man/systemd.xml

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   8   Copyright 2010 Lennart Poettering
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  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>Enable core dumping on crash. This switch has
 135         no effect when running as user instance. This setting may also
 136         be enabled during boot on the kernel command line via the
 137         <varname>systemd.dump_core=</varname> option, see
 138         below.</para></listitem>
 139       </varlistentry>
 140
 141       <varlistentry>
 142         <term><option>--crash-vt=</option><replaceable>VT</replaceable></term>
 143
 144         <listitem><para>Switch to a specific virtual console (VT) on
 145         crash. Takes a positive integer in the range 1–63, or a
 146         boolean argument. If an integer is passed, selects which VT to
 147         switch to. If <constant>yes</constant>, the VT kernel messages
 148         are written to is selected. If <constant>no</constant>, no VT
 149         switch is attempted. This switch has no effect when running as
 150         user instance. This setting may also be enabled during boot,
 151         on the kernel command line via the
 152         <varname>systemd.crash_vt=</varname> option, see
 153         below.</para></listitem>
 154       </varlistentry>
 155
 156       <varlistentry>
 157         <term><option>--crash-shell</option></term>
 158
 159         <listitem><para>Run a shell on crash. This switch has no
 160         effect when running as user instance. This setting may also be
 161         enabled during boot, on the kernel command line via the
 162         <varname>systemd.crash_shell=</varname> option, see
 163         below.</para></listitem>
 164       </varlistentry>
 165
 166       <varlistentry>
 167         <term><option>--crash-reboot</option></term>
 168
 169         <listitem><para>Automatically reboot the system on crash. This
 170         switch has no effect when running as user instance. This
 171         setting may also be enabled during boot, on the kernel command
 172         line via the <varname>systemd.crash_reboot=</varname> option,
 173         see below.</para></listitem>
 174       </varlistentry>
 175
 176       <varlistentry>
 177         <term><option>--confirm-spawn</option></term>
 178
 179         <listitem><para>Ask for confirmation when spawning processes.
 180         This switch has no effect when run as user
 181         instance.</para></listitem>
 182       </varlistentry>
 183       <varlistentry>
 184         <term><option>--show-status=</option></term>
 185
 186         <listitem><para>Show terse service status information while
 187         booting. This switch has no effect when run as user instance.
 188         Takes a boolean argument which may be omitted which is
 189         interpreted as <option>true</option>.</para></listitem>
 190       </varlistentry>
 191       <varlistentry>
 192         <term><option>--log-target=</option></term>
 193
 194         <listitem><para>Set log target. Argument must be one of
 195         <option>console</option>,
 196         <option>journal</option>,
 197         <option>kmsg</option>,
 198         <option>journal-or-kmsg</option>,
 199         <option>null</option>.</para></listitem>
 200       </varlistentry>
 201       <varlistentry>
 202         <term><option>--log-level=</option></term>
 203
 204         <listitem><para>Set log level. As
 205         argument this accepts a numerical log
 206         level or the well-known <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 207         symbolic names (lowercase):
 208         <option>emerg</option>,
 209         <option>alert</option>,
 210         <option>crit</option>,
 211         <option>err</option>,
 212         <option>warning</option>,
 213         <option>notice</option>,
 214         <option>info</option>,
 215         <option>debug</option>.</para></listitem>
 216       </varlistentry>
 217       <varlistentry>
 218         <term><option>--log-color=</option></term>
 219
 220         <listitem><para>Highlight important log messages. Argument is
 221         a boolean value. If the argument is omitted, it defaults to
 222         <option>true</option>.</para></listitem>
 223       </varlistentry>
 224       <varlistentry>
 225         <term><option>--log-location=</option></term>
 226
 227         <listitem><para>Include code location in log messages. This is
 228         mostly relevant for debugging purposes. Argument is a boolean
 229         value. If the argument is omitted it defaults to
 230         <option>true</option>.</para></listitem>
 231       </varlistentry>
 232       <varlistentry>
 233         <term><option>--default-standard-output=</option></term>
 234         <term><option>--default-standard-error=</option></term>
 235
 236         <listitem><para>Sets the default output or error output for
 237         all services and sockets, respectively. That is, controls the
 238         default for <option>StandardOutput=</option> and
 239         <option>StandardError=</option> (see
 240         <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 241         for details). Takes one of
 242         <option>inherit</option>,
 243         <option>null</option>,
 244         <option>tty</option>,
 245         <option>journal</option>,
 246         <option>journal+console</option>,
 247         <option>syslog</option>,
 248         <option>syslog+console</option>,
 249         <option>kmsg</option>,
 250         <option>kmsg+console</option>.  If the
 251         argument is omitted
 252         <option>--default-standard-output=</option> defaults to
 253         <option>journal</option> and
 254         <option>--default-standard-error=</option> to
 255         <option>inherit</option>.</para></listitem>
 256       </varlistentry>
 257
 258       <xi:include href="standard-options.xml" xpointer="help" />
 259       <xi:include href="standard-options.xml" xpointer="version" />
 260     </variablelist>
 261   </refsect1>
 262
 263   <refsect1>
 264     <title>Concepts</title>
 265
 266     <para>systemd provides a dependency system between various
 267     entities called "units" of 12 different types. Units encapsulate
 268     various objects that are relevant for system boot-up and
 269     maintenance. The majority of units are configured in unit
 270     configuration files, whose syntax and basic set of options is
 271     described in
 272     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 273     however some are created automatically from other configuration,
 274     dynamically from system state or programmatically at runtime.
