man/systemd.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   This file is part of systemd.
   7
   8   Copyright 2010 Lennart Poettering
   9
  10   systemd is free software; you can redistribute it and/or modify it
  11   under the terms of the GNU Lesser General Public License as published by
  12   the Free Software Foundation; either version 2.1 of the License, or
  13   (at your option) any later version.
  14
  15   systemd is distributed in the hope that it will be useful, but
  16   WITHOUT ANY WARRANTY; without even the implied warranty of
  17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  18   Lesser General Public License for more details.
  19
  20   You should have received a copy of the GNU Lesser General Public License
  21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  22 -->
  23
  24 <refentry id="systemd"
  25     xmlns:xi="http://www.w3.org/2001/XInclude">
  26
  27   <refentryinfo>
  28     <title>systemd</title>
  29     <productname>systemd</productname>
  30
  31     <authorgroup>
  32       <author>
  33         <contrib>Developer</contrib>
  34         <firstname>Lennart</firstname>
  35         <surname>Poettering</surname>
  36         <email>lennart@poettering.net</email>
  37       </author>
  38     </authorgroup>
  39   </refentryinfo>
  40
  41   <refmeta>
  42     <refentrytitle>systemd</refentrytitle>
  43     <manvolnum>1</manvolnum>
  44   </refmeta>
  45
  46   <refnamediv>
  47     <refname>systemd</refname>
  48     <refname>init</refname>
  49     <refpurpose>systemd system and service manager</refpurpose>
  50   </refnamediv>
  51
  52   <refsynopsisdiv>
  53     <cmdsynopsis>
  54       <command>systemd <arg choice="opt" rep="repeat">OPTIONS</arg></command>
  55     </cmdsynopsis>
  56     <cmdsynopsis>
  57       <command>init <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="req">COMMAND</arg></command>
  58     </cmdsynopsis>
  59   </refsynopsisdiv>
  60
  61   <refsect1>
  62     <title>Description</title>
  63
  64     <para>systemd is a system and service manager for Linux operating
  65     systems. When run as first process on boot (as PID 1), it acts as
  66     init system that brings up and maintains userspace
  67     services.</para>
  68
  69     <para>For compatibility with SysV, if systemd is called as
  70     <command>init</command> and a PID that is not 1, it will execute
  71     <command>telinit</command> and pass all command line arguments
  72     unmodified. That means <command>init</command> and
  73     <command>telinit</command> are mostly equivalent when invoked from
  74     normal login sessions. See
  75     <citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  76     for more information.</para>
  77
  78     <para>When run as a system instance, systemd interprets the
  79     configuration file <filename>system.conf</filename> and the files
  80     in <filename>system.conf.d</filename> directories; when run as a
  81     user instance, systemd interprets the configuration file
  82     <filename>user.conf</filename> and the files in
  83     <filename>user.conf.d</filename> directories. See
  84     <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  85     for more information.</para>
  86   </refsect1>
  87
  88   <refsect1>
  89     <title>Options</title>
  90
  91     <para>The following options are understood:</para>
  92
  93     <variablelist>
  94       <varlistentry>
  95         <term><option>--test</option></term>
  96
  97         <listitem><para>Determine startup sequence, dump it and exit.
  98         This is an option useful for debugging only.</para></listitem>
  99       </varlistentry>
 100       <varlistentry>
 101         <term><option>--dump-configuration-items</option></term>
 102
 103         <listitem><para>Dump understood unit configuration items. This
 104         outputs a terse but complete list of configuration items
 105         understood in unit definition files.</para></listitem>
 106       </varlistentry>
 107       <varlistentry>
 108         <term><option>--unit=</option></term>
 109
 110         <listitem><para>Set default unit to activate on startup. If
 111         not specified, defaults to
 112         <filename>default.target</filename>.</para></listitem>
 113       </varlistentry>
 114       <varlistentry>
 115         <term><option>--system</option></term>
 116         <term><option>--user</option></term>
 117
 118         <listitem><para>For <option>--system</option>, tell systemd to
 119         run a system instance, even if the process ID is not 1, i.e.
 120         systemd is not run as init process. <option>--user</option>
 121         does the opposite, running a user instance even if the process
 122         ID is 1. Normally it should not be necessary to pass these
 123         options, as systemd automatically detects the mode it is
 124         started in. These options are hence of little use except for
 125         debugging. Note that it is not supported booting and
 126         maintaining a full system with systemd running in
 127         <option>--system</option> mode, but PID not 1. In practice,
 128         passing <option>--system</option> explicitly is only useful in
 129         conjunction with <option>--test</option>.</para></listitem>
 130       </varlistentry>
 131       <varlistentry>
 132         <term><option>--dump-core</option></term>
 133
 134         <listitem><para>Dump core on crash. This switch has no effect
 135         when run as user instance.</para></listitem>
 136       </varlistentry>
 137       <varlistentry>
 138         <term><option>--crash-shell</option></term>
 139
 140         <listitem><para>Run shell on
 141         crash. This switch has no effect when
 142         run as user
 143         instance.</para></listitem>
 144       </varlistentry>
 145       <varlistentry>
 146         <term><option>--confirm-spawn</option></term>
 147
 148         <listitem><para>Ask for confirmation when spawning processes.
