man/systemd.xml

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  10   Copyright 2010 Lennart Poettering
  11
  12   systemd is free software; you can redistribute it and/or modify it
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  25
  26 <refentry id="systemd"
  27     xmlns:xi="http://www.w3.org/2001/XInclude">
  28
  29   <refentryinfo>
  30     <title>systemd</title>
  31     <productname>systemd</productname>
  32
  33     <authorgroup>
  34       <author>
  35         <contrib>Developer</contrib>
  36         <firstname>Lennart</firstname>
  37         <surname>Poettering</surname>
  38         <email>lennart@poettering.net</email>
  39       </author>
  40     </authorgroup>
  41   </refentryinfo>
  42
  43   <refmeta>
  44     <refentrytitle>systemd</refentrytitle>
  45     <manvolnum>1</manvolnum>
  46   </refmeta>
  47
  48   <refnamediv>
  49     <refname>systemd</refname>
  50     <refname>init</refname>
  51     <refpurpose>systemd system and service manager</refpurpose>
  52   </refnamediv>
  53
  54   <refsynopsisdiv>
  55     <cmdsynopsis>
  56       <command>/usr/lib/systemd/systemd</command>
  57       <arg choice="opt" rep="repeat">OPTIONS</arg>
  58     </cmdsynopsis>
  59     <cmdsynopsis>
  60       <command>init</command>
  61       <arg choice="opt" rep="repeat">OPTIONS</arg>
  62       <arg choice="req">COMMAND</arg>
  63     </cmdsynopsis>
  64   </refsynopsisdiv>
  65
  66   <refsect1>
  67     <title>Description</title>
  68
  69     <para>systemd is a system and service manager for Linux operating
  70     systems. When run as first process on boot (as PID 1), it acts as
  71     init system that brings up and maintains userspace
  72     services.</para>
  73
  74     <para>For compatibility with SysV, if systemd is called as
  75     <command>init</command> and a PID that is not 1, it will execute
  76     <command>telinit</command> and pass all command line arguments
  77     unmodified. That means <command>init</command> and
  78     <command>telinit</command> are mostly equivalent when invoked from
  79     normal login sessions. See
  80     <citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  81     for more information.</para>
  82
  83     <para>When run as a system instance, systemd interprets the
  84     configuration file <filename>system.conf</filename> and the files
  85     in <filename>system.conf.d</filename> directories; when run as a
  86     user instance, systemd interprets the configuration file
  87     <filename>user.conf</filename> and the files in
  88     <filename>user.conf.d</filename> directories. See
  89     <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  90     for more information.</para>
  91   </refsect1>
  92
  93   <refsect1>
  94     <title>Options</title>
  95
  96     <para>The following options are understood:</para>
  97
  98     <variablelist>
  99       <varlistentry>
 100         <term><option>--test</option></term>
 101
 102         <listitem><para>Determine startup sequence, dump it and exit.
 103         This is an option useful for debugging only.</para></listitem>
 104       </varlistentry>
 105       <varlistentry>
 106         <term><option>--dump-configuration-items</option></term>
 107
 108         <listitem><para>Dump understood unit configuration items. This
 109         outputs a terse but complete list of configuration items
 110         understood in unit definition files.</para></listitem>
 111       </varlistentry>
 112       <varlistentry>
 113         <term><option>--unit=</option></term>
 114
 115         <listitem><para>Set default unit to activate on startup. If
 116         not specified, defaults to
 117         <filename>default.target</filename>.</para></listitem>
 118       </varlistentry>
 119       <varlistentry>
 120         <term><option>--system</option></term>
 121         <term><option>--user</option></term>
 122
 123         <listitem><para>For <option>--system</option>, tell systemd to
 124         run a system instance, even if the process ID is not 1, i.e.
