <filename>.service</filename> suffix
+        removed).</para></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <variablelist>
+      <varlistentry>
+        <term>SysV runlevel link farm directory</term>
+
+        <listitem><para>The location of the SysV runlevel link farm
+        directory varies between distributions. systemd will take the
+        link farm into account when figuring out whether a service
+        shall be enabled. Note that a service unit with a native unit
+        configuration file cannot be started by activating it in the
+        SysV runlevel link farm.</para></listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>Signals</title>
+
+    <variablelist>
+      <varlistentry>
+        <term><constant>SIGTERM</constant></term>
+
+        <listitem><para>Upon receiving this signal the systemd system
+        manager serializes its state, reexecutes itself and
+        deserializes the saved state again. This is mostly equivalent
+        to <command>systemctl daemon-reexec</command>.</para>
+
+        <para>systemd user managers will start the
+        <filename>exit.target</filename> unit when this signal is
+        received. This is mostly equivalent to <command>systemctl
+        --user start exit.target
+        --job-mode=replace-irreversibly</command>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGINT</constant></term>
+
+        <listitem><para>Upon receiving this signal the systemd system manager will start the
+        <filename>ctrl-alt-del.target</filename> unit. This is mostly equivalent to
+        <command>systemctl start ctrl-alt-del.target --job-mode=replace-irreversibly</command>. If
+        this signal is received more than 7 times per 2s, an immediate reboot is triggered. Note
+        that pressing
+        <keycombo><keycap>Ctrl</keycap><keycap>Alt</keycap><keycap>Del</keycap></keycombo> on the
+        console will trigger this signal. Hence, if a reboot is hanging, pressing
+        <keycombo><keycap>Ctrl</keycap><keycap>Alt</keycap><keycap>Del</keycap></keycombo> more than
+        7 times in 2 seconds is a relatively safe way to trigger an immediate reboot.</para>
+
+        <para>systemd user managers treat this signal the same way as
+        <constant>SIGTERM</constant>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGWINCH</constant></term>
+
+        <listitem><para>When this signal is received the systemd
+        system manager will start the
+        <filename>kbrequest.target</filename> unit. This is mostly
+        equivalent to <command>systemctl start
+        kbrequest.target</command>.</para>
+
+        <para>This signal is ignored by systemd user
+        managers.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGPWR</constant></term>
+
+        <listitem><para>When this signal is received the systemd
+        manager will start the <filename>sigpwr.target</filename>
+        unit. This is mostly equivalent to <command>systemctl start
+        sigpwr.target</command>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGUSR1</constant></term>
+
+        <listitem><para>When this signal is received the systemd
+        manager will try to reconnect to the D-Bus
+        bus.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGUSR2</constant></term>
+
+        <listitem><para>When this signal is received the systemd
+        manager will log its complete state in human-readable form.
+        The data logged is the same as printed by
+        <command>systemd-analyze dump</command>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGHUP</constant></term>
+
+        <listitem><para>Reloads the complete daemon configuration.
+        This is mostly equivalent to <command>systemctl
+        daemon-reload</command>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+0</constant></term>
+
+        <listitem><para>Enters default mode, starts the
+        <filename>default.target</filename> unit. This is mostly
+        equivalent to <command>systemctl isolate
+        default.target</command>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+1</constant></term>
+
+        <listitem><para>Enters rescue mode, starts the
+        <filename>rescue.target</filename> unit. This is mostly
+        equivalent to <command>systemctl isolate
+        rescue.target</command>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+2</constant></term>
+
+        <listitem><para>Enters emergency mode, starts the
+        <filename>emergency.service</filename> unit. This is mostly
+        equivalent to <command>systemctl isolate
+        emergency.service</command>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+3</constant></term>
+
+        <listitem><para>Halts the machine, starts the
+        <filename>halt.target</filename> unit. This is mostly
+        equivalent to <command>systemctl start halt.target
+        --job-mode=replace-irreversibly</command>.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+4</constant></term>
+
+        <listitem><para>Powers off the machine, starts the
+        <filename>poweroff.target</filename> unit. This is mostly
+        equivalent to <command>systemctl start poweroff.target
+        --job-mode=replace-irreversibly</command>.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+5</constant></term>
+
+        <listitem><para>Reboots the machine, starts the
+        <filename>reboot.target</filename> unit. This is mostly
+        equivalent to <command>systemctl start reboot.target
+        --job-mode=replace-irreversibly</command>.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+6</constant></term>
+
+        <listitem><para>Reboots the machine via kexec, starts the
+        <filename>kexec.target</filename> unit. This is mostly
+        equivalent to <command>systemctl start kexec.target
+        --job-mode=replace-irreversibly</command>.</para>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+7</constant></term>
+
+        <listitem><para>Reboots userspace, starts the <filename>soft-reboot.target</filename> unit. This is
+        mostly equivalent to <command>systemctl start soft-reboot.target
