Fork of Original Code Base: anongit.freedesktop.org/systemd

This is the initial fork of the code base from freedsktop.org.
The code is provided here as a reference of the initial starting
point and for possible future checkouts after a large portion
of this code is removed.

Merge git://anongit.freedesktop.org/systemd/systemd

1 files changed, 1272 insertions, 0 deletions

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+<?xml version='1.0'?> <!--*-nxml-*-->
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+        "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+
+<!--
+  This file is part of systemd.
+
+  Copyright 2010 Lennart Poettering
+
+  systemd is free software; you can redistribute it and/or modify it
+  under the terms of the GNU Lesser General Public License as published by
+  the Free Software Foundation; either version 2.1 of the License, or
+  (at your option) any later version.
+
+  systemd is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public License
+  along with systemd; If not, see <http://www.gnu.org/licenses/>.
+-->
+
+<refentry id="systemd">
+
+        <refentryinfo>
+                <title>systemd</title>
+                <productname>systemd</productname>
+
+                <authorgroup>
+                        <author>
+                                <contrib>Developer</contrib>
+                                <firstname>Lennart</firstname>
+                                <surname>Poettering</surname>
+                                <email>lennart@poettering.net</email>
+                        </author>
+                </authorgroup>
+        </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>systemd <arg choice="opt" rep="repeat">OPTIONS</arg></command>
+                </cmdsynopsis>
+                <cmdsynopsis>
+                        <command>init <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="req">COMMAND</arg></command>
+                </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.</para>
+
+                <para>For compatibility with SysV, if systemd is called
+                as <command>init</command> and a PID that 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 system instance, systemd interprets
+                the configuration file
+                <filename>system.conf</filename>, otherwise
+                <filename>user.conf</filename>. See
+                <citerefentry><refentrytitle>systemd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+                for more information.</para>
+        </refsect1>
+
+        <refsect1>
+                <title>Options</title>
+
+                <para>The following options are understood:</para>
+
+                <variablelist>
+                        <varlistentry>
+                                <term><option>-h</option></term>
+                                <term><option>--help</option></term>
+
+                                <listitem><para>Prints a short help
+                                text and exits.</para></listitem>
+                        </varlistentry>
+                        <varlistentry>
+                                <term><option>--version</option></term>
+
+                                <listitem><para>Prints a systemd version
+                                identifier and exits.</para></listitem>
+                        </varlistentry>
+                        <varlistentry>
+                                <term><option>--test</option></term>
+
+                                <listitem><para>Determine startup
+                                sequence, dump it and exit. This is an
+                                option useful for debugging
+                                only.</para></listitem>
+                        </varlistentry>
+                        <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>--introspect=</option></term>
+
+                                <listitem><para>Extract D-Bus
+                                interface introspection data. This is
+                                mostly useful at install time
+                                to generate data suitable for the
+                                D-Bus interfaces
+                                repository. Optionally the interface
+                                name for the introspection data may be
+                                specified. If omitted, the
+                                introspection data for all interfaces
+                                is dumped.</para></listitem>
+                        </varlistentry>
+                        <varlistentry>
+                                <term><option>--unit=</option></term>
+
+                                <listitem><para>Set default unit to
+                                activate on startup. If not specified
+                                defaults to
+                                <filename>default.target</filename>.</para></listitem>
+                        </varlistentry>
+                        <varlistentry>
+                                <term><option>--system</option></term>
+                                <term><option>--user</option></term>
+
+                                <listitem><para>For <option>--system</option>,
+                                tell systemd to run a
+                                system instance, even if the process ID is
+                                not 1, i.e. systemd is not run as init process.
+                                <option>--user</option> does the opposite,
+                                running a user instance even if the process
+                                ID is 1.
