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>Snapshot units can be used to temporarily save
 322       the state of the set of systemd units, which later may be
 323       restored by activating the saved snapshot unit. For more
 324       information see
 325       <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 326
 327       <listitem><para>Timer units are useful for triggering activation
 328       of other units based on timers. You may find details in
 329       <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 330
 331       <listitem><para>Swap units are very similar to mount units and
 332       encapsulate memory swap partitions or files of the operating
 333       system. They are described in
 334       <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 335
 336       <listitem><para>Path units may be used to activate other
 337       services when file system objects change or are modified. See
 338       <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 339
 340       <listitem><para>Slice units may be used to group units which
 341       manage system processes (such as service and scope units) in a
 342       hierarchical tree for resource management purposes. See
 343       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 344
 345       <listitem><para>Scope units are similar to service units, but
 346       manage foreign processes instead of starting them as well. See
 347       <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 348
 349     </orderedlist>
 350
 351     <para>Units are named as their configuration files. Some units
 352     have special semantics. A detailed list is available in
 353     <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 354
 355     <para>systemd knows various kinds of dependencies, including
 356     positive and negative requirement dependencies (i.e.
 357     <varname>Requires=</varname> and <varname>Conflicts=</varname>) as
 358     well as ordering dependencies (<varname>After=</varname> and
 359     <varname>Before=</varname>). NB: ordering and requirement
 360     dependencies are orthogonal. If only a requirement dependency
 361     exists between two units (e.g. <filename>foo.service</filename>
 362     requires <filename>bar.service</filename>), but no ordering
 363     dependency (e.g. <filename>foo.service</filename> after
 364     <filename>bar.service</filename>) and both are requested to start,
 365     they will be started in parallel. It is a common pattern that both
 366     requirement and ordering dependencies are placed between two
 367     units. Also note that the majority of dependencies are implicitly
 368     created and maintained by systemd. In most cases, it should be
 369     unnecessary to declare additional dependencies manually, however
 370     it is possible to do this.</para>
 371
 372     <para>Application programs and units (via dependencies) may
 373     request state changes of units. In systemd, these requests are
 374     encapsulated as 'jobs' and maintained in a job queue. Jobs may
 375     succeed or can fail, their execution is ordered based on the
 376     ordering dependencies of the units they have been scheduled
 377     for.</para>
 378
 379     <para>On boot systemd activates the target unit
 380     <filename>default.target</filename> whose job is to activate
 381     on-boot services and other on-boot units by pulling them in via
 382     dependencies. Usually the unit name is just an alias (symlink) for
 383     either <filename>graphical.target</filename> (for fully-featured
 384     boots into the UI) or <filename>multi-user.target</filename> (for
 385     limited console-only boots for use in embedded or server
 386     environments, or similar; a subset of graphical.target). However,
 387     it is at the discretion of the administrator to configure it as an
 388     alias to any other target unit. See
 389     <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 390     for details about these target units.</para>
 391
 392     <para>Processes systemd spawns are placed in individual Linux
 393     control groups named after the unit which they belong to in the
 394     private systemd hierarchy. (see <ulink
 395     url="https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 396     for more information about control groups, or short "cgroups").