 125         systemd is not run as init process. <option>--user</option>
 126         does the opposite, running a user instance even if the process
 127         ID is 1. Normally, it should not be necessary to pass these
 128         options, as systemd automatically detects the mode it is
 129         started in. These options are hence of little use except for
 130         debugging. Note that it is not supported booting and
 131         maintaining a full system with systemd running in
 132         <option>--system</option> mode, but PID not 1. In practice,
 133         passing <option>--system</option> explicitly is only useful in
 134         conjunction with <option>--test</option>.</para></listitem>
 135       </varlistentry>
 136       <varlistentry>
 137         <term><option>--dump-core</option></term>
 138
 139         <listitem><para>Enable core dumping on crash. This switch has
 140         no effect when running as user instance. This setting may also
 141         be enabled during boot on the kernel command line via the
 142         <varname>systemd.dump_core=</varname> option, see
 143         below.</para></listitem>
 144       </varlistentry>
 145
 146       <varlistentry>
 147         <term><option>--crash-vt=</option><replaceable>VT</replaceable></term>
 148
 149         <listitem><para>Switch to a specific virtual console (VT) on
 150         crash. Takes a positive integer in the range 1–63, or a
 151         boolean argument. If an integer is passed, selects which VT to
 152         switch to. If <constant>yes</constant>, the VT kernel messages
 153         are written to is selected. If <constant>no</constant>, no VT
 154         switch is attempted. This switch has no effect when running as
 155         user instance. This setting may also be enabled during boot,
 156         on the kernel command line via the
 157         <varname>systemd.crash_vt=</varname> option, see
 158         <!-- FIXME: there is no crash_vt command line option? -->
 159         below.</para></listitem>
 160       </varlistentry>
 161
 162       <varlistentry>
 163         <term><option>--crash-shell</option></term>
 164
 165         <listitem><para>Run a shell on crash. This switch has no
 166         effect when running as user instance. This setting may also be
 167         enabled during boot, on the kernel command line via the
 168         <varname>systemd.crash_shell=</varname> option, see
 169         below.</para></listitem>
 170       </varlistentry>
 171
 172       <varlistentry>
 173         <term><option>--crash-reboot</option></term>
 174
 175         <listitem><para>Automatically reboot the system on crash. This
 176         switch has no effect when running as user instance. This
 177         setting may also be enabled during boot, on the kernel command
 178         line via the <varname>systemd.crash_reboot=</varname> option,
 179         see below.</para></listitem>
 180       </varlistentry>
 181
 182       <varlistentry>
 183         <term><option>--confirm-spawn</option></term>
 184
 185         <listitem><para>Ask for confirmation when spawning processes.
 186         This switch has no effect when run as user
 187         instance.</para></listitem>
 188       </varlistentry>
 189       <varlistentry>
 190         <term><option>--show-status=</option></term>
 191
 192         <listitem><para>Takes a boolean argument or the special value <constant>auto</constant>. If on, terse unit
 193         status information is shown on the console during boot-up and shutdown. If off, no such status information is
 194         shown. If set to <constant>auto</constant> behavior is similar to off, except that it is automatically switched
 195         to on, as soon as the first unit failure or significant boot delay is encountered. This switch has no effect
 196         when invoked as user instance. If specified, overrides both the kernel command line setting
 197         <varname>systemd.show_status=</varname> (see below) and the configuration file option
 198         <option>ShowStatus=</option>, see
 199         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 200       </varlistentry>
 201       <varlistentry>
 202         <term><option>--log-target=</option></term>
 203
 204         <listitem><para>Set log target. Argument must be one of
 205         <option>console</option>,
 206         <option>journal</option>,
 207         <option>kmsg</option>,
 208         <option>journal-or-kmsg</option>,
 209         <option>null</option>.</para></listitem>
 210       </varlistentry>
 211       <varlistentry>
 212         <term><option>--log-level=</option></term>
 213
 214         <listitem><para>Set log level. As
 215         argument this accepts a numerical log
 216         level or the well-known <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 217         symbolic names (lowercase):
 218         <option>emerg</option>,
 219         <option>alert</option>,
 220         <option>crit</option>,
 221         <option>err</option>,
 222         <option>warning</option>,
 223         <option>notice</option>,
 224         <option>info</option>,
 225         <option>debug</option>.</para></listitem>
 226       </varlistentry>
 227       <varlistentry>
 228         <term><option>--log-color=</option></term>
 229
 230         <listitem><para>Highlight important log messages. Argument is
 231         a boolean value. If the argument is omitted, it defaults to
 232         <option>true</option>.</para></listitem>
 233       </varlistentry>
 234       <varlistentry>
 235         <term><option>--log-location=</option></term>
 236
 237         <listitem><para>Include code location in log messages. This is
 238         mostly relevant for debugging purposes. Argument is a boolean
 239         value. If the argument is omitted it defaults to
 240         <option>true</option>.</para></listitem>
 241       </varlistentry>
 242       <varlistentry>
 243         <term><option>--default-standard-output=</option></term>
 244         <term><option>--default-standard-error=</option></term>
 245
 246         <listitem><para>Sets the default output or error output for
 247         all services and sockets, respectively. That is, controls the
 248         default for <option>StandardOutput=</option> and
 249         <option>StandardError=</option> (see
