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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"
xmlns:xi="http://www.w3.org/2001/XInclude">
<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-system.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>--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>--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>
<xi:include href="standard-options.xml" xpointer="help" />
<xi:include href="standard-options.xml" xpointer="version" />
</variablelist>
</refsect1>
<refsect1>
<title>Concepts</title>
<para>systemd provides a dependency system between
various entities called "units" of 12 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, 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, 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 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>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>
<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>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://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 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="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>/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="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. 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</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
ctl-alt-del.target</command>.</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>systemctl
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 start
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</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</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</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</command>.</para></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+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>
<term><constant>SIGRTMIN+23</constant></term>
<listitem><para>Sets the log level to
<literal>debug</literal>
(or <literal>info</literal> on
<constant>SIGRTMIN+23</constant>), as
controlled via
<varname>systemd.log_level=debug</varname>
(or <varname>systemd.log_level=info</varname>
on <constant>SIGRTMIN+23</constant>) on
the kernel command
line.</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>SIGRTMIN+24</constant></term>
<listitem><para>Immediately exits the
manager (only available for --user
instances).</para></listitem>
</varlistentry>
<varlistentry>
<term><constant>SIGRTMIN+26</constant></term>
<term><constant>SIGRTMIN+27</constant></term>
<term><constant>SIGRTMIN+28</constant></term>
<term><constant>SIGRTMIN+29</constant></term>
<listitem><para>Sets the log level to
<literal>journal-or-kmsg</literal>
(or <literal>console</literal> on
<constant>SIGRTMIN+27</constant>,
<literal>kmsg</literal> on
<constant>SIGRTMIN+28</constant>,
or <literal>syslog-or-kmsg</literal>
on <constant>SIGRTMIN+29</constant>), as
controlled via
<varname>systemd.log_target=journal-or-kmsg</varname>
(or <varname>systemd.log_target=console</varname>
on <constant>SIGRTMIN+27</constant>,
<varname>systemd.log_target=kmsg</varname>
on <constant>SIGRTMIN+28</constant>,
or
<varname>systemd.log_target=syslog-or-kmsg</varname>
on <constant>SIGRTMIN+29</constant>) on
the kernel command
line.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Environment</title>
<variablelist class='environment-variables'>
<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 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 initial RAM disk (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. 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
<constant>-1</constant>.</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 or the constant
<constant>auto</constant>. If
<option>true</option>, shows terse
service status updates on the console
during bootup.
<constant>auto</constant> behaves like
<option>false</option> until a service
fails or there is a significant delay
in boot. Defaults to
<option>true</option>, unless
<option>quiet</option> is passed as
kernel command line option in which
case it defaults to
<constant>auto</constant>.</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 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>quiet</varname></term>
<listitem><para>Turn 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. Passing this option
hence turns off the usual output from
both the system manager and the kernel.
</para></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></listitem>
</varlistentry>
<varlistentry>
<term><varname>-b</varname></term>
<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
<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/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 <constant>AF_UNIX</constant> 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
<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>See Also</title>
<para>
The <ulink url="http://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
<citerefentry><refentrytitle>systemd-system.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>,
<citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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