 275     Units may be "active" (meaning started, bound, plugged in, ...,
 276     depending on the unit type, see below), or "inactive" (meaning
 277     stopped, unbound, unplugged, ...), as well as in the process of
 278     being activated or deactivated, i.e. between the two states (these
 279     states are called "activating", "deactivating"). A special
 280     "failed" state is available as well, which is very similar to
 281     "inactive" and is entered when the service failed in some way
 282     (process returned error code on exit, or crashed, or an operation
 283     timed out). If this state is entered, the cause will be logged,
 284     for later reference. Note that the various unit types may have a
 285     number of additional substates, which are mapped to the five
 286     generalized unit states described here.</para>
 287
 288     <para>The following unit types are available:</para>
 289
 290     <orderedlist>
 291       <listitem><para>Service units, which start and control daemons
 292       and the processes they consist of. For details, see
 293       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 294
 295       <listitem><para>Socket units, which encapsulate local IPC or
 296       network sockets in the system, useful for socket-based
 297       activation. For details about socket units, see
 298       <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 299       for details on socket-based activation and other forms of
 300       activation, see
 301       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 302
 303       <listitem><para>Target units are useful to group units, or
 304       provide well-known synchronization points during boot-up, see
 305       <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 306
 307       <listitem><para>Device units expose kernel devices in systemd
 308       and may be used to implement device-based activation. For
 309       details, see
 310       <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 311
 312       <listitem><para>Mount units control mount points in the file
 313       system, for details see
 314       <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 315
 316       <listitem><para>Automount units provide automount capabilities,
 317       for on-demand mounting of file systems as well as parallelized
 318       boot-up. See
 319       <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 320
 321       <listitem><para>Timer units are useful for triggering activation
 322       of other units based on timers. You may find details in
 323       <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 324
 325       <listitem><para>Swap units are very similar to mount units and
 326       encapsulate memory swap partitions or files of the operating
 327       system. They are described in
 328       <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 329
 330       <listitem><para>Path units may be used to activate other
 331       services when file system objects change or are modified. See
 332       <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 333
 334       <listitem><para>Slice units may be used to group units which
 335       manage system processes (such as service and scope units) in a
 336       hierarchical tree for resource management purposes. See
 337       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 338
 339       <listitem><para>Scope units are similar to service units, but
 340       manage foreign processes instead of starting them as well. See
 341       <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 342
 343     </orderedlist>
 344
 345     <para>Units are named as their configuration files. Some units
 346     have special semantics. A detailed list is available in
 347     <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 348
 349     <para>systemd knows various kinds of dependencies, including
 350     positive and negative requirement dependencies (i.e.
 351     <varname>Requires=</varname> and <varname>Conflicts=</varname>) as
 352     well as ordering dependencies (<varname>After=</varname> and
 353     <varname>Before=</varname>). NB: ordering and requirement
 354     dependencies are orthogonal. If only a requirement dependency
 355     exists between two units (e.g. <filename>foo.service</filename>
 356     requires <filename>bar.service</filename>), but no ordering
 357     dependency (e.g. <filename>foo.service</filename> after
 358     <filename>bar.service</filename>) and both are requested to start,
 359     they will be started in parallel. It is a common pattern that both
 360     requirement and ordering dependencies are placed between two
 361     units. Also note that the majority of dependencies are implicitly
 362     created and maintained by systemd. In most cases, it should be
 363     unnecessary to declare additional dependencies manually, however
 364     it is possible to do this.</para>
 365
 366     <para>Application programs and units (via dependencies) may
 367     request state changes of units. In systemd, these requests are
 368     encapsulated as 'jobs' and maintained in a job queue. Jobs may
 369     succeed or can fail, their execution is ordered based on the
 370     ordering dependencies of the units they have been scheduled
 371     for.</para>
 372
 373     <para>On boot systemd activates the target unit
 374     <filename>default.target</filename> whose job is to activate
 375     on-boot services and other on-boot units by pulling them in via
 376     dependencies. Usually, the unit name is just an alias (symlink) for
 377     either <filename>graphical.target</filename> (for fully-featured
 378     boots into the UI) or <filename>multi-user.target</filename> (for
 379     limited console-only boots for use in embedded or server
 380     environments, or similar; a subset of graphical.target). However,
 381     it is at the discretion of the administrator to configure it as an
 382     alias to any other target unit. See
 383     <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 384     for details about these target units.</para>
 385
 386     <para>Processes systemd spawns are placed in individual Linux
 387     control groups named after the unit which they belong to in the
 388     private systemd hierarchy. (see <ulink
 389     url="https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 390     for more information about control groups, or short "cgroups").