+        --job-mode=replace-irreversibly</command>.</para>
+
+        <xi:include href="version-info.xml" xpointer="v254"/>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+13</constant></term>
+
+        <listitem><para>Immediately halts the machine.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+14</constant></term>
+
+        <listitem><para>Immediately powers off the machine.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+15</constant></term>
+
+        <listitem><para>Immediately reboots the machine.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+16</constant></term>
+
+        <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+17</constant></term>
+
+        <listitem><para>Immediately reboots the userspace.</para>
+
+        <xi:include href="version-info.xml" xpointer="v254"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+20</constant></term>
+
+        <listitem><para>Enables display of status messages on the
+        console, as controlled via
+        <varname>systemd.show_status=1</varname> on the kernel command
+        line.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+21</constant></term>
+
+        <listitem><para>Disables display of
+        status messages on the console, as
+        controlled via
+        <varname>systemd.show_status=0</varname>
+        on the kernel command
+        line.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+22</constant></term>
+
+        <listitem><para>Sets the service manager's log level to <literal>debug</literal>, in a fashion equivalent to
+        <varname>systemd.log_level=debug</varname> on the kernel command line.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+23</constant></term>
+
+        <listitem><para>Restores the log level to its configured value. The configured value is derived from – in order
+        of priority – the value specified with <varname>systemd.log-level=</varname> on the kernel command line, or the
+        value specified with <option>LogLevel=</option> in the configuration file, or the built-in default of
+        <literal>info</literal>.</para>
+
+        <xi:include href="version-info.xml" xpointer="v239"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+24</constant></term>
+
+        <listitem><para>Immediately exits the manager (only available
+        for --user instances).</para>
+
+        <xi:include href="version-info.xml" xpointer="v195"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+25</constant></term>
+
+        <listitem><para>Upon receiving this signal the systemd manager will reexecute itself. This
+        is mostly equivalent to <command>systemctl daemon-reexec</command> except that it will be
+        done asynchronously.</para>
+
+        <para>The systemd system manager treats this signal the same way as
+        <constant>SIGTERM</constant>.</para>
+
+        <xi:include href="version-info.xml" xpointer="v250"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+26</constant></term>
+
+        <listitem><para>Restores the log target to its configured value. The configured value is derived from – in
+        order of priority – the value specified with <varname>systemd.log-target=</varname> on the kernel command line,
+        or the value specified with <option>LogTarget=</option> in the configuration file, or the built-in
+        default.</para>
+
+        <xi:include href="version-info.xml" xpointer="v239"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><constant>SIGRTMIN+27</constant></term>
+        <term><constant>SIGRTMIN+28</constant></term>
+
+        <listitem><para>Sets the log target to <literal>console</literal> on <constant>SIGRTMIN+27</constant> (or
+        <literal>kmsg</literal> on <constant>SIGRTMIN+28</constant>), in a fashion equivalent to
+        <varname>systemd.log_target=console</varname> (or <varname>systemd.log_target=kmsg</varname> on
+        <constant>SIGRTMIN+28</constant>) on the kernel command line.</para>
+
+        <xi:include href="version-info.xml" xpointer="v239"/></listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>Environment</title>
+
+    <para>The environment block for the system manager is initially set by the kernel. (In particular,
+    <literal>key=value</literal> assignments on the kernel command line are turned into environment
+    variables for PID 1). For the user manager, the system manager sets the environment as described in the
+    "Environment Variables in Spawned Processes" section of
+    <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>. The
+    <varname>DefaultEnvironment=</varname> setting in the system manager applies to all services including
+    <filename>user@.service</filename>. Additional entries may be configured (as for any other service)
+    through the <varname>Environment=</varname> and <varname>EnvironmentFile=</varname> settings for
+    <filename>user@.service</filename> (see
+    <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>). Also,
+    additional environment variables may be set through the <varname>ManagerEnvironment=</varname> setting in
+    <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+    and
+    <citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+    </para>
+
+    <para>Some of the variables understood by <command>systemd</command>:</para>
+
+    <variablelist class='environment-variables'>
+      <varlistentry>
+        <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
+        <listitem><xi:include href="common-variables.xml" xpointer="log-level-body" />
+
+        <para>This can be overridden with <option>--log-level=</option>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
+        <listitem><xi:include href="common-variables.xml" xpointer="log-color-body" />
+
+        <para>This can be overridden with <option>--log-color=</option>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>$SYSTEMD_LOG_TIME</varname></term>
+        <listitem><xi:include href="common-variables.xml" xpointer="log-time-body" />
+