+                                Normally it should not be necessary to
+                                pass these options, as systemd
+                                automatically detects the mode it is
+                                started in. These options are hence of
+                                little use except for debugging. Note
+                                that it is not supported booting and
+                                maintaining a full system with systemd
+                                running in <option>--system</option>
+                                mode, but PID not 1. In practice,
+                                passing <option>--system</option> explicitly is
+                                only useful in conjunction with
+                                <option>--test</option>.</para></listitem>
+                        </varlistentry>
+                        <varlistentry>
+                                <term><option>--dump-core</option></term>
+
+                                <listitem><para>Dump core on
+                                crash. This switch has no effect when
+                                run as user
+                                instance.</para></listitem>
+                        </varlistentry>
+                        <varlistentry>
+                                <term><option>--crash-shell</option></term>
+
+                                <listitem><para>Run shell on
+                                crash. This switch has no effect when
+                                run as user
+                                instance.</para></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.</para></listitem>
+                        </varlistentry>
+                        <varlistentry>
+                                <term><option>--show-status=</option></term>
+
+                                <listitem><para>Show terse service
+                                status information while booting. This
+                                switch has no effect when run as user
+                                instance. Takes a boolean argument
+                                which may be omitted which is
+                                interpreted as
+                                <option>true</option>.</para></listitem>
+                        </varlistentry>
+                        <varlistentry>
+                                <term><option>--log-target=</option></term>
+
+                                <listitem><para>Set log
+                                target. Argument must be one of
+                                <option>console</option>,
+                                <option>journal</option>,
+                                <option>syslog</option>,
+                                <option>kmsg</option>,
+                                <option>journal-or-kmsg</option>,
+                                <option>syslog-or-kmsg</option>,
+                                <option>null</option>.</para></listitem>
+                        </varlistentry>
+                        <varlistentry>
+                                <term><option>--log-level=</option></term>
+
+                                <listitem><para>Set log level. As
+                                argument this accepts a numerical log
+                                level or the well-known <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                                symbolic names (lowercase):
+                                <option>emerg</option>,
+                                <option>alert</option>,
+                                <option>crit</option>,
+                                <option>err</option>,
+                                <option>warning</option>,
+                                <option>notice</option>,
+                                <option>info</option>,
+                                <option>debug</option>.</para></listitem>
+                        </varlistentry>
+                        <varlistentry>
+                                <term><option>--log-color=</option></term>
+
+                                <listitem><para>Highlight important
+                                log messages. Argument is a boolean
+                                value. If the argument is omitted it
+                                defaults to
+                                <option>true</option>.</para></listitem>
+                        </varlistentry>
+                        <varlistentry>
+                                <term><option>--log-location=</option></term>
+
+                                <listitem><para>Include code location
+                                in log messages. This is mostly
+                                relevant for debugging
+                                purposes. Argument is a boolean
+                                value. If the argument is omitted
+                                it defaults to
+                                <option>true</option>.</para></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. 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>syslog</option>,
+                                <option>syslog+console</option>,
+                                <option>kmsg</option>,
+                                <option>kmsg+console</option>.  If the
+                                argument is omitted
+                                <option>--default-standard-output=</option>
+                                defaults to <option>journal</option>
+                                and
+                                <option>--default-standard-error=</option>
+                                to
+                                <option>inherit</option>.</para></listitem>
+                        </varlistentry>
+                </variablelist>
+        </refsect1>
+
+        <refsect1>
+                <title>Concepts</title>
+
+                <para>systemd provides a dependency system between
+                various entities called "units". 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 or dynamically from system state. 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, or an operation timed out). 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 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>Snapshot units can be used to
+                        temporarily save the state of the set of
+                        systemd units, which later may be restored by
+                        activating the saved snapshot unit. For more
+                        information see
+                        <citerefentry><refentrytitle>systemd.snapshot</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>
+
+                </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>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="http://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</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/systemd/</filename>), or in tools
+                such as
+                <citerefentry><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>Systemd contains native implementations of
+                various tasks that need to be executed as part of the
+                boot process. For example, it sets the host name 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="http://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="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
+                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 the <ulink
+                url="http://www.freedesktop.org/wiki/Software/systemd/Generators">Generators
+                Specification</ulink>.</para>
+
+                <para>Systems which invoke systemd in a container
+                or initrd environment should implement the
+                <ulink
+                url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container
+                Interface</ulink> or <ulink
+                url="http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">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.</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="http://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.</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>SIGTERM</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</command>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGINT</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
+                                ctl-alt-del.target</command>.</para>
+
+                                <para>systemd user managers
+                                treat this signal the same way as