 391     systemd uses this to effectively keep track of processes. Control
 392     group information is maintained in the kernel, and is accessible
 393     via the file system hierarchy (beneath
 394     <filename>/sys/fs/cgroup/systemd/</filename>), or in tools such as
 395     <citerefentry project='man-pages'><refentrytitle>systemd-cgls</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 396     or
 397     <citerefentry project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 398     (<command>ps xawf -eo pid,user,cgroup,args</command> is
 399     particularly useful to list all processes and the systemd units
 400     they belong to.).</para>
 401
 402     <para>systemd is compatible with the SysV init system to a large
 403     degree: SysV init scripts are supported and simply read as an
 404     alternative (though limited) configuration file format. The SysV
 405     <filename>/dev/initctl</filename> interface is provided, and
 406     compatibility implementations of the various SysV client tools are
 407     available. In addition to that, various established Unix
 408     functionality such as <filename>/etc/fstab</filename> or the
 409     <filename>utmp</filename> database are supported.</para>
 410
 411     <para>systemd has a minimal transaction system: if a unit is
 412     requested to start up or shut down it will add it and all its
 413     dependencies to a temporary transaction. Then, it will verify if
 414     the transaction is consistent (i.e. whether the ordering of all
 415     units is cycle-free). If it is not, systemd will try to fix it up,
 416     and removes non-essential jobs from the transaction that might
 417     remove the loop. Also, systemd tries to suppress non-essential
 418     jobs in the transaction that would stop a running service. Finally
 419     it is checked whether the jobs of the transaction contradict jobs
 420     that have already been queued, and optionally the transaction is
 421     aborted then. If all worked out and the transaction is consistent
 422     and minimized in its impact it is merged with all already
 423     outstanding jobs and added to the run queue. Effectively this
 424     means that before executing a requested operation, systemd will
 425     verify that it makes sense, fixing it if possible, and only
 426     failing if it really cannot work.</para>
 427
 428     <para>Systemd contains native implementations of various tasks
 429     that need to be executed as part of the boot process. For example,
 430     it sets the hostname or configures the loopback network device. It
 431     also sets up and mounts various API file systems, such as
 432     <filename>/sys</filename> or <filename>/proc</filename>.</para>
 433
 434     <para>For more information about the concepts and
 435     ideas behind systemd, please refer to the
 436     <ulink url="http://0pointer.de/blog/projects/systemd.html">Original Design Document</ulink>.</para>
 437
 438     <para>Note that some but not all interfaces provided
 439     by systemd are covered by the
 440     <ulink url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 441     Stability Promise</ulink>.</para>
 442
 443     <para>Units may be generated dynamically at boot and system
 444     manager reload time, for example based on other configuration
 445     files or parameters passed on the kernel command line. For details, see
 446     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 447
 448     <para>Systems which invoke systemd in a container or initrd
 449     environment should implement the
 450     <ulink url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container Interface</ulink> or
 451     <ulink url="http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd Interface</ulink>
 452     specifications, respectively.</para>
 453   </refsect1>
 454
 455   <refsect1>
 456     <title>Directories</title>
 457
 458     <variablelist>
 459       <varlistentry>
 460         <term>System unit directories</term>
 461
 462         <listitem><para>The systemd system manager reads unit
 463         configuration from various directories. Packages that want to
 464         install unit files shall place them in the directory returned
 465         by <command>pkg-config systemd
 466         --variable=systemdsystemunitdir</command>. Other directories
 467         checked are <filename>/usr/local/lib/systemd/system</filename>
 468         and <filename>/usr/lib/systemd/system</filename>. User
 469         configuration always takes precedence. <command>pkg-config
 470         systemd --variable=systemdsystemconfdir</command> returns the
 471         path of the system configuration directory. Packages should
 472         alter the content of these directories only with the
 473         <command>enable</command> and <command>disable</command>
 474         commands of the
 475         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 476         tool. Full list of directories is provided in
 477         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 478         </para></listitem>
 479       </varlistentry>
 480     </variablelist>
 481
 482     <variablelist>
 483       <varlistentry>
 484         <term>User unit directories</term>
 485
 486         <listitem><para>Similar rules apply for the user unit
 487         directories. However, here the