 250         <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 251         for details). Takes one of
 252         <option>inherit</option>,
 253         <option>null</option>,
 254         <option>tty</option>,
 255         <option>journal</option>,
 256         <option>journal+console</option>,
 257         <option>syslog</option>,
 258         <option>syslog+console</option>,
 259         <option>kmsg</option>,
 260         <option>kmsg+console</option>.  If the
 261         argument is omitted
 262         <option>--default-standard-output=</option> defaults to
 263         <option>journal</option> and
 264         <option>--default-standard-error=</option> to
 265         <option>inherit</option>.</para></listitem>
 266       </varlistentry>
 267
 268       <varlistentry>
 269         <term><option>--machine-id=</option></term>
 270
 271         <listitem><para>Override the machine-id set on the hard drive,
 272         useful for network booting or for containers. May not be set
 273         to all zeros.</para></listitem>
 274       </varlistentry>
 275
 276       <varlistentry>
 277         <term><option>--service-watchdogs=</option></term>
 278
 279         <listitem><para>Globally enable/disable all service watchdog timeouts and emergency
 280         actions. This setting may also be specified during boot, on the kernel
 281         command line via the <varname>systemd.service_watchdogs=</varname>
 282         option, see below. Defaults to enabled.</para></listitem>
 283       </varlistentry>
 284
 285       <xi:include href="standard-options.xml" xpointer="help" />
 286       <xi:include href="standard-options.xml" xpointer="version" />
 287     </variablelist>
 288   </refsect1>
 289
 290   <refsect1>
 291     <title>Concepts</title>
 292
 293     <para>systemd provides a dependency system between various
 294     entities called "units" of 11 different types. Units encapsulate
 295     various objects that are relevant for system boot-up and
 296     maintenance. The majority of units are configured in unit
 297     configuration files, whose syntax and basic set of options is
 298     described in
 299     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 300     however some are created automatically from other configuration,
 301     dynamically from system state or programmatically at runtime.
 302     Units may be "active" (meaning started, bound, plugged in, …,
 303     depending on the unit type, see below), or "inactive" (meaning
 304     stopped, unbound, unplugged, …), as well as in the process of
 305     being activated or deactivated, i.e. between the two states (these
 306     states are called "activating", "deactivating"). A special
 307     "failed" state is available as well, which is very similar to
 308     "inactive" and is entered when the service failed in some way
 309     (process returned error code on exit, or crashed, an operation
 310     timed out, or after too many restarts). If this state is entered,
 311     the cause will be logged, for later reference. Note that the
 312     various unit types may have a number of additional substates,
 313     which are mapped to the five generalized unit states described
 314     here.</para>
 315
 316     <para>The following unit types are available:</para>
 317
 318     <orderedlist>
 319       <listitem><para>Service units, which start and control daemons
 320       and the processes they consist of. For details, see
 321       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 322
 323       <listitem><para>Socket units, which encapsulate local IPC or
 324       network sockets in the system, useful for socket-based
 325       activation. For details about socket units, see
 326       <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 327       for details on socket-based activation and other forms of
 328       activation, see
 329       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 330
 331       <listitem><para>Target units are useful to group units, or
 332       provide well-known synchronization points during boot-up, see
 333       <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 334
 335       <listitem><para>Device units expose kernel devices in systemd
 336       and may be used to implement device-based activation. For
 337       details, see
 338       <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 339
 340       <listitem><para>Mount units control mount points in the file
 341       system, for details see
 342       <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 343
 344       <listitem><para>Automount units provide automount capabilities,
 345       for on-demand mounting of file systems as well as parallelized
 346       boot-up. See
 347       <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 348
 349       <listitem><para>Timer units are useful for triggering activation
 350       of other units based on timers. You may find details in
 351       <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 352
 353       <listitem><para>Swap units are very similar to mount units and
 354       encapsulate memory swap partitions or files of the operating
 355       system. They are described in
 356       <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 357
 358       <listitem><para>Path units may be used to activate other
 359       services when file system objects change or are modified. See
 360       <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 361
 362       <listitem><para>Slice units may be used to group units which
 363       manage system processes (such as service and scope units) in a
 364       hierarchical tree for resource management purposes. See
 365       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 366
 367       <listitem><para>Scope units are similar to service units, but
 368       manage foreign processes instead of starting them as well. See
 369       <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 370
 371     </orderedlist>
 372
 373     <para>Units are named as their configuration files. Some units
 374     have special semantics. A detailed list is available in
 375     <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 376
 377     <para>systemd knows various kinds of dependencies, including
 378     positive and negative requirement dependencies (i.e.