+        <para>This can be overridden with <option>--log-time=</option>.</para>
+
+        <xi:include href="version-info.xml" xpointer="v246"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
+        <listitem><xi:include href="common-variables.xml" xpointer="log-location-body" />
+
+        <para>This can be overridden with <option>--log-location=</option>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>$SYSTEMD_LOG_TID</varname></term>
+        <listitem><xi:include href="common-variables.xml" xpointer="log-tid-body" />
+
+        <xi:include href="version-info.xml" xpointer="v247"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
+        <listitem><xi:include href="common-variables.xml" xpointer="log-target-body" />
+
+        <para>This can be overridden with <option>--log-target=</option>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>$SYSTEMD_LOG_RATELIMIT_KMSG</varname></term>
+        <listitem><xi:include href="common-variables.xml" xpointer="log-ratelimit-kmsg-body" />
+
+        <xi:include href="version-info.xml" xpointer="v254"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>$XDG_CONFIG_HOME</varname></term>
+        <term><varname>$XDG_CONFIG_DIRS</varname></term>
+        <term><varname>$XDG_DATA_HOME</varname></term>
+        <term><varname>$XDG_DATA_DIRS</varname></term>
+
+        <listitem><para>The systemd user manager uses these variables
+        in accordance to the <ulink
+        url="https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
+        Base Directory specification</ulink> to find its
+        configuration.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
+        <term><varname>$SYSTEMD_GENERATOR_PATH</varname></term>
+        <term><varname>$SYSTEMD_ENVIRONMENT_GENERATOR_PATH</varname></term>
+
+        <listitem><para>Controls where systemd looks for unit files and
+        generators.</para>
+        <para>These variables may contain a list of paths, separated by colons
+        (<literal>:</literal>). When set, if the list ends with an empty
+        component (<literal>...:</literal>), this list is prepended to the
+        usual set of paths. Otherwise, the specified list replaces the usual
+        set of paths.
+        </para></listitem>
+      </varlistentry>
+
+      <xi:include href="common-variables.xml" xpointer="pager"/>
+      <xi:include href="common-variables.xml" xpointer="less"/>
+      <xi:include href="common-variables.xml" xpointer="lesscharset"/>
+      <xi:include href="common-variables.xml" xpointer="lesssecure"/>
+      <xi:include href="common-variables.xml" xpointer="colors"/>
+      <xi:include href="common-variables.xml" xpointer="urlify"/>
+
+      <varlistentry>
+        <term><varname>$LISTEN_PID</varname></term>
+        <term><varname>$LISTEN_FDS</varname></term>
+        <term><varname>$LISTEN_FDNAMES</varname></term>
+
+        <listitem><para>Set by systemd for supervised processes during
+        socket-based activation. See
+        <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+        for more information.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>$NOTIFY_SOCKET</varname></term>
+
+        <listitem><para>Set by systemd for supervised processes for
+        status and start-up completion notification. See
+        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+        for more information.</para></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <para>For further environment variables understood by systemd and its various components, see <ulink
+    url="https://systemd.io/ENVIRONMENT">Known Environment Variables</ulink>.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>Kernel Command Line</title>
+
+    <para>When run as the system instance, systemd parses a number of options listed below. They can be
+    specified as kernel command line arguments which are parsed from a number of sources depending on the
+    environment in which systemd is executed. If run inside a Linux container, these options are parsed from
+    the command line arguments passed to systemd itself, next to any of the command line options listed in
+    the Options section above. If run outside of Linux containers, these arguments are parsed from
+    <filename>/proc/cmdline</filename> and from the <literal>SystemdOptions</literal> EFI variable
+    (on EFI systems) instead. Options from <filename>/proc/cmdline</filename> have higher priority.</para>
+
+    <para>Note: use of <literal>SystemdOptions</literal> is deprecated.</para>
+
+    <para>The following variables are understood:</para>
+
+    <variablelist class='kernel-commandline-options'>
+      <varlistentry>
+        <term><varname>systemd.unit=</varname></term>
+        <term><varname>rd.systemd.unit=</varname></term>
+
+        <listitem><para>Overrides the unit to activate on boot.  Defaults to
+        <filename>default.target</filename>. This may be used to temporarily boot into a different boot unit,
+        for example <filename>rescue.target</filename> or <filename>emergency.service</filename>. See
+        <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+        for details about these units. The option prefixed with <literal>rd.</literal> is honored only in the
+        initrd, while the one that is not prefixed only in the main system.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.dump_core</varname></term>
+
+        <listitem><para>Takes a boolean argument or enables the option if specified
+        without an argument. If enabled, the systemd manager (PID 1) dumps core when
+        it crashes. Otherwise, no core dump is created. Defaults to enabled.</para>
+
+        <xi:include href="version-info.xml" xpointer="v233"/>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.crash_chvt</varname></term>
+
+        <listitem><para>Takes a positive integer, or a boolean argument. Can be also specified without an
+        argument, with the same effect as a positive boolean. If a positive integer (in the range 1–63) is
+        specified, the system manager (PID 1) will activate the specified virtual terminal when it crashes.