 149         This switch has no effect when run as user
 150         instance.</para></listitem>
 151       </varlistentry>
 152       <varlistentry>
 153         <term><option>--show-status=</option></term>
 154
 155         <listitem><para>Show terse service status information while
 156         booting. This switch has no effect when run as user instance.
 157         Takes a boolean argument which may be omitted which is
 158         interpreted as <option>true</option>.</para></listitem>
 159       </varlistentry>
 160       <varlistentry>
 161         <term><option>--log-target=</option></term>
 162
 163         <listitem><para>Set log target. Argument must be one of
 164         <option>console</option>,
 165         <option>journal</option>,
 166         <option>kmsg</option>,
 167         <option>journal-or-kmsg</option>,
 168         <option>null</option>.</para></listitem>
 169       </varlistentry>
 170       <varlistentry>
 171         <term><option>--log-level=</option></term>
 172
 173         <listitem><para>Set log level. As
 174         argument this accepts a numerical log
 175         level or the well-known <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 176         symbolic names (lowercase):
 177         <option>emerg</option>,
 178         <option>alert</option>,
 179         <option>crit</option>,
 180         <option>err</option>,
 181         <option>warning</option>,
 182         <option>notice</option>,
 183         <option>info</option>,
 184         <option>debug</option>.</para></listitem>
 185       </varlistentry>
 186       <varlistentry>
 187         <term><option>--log-color=</option></term>
 188
 189         <listitem><para>Highlight important log messages. Argument is
 190         a boolean value. If the argument is omitted, it defaults to
 191         <option>true</option>.</para></listitem>
 192       </varlistentry>
 193       <varlistentry>
 194         <term><option>--log-location=</option></term>
 195
 196         <listitem><para>Include code location in log messages. This is
 197         mostly relevant for debugging purposes. Argument is a boolean
 198         value. If the argument is omitted it defaults to
 199         <option>true</option>.</para></listitem>
 200       </varlistentry>
 201       <varlistentry>
 202         <term><option>--default-standard-output=</option></term>
 203         <term><option>--default-standard-error=</option></term>
 204
 205         <listitem><para>Sets the default output or error output for
 206         all services and sockets, respectively. That is, controls the
 207         default for <option>StandardOutput=</option> and
 208         <option>StandardError=</option> (see
 209         <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 210         for details). Takes one of
 211         <option>inherit</option>,
 212         <option>null</option>,
 213         <option>tty</option>,
 214         <option>journal</option>,
 215         <option>journal+console</option>,
 216         <option>syslog</option>,
 217         <option>syslog+console</option>,
 218         <option>kmsg</option>,
 219         <option>kmsg+console</option>.  If the
 220         argument is omitted
 221         <option>--default-standard-output=</option> defaults to
 222         <option>journal</option> and
 223         <option>--default-standard-error=</option> to
 224         <option>inherit</option>.</para></listitem>
 225       </varlistentry>
 226
 227       <xi:include href="standard-options.xml" xpointer="help" />
 228       <xi:include href="standard-options.xml" xpointer="version" />
 229     </variablelist>
 230   </refsect1>
 231
 232   <refsect1>
 233     <title>Concepts</title>
 234
 235     <para>systemd provides a dependency system between various
 236     entities called "units" of 12 different types. Units encapsulate
 237     various objects that are relevant for system boot-up and
 238     maintenance. The majority of units are configured in unit
 239     configuration files, whose syntax and basic set of options is
 240     described in
 241     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 242     however some are created automatically from other configuration,
 243     dynamically from system state or programmatically at runtime.
 244     Units may be "active" (meaning started, bound, plugged in, ...,
 245     depending on the unit type, see below), or "inactive" (meaning
 246     stopped, unbound, unplugged, ...), as well as in the process of
 247     being activated or deactivated, i.e. between the two states (these
 248     states are called "activating", "deactivating"). A special
 249     "failed" state is available as well, which is very similar to
 250     "inactive" and is entered when the service failed in some way
 251     (process returned error code on exit, or crashed, or an operation
 252     timed out). If this state is entered, the cause will be logged,
 253     for later reference. Note that the various unit types may have a
 254     number of additional substates, which are mapped to the five
 255     generalized unit states described here.</para>
 256
 257     <para>The following unit types are available:</para>
 258
 259     <orderedlist>
 260       <listitem><para>Service units, which start and control daemons
 261       and the processes they consist of. For details see
 262       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 263
 264       <listitem><para>Socket units, which encapsulate local IPC or
 265       network sockets in the system, useful for socket-based
 266       activation. For details about socket units see
 267       <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 268       for details on socket-based activation and other forms of
 269       activation, see
 270       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 271
 272       <listitem><para>Target units are useful to group units, or
 273       provide well-known synchronization points during boot-up, see
 274       <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 275
 276       <listitem><para>Device units expose kernel devices in systemd
 277       and may be used to implement device-based activation. For
 278       details see
 279       <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 280
 281       <listitem><para>Mount units control mount points in the file
 282       system, for details see
 283       <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 284
 285       <listitem><para>Automount units provide automount capabilities,
 286       for on-demand mounting of file systems as well as parallelized
 287       boot-up. See
 288       <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 289
 290       <listitem><para>Snapshot units can be used to temporarily save
 291       the state of the set of systemd units, which later may be
 292       restored by activating the saved snapshot unit. For more
 293       information see
 294       <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 295
 296       <listitem><para>Timer units are useful for triggering activation
 297       of other units based on timers. You may find details in
 298       <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 299
 300       <listitem><para>Swap units are very similar to mount units and
 301       encapsulate memory swap partitions or files of the operating
 302       system. They are described in
 303       <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 304
 305       <listitem><para>Path units may be used to activate other
 306       services when file system objects change or are modified. See
 307       <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 308
 309       <listitem><para>Slice units may be used to group units which
 310       manage system processes (such as service and scope units) in a
 311       hierarchical tree for resource management purposes. See
 312       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 313
 314       <listitem><para>Scope units are similar to service units, but
 315       manage foreign processes instead of starting them as well. See
 316       <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 317
 318     </orderedlist>
 319
 320     <para>Units are named as their configuration files. Some units
 321     have special semantics. A detailed list is available in
 322     <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 323
 324     <para>systemd knows various kinds of dependencies, including
 325     positive and negative requirement dependencies (i.e.