 379     <varname>Requires=</varname> and <varname>Conflicts=</varname>) as
 380     well as ordering dependencies (<varname>After=</varname> and
 381     <varname>Before=</varname>). NB: ordering and requirement
 382     dependencies are orthogonal. If only a requirement dependency
 383     exists between two units (e.g. <filename>foo.service</filename>
 384     requires <filename>bar.service</filename>), but no ordering
 385     dependency (e.g. <filename>foo.service</filename> after
 386     <filename>bar.service</filename>) and both are requested to start,
 387     they will be started in parallel. It is a common pattern that both
 388     requirement and ordering dependencies are placed between two
 389     units. Also note that the majority of dependencies are implicitly
 390     created and maintained by systemd. In most cases, it should be
 391     unnecessary to declare additional dependencies manually, however
 392     it is possible to do this.</para>
 393
 394     <para>Application programs and units (via dependencies) may
 395     request state changes of units. In systemd, these requests are
 396     encapsulated as 'jobs' and maintained in a job queue. Jobs may
 397     succeed or can fail, their execution is ordered based on the
 398     ordering dependencies of the units they have been scheduled
 399     for.</para>
 400
 401     <para>On boot systemd activates the target unit
 402     <filename>default.target</filename> whose job is to activate
 403     on-boot services and other on-boot units by pulling them in via
 404     dependencies. Usually, the unit name is just an alias (symlink) for
 405     either <filename>graphical.target</filename> (for fully-featured
 406     boots into the UI) or <filename>multi-user.target</filename> (for
 407     limited console-only boots for use in embedded or server
 408     environments, or similar; a subset of graphical.target). However,
 409     it is at the discretion of the administrator to configure it as an
 410     alias to any other target unit. See
 411     <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 412     for details about these target units.</para>
 413
 414     <para>Processes systemd spawns are placed in individual Linux
 415     control groups named after the unit which they belong to in the
 416     private systemd hierarchy. (see <ulink
 417     url="https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt">cgroups.txt</ulink>
 418     for more information about control groups, or short "cgroups").
 419     systemd uses this to effectively keep track of processes. Control
 420     group information is maintained in the kernel, and is accessible
 421     via the file system hierarchy (beneath
 422     <filename>/sys/fs/cgroup/systemd/</filename>), or in tools such as
 423     <citerefentry project='man-pages'><refentrytitle>systemd-cgls</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 424     or
 425     <citerefentry project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 426     (<command>ps xawf -eo pid,user,cgroup,args</command> is
 427     particularly useful to list all processes and the systemd units
 428     they belong to.).</para>
 429
 430     <para>systemd is compatible with the SysV init system to a large
 431     degree: SysV init scripts are supported and simply read as an
 432     alternative (though limited) configuration file format. The SysV
 433     <filename>/dev/initctl</filename> interface is provided, and
 434     compatibility implementations of the various SysV client tools are
 435     available. In addition to that, various established Unix
 436     functionality such as <filename>/etc/fstab</filename> or the
 437     <filename>utmp</filename> database are supported.</para>
 438
 439     <para>systemd has a minimal transaction system: if a unit is
 440     requested to start up or shut down it will add it and all its
 441     dependencies to a temporary transaction. Then, it will verify if
 442     the transaction is consistent (i.e. whether the ordering of all
 443     units is cycle-free). If it is not, systemd will try to fix it up,
 444     and removes non-essential jobs from the transaction that might
 445     remove the loop. Also, systemd tries to suppress non-essential
 446     jobs in the transaction that would stop a running service. Finally
 447     it is checked whether the jobs of the transaction contradict jobs
 448     that have already been queued, and optionally the transaction is
 449     aborted then. If all worked out and the transaction is consistent
 450     and minimized in its impact it is merged with all already
 451     outstanding jobs and added to the run queue. Effectively this
 452     means that before executing a requested operation, systemd will
 453     verify that it makes sense, fixing it if possible, and only
 454     failing if it really cannot work.</para>
 455
 456     <para>systemd contains native implementations of various tasks
 457     that need to be executed as part of the boot process. For example,