 397     systemd uses this to effectively keep track of processes. Control
 398     group information is maintained in the kernel, and is accessible
 399     via the file system hierarchy (beneath
 400     <filename>/sys/fs/cgroup/systemd/</filename>), or in tools such as
 401     <citerefentry project='man-pages'><refentrytitle>systemd-cgls</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 402     or
 403     <citerefentry project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 404     (<command>ps xawf -eo pid,user,cgroup,args</command> is
 405     particularly useful to list all processes and the systemd units
 406     they belong to.).</para>
 407
 408     <para>systemd is compatible with the SysV init system to a large
 409     degree: SysV init scripts are supported and simply read as an
 410     alternative (though limited) configuration file format. The SysV
 411     <filename>/dev/initctl</filename> interface is provided, and
 412     compatibility implementations of the various SysV client tools are
 413     available. In addition to that, various established Unix
 414     functionality such as <filename>/etc/fstab</filename> or the
 415     <filename>utmp</filename> database are supported.</para>
 416
 417     <para>systemd has a minimal transaction system: if a unit is
 418     requested to start up or shut down it will add it and all its
 419     dependencies to a temporary transaction. Then, it will verify if
 420     the transaction is consistent (i.e. whether the ordering of all
 421     units is cycle-free). If it is not, systemd will try to fix it up,
 422     and removes non-essential jobs from the transaction that might
 423     remove the loop. Also, systemd tries to suppress non-essential
 424     jobs in the transaction that would stop a running service. Finally
 425     it is checked whether the jobs of the transaction contradict jobs
 426     that have already been queued, and optionally the transaction is
 427     aborted then. If all worked out and the transaction is consistent
 428     and minimized in its impact it is merged with all already
 429     outstanding jobs and added to the run queue. Effectively this
 430     means that before executing a requested operation, systemd will
 431     verify that it makes sense, fixing it if possible, and only
 432     failing if it really cannot work.</para>
 433
 434     <para>Systemd contains native implementations of various tasks
 435     that need to be executed as part of the boot process. For example,
 436     it sets the hostname or configures the loopback network device. It
 437     also sets up and mounts various API file systems, such as
 438     <filename>/sys</filename> or <filename>/proc</filename>.</para>
 439
 440     <para>For more information about the concepts and
 441     ideas behind systemd, please refer to the
 442     <ulink url="http://0pointer.de/blog/projects/systemd.html">Original Design Document</ulink>.</para>
 443
 444     <para>Note that some but not all interfaces provided
 445     by systemd are covered by the
 446     <ulink url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 447     Stability Promise</ulink>.</para>
 448
 449     <para>Units may be generated dynamically at boot and system
 450     manager reload time, for example based on other configuration
 451     files or parameters passed on the kernel command line. For details see
 452     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 453
 454     <para>Systems which invoke systemd in a container or initrd
 455     environment should implement the
 456     <ulink url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container Interface</ulink> or
 457     <ulink url="http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd Interface</ulink>
 458     specifications, respectively.</para>
 459   </refsect1>
 460
 461   <refsect1>
 462     <title>Directories</title>
 463
 464     <variablelist>
 465       <varlistentry>
 466         <term>System unit directories</term>
 467
 468         <listitem><para>The systemd system manager reads unit
 469         configuration from various directories. Packages that want to
 470         install unit files shall place them in the directory returned
 471         by <command>pkg-config systemd
 472         --variable=systemdsystemunitdir</command>. Other directories
 473         checked are <filename>/usr/local/lib/systemd/system</filename>
 474         and <filename>/usr/lib/systemd/system</filename>. User
 475         configuration always takes precedence. <command>pkg-config
 476         systemd --variable=systemdsystemconfdir</command> returns the
 477         path of the system configuration directory. Packages should
 478         alter the content of these directories only with the
 479         <command>enable</command> and <command>disable</command>
 480         commands of the
 481         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 482         tool. Full list of directories is provided in
 483         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 484         </para></listitem>
 485       </varlistentry>
 486     </variablelist>
 487
 488     <variablelist>
 489       <varlistentry>
 490         <term>User unit directories</term>
 491
 492         <listitem><para>Similar rules apply for the user unit
 493         directories. However, here the