 326     <varname>Requires=</varname> and <varname>Conflicts=</varname>) as
 327     well as ordering dependencies (<varname>After=</varname> and
 328     <varname>Before=</varname>). NB: ordering and requirement
 329     dependencies are orthogonal. If only a requirement dependency
 330     exists between two units (e.g. <filename>foo.service</filename>
 331     requires <filename>bar.service</filename>), but no ordering
 332     dependency (e.g. <filename>foo.service</filename> after
 333     <filename>bar.service</filename>) and both are requested to start,
 334     they will be started in parallel. It is a common pattern that both
 335     requirement and ordering dependencies are placed between two
 336     units. Also note that the majority of dependencies are implicitly
 337     created and maintained by systemd. In most cases, it should be
 338     unnecessary to declare additional dependencies manually, however
 339     it is possible to do this.</para>
 340
 341     <para>Application programs and units (via dependencies) may
 342     request state changes of units. In systemd, these requests are
 343     encapsulated as 'jobs' and maintained in a job queue. Jobs may
 344     succeed or can fail, their execution is ordered based on the
 345     ordering dependencies of the units they have been scheduled
 346     for.</para>
 347
 348     <para>On boot systemd activates the target unit
 349     <filename>default.target</filename> whose job is to activate
 350     on-boot services and other on-boot units by pulling them in via
 351     dependencies. Usually the unit name is just an alias (symlink) for
 352     either <filename>graphical.target</filename> (for fully-featured
 353     boots into the UI) or <filename>multi-user.target</filename> (for
 354     limited console-only boots for use in embedded or server
 355     environments, or similar; a subset of graphical.target). However,
 356     it is at the discretion of the administrator to configure it as an
 357     alias to any other target unit. See
 358     <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 359     for details about these target units.</para>
 360
 361     <para>Processes systemd spawns are placed in individual Linux
 362     control groups named after the unit which they belong to in the
 363     private systemd hierarchy. (see <ulink
 364     url="https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 365     for more information about control groups, or short "cgroups").
 366     systemd uses this to effectively keep track of processes. Control
 367     group information is maintained in the kernel, and is accessible
 368     via the file system hierarchy (beneath
 369     <filename>/sys/fs/cgroup/systemd/</filename>), or in tools such as
 370     <citerefentry project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 371     (<command>ps xawf -eo pid,user,cgroup,args</command> is
 372     particularly useful to list all processes and the systemd units
 373     they belong to.).</para>
 374
 375     <para>systemd is compatible with the SysV init system to a large
 376     degree: SysV init scripts are supported and simply read as an
 377     alternative (though limited) configuration file format. The SysV
 378     <filename>/dev/initctl</filename> interface is provided, and
 379     compatibility implementations of the various SysV client tools are
 380     available. In addition to that, various established Unix
 381     functionality such as <filename>/etc/fstab</filename> or the
 382     <filename>utmp</filename> database are supported.</para>
 383
 384     <para>systemd has a minimal transaction system: if a unit is
 385     requested to start up or shut down it will add it and all its
 386     dependencies to a temporary transaction. Then, it will verify if
 387     the transaction is consistent (i.e. whether the ordering of all
 388     units is cycle-free). If it is not, systemd will try to fix it up,
 389     and removes non-essential jobs from the transaction that might
 390     remove the loop. Also, systemd tries to suppress non-essential
 391     jobs in the transaction that would stop a running service. Finally
 392     it is checked whether the jobs of the transaction contradict jobs
 393     that have already been queued, and optionally the transaction is
 394     aborted then. If all worked out and the transaction is consistent
 395     and minimized in its impact it is merged with all already
 396     outstanding jobs and added to the run queue. Effectively this
 397     means that before executing a requested operation, systemd will
 398     verify that it makes sense, fixing it if possible, and only
 399     failing if it really cannot work.</para>
 400
 401     <para>Systemd contains native implementations of various tasks
 402     that need to be executed as part of the boot process. For example,
 403     it sets the hostname or configures the loopback network device. It
 404     also sets up and mounts various API file systems, such as
 405     <filename>/sys</filename> or <filename>/proc</filename>.</para>
 406
 407     <para>For more information about the concepts and
 408     ideas behind systemd, please refer to the
 409     <ulink url="http://0pointer.de/blog/projects/systemd.html">Original Design Document</ulink>.</para>
 410
 411     <para>Note that some but not all interfaces provided
 412     by systemd are covered by the
 413     <ulink url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 414     Stability Promise</ulink>.</para>