+        Defaults to disabled, meaning that no such switch is attempted. If set to enabled, the virtual
+        terminal the kernel messages are written to is used instead.</para>
+
+        <xi:include href="version-info.xml" xpointer="v233"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.crash_shell</varname></term>
+
+        <listitem><para>Takes a boolean argument or enables the option if specified
+        without an argument. If enabled, the system manager (PID 1) spawns a shell
+        when it crashes, after a 10s delay. Otherwise, no shell is spawned. Defaults
+        to disabled, for security reasons, as the shell is not protected by password
+        authentication.</para>
+
+        <xi:include href="version-info.xml" xpointer="v233"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.crash_reboot</varname></term>
+
+        <listitem><para>Takes a boolean argument or enables the option if specified
+        without an argument. If enabled, the system manager (PID 1) will reboot the
+        machine automatically when it crashes, after a 10s delay.  Otherwise, the
+        system will hang indefinitely. Defaults to disabled, in order to avoid a
+        reboot loop. If combined with <varname>systemd.crash_shell</varname>, the
+        system is rebooted after the shell exits.</para>
+
+        <xi:include href="version-info.xml" xpointer="v227"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.confirm_spawn</varname></term>
+
+        <listitem><para>Takes a boolean argument or a path to the virtual console
+        where the confirmation messages should be emitted. Can be also specified
+        without an argument, with the same effect as a positive boolean. If enabled,
+        the system manager (PID 1) asks for confirmation when spawning processes
+        using <option>/dev/console</option>. If a path or a console name (such as
+        <literal>ttyS0</literal>) is provided, the virtual console pointed to by this
+        path or described by the give name will be used instead. Defaults to disabled.
+        </para>
+
+        <xi:include href="version-info.xml" xpointer="v233"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.service_watchdogs=</varname></term>
+
+        <listitem><para>Takes a boolean argument. If disabled, all service runtime
+        watchdogs (<option>WatchdogSec=</option>) and emergency actions (e.g.
+        <option>OnFailure=</option> or <option>StartLimitAction=</option>) are
+        ignored by the system manager (PID 1); see
+        <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+        Defaults to enabled, i.e. watchdogs and failure actions are processed
+        normally. The hardware watchdog is not affected by this
+        option.</para>
+
+        <xi:include href="version-info.xml" xpointer="v237"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.show_status</varname></term>
+
+        <listitem><para>Takes a boolean argument or the constants <constant>error</constant> and
+        <constant>auto</constant>. Can be also specified without an argument, with the same effect as a
+        positive boolean. If enabled, the systemd manager (PID 1) shows terse service status updates on the
+        console during bootup. With <constant>error</constant>, only messages about failures are shown, but
+        boot is otherwise quiet. <constant>auto</constant> behaves like <option>false</option> until there is
+        a significant delay in boot. Defaults to enabled, unless <option>quiet</option> is passed as kernel
+        command line option, in which case it defaults to <constant>error</constant>. If specified overrides
+        the system manager configuration file option <option>ShowStatus=</option>, see
+        <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+        </para>
+
+        <xi:include href="version-info.xml" xpointer="v233"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.status_unit_format=</varname></term>
+
+        <listitem><para>Takes <option>name</option>, <option>description</option> or
+        <option>combined</option> as the value. If <option>name</option>, the system manager will use unit
+        names in status messages. If <option>combined</option>, the system manager will use unit names and
+        description in status messages. When specified, overrides the system manager configuration file
+        option <option>StatusUnitFormat=</option>, see
+        <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
+        </para>
+
+        <xi:include href="version-info.xml" xpointer="v243"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.log_color</varname></term>
+        <term><varname>systemd.log_level=</varname></term>
+        <term><varname>systemd.log_location</varname></term>
+        <term><varname>systemd.log_target=</varname></term>
+        <term><varname>systemd.log_time</varname></term>
+        <term><varname>systemd.log_tid</varname></term>
+        <term><varname>systemd.log_ratelimit_kmsg</varname></term>
+
+        <listitem><para>Controls log output, with the same effect as the
+        <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>,
+        <varname>$SYSTEMD_LOG_LOCATION</varname>, <varname>$SYSTEMD_LOG_TARGET</varname>,
+        <varname>$SYSTEMD_LOG_TIME</varname>, <varname>$SYSTEMD_LOG_TID</varname> and
+        <varname>$SYSTEMD_LOG_RATELIMIT_KMSG</varname> environment variables described above.