 458     it sets the hostname or configures the loopback network device. It
 459     also sets up and mounts various API file systems, such as
 460     <filename>/sys</filename> or <filename>/proc</filename>.</para>
 461
 462     <para>For more information about the concepts and
 463     ideas behind systemd, please refer to the
 464     <ulink url="http://0pointer.de/blog/projects/systemd.html">Original Design Document</ulink>.</para>
 465
 466     <para>Note that some but not all interfaces provided
 467     by systemd are covered by the
 468     <ulink url="https://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 469     Stability Promise</ulink>.</para>
 470
 471     <para>Units may be generated dynamically at boot and system
 472     manager reload time, for example based on other configuration
 473     files or parameters passed on the kernel command line. For details, see
 474     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 475
 476     <para>Systems which invoke systemd in a container or initrd
 477     environment should implement the
 478     <ulink url="https://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container Interface</ulink> or
 479     <ulink url="https://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd Interface</ulink>
 480     specifications, respectively.</para>
 481   </refsect1>
 482
 483   <refsect1>
 484     <title>Directories</title>
 485
 486     <variablelist>
 487       <varlistentry>
 488         <term>System unit directories</term>
 489
 490         <listitem><para>The systemd system manager reads unit
 491         configuration from various directories. Packages that want to
 492         install unit files shall place them in the directory returned
 493         by <command>pkg-config systemd
 494         --variable=systemdsystemunitdir</command>. Other directories
 495         checked are <filename>/usr/local/lib/systemd/system</filename>
 496         and <filename>/usr/lib/systemd/system</filename>. User
 497         configuration always takes precedence. <command>pkg-config
 498         systemd --variable=systemdsystemconfdir</command> returns the
 499         path of the system configuration directory. Packages should
 500         alter the content of these directories only with the
 501         <command>enable</command> and <command>disable</command>
 502         commands of the
 503         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 504         tool. Full list of directories is provided in
 505         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 506         </para></listitem>
 507       </varlistentry>
 508     </variablelist>
 509
 510     <variablelist>
 511       <varlistentry>
 512         <term>User unit directories</term>
 513
 514         <listitem><para>Similar rules apply for the user unit
 515         directories. However, here the
 516         <ulink url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 517         Base Directory specification</ulink> is followed to find
 518         units. Applications should place their unit files in the
 519         directory returned by <command>pkg-config systemd
 520         --variable=systemduserunitdir</command>. Global configuration
 521         is done in the directory reported by <command>pkg-config
 522         systemd --variable=systemduserconfdir</command>. The
 523         <command>enable</command> and <command>disable</command>
 524         commands of the
 525         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 526         tool can handle both global (i.e. for all users) and private
 527         (for one user) enabling/disabling of units. Full list of
 528         directories is provided in
 529         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 530         </para></listitem>
 531       </varlistentry>
 532     </variablelist>
 533
 534     <variablelist>
 535       <varlistentry>
 536         <term>SysV init scripts directory</term>
 537
 538         <listitem><para>The location of the SysV init script directory
 539         varies between distributions. If systemd cannot find a native
 540         unit file for a requested service, it will look for a SysV
 541         init script of the same name (with the
 542         <filename>.service</filename> suffix
 543         removed).</para></listitem>
 544       </varlistentry>
 545     </variablelist>
 546
 547     <variablelist>
 548       <varlistentry>
 549         <term>SysV runlevel link farm directory</term>
 550
 551         <listitem><para>The location of the SysV runlevel link farm
 552         directory varies between distributions. systemd will take the
 553         link farm into account when figuring out whether a service
 554         shall be enabled. Note that a service unit with a native unit
 555         configuration file cannot be started by activating it in the
 556         SysV runlevel link farm.</para></listitem>
 557       </varlistentry>
 558     </variablelist>
 559   </refsect1>
 560
 561   <refsect1>