 415
 416     <para>Units may be generated dynamically at boot and system
 417     manager reload time, for example based on other configuration
 418     files or parameters passed on the kernel command line. For details see
 419     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 420
 421     <para>Systems which invoke systemd in a container or initrd
 422     environment should implement the
 423     <ulink url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container Interface</ulink> or
 424     <ulink url="http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd Interface</ulink>
 425     specifications, respectively.</para>
 426   </refsect1>
 427
 428   <refsect1>
 429     <title>Directories</title>
 430
 431     <variablelist>
 432       <varlistentry>
 433         <term>System unit directories</term>
 434
 435         <listitem><para>The systemd system manager reads unit
 436         configuration from various directories. Packages that want to
 437         install unit files shall place them in the directory returned
 438         by <command>pkg-config systemd
 439         --variable=systemdsystemunitdir</command>. Other directories
 440         checked are <filename>/usr/local/lib/systemd/system</filename>
 441         and <filename>/usr/lib/systemd/system</filename>. User
 442         configuration always takes precedence. <command>pkg-config
 443         systemd --variable=systemdsystemconfdir</command> returns the
 444         path of the system configuration directory. Packages should
 445         alter the content of these directories only with the
 446         <command>enable</command> and <command>disable</command>
 447         commands of the
 448         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 449         tool. Full list of directories is provided in
 450         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 451         </para></listitem>
 452       </varlistentry>
 453     </variablelist>
 454
 455     <variablelist>
 456       <varlistentry>
 457         <term>User unit directories</term>
 458
 459         <listitem><para>Similar rules apply for the user unit
 460         directories. However, here the
 461         <ulink url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 462         Base Directory specification</ulink> is followed to find
 463         units. Applications should place their unit files in the
 464         directory returned by <command>pkg-config systemd
 465         --variable=systemduserunitdir</command>. Global configuration
 466         is done in the directory reported by <command>pkg-config
 467         systemd --variable=systemduserconfdir</command>. The
 468         <command>enable</command> and <command>disable</command>
 469         commands of the
 470         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 471         tool can handle both global (i.e. for all users) and private
 472         (for one user) enabling/disabling of units. Full list of
 473         directories is provided in
 474         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 475         </para></listitem>
 476       </varlistentry>
 477     </variablelist>
 478
 479     <variablelist>
 480       <varlistentry>
 481         <term>SysV init scripts directory</term>
 482
 483         <listitem><para>The location of the SysV init script directory
 484         varies between distributions. If systemd cannot find a native
 485         unit file for a requested service, it will look for a SysV
 486         init script of the same name (with the
 487         <filename>.service</filename> suffix
 488         removed).</para></listitem>
 489       </varlistentry>
 490     </variablelist>
 491
 492     <variablelist>
 493       <varlistentry>
 494         <term>SysV runlevel link farm directory</term>
 495
 496         <listitem><para>The location of the SysV runlevel link farm
 497         directory varies between distributions. systemd will take the
 498         link farm into account when figuring out whether a service
 499         shall be enabled. Note that a service unit with a native unit
 500         configuration file cannot be started by activating it in the
 501         SysV runlevel link farm.</para></listitem>
 502       </varlistentry>
 503     </variablelist>
 504   </refsect1>
 505
 506   <refsect1>
 507     <title>Signals</title>
 508
 509     <variablelist>
 510       <varlistentry>
 511         <term><constant>SIGTERM</constant></term>
 512
 513         <listitem><para>Upon receiving this signal the systemd system
 514         manager serializes its state, reexecutes itself and
 515         deserializes the saved state again. This is mostly equivalent
 516         to <command>systemctl daemon-reexec</command>.</para>
 517
 518         <para>systemd user managers will start the
 519         <filename>exit.target</filename> unit when this signal is
 520         received. This is mostly equivalent to <command>systemctl
 521         --user start exit.target</command>.</para></listitem>
 522       </varlistentry>
 523
 524       <varlistentry>
 525         <term><constant>SIGINT</constant></term>
 526
 527         <listitem><para>Upon receiving this signal the systemd system
 528         manager will start the
 529         <filename>ctrl-alt-del.target</filename> unit. This is mostly
 530         equivalent to <command>systemctl start
 531         ctl-alt-del.target</command>. If this signal is received more
 532         often than 7 times per 2s an immediate reboot is triggered.