 488         <ulink url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 489         Base Directory specification</ulink> is followed to find
 490         units. Applications should place their unit files in the
 491         directory returned by <command>pkg-config systemd
 492         --variable=systemduserunitdir</command>. Global configuration
 493         is done in the directory reported by <command>pkg-config
 494         systemd --variable=systemduserconfdir</command>. The
 495         <command>enable</command> and <command>disable</command>
 496         commands of the
 497         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 498         tool can handle both global (i.e. for all users) and private
 499         (for one user) enabling/disabling of units. Full list of
 500         directories is provided in
 501         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 502         </para></listitem>
 503       </varlistentry>
 504     </variablelist>
 505
 506     <variablelist>
 507       <varlistentry>
 508         <term>SysV init scripts directory</term>
 509
 510         <listitem><para>The location of the SysV init script directory
 511         varies between distributions. If systemd cannot find a native
 512         unit file for a requested service, it will look for a SysV
 513         init script of the same name (with the
 514         <filename>.service</filename> suffix
 515         removed).</para></listitem>
 516       </varlistentry>
 517     </variablelist>
 518
 519     <variablelist>
 520       <varlistentry>
 521         <term>SysV runlevel link farm directory</term>
 522
 523         <listitem><para>The location of the SysV runlevel link farm
 524         directory varies between distributions. systemd will take the
 525         link farm into account when figuring out whether a service
 526         shall be enabled. Note that a service unit with a native unit
 527         configuration file cannot be started by activating it in the
 528         SysV runlevel link farm.</para></listitem>
 529       </varlistentry>
 530     </variablelist>
 531   </refsect1>
 532
 533   <refsect1>
 534     <title>Signals</title>
 535
 536     <variablelist>
 537       <varlistentry>
 538         <term><constant>SIGTERM</constant></term>
 539
 540         <listitem><para>Upon receiving this signal the systemd system
 541         manager serializes its state, reexecutes itself and
 542         deserializes the saved state again. This is mostly equivalent
 543         to <command>systemctl daemon-reexec</command>.</para>
 544
 545         <para>systemd user managers will start the
 546         <filename>exit.target</filename> unit when this signal is
 547         received. This is mostly equivalent to <command>systemctl
 548         --user start exit.target</command>.</para></listitem>
 549       </varlistentry>
 550
 551       <varlistentry>
 552         <term><constant>SIGINT</constant></term>
 553
 554         <listitem><para>Upon receiving this signal the systemd system
 555         manager will start the
 556         <filename>ctrl-alt-del.target</filename> unit. This is mostly
 557         equivalent to <command>systemctl start
 558         ctl-alt-del.target</command>. If this signal is received more
 559         than 7 times per 2s, an immediate reboot is triggered.
 560         Note that pressing Ctrl-Alt-Del on the console will trigger
 561         this signal. Hence, if a reboot is hanging, pressing
 562         Ctrl-Alt-Del more than 7 times in 2s is a relatively safe way
 563         to trigger an immediate reboot.</para>
 564
 565         <para>systemd user managers treat this signal the same way as
 566         <constant>SIGTERM</constant>.</para></listitem>
 567       </varlistentry>
 568
 569       <varlistentry>
 570         <term><constant>SIGWINCH</constant></term>
 571
 572         <listitem><para>When this signal is received the systemd
 573         system manager will start the
 574         <filename>kbrequest.target</filename> unit. This is mostly
 575         equivalent to <command>systemctl start
 576         kbrequest.target</command>.</para>
 577
 578         <para>This signal is ignored by systemd user
 579         managers.</para></listitem>
 580       </varlistentry>
 581
 582       <varlistentry>
 583         <term><constant>SIGPWR</constant></term>
 584
 585         <listitem><para>When this signal is received the systemd
 586         manager will start the <filename>sigpwr.target</filename>
 587         unit. This is mostly equivalent to <command>systemctl start
 588         sigpwr.target</command>.</para></listitem>
 589       </varlistentry>
 590
 591       <varlistentry>
 592         <term><constant>SIGUSR1</constant></term>
 593
 594         <listitem><para>When this signal is received the systemd
 595         manager will try to reconnect to the D-Bus
 596         bus.</para></listitem>
 597       </varlistentry>
 598
 599       <varlistentry>
 600         <term><constant>SIGUSR2</constant></term>
 601
 602         <listitem><para>When this signal is received the systemd
 603         manager will log its complete state in human-readable form.
 604         The data logged is the same as printed by
 605         <command>systemd-analyze dump</command>.</para></listitem>
 606       </varlistentry>
 607
 608       <varlistentry>
 609         <term><constant>SIGHUP</constant></term>
 610
 611         <listitem><para>Reloads the complete daemon configuration.