+        <varname>systemd.log_color</varname>, <varname>systemd.log_location</varname>,
+        <varname>systemd.log_time</varname>, <varname>systemd.log_tid</varname> and
+        <varname>systemd.log_ratelimit_kmsg</varname> can be specified without
+        an argument, with the same effect as a positive boolean.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.default_standard_output=</varname></term>
+        <term><varname>systemd.default_standard_error=</varname></term>
+
+        <listitem><para>Controls default standard output and error output for services and sockets. That is,
+        controls the default for <option>StandardOutput=</option> and <option>StandardError=</option> (see
+        <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
+        details). Takes one of <option>inherit</option>, <option>null</option>, <option>tty</option>,
+        <option>journal</option>, <option>journal+console</option>, <option>kmsg</option>,
+        <option>kmsg+console</option>. If the argument is omitted
+        <varname>systemd.default-standard-output=</varname> defaults to <option>journal</option> and
+        <varname>systemd.default-standard-error=</varname> to <option>inherit</option>.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.setenv=</varname></term>
+
+        <listitem><para>Takes a string argument in the form
+        VARIABLE=VALUE. May be used to set default environment
+        variables to add to forked child processes. May be used more
+        than once to set multiple variables.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.machine_id=</varname></term>
+
+        <listitem><para>Takes a 32 character hex value to be
+        used for setting the machine-id. Intended mostly for
+        network booting where the same machine-id is desired
+        for every boot.</para>
+
+        <xi:include href="version-info.xml" xpointer="v229"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.set_credential=</varname></term>
+        <term><varname>systemd.set_credential_binary=</varname></term>
+
+        <listitem><para>Sets a system credential, which can then be propagated to system services using the
+        <varname>ImportCredential=</varname> or <varname>LoadCredential=</varname> setting, see
+        <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
+        details. Takes a pair of credential name and value, separated by a colon. The
+        <varname>systemd.set_credential=</varname> parameter expects the credential value in literal text
+        form, the <varname>systemd.set_credential_binary=</varname> parameter takes binary data encoded in
+        Base64. Note that the kernel command line is typically accessible by unprivileged programs in
+        <filename>/proc/cmdline</filename>. Thus, this mechanism is not suitable for transferring sensitive
+        data. Use it only for data that is not sensitive (e.g. public keys/certificates, rather than private
+        keys), or in testing/debugging environments.</para>
+
+        <para>For further information see <ulink url="https://systemd.io/CREDENTIALS">System and Service
+        Credentials</ulink> documentation.</para>
+
+        <xi:include href="version-info.xml" xpointer="v251"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>systemd.import_credentials=</varname></term>
+
+        <listitem><para>Takes a boolean argument. If false disables importing credentials from the kernel
+        command line, the DMI/SMBIOS OEM string table, the qemu_fw_cfg subsystem or the EFI kernel
+        stub.</para>
+
+        <xi:include href="version-info.xml" xpointer="v251"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>quiet</varname></term>
+
+        <listitem><para>Turn off status output at boot, much like
+        <varname>systemd.show_status=no</varname> would. Note that
+        this option is also read by the kernel itself and disables
+        kernel log output. Passing this option hence turns off the
+        usual output from both the system manager and the kernel.
+        </para>
+
+        <xi:include href="version-info.xml" xpointer="v186"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>debug</varname></term>
+
+        <listitem><para>Turn on debugging output. This is equivalent
+        to <varname>systemd.log_level=debug</varname>. Note that this
+        option is also read by the kernel itself and enables kernel
+        debug output. Passing this option hence turns on the debug
+        output from both the system manager and the
+        kernel.</para>
+
+        <xi:include href="version-info.xml" xpointer="v205"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>emergency</varname></term>
+        <term><varname>rd.emergency</varname></term>
+        <term><varname>-b</varname></term>
+
+        <listitem><para>Boot into emergency mode. This is equivalent
+        to <varname>systemd.unit=emergency.target</varname> or
+        <varname>rd.systemd.unit=emergency.target</varname>, respectively, and
+        provided for compatibility reasons and to be easier to type.</para>
+
+        <xi:include href="version-info.xml" xpointer="v186"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>rescue</varname></term>
+        <term><varname>rd.rescue</varname></term>
+        <term><varname>single</varname></term>
+        <term><varname>s</varname></term>
+        <term><varname>S</varname></term>
+        <term><varname>1</varname></term>
+
+        <listitem><para>Boot into rescue mode. This is equivalent to
+        <varname>systemd.unit=rescue.target</varname> or
+        <varname>rd.systemd.unit=rescue.target</varname>, respectively, and
+        provided for compatibility reasons and to be easier to type.</para>
+
+        <xi:include href="version-info.xml" xpointer="v186"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>2</varname></term>
+        <term><varname>3</varname></term>
+        <term><varname>4</varname></term>
+        <term><varname>5</varname></term>
+
+        <listitem><para>Boot into the specified legacy SysV runlevel.