 533         Note that pressing Ctrl-Alt-Del on the console will trigger
 534         this signal. Hence, if a reboot is hanging pressing
 535         Ctrl-Alt-Del more than 7 times in 2s is a relatively safe way
 536         to trigger an immediate reboot.</para>
 537
 538         <para>systemd user managers treat this signal the same way as
 539         <constant>SIGTERM</constant>.</para></listitem>
 540       </varlistentry>
 541
 542       <varlistentry>
 543         <term><constant>SIGWINCH</constant></term>
 544
 545         <listitem><para>When this signal is received the systemd
 546         system manager will start the
 547         <filename>kbrequest.target</filename> unit. This is mostly
 548         equivalent to <command>systemctl start
 549         kbrequest.target</command>.</para>
 550
 551         <para>This signal is ignored by systemd user
 552         managers.</para></listitem>
 553       </varlistentry>
 554
 555       <varlistentry>
 556         <term><constant>SIGPWR</constant></term>
 557
 558         <listitem><para>When this signal is received the systemd
 559         manager will start the <filename>sigpwr.target</filename>
 560         unit. This is mostly equivalent to <command>systemctl start
 561         sigpwr.target</command>.</para></listitem>
 562       </varlistentry>
 563
 564       <varlistentry>
 565         <term><constant>SIGUSR1</constant></term>
 566
 567         <listitem><para>When this signal is received the systemd
 568         manager will try to reconnect to the D-Bus
 569         bus.</para></listitem>
 570       </varlistentry>
 571
 572       <varlistentry>
 573         <term><constant>SIGUSR2</constant></term>
 574
 575         <listitem><para>When this signal is received the systemd
 576         manager will log its complete state in human readable form.
 577         The data logged is the same as printed by
 578         <command>systemd-analyze dump</command>.</para></listitem>
 579       </varlistentry>
 580
 581       <varlistentry>
 582         <term><constant>SIGHUP</constant></term>
 583
 584         <listitem><para>Reloads the complete daemon configuration.
 585         This is mostly equivalent to <command>systemctl
 586         daemon-reload</command>.</para></listitem>
 587       </varlistentry>
 588
 589       <varlistentry>
 590         <term><constant>SIGRTMIN+0</constant></term>
 591
 592         <listitem><para>Enters default mode, starts the
 593         <filename>default.target</filename> unit. This is mostly
 594         equivalent to <command>systemctl start
 595         default.target</command>.</para></listitem>
 596       </varlistentry>
 597
 598       <varlistentry>
 599         <term><constant>SIGRTMIN+1</constant></term>
 600
 601         <listitem><para>Enters rescue mode, starts the
 602         <filename>rescue.target</filename> unit. This is mostly
 603         equivalent to <command>systemctl isolate
 604         rescue.target</command>.</para></listitem>
 605       </varlistentry>
 606
 607       <varlistentry>
 608         <term><constant>SIGRTMIN+2</constant></term>
 609
 610         <listitem><para>Enters emergency mode, starts the
 611         <filename>emergency.service</filename> unit. This is mostly
 612         equivalent to <command>systemctl isolate
 613         emergency.service</command>.</para></listitem>
 614       </varlistentry>
 615
 616       <varlistentry>
 617         <term><constant>SIGRTMIN+3</constant></term>
 618
 619         <listitem><para>Halts the machine, starts the
 620         <filename>halt.target</filename> unit. This is mostly
 621         equivalent to <command>systemctl start
 622         halt.target</command>.</para></listitem>
 623       </varlistentry>
 624
 625       <varlistentry>
 626         <term><constant>SIGRTMIN+4</constant></term>
 627
 628         <listitem><para>Powers off the machine, starts the
 629         <filename>poweroff.target</filename> unit. This is mostly
 630         equivalent to <command>systemctl start
 631         poweroff.target</command>.</para></listitem>
 632       </varlistentry>
 633
 634       <varlistentry>
 635         <term><constant>SIGRTMIN+5</constant></term>
 636
 637         <listitem><para>Reboots the machine, starts the
 638         <filename>reboot.target</filename> unit. This is mostly
 639         equivalent to <command>systemctl start
 640         reboot.target</command>.</para></listitem>
 641       </varlistentry>
 642
 643       <varlistentry>
 644         <term><constant>SIGRTMIN+6</constant></term>
 645
 646         <listitem><para>Reboots the machine via kexec, starts the
 647         <filename>kexec.target</filename> unit. This is mostly
 648         equivalent to <command>systemctl start
 649         kexec.target</command>.</para></listitem>
 650       </varlistentry>
 651
 652       <varlistentry>
 653         <term><constant>SIGRTMIN+13</constant></term>
 654
 655         <listitem><para>Immediately halts the machine.</para></listitem>
 656       </varlistentry>
 657
 658       <varlistentry>
 659         <term><constant>SIGRTMIN+14</constant></term>
 660
 661         <listitem><para>Immediately powers off the machine.</para></listitem>
 662       </varlistentry>
 663
 664       <varlistentry>
 665         <term><constant>SIGRTMIN+15</constant></term>
 666
 667         <listitem><para>Immediately reboots the machine.</para></listitem>
 668       </varlistentry>
 669
 670       <varlistentry>
 671         <term><constant>SIGRTMIN+16</constant></term>
 672
 673         <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
 674       </varlistentry>
 675
 676       <varlistentry>
 677         <term><constant>SIGRTMIN+20</constant></term>
 678
 679         <listitem><para>Enables display of status messages on the
 680         console, as controlled via
 681         <varname>systemd.show_status=1</varname> on the kernel command
 682         line.</para></listitem>
 683       </varlistentry>
 684
 685       <varlistentry>
 686         <term><constant>SIGRTMIN+21</constant></term>
 687
 688         <listitem><para>Disables display of
 689         status messages on the console, as
 690         controlled via
 691         <varname>systemd.show_status=0</varname>