 612         This is mostly equivalent to <command>systemctl
 613         daemon-reload</command>.</para></listitem>
 614       </varlistentry>
 615
 616       <varlistentry>
 617         <term><constant>SIGRTMIN+0</constant></term>
 618
 619         <listitem><para>Enters default mode, starts the
 620         <filename>default.target</filename> unit. This is mostly
 621         equivalent to <command>systemctl start
 622         default.target</command>.</para></listitem>
 623       </varlistentry>
 624
 625       <varlistentry>
 626         <term><constant>SIGRTMIN+1</constant></term>
 627
 628         <listitem><para>Enters rescue mode, starts the
 629         <filename>rescue.target</filename> unit. This is mostly
 630         equivalent to <command>systemctl isolate
 631         rescue.target</command>.</para></listitem>
 632       </varlistentry>
 633
 634       <varlistentry>
 635         <term><constant>SIGRTMIN+2</constant></term>
 636
 637         <listitem><para>Enters emergency mode, starts the
 638         <filename>emergency.service</filename> unit. This is mostly
 639         equivalent to <command>systemctl isolate
 640         emergency.service</command>.</para></listitem>
 641       </varlistentry>
 642
 643       <varlistentry>
 644         <term><constant>SIGRTMIN+3</constant></term>
 645
 646         <listitem><para>Halts the machine, starts the
 647         <filename>halt.target</filename> unit. This is mostly
 648         equivalent to <command>systemctl start
 649         halt.target</command>.</para></listitem>
 650       </varlistentry>
 651
 652       <varlistentry>
 653         <term><constant>SIGRTMIN+4</constant></term>
 654
 655         <listitem><para>Powers off the machine, starts the
 656         <filename>poweroff.target</filename> unit. This is mostly
 657         equivalent to <command>systemctl start
 658         poweroff.target</command>.</para></listitem>
 659       </varlistentry>
 660
 661       <varlistentry>
 662         <term><constant>SIGRTMIN+5</constant></term>
 663
 664         <listitem><para>Reboots the machine, starts the
 665         <filename>reboot.target</filename> unit. This is mostly
 666         equivalent to <command>systemctl start
 667         reboot.target</command>.</para></listitem>
 668       </varlistentry>
 669
 670       <varlistentry>
 671         <term><constant>SIGRTMIN+6</constant></term>
 672
 673         <listitem><para>Reboots the machine via kexec, starts the
 674         <filename>kexec.target</filename> unit. This is mostly
 675         equivalent to <command>systemctl start
 676         kexec.target</command>.</para></listitem>
 677       </varlistentry>
 678
 679       <varlistentry>
 680         <term><constant>SIGRTMIN+13</constant></term>
 681
 682         <listitem><para>Immediately halts the machine.</para></listitem>
 683       </varlistentry>
 684
 685       <varlistentry>
 686         <term><constant>SIGRTMIN+14</constant></term>
 687
 688         <listitem><para>Immediately powers off the machine.</para></listitem>
 689       </varlistentry>
 690
 691       <varlistentry>
 692         <term><constant>SIGRTMIN+15</constant></term>
 693
 694         <listitem><para>Immediately reboots the machine.</para></listitem>
 695       </varlistentry>
 696
 697       <varlistentry>
 698         <term><constant>SIGRTMIN+16</constant></term>
 699
 700         <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
 701       </varlistentry>
 702
 703       <varlistentry>
 704         <term><constant>SIGRTMIN+20</constant></term>
 705
 706         <listitem><para>Enables display of status messages on the
 707         console, as controlled via
 708         <varname>systemd.show_status=1</varname> on the kernel command
 709         line.</para></listitem>
 710       </varlistentry>
 711
 712       <varlistentry>
 713         <term><constant>SIGRTMIN+21</constant></term>
 714
 715         <listitem><para>Disables display of
 716         status messages on the console, as
 717         controlled via
 718         <varname>systemd.show_status=0</varname>
 719         on the kernel command
 720         line.</para></listitem>
 721       </varlistentry>
 722
 723       <varlistentry>
 724         <term><constant>SIGRTMIN+22</constant></term>
 725         <term><constant>SIGRTMIN+23</constant></term>
 726
 727         <listitem><para>Sets the log level to <literal>debug</literal>
 728         (or <literal>info</literal> on
 729         <constant>SIGRTMIN+23</constant>), as controlled via
 730         <varname>systemd.log_level=debug</varname> (or
 731         <varname>systemd.log_level=info</varname> on
 732         <constant>SIGRTMIN+23</constant>) on the kernel command
 733         line.</para></listitem>
 734       </varlistentry>
 735
 736       <varlistentry>
 737         <term><constant>SIGRTMIN+24</constant></term>
 738
 739         <listitem><para>Immediately exits the manager (only available
 740         for --user instances).</para></listitem>
 741       </varlistentry>
 742
 743       <varlistentry>
 744         <term><constant>SIGRTMIN+26</constant></term>
 745         <term><constant>SIGRTMIN+27</constant></term>
 746         <term><constant>SIGRTMIN+28</constant></term>