+                                SIGTERM.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGWINCH</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>SIGPWR</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>SIGUSR1</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>SIGUSR2</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>systemctl
+                                dump</command>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGHUP</term>
+
+                                <listitem><para>Reloads the complete
+                                daemon configuration. This is mostly
+                                equivalent to <command>systemctl
+                                daemon-reload</command>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGRTMIN+0</term>
+
+                                <listitem><para>Enters default mode, starts the
+                                <filename>default.target</filename>
+                                unit. This is mostly equivalent to
+                                <command>systemctl start
+                                default.target</command>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGRTMIN+1</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>SIGRTMIN+2</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>SIGRTMIN+3</term>
+
+                                <listitem><para>Halts the machine,
+                                starts the
+                                <filename>halt.target</filename>
+                                unit. This is mostly equivalent to
+                                <command>systemctl start
+                                halt.target</command>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGRTMIN+4</term>
+
+                                <listitem><para>Powers off the machine,
+                                starts the
+                                <filename>poweroff.target</filename>
+                                unit. This is mostly equivalent to
+                                <command>systemctl start
+                                poweroff.target</command>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGRTMIN+5</term>
+
+                                <listitem><para>Reboots the machine,
+                                starts the
+                                <filename>reboot.target</filename>
+                                unit. This is mostly equivalent to
+                                <command>systemctl start
+                                reboot.target</command>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGRTMIN+6</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</command>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGRTMIN+13</term>
+
+                                <listitem><para>Immediately halts the machine.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGRTMIN+14</term>
+
+                                <listitem><para>Immediately powers off the machine.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGRTMIN+15</term>
+
+                                <listitem><para>Immediately reboots the machine.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGRTMIN+16</term>
+
+                                <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGRTMIN+20</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>SIGRTMIN+21</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>SIGRTMIN+22</term>
+                                <term>SIGRTMIN+23</term>
+
+                                <listitem><para>Sets the log level to
+                                <literal>debug</literal>
+                                (or <literal>info</literal> on
+                                <literal>SIGRTMIN+23</literal>), as
+                                controlled via
+                                <varname>systemd.log_level=debug</varname>
+                                (or <varname>systemd.log_level=info</varname>
+                                on <literal>SIGRTMIN+23</literal>) on
+                                the kernel command
+                                line.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGRTMIN+24</term>
+
+                                <listitem><para>Immediately exits the
+                                manager (only available for --user
+                                instances).</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term>SIGRTMIN+26</term>
+                                <term>SIGRTMIN+27</term>
+                                <term>SIGRTMIN+28</term>
+                                <term>SIGRTMIN+29</term>
+
+                                <listitem><para>Sets the log level to
+                                <literal>journal-or-kmsg</literal>
+                                (or <literal>console</literal> on
+                                <literal>SIGRTMIN+27</literal>,
+                                <literal>kmsg</literal> on
+                                <literal>SIGRTMIN+28</literal>,
+                                or <literal>syslog-or-kmsg</literal>
+                                on <literal>SIGRTMIN+29</literal>), as
+                                controlled via
+                                <varname>systemd.log_target=journal-or-kmsg</varname>
+                                (or <varname>systemd.log_target=console</varname>
+                                on <literal>SIGRTMIN+27</literal>,
+                                <varname>systemd.log_target=kmsg</varname>
+                                on <literal>SIGRTMIN+28</literal>,
+                                or
+                                <varname>systemd.log_target=syslog-or-kmsg</varname>
+                                on <literal>SIGRTMIN+29</literal>) on
+                                the kernel command
+                                line.</para></listitem>
+                        </varlistentry>
+                </variablelist>
+        </refsect1>
+
+        <refsect1>
+                <title>Environment</title>
+
+                <variablelist>
+                        <varlistentry>
+                                <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
+                                <listitem><para>systemd reads the
+                                log level from this environment
+                                variable. This can be overridden with
+                                <option>--log-level=</option>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
+                                <listitem><para>systemd reads the
+                                log target from this environment
+                                variable. This can be overridden with
+                                <option>--log-target=</option>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
+                                <listitem><para>Controls whether
+                                systemd highlights important log
+                                messages. This can be overridden with
+                                <option>--log-color=</option>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
+                                <listitem><para>Controls whether
+                                systemd prints the code location along
+                                with log messages. This can be
+                                overridden with
+                                <option>--log-location=</option>.</para></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="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
+                                Base Directory specification</ulink>
+                                to find its configuration.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
+
+                                <listitem><para>Controls where systemd
+                                looks for unit
+                                files.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
+
+                                <listitem><para>Controls where systemd
+                                looks for SysV init scripts.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
+
+                                <listitem><para>Controls where systemd
+                                looks for SysV init script runlevel link
+                                farms.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>$LISTEN_PID</varname></term>
+                                <term><varname>$LISTEN_FDS</varname></term>
+
+                                <listitem><para>Set by systemd for
+                                supervised processes during
+                                socket-based activation. See
+                                <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+                                for more information.
