+ <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. 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 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>
+