 747
 748         <listitem><para>Sets the log level to
 749         <literal>journal-or-kmsg</literal> (or
 750         <literal>console</literal> on
 751         <constant>SIGRTMIN+27</constant>, <literal>kmsg</literal> on
 752         <constant>SIGRTMIN+28</constant>), as controlled via
 753         <varname>systemd.log_target=journal-or-kmsg</varname> (or
 754         <varname>systemd.log_target=console</varname> on
 755         <constant>SIGRTMIN+27</constant> or
 756         <varname>systemd.log_target=kmsg</varname> on
 757         <constant>SIGRTMIN+28</constant>) on the kernel command
 758         line.</para></listitem>
 759       </varlistentry>
 760     </variablelist>
 761   </refsect1>
 762
 763   <refsect1>
 764     <title>Environment</title>
 765
 766     <variablelist class='environment-variables'>
 767       <varlistentry>
 768         <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 769         <listitem><para>systemd reads the log level from this
 770         environment variable. This can be overridden with
 771         <option>--log-level=</option>.</para></listitem>
 772       </varlistentry>
 773
 774       <varlistentry>
 775         <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 776         <listitem><para>systemd reads the log target from this
 777         environment variable. This can be overridden with
 778         <option>--log-target=</option>.</para></listitem>
 779       </varlistentry>
 780
 781       <varlistentry>
 782         <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 783         <listitem><para>Controls whether systemd highlights important
 784         log messages. This can be overridden with
 785         <option>--log-color=</option>.</para></listitem>
 786       </varlistentry>
 787
 788       <varlistentry>
 789         <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 790         <listitem><para>Controls whether systemd prints the code
 791         location along with log messages. This can be overridden with
 792         <option>--log-location=</option>.</para></listitem>
 793       </varlistentry>
 794
 795       <varlistentry>
 796         <term><varname>$XDG_CONFIG_HOME</varname></term>
 797         <term><varname>$XDG_CONFIG_DIRS</varname></term>
 798         <term><varname>$XDG_DATA_HOME</varname></term>
 799         <term><varname>$XDG_DATA_DIRS</varname></term>
 800
 801         <listitem><para>The systemd user manager uses these variables
 802         in accordance to the <ulink
 803         url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 804         Base Directory specification</ulink> to find its
 805         configuration.</para></listitem>
 806       </varlistentry>
 807
 808       <varlistentry>
 809         <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 810
 811         <listitem><para>Controls where systemd looks for unit
 812         files.</para></listitem>
 813       </varlistentry>
 814
 815       <varlistentry>
 816         <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 817
 818         <listitem><para>Controls where systemd looks for SysV init
 819         scripts.</para></listitem>
 820       </varlistentry>
 821
 822       <varlistentry>
 823         <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 824
 825         <listitem><para>Controls where systemd looks for SysV init
 826         script runlevel link farms.</para></listitem>
 827       </varlistentry>
 828
 829       <varlistentry>
 830         <term><varname>$LISTEN_PID</varname></term>
 831         <term><varname>$LISTEN_FDS</varname></term>
 832         <term><varname>$LISTEN_FDNAMES</varname></term>
 833
 834         <listitem><para>Set by systemd for supervised processes during
 835         socket-based activation. See
 836         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 837         for more information. </para></listitem>
 838       </varlistentry>
 839
 840       <varlistentry>
 841         <term><varname>$NOTIFY_SOCKET</varname></term>
 842
 843         <listitem><para>Set by systemd for supervised processes for
 844         status and start-up completion notification. See
 845         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 846         for more information. </para></listitem>
 847       </varlistentry>
 848     </variablelist>
 849   </refsect1>
 850
 851   <refsect1>
 852     <title>Kernel Command Line</title>
 853
 854     <para>When run as system instance systemd parses a number of
 855     kernel command line arguments<footnote><para>If run inside a Linux
 856     container these arguments may be passed as command line arguments
 857     to systemd itself, next to any of the command line options listed
 858     in the Options section above. If run outside of Linux containers,
 859     these arguments are parsed from <filename>/proc/cmdline</filename>
 860     instead.</para></footnote>:</para>
 861
 862     <variablelist class='kernel-commandline-options'>
 863       <varlistentry>
 864         <term><varname>systemd.unit=</varname></term>
 865         <term><varname>rd.systemd.unit=</varname></term>
 866
 867         <listitem><para>Overrides the unit to activate on boot.