 494         <ulink url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 495         Base Directory specification</ulink> is followed to find
 496         units. Applications should place their unit files in the
 497         directory returned by <command>pkg-config systemd
 498         --variable=systemduserunitdir</command>. Global configuration
 499         is done in the directory reported by <command>pkg-config
 500         systemd --variable=systemduserconfdir</command>. The
 501         <command>enable</command> and <command>disable</command>
 502         commands of the
 503         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 504         tool can handle both global (i.e. for all users) and private
 505         (for one user) enabling/disabling of units. Full list of
 506         directories is provided in
 507         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 508         </para></listitem>
 509       </varlistentry>
 510     </variablelist>
 511
 512     <variablelist>
 513       <varlistentry>
 514         <term>SysV init scripts directory</term>
 515
 516         <listitem><para>The location of the SysV init script directory
 517         varies between distributions. If systemd cannot find a native
 518         unit file for a requested service, it will look for a SysV
 519         init script of the same name (with the
 520         <filename>.service</filename> suffix
 521         removed).</para></listitem>
 522       </varlistentry>
 523     </variablelist>
 524
 525     <variablelist>
 526       <varlistentry>
 527         <term>SysV runlevel link farm directory</term>
 528
 529         <listitem><para>The location of the SysV runlevel link farm
 530         directory varies between distributions. systemd will take the
 531         link farm into account when figuring out whether a service
 532         shall be enabled. Note that a service unit with a native unit
 533         configuration file cannot be started by activating it in the
 534         SysV runlevel link farm.</para></listitem>
 535       </varlistentry>
 536     </variablelist>
 537   </refsect1>
 538
 539   <refsect1>
 540     <title>Signals</title>
 541
 542     <variablelist>
 543       <varlistentry>
 544         <term><constant>SIGTERM</constant></term>
 545
 546         <listitem><para>Upon receiving this signal the systemd system
 547         manager serializes its state, reexecutes itself and
 548         deserializes the saved state again. This is mostly equivalent
 549         to <command>systemctl daemon-reexec</command>.</para>
 550
 551         <para>systemd user managers will start the
 552         <filename>exit.target</filename> unit when this signal is
 553         received. This is mostly equivalent to <command>systemctl
 554         --user start exit.target</command>.</para></listitem>
 555       </varlistentry>
 556
 557       <varlistentry>
 558         <term><constant>SIGINT</constant></term>
 559
 560         <listitem><para>Upon receiving this signal the systemd system
 561         manager will start the
 562         <filename>ctrl-alt-del.target</filename> unit. This is mostly
 563         equivalent to <command>systemctl start
 564         ctl-alt-del.target</command>. If this signal is received more
 565         often than 7 times per 2s an immediate reboot is triggered.
 566         Note that pressing Ctrl-Alt-Del on the console will trigger
 567         this signal. Hence, if a reboot is hanging pressing
 568         Ctrl-Alt-Del more than 7 times in 2s is a relatively safe way
 569         to trigger an immediate reboot.</para>
 570
 571         <para>systemd user managers treat this signal the same way as
 572         <constant>SIGTERM</constant>.</para></listitem>
 573       </varlistentry>
 574
 575       <varlistentry>
 576         <term><constant>SIGWINCH</constant></term>
 577
 578         <listitem><para>When this signal is received the systemd
 579         system manager will start the
 580         <filename>kbrequest.target</filename> unit. This is mostly
 581         equivalent to <command>systemctl start
 582         kbrequest.target</command>.</para>
 583
 584         <para>This signal is ignored by systemd user
 585         managers.</para></listitem>
 586       </varlistentry>
 587
 588       <varlistentry>
 589         <term><constant>SIGPWR</constant></term>
 590
 591         <listitem><para>When this signal is received the systemd
 592         manager will start the <filename>sigpwr.target</filename>
 593         unit. This is mostly equivalent to <command>systemctl start
 594         sigpwr.target</command>.</para></listitem>
 595       </varlistentry>
 596
 597       <varlistentry>
 598         <term><constant>SIGUSR1</constant></term>
 599
 600         <listitem><para>When this signal is received the systemd
 601         manager will try to reconnect to the D-Bus
 602         bus.</para></listitem>
 603       </varlistentry>
 604
 605       <varlistentry>
 606         <term><constant>SIGUSR2</constant></term>
 607
 608         <listitem><para>When this signal is received the systemd
 609         manager will log its complete state in human readable form.
 610         The data logged is the same as printed by
 611         <command>systemd-analyze dump</command>.</para></listitem>
 612       </varlistentry>
 613
 614       <varlistentry>
 615         <term><constant>SIGHUP</constant></term>
 616
 617         <listitem><para>Reloads the complete daemon configuration.