 692         on the kernel command
 693         line.</para></listitem>
 694       </varlistentry>
 695
 696       <varlistentry>
 697         <term><constant>SIGRTMIN+22</constant></term>
 698         <term><constant>SIGRTMIN+23</constant></term>
 699
 700         <listitem><para>Sets the log level to <literal>debug</literal>
 701         (or <literal>info</literal> on
 702         <constant>SIGRTMIN+23</constant>), as controlled via
 703         <varname>systemd.log_level=debug</varname> (or
 704         <varname>systemd.log_level=info</varname> on
 705         <constant>SIGRTMIN+23</constant>) on the kernel command
 706         line.</para></listitem>
 707       </varlistentry>
 708
 709       <varlistentry>
 710         <term><constant>SIGRTMIN+24</constant></term>
 711
 712         <listitem><para>Immediately exits the manager (only available
 713         for --user instances).</para></listitem>
 714       </varlistentry>
 715
 716       <varlistentry>
 717         <term><constant>SIGRTMIN+26</constant></term>
 718         <term><constant>SIGRTMIN+27</constant></term>
 719         <term><constant>SIGRTMIN+28</constant></term>
 720
 721         <listitem><para>Sets the log level to
 722         <literal>journal-or-kmsg</literal> (or
 723         <literal>console</literal> on
 724         <constant>SIGRTMIN+27</constant>, <literal>kmsg</literal> on
 725         <constant>SIGRTMIN+28</constant>), as controlled via
 726         <varname>systemd.log_target=journal-or-kmsg</varname> (or
 727         <varname>systemd.log_target=console</varname> on
 728         <constant>SIGRTMIN+27</constant> or
 729         <varname>systemd.log_target=kmsg</varname> on
 730         <constant>SIGRTMIN+28</constant>) on the kernel command
 731         line.</para></listitem>
 732       </varlistentry>
 733     </variablelist>
 734   </refsect1>
 735
 736   <refsect1>
 737     <title>Environment</title>
 738
 739     <variablelist class='environment-variables'>
 740       <varlistentry>
 741         <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 742         <listitem><para>systemd reads the log level from this
 743         environment variable. This can be overridden with
 744         <option>--log-level=</option>.</para></listitem>
 745       </varlistentry>
 746
 747       <varlistentry>
 748         <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 749         <listitem><para>systemd reads the log target from this
 750         environment variable. This can be overridden with
 751         <option>--log-target=</option>.</para></listitem>
 752       </varlistentry>
 753
 754       <varlistentry>
 755         <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 756         <listitem><para>Controls whether systemd highlights important
 757         log messages. This can be overridden with
 758         <option>--log-color=</option>.</para></listitem>
 759       </varlistentry>
 760
 761       <varlistentry>
 762         <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 763         <listitem><para>Controls whether systemd prints the code
 764         location along with log messages. This can be overridden with
 765         <option>--log-location=</option>.</para></listitem>
 766       </varlistentry>
 767
 768       <varlistentry>
 769         <term><varname>$XDG_CONFIG_HOME</varname></term>
 770         <term><varname>$XDG_CONFIG_DIRS</varname></term>
 771         <term><varname>$XDG_DATA_HOME</varname></term>
 772         <term><varname>$XDG_DATA_DIRS</varname></term>
 773
 774         <listitem><para>The systemd user manager uses these variables
 775         in accordance to the <ulink
 776         url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 777         Base Directory specification</ulink> to find its
 778         configuration.</para></listitem>
 779       </varlistentry>
 780
 781       <varlistentry>
 782         <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 783
 784         <listitem><para>Controls where systemd looks for unit
 785         files.</para></listitem>
 786       </varlistentry>
 787
 788       <varlistentry>
 789         <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 790
 791         <listitem><para>Controls where systemd looks for SysV init
 792         scripts.</para></listitem>
 793       </varlistentry>
 794
 795       <varlistentry>
 796         <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 797
 798         <listitem><para>Controls where systemd looks for SysV init
 799         script runlevel link farms.</para></listitem>
 800       </varlistentry>
 801
 802       <varlistentry>
 803         <term><varname>$LISTEN_PID</varname></term>
 804         <term><varname>$LISTEN_FDS</varname></term>
 805
 806         <listitem><para>Set by systemd for supervised processes during
 807         socket-based activation. See
 808         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 809         for more information. </para></listitem>
 810       </varlistentry>
 811
 812       <varlistentry>
 813         <term><varname>$NOTIFY_SOCKET</varname></term>
 814
 815         <listitem><para>Set by systemd for supervised processes for
 816         status and start-up completion notification. See
 817         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 818         for more information. </para></listitem>
 819       </varlistentry>
 820     </variablelist>
 821   </refsect1>
 822
 823   <refsect1>
 824     <title>Kernel Command Line</title>
 825
 826     <para>When run as system instance systemd parses a number of
 827     kernel command line arguments<footnote><para>If run inside a Linux
 828     container these arguments may be passed as command line arguments
 829     to systemd itself, next to any of the command line options listed
 830     in the Options section above. If run outside of Linux containers,
 831     these arguments are parsed from <filename>/proc/cmdline</filename>
 832     instead.</para></footnote>:</para>
 833
 834     <variablelist class='kernel-commandline-options'>
 835       <varlistentry>
 836         <term><varname>systemd.unit=</varname></term>
 837         <term><varname>rd.systemd.unit=</varname></term>
 838
 839         <listitem><para>Overrides the unit to activate on boot.