 868         Defaults to <filename>default.target</filename>. This may be
 869         used to temporarily boot into a different boot unit, for
 870         example <filename>rescue.target</filename> or
 871         <filename>emergency.service</filename>. See
 872         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 873         for details about these units. The option prefixed with
 874         <literal>rd.</literal> is honored only in the initial RAM disk
 875         (initrd), while the one that is not prefixed only in the main
 876         system.</para></listitem>
 877       </varlistentry>
 878
 879       <varlistentry>
 880         <term><varname>systemd.dump_core=</varname></term>
 881
 882         <listitem><para>Takes a boolean argument. If
 883         <option>yes</option>, the systemd manager (PID 1) dumps core
 884         when it crashes.  Otherwise, no core dump is created. Defaults
 885         to <option>yes</option>.</para></listitem>
 886       </varlistentry>
 887
 888       <varlistentry>
 889         <term><varname>systemd.crash_chvt=</varname></term>
 890
 891         <listitem><para>Takes a positive integer, or a boolean
 892         argument. If a positive integer (in the range 1–63) is
 893         specified, the system manager (PID 1) will activate the specified
 894         virtual terminal (VT) when it crashes. Defaults to
 895         <constant>no</constant>, meaning that no such switch is
 896         attempted. If set to <constant>yes</constant>, the VT the
 897         kernel messages are written to is selected.</para></listitem>
 898       </varlistentry>
 899
 900       <varlistentry>
 901         <term><varname>systemd.crash_shell=</varname></term>
 902
 903         <listitem><para>Takes a boolean argument. If
 904         <option>yes</option>, the system manager (PID 1) spawns a
 905         shell when it crashes, after a 10s delay. Otherwise, no shell
 906         is spawned. Defaults to <option>no</option>, for security
 907         reasons, as the shell is not protected by password
 908         authentication.</para></listitem>
 909       </varlistentry>
 910
 911       <varlistentry>
 912         <term><varname>systemd.crash_reboot=</varname></term>
 913
 914         <listitem><para>Takes a boolean argument. If
 915         <option>yes</option>, the system manager (PID 1) will reboot
 916         the machine automatically when it crashes, after a 10s delay.
 917         Otherwise, the system will hang indefinitely. Defaults to
 918         <option>no</option>, in order to avoid a reboot loop. If
 919         combined with <varname>systemd.crash_shell=</varname>, the
 920         system is rebooted after the shell exits.</para></listitem>
 921       </varlistentry>
 922
 923       <varlistentry>
 924         <term><varname>systemd.confirm_spawn=</varname></term>
 925
 926         <listitem><para>Takes a boolean argument. If
 927         <option>yes</option>, the system manager (PID 1) asks for
 928         confirmation when spawning processes. Defaults to
 929         <option>no</option>.</para></listitem>
 930       </varlistentry>
 931
 932       <varlistentry>
 933         <term><varname>systemd.show_status=</varname></term>
 934
 935         <listitem><para>Takes a boolean argument or the constant
 936         <constant>auto</constant>. If <option>yes</option>, the
 937         systemd manager (PID 1) shows terse service status updates on
 938         the console during bootup.  <constant>auto</constant> behaves
 939         like <option>false</option> until a service fails or there is
 940         a significant delay in boot.  Defaults to
 941         <option>yes</option>, unless <option>quiet</option> is passed
 942         as kernel command line option, in which case it defaults to
 943         <constant>auto</constant>.</para></listitem>
 944       </varlistentry>
 945
 946       <varlistentry>
 947         <term><varname>systemd.log_target=</varname></term>
 948         <term><varname>systemd.log_level=</varname></term>
 949         <term><varname>systemd.log_color=</varname></term>
 950         <term><varname>systemd.log_location=</varname></term>
 951
 952         <listitem><para>Controls log output, with the same effect as
 953         the <varname>$SYSTEMD_LOG_TARGET</varname>,
 954         <varname>$SYSTEMD_LOG_LEVEL</varname>,
 955         <varname>$SYSTEMD_LOG_COLOR</varname>,
 956         <varname>$SYSTEMD_LOG_LOCATION</varname> environment variables
 957         described above.</para></listitem>
 958       </varlistentry>
 959
 960       <varlistentry>
 961         <term><varname>systemd.default_standard_output=</varname></term>
 962         <term><varname>systemd.default_standard_error=</varname></term>
 963         <listitem><para>Controls default standard output and error
 964         output for services, with the same effect as the
 965         <option>--default-standard-output=</option> and
 966         <option>--default-standard-error=</option> command line
 967         arguments described above, respectively.</para></listitem>
 968       </varlistentry>
 969
 970       <varlistentry>
 971         <term><varname>systemd.setenv=</varname></term>
 972
 973         <listitem><para>Takes a string argument in the form
 974         VARIABLE=VALUE. May be used to set default environment
 975         variables to add to forked child processes. May be used more
 976         than once to set multiple variables.</para></listitem>
 977       </varlistentry>
 978
 979       <varlistentry>
 980         <term><varname>quiet</varname></term>
 981
 982         <listitem><para>Turn off status output at boot, much like
 983         <varname>systemd.show_status=false</varname> would. Note that
 984         this option is also read by the kernel itself and disables
 985         kernel log output. Passing this option hence turns off the
 986         usual output from both the system manager and the kernel.