+                                </para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>$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>
+        </refsect1>
+
+        <refsect1>
+                <title>Kernel Command Line</title>
+
+                <para>When run as system instance systemd parses a
+                number of kernel command line
+                arguments<footnote><para>If run inside a Linux
+                container these arguments may be passed as command
+                line arguments 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>
+                instead.</para></footnote>:</para>
+
+                <variablelist>
+                        <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 initial RAM disk (initrd),
+                                while the one that isn't prefixed only
+                                in the main system.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>systemd.dump_core=</varname></term>
+
+                                <listitem><para>Takes a boolean
+                                argument. If <option>true</option>
+                                systemd dumps core when it
+                                crashes. Otherwise no core dump is
+                                created. Defaults to
+                                <option>true</option>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>systemd.crash_shell=</varname></term>
+
+                                <listitem><para>Takes a boolean
+                                argument. If <option>true</option>
+                                systemd spawns a shell when it
+                                crashes. Otherwise no shell is
+                                spawned. Defaults to
+                                <option>false</option>, for security
+                                reasons, as the shell is not protected
+                                by any password
+                                authentication.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>systemd.crash_chvt=</varname></term>
+
+                                <listitem><para>Takes an integer
+                                argument. If positive systemd
+                                activates the specified virtual
+                                terminal when it crashes. Defaults to
+                                <literal>-1</literal>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>systemd.confirm_spawn=</varname></term>
+
+                                <listitem><para>Takes a boolean
+                                argument. If <option>true</option>
+                                asks for confirmation when spawning
+                                processes. Defaults to
+                                <option>false</option>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>systemd.show_status=</varname></term>
+
+                                <listitem><para>Takes a boolean
+                                argument. If <option>true</option>
+                                shows terse service status updates on
+                                the console during bootup. Defaults to
+                                <option>true</option>, unless
+                                <option>quiet</option> is passed as
+                                kernel command line option in which
+                                case it defaults to
+                                <option>false</option>.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>systemd.log_target=</varname></term>
+                                <term><varname>systemd.log_level=</varname></term>
+                                <term><varname>systemd.log_color=</varname></term>
+                                <term><varname>systemd.log_location=</varname></term>
+
+                                <listitem><para>Controls log output,
+                                with the same effect as the
+                                <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
+                                environment variables described above.</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, with the same effect as the
+                                <option>--default-standard-output=</option>
+                                and <option>--default-standard-error=</option>
+                                command line arguments described
+                                above, respectively.</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
+                                environment variables for the init
+                                process and all its children at boot
+                                time. May be used more than once to
+                                set multiple variables. If the equal
+                                sign and variable are missing it unsets
+                                an environment variable which might be
+                                passed in from the initial ram
+                                disk.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>quiet</varname></term>
+
+                                <listitem><para>If passed turns off
+                                status output at boot, much like
+                                <varname>systemd.show_status=false</varname>
+                                would. Note that this option is also
+                                read by the kernel itself and disables
+                                kernel log output to the
+                                kernel. Passing this option hence
+                                turns off the usual output from both
+                                the system manager and the
+                                kernel.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <term><varname>emergency</varname></term>
+
+                                <listitem><para>Boot into emergency
+                                mode. This is equivalent to
+                                <varname>systemd.unit=emergency.target</varname>
+                                and provided for compatibility
+                                reasons and to be easier to type.</para></listitem>
+                        </varlistentry>
+
+                        <varlistentry>
+                                <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>
+                                and provided for compatibility reasons
+                                and to be easier to
+                                type.</para></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></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><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+                                and
+                                <citerefentry><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
+                                </para></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>Sockets and FIFOs</title>
+
+                <variablelist>
+                        <varlistentry>
+                                <term><filename>/run/systemd/notify</filename></term>
+
+                                <listitem><para>Daemon status
+                                notification socket. This is an
+                                AF_UNIX 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/shutdownd</filename></term>
+
+                                <listitem><para>Used internally by the
+                                <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+                                tool to implement delayed
+                                shutdowns. This is an AF_UNIX datagram
+                                socket.</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
+                                AF_UNIX 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>See Also</title>
+                <para>
+                        <citerefentry><refentrytitle>systemd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+                        <citerefentry><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>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
+                        <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+                </para>
+        </refsect1>
+
+</refentry>