 618         This is mostly equivalent to <command>systemctl
 619         daemon-reload</command>.</para></listitem>
 620       </varlistentry>
 621
 622       <varlistentry>
 623         <term><constant>SIGRTMIN+0</constant></term>
 624
 625         <listitem><para>Enters default mode, starts the
 626         <filename>default.target</filename> unit. This is mostly
 627         equivalent to <command>systemctl start
 628         default.target</command>.</para></listitem>
 629       </varlistentry>
 630
 631       <varlistentry>
 632         <term><constant>SIGRTMIN+1</constant></term>
 633
 634         <listitem><para>Enters rescue mode, starts the
 635         <filename>rescue.target</filename> unit. This is mostly
 636         equivalent to <command>systemctl isolate
 637         rescue.target</command>.</para></listitem>
 638       </varlistentry>
 639
 640       <varlistentry>
 641         <term><constant>SIGRTMIN+2</constant></term>
 642
 643         <listitem><para>Enters emergency mode, starts the
 644         <filename>emergency.service</filename> unit. This is mostly
 645         equivalent to <command>systemctl isolate
 646         emergency.service</command>.</para></listitem>
 647       </varlistentry>
 648
 649       <varlistentry>
 650         <term><constant>SIGRTMIN+3</constant></term>
 651
 652         <listitem><para>Halts the machine, starts the
 653         <filename>halt.target</filename> unit. This is mostly
 654         equivalent to <command>systemctl start
 655         halt.target</command>.</para></listitem>
 656       </varlistentry>
 657
 658       <varlistentry>
 659         <term><constant>SIGRTMIN+4</constant></term>
 660
 661         <listitem><para>Powers off the machine, starts the
 662         <filename>poweroff.target</filename> unit. This is mostly
 663         equivalent to <command>systemctl start
 664         poweroff.target</command>.</para></listitem>
 665       </varlistentry>
 666
 667       <varlistentry>
 668         <term><constant>SIGRTMIN+5</constant></term>
 669
 670         <listitem><para>Reboots the machine, starts the
 671         <filename>reboot.target</filename> unit. This is mostly
 672         equivalent to <command>systemctl start
 673         reboot.target</command>.</para></listitem>
 674       </varlistentry>
 675
 676       <varlistentry>
 677         <term><constant>SIGRTMIN+6</constant></term>
 678
 679         <listitem><para>Reboots the machine via kexec, starts the
 680         <filename>kexec.target</filename> unit. This is mostly
 681         equivalent to <command>systemctl start
 682         kexec.target</command>.</para></listitem>
 683       </varlistentry>
 684
 685       <varlistentry>
 686         <term><constant>SIGRTMIN+13</constant></term>
 687
 688         <listitem><para>Immediately halts the machine.</para></listitem>
 689       </varlistentry>
 690
 691       <varlistentry>
 692         <term><constant>SIGRTMIN+14</constant></term>
 693
 694         <listitem><para>Immediately powers off the machine.</para></listitem>
 695       </varlistentry>
 696
 697       <varlistentry>
 698         <term><constant>SIGRTMIN+15</constant></term>
 699
 700         <listitem><para>Immediately reboots the machine.</para></listitem>
 701       </varlistentry>
 702
 703       <varlistentry>
 704         <term><constant>SIGRTMIN+16</constant></term>
 705
 706         <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
 707       </varlistentry>
 708
 709       <varlistentry>
 710         <term><constant>SIGRTMIN+20</constant></term>
 711
 712         <listitem><para>Enables display of status messages on the
 713         console, as controlled via
 714         <varname>systemd.show_status=1</varname> on the kernel command
 715         line.</para></listitem>
 716       </varlistentry>
 717
 718       <varlistentry>
 719         <term><constant>SIGRTMIN+21</constant></term>
 720
 721         <listitem><para>Disables display of
 722         status messages on the console, as
 723         controlled via
 724         <varname>systemd.show_status=0</varname>
 725         on the kernel command
 726         line.</para></listitem>
 727       </varlistentry>
 728
 729       <varlistentry>
 730         <term><constant>SIGRTMIN+22</constant></term>