 562     <title>Signals</title>
 563
 564     <variablelist>
 565       <varlistentry>
 566         <term><constant>SIGTERM</constant></term>
 567
 568         <listitem><para>Upon receiving this signal the systemd system
 569         manager serializes its state, reexecutes itself and
 570         deserializes the saved state again. This is mostly equivalent
 571         to <command>systemctl daemon-reexec</command>.</para>
 572
 573         <para>systemd user managers will start the
 574         <filename>exit.target</filename> unit when this signal is
 575         received. This is mostly equivalent to <command>systemctl
 576         --user start exit.target
 577         --job-mode=replace-irreversible</command>.</para></listitem>
 578       </varlistentry>
 579
 580       <varlistentry>
 581         <term><constant>SIGINT</constant></term>
 582
 583         <listitem><para>Upon receiving this signal the systemd system
 584         manager will start the
 585         <filename>ctrl-alt-del.target</filename> unit. This is mostly
 586         equivalent to <command>systemctl start ctrl-alt-del.target
 587         --job-mode=replace-irreversible</command>. If this signal is
 588         received more than 7 times per 2s, an immediate reboot is
 589         triggered.  Note that pressing Ctrl-Alt-Del on the console
 590         will trigger this signal. Hence, if a reboot is hanging,
 591         pressing Ctrl-Alt-Del more than 7 times in 2s is a relatively
 592         safe way to trigger an immediate reboot.</para>
 593
 594         <para>systemd user managers treat this signal the same way as
 595         <constant>SIGTERM</constant>.</para></listitem>
 596       </varlistentry>
 597
 598       <varlistentry>
 599         <term><constant>SIGWINCH</constant></term>
 600
 601         <listitem><para>When this signal is received the systemd
 602         system manager will start the
 603         <filename>kbrequest.target</filename> unit. This is mostly
 604         equivalent to <command>systemctl start
 605         kbrequest.target</command>.</para>
 606
 607         <para>This signal is ignored by systemd user
 608         managers.</para></listitem>
 609       </varlistentry>
 610
 611       <varlistentry>
 612         <term><constant>SIGPWR</constant></term>
 613
 614         <listitem><para>When this signal is received the systemd
 615         manager will start the <filename>sigpwr.target</filename>
 616         unit. This is mostly equivalent to <command>systemctl start
 617         sigpwr.target</command>.</para></listitem>
 618       </varlistentry>
 619
 620       <varlistentry>
 621         <term><constant>SIGUSR1</constant></term>
 622
 623         <listitem><para>When this signal is received the systemd
 624         manager will try to reconnect to the D-Bus
 625         bus.</para></listitem>
 626       </varlistentry>
 627
 628       <varlistentry>
 629         <term><constant>SIGUSR2</constant></term>
 630
 631         <listitem><para>When this signal is received the systemd
 632         manager will log its complete state in human-readable form.
 633         The data logged is the same as printed by
 634         <command>systemd-analyze dump</command>.</para></listitem>
 635       </varlistentry>
 636
 637       <varlistentry>
 638         <term><constant>SIGHUP</constant></term>
 639
 640         <listitem><para>Reloads the complete daemon configuration.
 641         This is mostly equivalent to <command>systemctl
 642         daemon-reload</command>.</para></listitem>
 643       </varlistentry>
 644
 645       <varlistentry>
 646         <term><constant>SIGRTMIN+0</constant></term>
 647
 648         <listitem><para>Enters default mode, starts the
 649         <filename>default.target</filename> unit. This is mostly
 650         equivalent to <command>systemctl isolate
 651         default.target</command>.</para></listitem>
 652       </varlistentry>
 653
 654       <varlistentry>
 655         <term><constant>SIGRTMIN+1</constant></term>
 656
 657         <listitem><para>Enters rescue mode, starts the
 658         <filename>rescue.target</filename> unit. This is mostly
 659         equivalent to <command>systemctl isolate
 660         rescue.target</command>.</para></listitem>
 661       </varlistentry>
 662
 663       <varlistentry>
 664         <term><constant>SIGRTMIN+2</constant></term>
 665
 666         <listitem><para>Enters emergency mode, starts the
 667         <filename>emergency.service</filename> unit. This is mostly
 668         equivalent to <command>systemctl isolate
 669         emergency.service</command>.</para></listitem>
 670       </varlistentry>
 671
 672       <varlistentry>
 673         <term><constant>SIGRTMIN+3</constant></term>
 674
 675         <listitem><para>Halts the machine, starts the
 676         <filename>halt.target</filename> unit. This is mostly
 677         equivalent to <command>systemctl start halt.target
 678         --job-mode=replace-irreversible</command>.</para>
 679         </listitem>