 840         Defaults to <filename>default.target</filename>. This may be
 841         used to temporarily boot into a different boot unit, for
 842         example <filename>rescue.target</filename> or
 843         <filename>emergency.service</filename>. See
 844         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 845         for details about these units. The option prefixed with
 846         <literal>rd.</literal> is honored only in the initial RAM disk
 847         (initrd), while the one that is not prefixed only in the main
 848         system.</para></listitem>
 849       </varlistentry>
 850
 851       <varlistentry>
 852         <term><varname>systemd.dump_core=</varname></term>
 853
 854         <listitem><para>Takes a boolean argument. If
 855         <option>true</option>, systemd dumps core when it crashes.
 856         Otherwise, no core dump is created. Defaults to
 857         <option>true</option>.</para></listitem>
 858       </varlistentry>
 859
 860       <varlistentry>
 861         <term><varname>systemd.crash_shell=</varname></term>
 862
 863         <listitem><para>Takes a boolean argument. If
 864         <option>true</option>, systemd spawns a shell when it crashes.
 865         Otherwise, no shell is spawned. Defaults to
 866         <option>false</option>, for security reasons, as the shell is
 867         not protected by any password
 868         authentication.</para></listitem>
 869       </varlistentry>
 870
 871       <varlistentry>
 872         <term><varname>systemd.crash_chvt=</varname></term>
 873
 874         <listitem><para>Takes an integer argument. If positive systemd
 875         activates the specified virtual terminal when it crashes.
 876         Defaults to <constant>-1</constant>.</para></listitem>
 877       </varlistentry>
 878
 879       <varlistentry>
 880         <term><varname>systemd.confirm_spawn=</varname></term>
 881
 882         <listitem><para>Takes a boolean argument. If
 883         <option>true</option>, asks for confirmation when spawning
 884         processes. Defaults to
 885         <option>false</option>.</para></listitem>
 886       </varlistentry>
 887
 888       <varlistentry>
 889         <term><varname>systemd.show_status=</varname></term>
 890
 891         <listitem><para>Takes a boolean argument or the constant
 892         <constant>auto</constant>. If <option>true</option>, shows
 893         terse service status updates on the console during bootup.
 894         <constant>auto</constant> behaves like <option>false</option>
 895         until a service fails or there is a significant delay in boot.
 896         Defaults to <option>true</option>, unless
 897         <option>quiet</option> is passed as kernel command line option
 898         in which case it defaults to
 899         <constant>auto</constant>.</para></listitem>
 900       </varlistentry>
 901
 902       <varlistentry>
 903         <term><varname>systemd.log_target=</varname></term>
 904         <term><varname>systemd.log_level=</varname></term>
 905         <term><varname>systemd.log_color=</varname></term>
 906         <term><varname>systemd.log_location=</varname></term>
 907
 908         <listitem><para>Controls log output, with the same effect as
 909         the <varname>$SYSTEMD_LOG_TARGET</varname>,
 910         <varname>$SYSTEMD_LOG_LEVEL</varname>,
 911         <varname>$SYSTEMD_LOG_COLOR</varname>,
 912         <varname>$SYSTEMD_LOG_LOCATION</varname> environment variables
 913         described above.</para></listitem>
 914       </varlistentry>
 915
 916       <varlistentry>
 917         <term><varname>systemd.default_standard_output=</varname></term>
 918         <term><varname>systemd.default_standard_error=</varname></term>
 919         <listitem><para>Controls default standard output and error
 920         output for services, with the same effect as the
 921         <option>--default-standard-output=</option> and
 922         <option>--default-standard-error=</option> command line
 923         arguments described above, respectively.</para></listitem>
 924       </varlistentry>
 925
 926       <varlistentry>
 927         <term><varname>systemd.setenv=</varname></term>
 928
 929         <listitem><para>Takes a string argument in the form
 930         VARIABLE=VALUE. May be used to set default environment
 931         variables to add to forked child processes. May be used more
 932         than once to set multiple variables.</para></listitem>
 933       </varlistentry>
 934
 935       <varlistentry>
 936         <term><varname>quiet</varname></term>
 937
 938         <listitem><para>Turn off status output at boot, much like
 939         <varname>systemd.show_status=false</varname> would. Note that
 940         this option is also read by the kernel itself and disables
 941         kernel log output. Passing this option hence turns off the
 942         usual output from both the system manager and the kernel.