 731         <term><constant>SIGRTMIN+23</constant></term>
 732
 733         <listitem><para>Sets the log level to <literal>debug</literal>
 734         (or <literal>info</literal> on
 735         <constant>SIGRTMIN+23</constant>), as controlled via
 736         <varname>systemd.log_level=debug</varname> (or
 737         <varname>systemd.log_level=info</varname> on
 738         <constant>SIGRTMIN+23</constant>) on the kernel command
 739         line.</para></listitem>
 740       </varlistentry>
 741
 742       <varlistentry>
 743         <term><constant>SIGRTMIN+24</constant></term>
 744
 745         <listitem><para>Immediately exits the manager (only available
 746         for --user instances).</para></listitem>
 747       </varlistentry>
 748
 749       <varlistentry>
 750         <term><constant>SIGRTMIN+26</constant></term>
 751         <term><constant>SIGRTMIN+27</constant></term>
 752         <term><constant>SIGRTMIN+28</constant></term>
 753
 754         <listitem><para>Sets the log level to
 755         <literal>journal-or-kmsg</literal> (or
 756         <literal>console</literal> on
 757         <constant>SIGRTMIN+27</constant>, <literal>kmsg</literal> on
 758         <constant>SIGRTMIN+28</constant>), as controlled via
 759         <varname>systemd.log_target=journal-or-kmsg</varname> (or
 760         <varname>systemd.log_target=console</varname> on
 761         <constant>SIGRTMIN+27</constant> or
 762         <varname>systemd.log_target=kmsg</varname> on
 763         <constant>SIGRTMIN+28</constant>) on the kernel command
 764         line.</para></listitem>
 765       </varlistentry>
 766     </variablelist>
 767   </refsect1>
 768
 769   <refsect1>
 770     <title>Environment</title>
 771
 772     <variablelist class='environment-variables'>
 773       <varlistentry>
 774         <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 775         <listitem><para>systemd reads the log level from this
 776         environment variable. This can be overridden with
 777         <option>--log-level=</option>.</para></listitem>
 778       </varlistentry>
 779
 780       <varlistentry>
 781         <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 782         <listitem><para>systemd reads the log target from this
 783         environment variable. This can be overridden with
 784         <option>--log-target=</option>.</para></listitem>
 785       </varlistentry>
 786
 787       <varlistentry>
 788         <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 789         <listitem><para>Controls whether systemd highlights important
 790         log messages. This can be overridden with
 791         <option>--log-color=</option>.</para></listitem>
 792       </varlistentry>
 793
 794       <varlistentry>
 795         <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 796         <listitem><para>Controls whether systemd prints the code
 797         location along with log messages. This can be overridden with
 798         <option>--log-location=</option>.</para></listitem>
 799       </varlistentry>
 800
 801       <varlistentry>
 802         <term><varname>$XDG_CONFIG_HOME</varname></term>
 803         <term><varname>$XDG_CONFIG_DIRS</varname></term>
 804         <term><varname>$XDG_DATA_HOME</varname></term>
 805         <term><varname>$XDG_DATA_DIRS</varname></term>
 806
 807         <listitem><para>The systemd user manager uses these variables
 808         in accordance to the <ulink
 809         url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 810         Base Directory specification</ulink> to find its
 811         configuration.</para></listitem>
 812       </varlistentry>
 813
 814       <varlistentry>
 815         <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 816
 817         <listitem><para>Controls where systemd looks for unit
 818         files.</para></listitem>
 819       </varlistentry>
 820
 821       <varlistentry>
 822         <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 823
 824         <listitem><para>Controls where systemd looks for SysV init
 825         scripts.</para></listitem>
 826       </varlistentry>
 827
 828       <varlistentry>
 829         <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 830
 831         <listitem><para>Controls where systemd looks for SysV init