+        These are equivalent to
+        <varname>systemd.unit=runlevel2.target</varname>,
+        <varname>systemd.unit=runlevel3.target</varname>,
+        <varname>systemd.unit=runlevel4.target</varname>, and
+        <varname>systemd.unit=runlevel5.target</varname>,
+        respectively, and provided for compatibility reasons and to be
+        easier to type.</para>
+
+        <xi:include href="version-info.xml" xpointer="v186"/></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>locale.LANG=</varname></term>
+        <term><varname>locale.LANGUAGE=</varname></term>
+        <term><varname>locale.LC_CTYPE=</varname></term>
+        <term><varname>locale.LC_NUMERIC=</varname></term>
+        <term><varname>locale.LC_TIME=</varname></term>
+        <term><varname>locale.LC_COLLATE=</varname></term>
+        <term><varname>locale.LC_MONETARY=</varname></term>
+        <term><varname>locale.LC_MESSAGES=</varname></term>
+        <term><varname>locale.LC_PAPER=</varname></term>
+        <term><varname>locale.LC_NAME=</varname></term>
+        <term><varname>locale.LC_ADDRESS=</varname></term>
+        <term><varname>locale.LC_TELEPHONE=</varname></term>
+        <term><varname>locale.LC_MEASUREMENT=</varname></term>
+        <term><varname>locale.LC_IDENTIFICATION=</varname></term>
+
+        <listitem><para>Set the system locale to use. This overrides
+        the settings in <filename>/etc/locale.conf</filename>. For
+        more information, see
+        <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+        and
+        <citerefentry project='man-pages'><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
+        </para>
+
+        <xi:include href="version-info.xml" xpointer="v186"/></listitem>
+      </varlistentry>
+    </variablelist>
+
+    <para>For other kernel command line parameters understood by
+    components of the core OS, please refer to
+    <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
+  </refsect1>
+
+  <refsect1>
+    <title>System credentials</title>
+
+    <para>During initialization the service manager will import credentials from various sources into the
+    system's set of credentials, which can then be propagated into services and consumed by
+    generators:</para>
+
+    <itemizedlist>
+      <listitem><para>When the service manager first initializes it will read system credentials from SMBIOS
+      Type 11 vendor strings
+      <varname>io.systemd.credential:<replaceable>name</replaceable>=<replaceable>value</replaceable></varname>,
+      and
+      <varname>io.systemd.credential.binary:<replaceable>name</replaceable>=<replaceable>value</replaceable></varname>.</para></listitem>
+
+      <listitem><para>At the same time it will import credentials from QEMU <literal>fw_cfg</literal>. (Note
+      that the SMBIOS mechanism is generally preferred, because it is faster and generic.)</para></listitem>
+
+      <listitem><para>Credentials may be passed via the kernel command line, using the
+      <varname>systemd.set-credential=</varname> parameter, see above.</para></listitem>
+
+      <listitem><para>Credentials may be passed from the UEFI environment via
+      <citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
+
+      <listitem><para>When the service manager is invoked during the initrd → host transition it will import
+      all files in <filename>/run/credentials/@initrd/</filename> as system credentials.</para></listitem>
+    </itemizedlist>
+
+    <para>Invoke
+    <citerefentry><refentrytitle>systemd-creds</refentrytitle><manvolnum>1</manvolnum></citerefentry> as
+    follows to see the list of credentials passed into the system:</para>
+
+    <programlisting># systemd-creds --system list</programlisting>
+
+    <para>For further information see <ulink url="https://systemd.io/CREDENTIALS">System and Service
+    Credentials</ulink> documentation.</para>
+
+    <para>The service manager when run as PID 1 consumes the following system credentials:</para>
+
+    <variablelist class='system-credentials'>
+      <varlistentry>
+        <term><varname>vmm.notify_socket</varname></term>
+        <listitem>
+          <para>Contains a <constant>AF_VSOCK</constant> or <constant>AF_UNIX</constant> address where to
+          send a <constant>READY=1</constant> notification datagram when the system has finished booting. See
+          <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry> for
+          more information. Note that in case the hypervisor does not support <constant>SOCK_DGRAM</constant>
+          over <constant>AF_VSOCK</constant>, <constant>SOCK_SEQPACKET</constant> will be tried instead. The
+          credential payload for <constant>AF_VSOCK</constant> should be in the form
+          <literal>vsock:CID:PORT</literal>.</para>
+
+          <para>This feature is useful for hypervisors/VMMs or other processes on the host to receive a
+          notification via VSOCK when a virtual machine has finished booting.</para>
+
+          <xi:include href="version-info.xml" xpointer="v254"/>
+        </listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><varname>system.machine_id</varname></term>
+        <listitem>
+          <para>Takes a 128bit hexadecimal ID to initialize <filename>/etc/machine-id</filename> from, if the
+          file is not set up yet. See
+          <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
+          details.</para>
+
+        <xi:include href="version-info.xml" xpointer="v254"/>
+        </listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>Options</title>
+
+    <para><command>systemd</command> is only very rarely invoked directly, since it is started early and is
+    already running by the time users may interact with it. Normally, tools like
+    <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> are used to
+    give commands to the manager. Since <command>systemd</command> is usually not invoked directly, the
+    options listed below are mostly useful for debugging and special purposes.</para>
+
+    <refsect2>
+      <title>Introspection and debugging options</title>
+
+      <para>Those options are used for testing and introspection, and <command>systemd</command> may