 943         </para></listitem>
 944       </varlistentry>
 945
 946       <varlistentry>
 947         <term><varname>debug</varname></term>
 948
 949         <listitem><para>Turn on debugging output. This is equivalent
 950         to <varname>systemd.log_level=debug</varname>. Note that this
 951         option is also read by the kernel itself and enables kernel
 952         debug output. Passing this option hence turns on the debug
 953         output from both the system manager and the
 954         kernel.</para></listitem>
 955       </varlistentry>
 956
 957       <varlistentry>
 958         <term><varname>emergency</varname></term>
 959         <term><varname>-b</varname></term>
 960
 961         <listitem><para>Boot into emergency mode. This is equivalent
 962         to <varname>systemd.unit=emergency.target</varname> and
 963         provided for compatibility reasons and to be easier to
 964         type.</para></listitem>
 965       </varlistentry>
 966
 967       <varlistentry>
 968         <term><varname>rescue</varname></term>
 969         <term><varname>single</varname></term>
 970         <term><varname>s</varname></term>
 971         <term><varname>S</varname></term>
 972         <term><varname>1</varname></term>
 973
 974         <listitem><para>Boot into rescue mode. This is equivalent to
 975         <varname>systemd.unit=rescue.target</varname> and provided for
 976         compatibility reasons and to be easier to
 977         type.</para></listitem>
 978       </varlistentry>
 979
 980       <varlistentry>
 981         <term><varname>2</varname></term>
 982         <term><varname>3</varname></term>
 983         <term><varname>4</varname></term>
 984         <term><varname>5</varname></term>
 985
 986         <listitem><para>Boot into the specified legacy SysV runlevel.
 987         These are equivalent to
 988         <varname>systemd.unit=runlevel2.target</varname>,
 989         <varname>systemd.unit=runlevel3.target</varname>,
 990         <varname>systemd.unit=runlevel4.target</varname>, and
 991         <varname>systemd.unit=runlevel5.target</varname>,
 992         respectively, and provided for compatibility reasons and to be
 993         easier to type.</para></listitem>
 994       </varlistentry>
 995
 996       <varlistentry>
 997         <term><varname>locale.LANG=</varname></term>
 998         <term><varname>locale.LANGUAGE=</varname></term>
 999         <term><varname>locale.LC_CTYPE=</varname></term>
1000         <term><varname>locale.LC_NUMERIC=</varname></term>
1001         <term><varname>locale.LC_TIME=</varname></term>
1002         <term><varname>locale.LC_COLLATE=</varname></term>
1003         <term><varname>locale.LC_MONETARY=</varname></term>
1004         <term><varname>locale.LC_MESSAGES=</varname></term>
1005         <term><varname>locale.LC_PAPER=</varname></term>
1006         <term><varname>locale.LC_NAME=</varname></term>
1007         <term><varname>locale.LC_ADDRESS=</varname></term>
1008         <term><varname>locale.LC_TELEPHONE=</varname></term>
1009         <term><varname>locale.LC_MEASUREMENT=</varname></term>
1010         <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1011
1012         <listitem><para>Set the system locale to use. This overrides
1013         the settings in <filename>/etc/locale.conf</filename>. For
1014         more information see
1015         <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1016         and
1017         <citerefentry project='man-pages'><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1018         </para></listitem>
1019       </varlistentry>
1020     </variablelist>
1021
1022     <para>For other kernel command line parameters understood by
1023     components of the core OS, please refer to
1024     <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1025   </refsect1>
1026
1027   <refsect1>
1028     <title>Sockets and FIFOs</title>
1029
1030     <variablelist>
1031       <varlistentry>
1032         <term><filename>/run/systemd/notify</filename></term>
1033
1034         <listitem><para>Daemon status notification socket. This is an
1035         <constant>AF_UNIX</constant> datagram socket and is used to
1036         implement the daemon notification logic as implemented by
1037         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1038
1039       </varlistentry>
1040
1041       <varlistentry>
1042         <term><filename>/run/systemd/private</filename></term>
1043
1044         <listitem><para>Used internally as communication channel
1045         between
1046         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1047         and the systemd process. This is an
1048         <constant>AF_UNIX</constant> stream socket. This interface is
1049         private to systemd and should not be used in external
1050         projects.</para></listitem>
1051       </varlistentry>
1052
1053       <varlistentry>
1054         <term><filename>/dev/initctl</filename></term>
1055
1056         <listitem><para>Limited compatibility support for the SysV
1057         client interface, as implemented by the
1058         <filename>systemd-initctl.service</filename> unit. This is a
1059         named pipe in the file system. This interface is obsolete and
1060         should not be used in new applications.</para></listitem>
1061       </varlistentry>
1062     </variablelist>
1063   </refsect1>
1064
1065   <refsect1>
1066     <title>See Also</title>
1067     <para>
1068       The <ulink url="http://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
1069       <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1070       <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1071       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1072       <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1073       <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1074       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1075       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1076       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1077       <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1078       <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1079       <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1080       <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1081       <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1082     </para>
1083   </refsect1>
1084
1085 </refentry>