 832         script runlevel link farms.</para></listitem>
 833       </varlistentry>
 834
 835       <varlistentry>
 836         <term><varname>$LISTEN_PID</varname></term>
 837         <term><varname>$LISTEN_FDS</varname></term>
 838         <term><varname>$LISTEN_FDNAMES</varname></term>
 839
 840         <listitem><para>Set by systemd for supervised processes during
 841         socket-based activation. See
 842         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 843         for more information. </para></listitem>
 844       </varlistentry>
 845
 846       <varlistentry>
 847         <term><varname>$NOTIFY_SOCKET</varname></term>
 848
 849         <listitem><para>Set by systemd for supervised processes for
 850         status and start-up completion notification. See
 851         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 852         for more information. </para></listitem>
 853       </varlistentry>
 854     </variablelist>
 855   </refsect1>
 856
 857   <refsect1>
 858     <title>Kernel Command Line</title>
 859
 860     <para>When run as system instance systemd parses a number of
 861     kernel command line arguments<footnote><para>If run inside a Linux
 862     container these arguments may be passed as command line arguments
 863     to systemd itself, next to any of the command line options listed
 864     in the Options section above. If run outside of Linux containers,
 865     these arguments are parsed from <filename>/proc/cmdline</filename>
 866     instead.</para></footnote>:</para>
 867
 868     <variablelist class='kernel-commandline-options'>
 869       <varlistentry>
 870         <term><varname>systemd.unit=</varname></term>
 871         <term><varname>rd.systemd.unit=</varname></term>
 872
 873         <listitem><para>Overrides the unit to activate on boot.
 874         Defaults to <filename>default.target</filename>. This may be
 875         used to temporarily boot into a different boot unit, for
 876         example <filename>rescue.target</filename> or
 877         <filename>emergency.service</filename>. See
 878         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 879         for details about these units. The option prefixed with
 880         <literal>rd.</literal> is honored only in the initial RAM disk
 881         (initrd), while the one that is not prefixed only in the main
 882         system.</para></listitem>
 883       </varlistentry>
 884
 885       <varlistentry>
 886         <term><varname>systemd.dump_core=</varname></term>
 887
 888         <listitem><para>Takes a boolean argument. If
 889         <option>yes</option>, the systemd manager (PID 1) dumps core
 890         when it crashes.  Otherwise, no core dump is created. Defaults
 891         to <option>yes</option>.</para></listitem>
 892       </varlistentry>
 893
 894       <varlistentry>
 895         <term><varname>systemd.crash_chvt=</varname></term>
 896
 897         <listitem><para>Takes a positive integer, or a boolean
 898         argument. If a positive integer (in the range 1..63) is
 899         specified the system manager (PID 1) will activate the specified
 900         virtual terminal (VT) when it crashes. Defaults to
 901         <constant>no</constant>, meaning that no such switch is
 902         attempted. If set to <constant>yes</constant> the VT the
 903         kernel messages are written to is selected.</para></listitem>
 904       </varlistentry>
 905
 906       <varlistentry>
 907         <term><varname>systemd.crash_shell=</varname></term>
 908
 909         <listitem><para>Takes a boolean argument. If
 910         <option>yes</option>, the system manager (PID 1) spawns a
 911         shell when it crashes, after a 10s delay. Otherwise, no shell
 912         is spawned. Defaults to <option>no</option>, for security
 913         reasons, as the shell is not protected by password
 914         authentication.</para></listitem>
 915       </varlistentry>
 916
 917       <varlistentry>
 918         <term><varname>systemd.crash_reboot=</varname></term>
 919
 920         <listitem><para>Takes a boolean argument. If
 921         <option>yes</option>, the system manager (PID 1) will reboot
 922         the machine automatically when it crashes, after a 10s delay.