 987         </para></listitem>
 988       </varlistentry>
 989
 990       <varlistentry>
 991         <term><varname>debug</varname></term>
 992
 993         <listitem><para>Turn on debugging output. This is equivalent
 994         to <varname>systemd.log_level=debug</varname>. Note that this
 995         option is also read by the kernel itself and enables kernel
 996         debug output. Passing this option hence turns on the debug
 997         output from both the system manager and the
 998         kernel.</para></listitem>
 999       </varlistentry>
1000
1001       <varlistentry>
1002         <term><varname>emergency</varname></term>
1003         <term><varname>-b</varname></term>
1004
1005         <listitem><para>Boot into emergency mode. This is equivalent
1006         to <varname>systemd.unit=emergency.target</varname> and
1007         provided for compatibility reasons and to be easier to
1008         type.</para></listitem>
1009       </varlistentry>
1010
1011       <varlistentry>
1012         <term><varname>rescue</varname></term>
1013         <term><varname>single</varname></term>
1014         <term><varname>s</varname></term>
1015         <term><varname>S</varname></term>
1016         <term><varname>1</varname></term>
1017
1018         <listitem><para>Boot into rescue mode. This is equivalent to
1019         <varname>systemd.unit=rescue.target</varname> and provided for
1020         compatibility reasons and to be easier to
1021         type.</para></listitem>
1022       </varlistentry>
1023
1024       <varlistentry>
1025         <term><varname>2</varname></term>
1026         <term><varname>3</varname></term>
1027         <term><varname>4</varname></term>
1028         <term><varname>5</varname></term>
1029
1030         <listitem><para>Boot into the specified legacy SysV runlevel.
1031         These are equivalent to
1032         <varname>systemd.unit=runlevel2.target</varname>,
1033         <varname>systemd.unit=runlevel3.target</varname>,
1034         <varname>systemd.unit=runlevel4.target</varname>, and
1035         <varname>systemd.unit=runlevel5.target</varname>,
1036         respectively, and provided for compatibility reasons and to be
1037         easier to type.</para></listitem>
1038       </varlistentry>
1039
1040       <varlistentry>
1041         <term><varname>locale.LANG=</varname></term>
1042         <term><varname>locale.LANGUAGE=</varname></term>
1043         <term><varname>locale.LC_CTYPE=</varname></term>
1044         <term><varname>locale.LC_NUMERIC=</varname></term>
1045         <term><varname>locale.LC_TIME=</varname></term>
1046         <term><varname>locale.LC_COLLATE=</varname></term>
1047         <term><varname>locale.LC_MONETARY=</varname></term>
1048         <term><varname>locale.LC_MESSAGES=</varname></term>
1049         <term><varname>locale.LC_PAPER=</varname></term>
1050         <term><varname>locale.LC_NAME=</varname></term>
1051         <term><varname>locale.LC_ADDRESS=</varname></term>
1052         <term><varname>locale.LC_TELEPHONE=</varname></term>
1053         <term><varname>locale.LC_MEASUREMENT=</varname></term>
1054         <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1055
1056         <listitem><para>Set the system locale to use. This overrides
1057         the settings in <filename>/etc/locale.conf</filename>. For
1058         more information, see
1059         <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1060         and
1061         <citerefentry project='man-pages'><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1062         </para></listitem>
1063       </varlistentry>
1064     </variablelist>
1065
1066     <para>For other kernel command line parameters understood by
1067     components of the core OS, please refer to
1068     <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1069   </refsect1>
1070
1071   <refsect1>
1072     <title>Sockets and FIFOs</title>
1073
1074     <variablelist>
1075       <varlistentry>
1076         <term><filename>/run/systemd/notify</filename></term>
1077
1078         <listitem><para>Daemon status notification socket. This is an
1079         <constant>AF_UNIX</constant> datagram socket and is used to
1080         implement the daemon notification logic as implemented by
1081         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1082
1083       </varlistentry>
1084
1085       <varlistentry>
1086         <term><filename>/run/systemd/private</filename></term>
1087
1088         <listitem><para>Used internally as communication channel
1089         between
1090         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1091         and the systemd process. This is an
1092         <constant>AF_UNIX</constant> stream socket. This interface is
1093         private to systemd and should not be used in external
1094         projects.</para></listitem>
1095       </varlistentry>
1096
1097       <varlistentry>
1098         <term><filename>/dev/initctl</filename></term>
1099
1100         <listitem><para>Limited compatibility support for the SysV
1101         client interface, as implemented by the
1102         <filename>systemd-initctl.service</filename> unit. This is a
1103         named pipe in the file system. This interface is obsolete and
1104         should not be used in new applications.</para></listitem>
1105       </varlistentry>
1106     </variablelist>
1107   </refsect1>
1108
1109   <refsect1>
1110     <title>See Also</title>
1111     <para>
1112       The <ulink url="http://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
1113       <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1114       <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1115       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1116       <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1117       <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1118       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1119       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1120       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1121       <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1122       <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1123       <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1124       <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1125       <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1126     </para>
1127   </refsect1>
1128
1129 </refentry>