+      be invoked with them at any time:</para>
+
+      <variablelist>
+        <varlistentry>
+          <term><option>--dump-configuration-items</option></term>
+
+          <listitem><para>Dump understood unit configuration items. This outputs a terse but complete list of
+          configuration items understood in unit definition files.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--dump-bus-properties</option></term>
+
+          <listitem><para>Dump exposed bus properties. This outputs a terse but complete list of properties
+          exposed on D-Bus.</para>
+
+          <xi:include href="version-info.xml" xpointer="v239"/></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--test</option></term>
+
+          <listitem><para>Determine the initial start-up transaction (i.e. the list of jobs enqueued at
+          start-up), dump it and exit — without actually executing any of the determined jobs. This option is
+          useful for debugging only. Note that during regular service manager start-up additional units not
+          shown by this operation may be started, because hardware, socket, bus or other kinds of activation
+          might add additional jobs as the transaction is executed. Use <option>--system</option> to request
+          the initial transaction of the system service manager (this is also the implied default), combine
+          with <option>--user</option> to request the initial transaction of the per-user service manager
+          instead.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--system</option></term>
+          <term><option>--user</option></term>
+
+          <listitem><para>When used in conjunction with <option>--test</option>, selects whether to calculate
+          the initial transaction for the system instance or for a per-user instance. These options have no
+          effect when invoked without <option>--test</option>, as during regular
+          (i.e. non-<option>--test</option>) invocations the service manager will automatically detect
+          whether it shall operate in system or per-user mode, by checking whether the PID it is run as is 1
+          or not. Note that it is not supported booting and maintaining a system with the service manager
+          running in <option>--system</option> mode but with a PID other than 1.</para></listitem>
+        </varlistentry>
+
+        <xi:include href="standard-options.xml" xpointer="help" />
+        <xi:include href="standard-options.xml" xpointer="version" />
+      </variablelist>
+    </refsect2>
+
+    <refsect2>
+      <title>Options that duplicate kernel command line settings</title>
+
+      <para>Those options correspond directly to options listed above in "Kernel Command Line". Both forms
+      may be used equivalently for the system manager, but it is recommended to use the forms listed above in
+      this context, because they are properly namespaced. When an option is specified both on the kernel
+      command line and as a normal command line argument, the latter has higher precedence.</para>
+
+      <para>When <command>systemd</command> is used as a user manager, the kernel command line is ignored and
+      only the options described below are understood. Nevertheless, <command>systemd</command> is usually
+      started in this mode through the
+      <citerefentry><refentrytitle>user@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+      service, which is shared between all users. It may be more convenient to use configuration files to
+      modify settings (see
+      <citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>),
+      or environment variables. See the "Environment" section above for a discussion of how the environment
+      block is set.</para>
+
+      <variablelist>
+        <varlistentry>
+          <term><option>--unit=</option></term>
+
+          <listitem><para>Set default unit to activate on startup. If not specified, defaults to
+          <filename>default.target</filename>. See <varname>systemd.unit=</varname> above.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--dump-core</option></term>
+
+          <listitem><para>Enable core dumping on crash. This switch has no effect when running as user
+          instance. Same as <varname>systemd.dump_core=</varname> above.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--crash-vt=</option><replaceable>VT</replaceable></term>
+
+          <listitem><para>Switch to a specific virtual console (VT) on crash. This switch has no effect when
+          running as user instance. Same as <varname>systemd.crash_chvt=</varname> above (but not the
+          different spelling!).</para>
+
+          <xi:include href="version-info.xml" xpointer="v227"/></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--crash-shell</option></term>
+
+          <listitem><para>Run a shell on crash. This switch has no effect when running as user instance. See
+          <varname>systemd.crash_shell=</varname> above.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--crash-reboot</option></term>
+
+          <listitem><para>Automatically reboot the system on crash. This switch has no effect when running as
+          user instance. See <varname>systemd.crash_reboot</varname> above.</para>
+
+          <xi:include href="version-info.xml" xpointer="v227"/></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--confirm-spawn</option></term>
+
+          <listitem><para>Ask for confirmation when spawning processes. This switch has no effect when run as
+          user instance. See <varname>systemd.confirm_spawn</varname> above.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--show-status</option></term>
+
+          <listitem><para>Show terse unit status information on the console during boot-up and shutdown. See
+          <varname>systemd.show_status</varname> above.</para>
+
+          <xi:include href="version-info.xml" xpointer="v244"/></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--log-color</option></term>
+
+          <listitem><para>Highlight important log messages. See <varname>systemd.log_color</varname> above.