 680       </varlistentry>
 681
 682       <varlistentry>
 683         <term><constant>SIGRTMIN+4</constant></term>
 684
 685         <listitem><para>Powers off the machine, starts the
 686         <filename>poweroff.target</filename> unit. This is mostly
 687         equivalent to <command>systemctl start poweroff.target
 688         --job-mode=replace-irreversible</command>.</para>
 689         </listitem>
 690       </varlistentry>
 691
 692       <varlistentry>
 693         <term><constant>SIGRTMIN+5</constant></term>
 694
 695         <listitem><para>Reboots the machine, starts the
 696         <filename>reboot.target</filename> unit. This is mostly
 697         equivalent to <command>systemctl start reboot.target
 698         --job-mode=replace-irreversible</command>.</para>
 699         </listitem>
 700       </varlistentry>
 701
 702       <varlistentry>
 703         <term><constant>SIGRTMIN+6</constant></term>
 704
 705         <listitem><para>Reboots the machine via kexec, starts the
 706         <filename>kexec.target</filename> unit. This is mostly
 707         equivalent to <command>systemctl start kexec.target
 708         --job-mode=replace-irreversible</command>.</para>
 709         </listitem>
 710       </varlistentry>
 711
 712       <varlistentry>
 713         <term><constant>SIGRTMIN+13</constant></term>
 714
 715         <listitem><para>Immediately halts the machine.</para></listitem>
 716       </varlistentry>
 717
 718       <varlistentry>
 719         <term><constant>SIGRTMIN+14</constant></term>
 720
 721         <listitem><para>Immediately powers off the machine.</para></listitem>
 722       </varlistentry>
 723
 724       <varlistentry>
 725         <term><constant>SIGRTMIN+15</constant></term>
 726
 727         <listitem><para>Immediately reboots the machine.</para></listitem>
 728       </varlistentry>
 729
 730       <varlistentry>
 731         <term><constant>SIGRTMIN+16</constant></term>
 732
 733         <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
 734       </varlistentry>
 735
 736       <varlistentry>
 737         <term><constant>SIGRTMIN+20</constant></term>
 738
 739         <listitem><para>Enables display of status messages on the
 740         console, as controlled via
 741         <varname>systemd.show_status=1</varname> on the kernel command
 742         line.</para></listitem>
 743       </varlistentry>
 744
 745       <varlistentry>
 746         <term><constant>SIGRTMIN+21</constant></term>
 747
 748         <listitem><para>Disables display of
 749         status messages on the console, as
 750         controlled via
 751         <varname>systemd.show_status=0</varname>
 752         on the kernel command
 753         line.</para></listitem>
 754       </varlistentry>
 755
 756       <varlistentry>
 757         <term><constant>SIGRTMIN+22</constant></term>
 758         <term><constant>SIGRTMIN+23</constant></term>
 759
 760         <listitem><para>Sets the log level to <literal>debug</literal>
 761         (or <literal>info</literal> on
 762         <constant>SIGRTMIN+23</constant>), as controlled via
 763         <varname>systemd.log_level=debug</varname> (or
 764         <varname>systemd.log_level=info</varname> on
 765         <constant>SIGRTMIN+23</constant>) on the kernel command
 766         line.</para></listitem>
 767       </varlistentry>
 768
 769       <varlistentry>
 770         <term><constant>SIGRTMIN+24</constant></term>
 771
 772         <listitem><para>Immediately exits the manager (only available
 773         for --user instances).</para></listitem>
 774       </varlistentry>
 775
 776       <varlistentry>
 777         <term><constant>SIGRTMIN+26</constant></term>
 778         <term><constant>SIGRTMIN+27</constant></term>
 779         <term><constant>SIGRTMIN+28</constant></term>
 780
 781         <listitem><para>Sets the log target to
 782         <literal>journal-or-kmsg</literal> (or
 783         <literal>console</literal> on
 784         <constant>SIGRTMIN+27</constant>, <literal>kmsg</literal> on
 785         <constant>SIGRTMIN+28</constant>), as controlled via
 786         <varname>systemd.log_target=journal-or-kmsg</varname> (or
 787         <varname>systemd.log_target=console</varname> on
 788         <constant>SIGRTMIN+27</constant> or
 789         <varname>systemd.log_target=kmsg</varname> on
 790         <constant>SIGRTMIN+28</constant>) on the kernel command
 791         line.</para></listitem>
 792       </varlistentry>
 793     </variablelist>
 794   </refsect1>
 795
 796   <refsect1>
 797     <title>Environment</title>
 798
 799     <variablelist class='environment-variables'>
 800       <varlistentry>
 801         <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 802         <listitem><para>systemd reads the log level from this
 803         environment variable. This can be overridden with
 804         <option>--log-level=</option>.</para></listitem>
 805       </varlistentry>
 806
 807       <varlistentry>