 923         Otherwise, the system will hang indefinitely. Defaults to
 924         <option>no</option>, in order to avoid a reboot loop. If
 925         combined with <varname>systemd.crash_shell=</varname>, the
 926         system is rebooted after the shell exits.</para></listitem>
 927       </varlistentry>
 928
 929       <varlistentry>
 930         <term><varname>systemd.confirm_spawn=</varname></term>
 931
 932         <listitem><para>Takes a boolean argument. If
 933         <option>yes</option>, the system manager (PID 1) asks for
 934         confirmation when spawning processes. Defaults to
 935         <option>no</option>.</para></listitem>
 936       </varlistentry>
 937
 938       <varlistentry>
 939         <term><varname>systemd.show_status=</varname></term>
 940
 941         <listitem><para>Takes a boolean argument or the constant
 942         <constant>auto</constant>. If <option>yes</option>, the
 943         systemd manager (PID 1) shows terse service status updates on
 944         the console during bootup.  <constant>auto</constant> behaves
 945         like <option>false</option> until a service fails or there is
 946         a significant delay in boot.  Defaults to
 947         <option>yes</option>, unless <option>quiet</option> is passed
 948         as kernel command line option in which case it defaults to
 949         <constant>auto</constant>.</para></listitem>
 950       </varlistentry>
 951
 952       <varlistentry>
 953         <term><varname>systemd.log_target=</varname></term>
 954         <term><varname>systemd.log_level=</varname></term>
 955         <term><varname>systemd.log_color=</varname></term>
 956         <term><varname>systemd.log_location=</varname></term>
 957
 958         <listitem><para>Controls log output, with the same effect as
 959         the <varname>$SYSTEMD_LOG_TARGET</varname>,
 960         <varname>$SYSTEMD_LOG_LEVEL</varname>,
 961         <varname>$SYSTEMD_LOG_COLOR</varname>,
 962         <varname>$SYSTEMD_LOG_LOCATION</varname> environment variables
 963         described above.</para></listitem>
 964       </varlistentry>
 965
 966       <varlistentry>
 967         <term><varname>systemd.default_standard_output=</varname></term>
 968         <term><varname>systemd.default_standard_error=</varname></term>
 969         <listitem><para>Controls default standard output and error
 970         output for services, with the same effect as the
 971         <option>--default-standard-output=</option> and
 972         <option>--default-standard-error=</option> command line
 973         arguments described above, respectively.</para></listitem>
 974       </varlistentry>
 975
 976       <varlistentry>
 977         <term><varname>systemd.setenv=</varname></term>
 978
 979         <listitem><para>Takes a string argument in the form
 980         VARIABLE=VALUE. May be used to set default environment
 981         variables to add to forked child processes. May be used more
 982         than once to set multiple variables.</para></listitem>
 983       </varlistentry>
 984
 985       <varlistentry>
 986         <term><varname>quiet</varname></term>
 987
 988         <listitem><para>Turn off status output at boot, much like
 989         <varname>systemd.show_status=false</varname> would. Note that
 990         this option is also read by the kernel itself and disables
 991         kernel log output. Passing this option hence turns off the
 992         usual output from both the system manager and the kernel.
 993         </para></listitem>
 994       </varlistentry>
 995
 996       <varlistentry>
 997         <term><varname>debug</varname></term>
 998
 999         <listitem><para>Turn on debugging output. This is equivalent
1000         to <varname>systemd.log_level=debug</varname>. Note that this
1001         option is also read by the kernel itself and enables kernel
1002         debug output. Passing this option hence turns on the debug
1003         output from both the system manager and the
1004         kernel.</para></listitem>
1005       </varlistentry>
1006
1007       <varlistentry>
1008         <term><varname>emergency</varname></term>
1009         <term><varname>-b</varname></term>
1010
1011         <listitem><para>Boot into emergency mode. This is equivalent
1012         to <varname>systemd.unit=emergency.target</varname> and
1013         provided for compatibility reasons and to be easier to
1014         type.</para></listitem>
1015       </varlistentry>
1016
1017       <varlistentry>
1018         <term><varname>rescue</varname></term>
1019         <term><varname>single</varname></term>
1020         <term><varname>s</varname></term>
1021         <term><varname>S</varname></term>
1022         <term><varname>1</varname></term>
1023
1024         <listitem><para>Boot into rescue mode. This is equivalent to
1025         <varname>systemd.unit=rescue.target</varname> and provided for
1026         compatibility reasons and to be easier to
1027         type.</para></listitem>
1028       </varlistentry>
1029
1030       <varlistentry>
1031         <term><varname>2</varname></term>
1032         <term><varname>3</varname></term>
1033         <term><varname>4</varname></term>
1034         <term><varname>5</varname></term>
1035
1036         <listitem><para>Boot into the specified legacy SysV runlevel.