+          </para>
+
+          <xi:include href="version-info.xml" xpointer="v244"/></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--log-level=</option></term>
+
+          <listitem><para>Set log level. See <varname>systemd.log_level</varname> above.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--log-location</option></term>
+
+          <listitem><para>Include code location in log messages. See <varname>systemd.log_location</varname>
+          above.</para>
+
+          <xi:include href="version-info.xml" xpointer="v244"/></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--log-target=</option></term>
+
+          <listitem><para>Set log target. See <varname>systemd.log_target</varname> above.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--log-time=</option></term>
+
+          <listitem><para>Prefix console messages with timestamp. See <varname>systemd.log_time</varname> above.
+          </para>
+
+          <xi:include href="version-info.xml" xpointer="v246"/></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--machine-id=</option></term>
+
+          <listitem><para>Override the machine-id set on the hard drive. See
+          <varname>systemd.machine_id=</varname> above.</para>
+
+          <xi:include href="version-info.xml" xpointer="v229"/></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--service-watchdogs</option></term>
+
+          <listitem><para>Globally enable/disable all service watchdog timeouts and emergency actions. See
+          <varname>systemd.service_watchdogs</varname> above.</para>
+
+          <xi:include href="version-info.xml" xpointer="v237"/></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><option>--default-standard-output=</option></term>
+          <term><option>--default-standard-error=</option></term>
+
+          <listitem><para>Sets the default output or error output for all services and sockets,
+          respectively. See <varname>systemd.default_standard_output=</varname> and
+          <varname>systemd.default_standard_error=</varname> above.</para></listitem>
+        </varlistentry>
+      </variablelist>
+    </refsect2>
+  </refsect1>
+
+  <refsect1>
+    <title>Sockets and FIFOs</title>
+
+    <variablelist>
+      <varlistentry>
+        <term><filename>/run/systemd/notify</filename></term>
+
+        <listitem><para>Daemon status notification socket. This is an
+        <constant>AF_UNIX</constant> datagram socket and is used to
+        implement the daemon notification logic as implemented by
+        <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
+
+      </varlistentry>
+
+      <varlistentry>
+        <term><filename>/run/systemd/private</filename></term>
+
+        <listitem><para>Used internally as communication channel
+        between
+        <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+        and the systemd process. This is an
+        <constant>AF_UNIX</constant> stream socket. This interface is
+        private to systemd and should not be used in external
+        projects.</para></listitem>
+      </varlistentry>
+
+      <varlistentry>
+        <term><filename>/dev/initctl</filename></term>
+
+        <listitem><para>Limited compatibility support for the SysV
+        client interface, as implemented by the
+        <filename>systemd-initctl.service</filename> unit. This is a
+        named pipe in the file system. This interface is obsolete and
+        should not be used in new applications.</para></listitem>
+      </varlistentry>
+    </variablelist>
+  </refsect1>
+
+  <refsect1>
+      <title>History</title>
+
+      <variablelist>
+        <varlistentry>
+          <term>systemd 252</term>
+          <listitem><para>Kernel command-line arguments <varname>systemd.unified_cgroup_hierarchy</varname>
+          and <varname>systemd.legacy_systemd_cgroup_controller</varname> were deprecated. Please switch to
+          the unified cgroup hierarchy.</para>
+
+          <xi:include href="version-info.xml" xpointer="v252"/></listitem>
+        </varlistentry>
+      </variablelist>
+  </refsect1>
+
+  <refsect1>
+    <title>See Also</title>
+    <para>
+      The <ulink url="https://systemd.io/">systemd Homepage</ulink>,
+      <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>org.freedesktop.systemd1</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+      <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+      <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+      <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+    </para>
+  </refsect1>
+
+</refentry>