1037         These are equivalent to
1038         <varname>systemd.unit=runlevel2.target</varname>,
1039         <varname>systemd.unit=runlevel3.target</varname>,
1040         <varname>systemd.unit=runlevel4.target</varname>, and
1041         <varname>systemd.unit=runlevel5.target</varname>,
1042         respectively, and provided for compatibility reasons and to be
1043         easier to type.</para></listitem>
1044       </varlistentry>
1045
1046       <varlistentry>
1047         <term><varname>locale.LANG=</varname></term>
1048         <term><varname>locale.LANGUAGE=</varname></term>
1049         <term><varname>locale.LC_CTYPE=</varname></term>
1050         <term><varname>locale.LC_NUMERIC=</varname></term>
1051         <term><varname>locale.LC_TIME=</varname></term>
1052         <term><varname>locale.LC_COLLATE=</varname></term>
1053         <term><varname>locale.LC_MONETARY=</varname></term>
1054         <term><varname>locale.LC_MESSAGES=</varname></term>
1055         <term><varname>locale.LC_PAPER=</varname></term>
1056         <term><varname>locale.LC_NAME=</varname></term>
1057         <term><varname>locale.LC_ADDRESS=</varname></term>
1058         <term><varname>locale.LC_TELEPHONE=</varname></term>
1059         <term><varname>locale.LC_MEASUREMENT=</varname></term>
1060         <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1061
1062         <listitem><para>Set the system locale to use. This overrides
1063         the settings in <filename>/etc/locale.conf</filename>. For
1064         more information see
1065         <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1066         and
1067         <citerefentry project='man-pages'><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1068         </para></listitem>
1069       </varlistentry>
1070     </variablelist>
1071
1072     <para>For other kernel command line parameters understood by
1073     components of the core OS, please refer to
1074     <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1075   </refsect1>
1076
1077   <refsect1>
1078     <title>Sockets and FIFOs</title>
1079
1080     <variablelist>
1081       <varlistentry>
1082         <term><filename>/run/systemd/notify</filename></term>
1083
1084         <listitem><para>Daemon status notification socket. This is an
1085         <constant>AF_UNIX</constant> datagram socket and is used to
1086         implement the daemon notification logic as implemented by
1087         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1088
1089       </varlistentry>
1090
1091       <varlistentry>
1092         <term><filename>/run/systemd/private</filename></term>
1093
1094         <listitem><para>Used internally as communication channel
1095         between
1096         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1097         and the systemd process. This is an
1098         <constant>AF_UNIX</constant> stream socket. This interface is
1099         private to systemd and should not be used in external
1100         projects.</para></listitem>
1101       </varlistentry>
1102
1103       <varlistentry>
1104         <term><filename>/dev/initctl</filename></term>
1105
1106         <listitem><para>Limited compatibility support for the SysV
1107         client interface, as implemented by the
1108         <filename>systemd-initctl.service</filename> unit. This is a
1109         named pipe in the file system. This interface is obsolete and
1110         should not be used in new applications.</para></listitem>
1111       </varlistentry>
1112     </variablelist>
1113   </refsect1>
1114
1115   <refsect1>
1116     <title>See Also</title>
1117     <para>
1118       The <ulink url="http://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
1119       <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1120       <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1121       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1122       <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1123       <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1124       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1125       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1126       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1127       <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1128       <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1129       <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1130       <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1131       <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1132     </para>
1133   </refsect1>
1134
1135 </refentry>