 808         <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 809         <listitem><para>systemd reads the log target from this
 810         environment variable. This can be overridden with
 811         <option>--log-target=</option>.</para></listitem>
 812       </varlistentry>
 813
 814       <varlistentry>
 815         <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 816         <listitem><para>Controls whether systemd highlights important
 817         log messages. This can be overridden with
 818         <option>--log-color=</option>.</para></listitem>
 819       </varlistentry>
 820
 821       <varlistentry>
 822         <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 823         <listitem><para>Controls whether systemd prints the code
 824         location along with log messages. This can be overridden with
 825         <option>--log-location=</option>.</para></listitem>
 826       </varlistentry>
 827
 828       <varlistentry>
 829         <term><varname>$XDG_CONFIG_HOME</varname></term>
 830         <term><varname>$XDG_CONFIG_DIRS</varname></term>
 831         <term><varname>$XDG_DATA_HOME</varname></term>
 832         <term><varname>$XDG_DATA_DIRS</varname></term>
 833
 834         <listitem><para>The systemd user manager uses these variables
 835         in accordance to the <ulink
 836         url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 837         Base Directory specification</ulink> to find its
 838         configuration.</para></listitem>
 839       </varlistentry>
 840
 841       <varlistentry>
 842         <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 843
 844         <listitem><para>Controls where systemd looks for unit
 845         files.</para></listitem>
 846       </varlistentry>
 847
 848       <varlistentry>
 849         <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 850
 851         <listitem><para>Controls where systemd looks for SysV init
 852         scripts.</para></listitem>
 853       </varlistentry>
 854
 855       <varlistentry>
 856         <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 857
 858         <listitem><para>Controls where systemd looks for SysV init
 859         script runlevel link farms.</para></listitem>
 860       </varlistentry>
 861
 862       <varlistentry>
 863         <term><varname>$SYSTEMD_COLORS</varname></term>
 864
 865         <listitem><para>The value must be a boolean. Controls whether colorized output should be
 866         generated. This can be specified to override the decision that <command>systemd</command>
 867         makes based on <varname>$TERM</varname> and what the console is connected to.</para>
 868         </listitem>
 869       </varlistentry>
 870
 871       <varlistentry>
 872         <term><varname>$LISTEN_PID</varname></term>
 873         <term><varname>$LISTEN_FDS</varname></term>
 874         <term><varname>$LISTEN_FDNAMES</varname></term>
 875
 876         <listitem><para>Set by systemd for supervised processes during
 877         socket-based activation. See
 878         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 879         for more information.</para></listitem>
 880       </varlistentry>
 881
 882       <varlistentry>
 883         <term><varname>$NOTIFY_SOCKET</varname></term>
 884
 885         <listitem><para>Set by systemd for supervised processes for
 886         status and start-up completion notification. See
 887         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 888         for more information.</para></listitem>
 889       </varlistentry>
 890     </variablelist>
 891   </refsect1>
 892
 893   <refsect1>
 894     <title>Kernel Command Line</title>
 895
 896     <para>When run as system instance systemd parses a number of
 897     kernel command line arguments<footnote><para>If run inside a Linux
 898     container these arguments may be passed as command line arguments
 899     to systemd itself, next to any of the command line options listed
 900     in the Options section above. If run outside of Linux containers,
 901     these arguments are parsed from <filename>/proc/cmdline</filename>
 902     instead.</para></footnote>:</para>
 903
 904     <variablelist class='kernel-commandline-options'>
 905       <varlistentry>
 906         <term><varname>systemd.unit=</varname></term>
 907         <term><varname>rd.systemd.unit=</varname></term>
 908
 909         <listitem><para>Overrides the unit to activate on boot.
 910         Defaults to <filename>default.target</filename>. This may be
 911         used to temporarily boot into a different boot unit, for
 912         example <filename>rescue.target</filename> or
 913         <filename>emergency.service</filename>. See
 914         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 915         for details about these units. The option prefixed with
 916         <literal>rd.</literal> is honored only in the initial RAM disk
 917         (initrd), while the one that is not prefixed only in the main
 918         system.</para></listitem>
 919       </varlistentry>
 920
 921       <varlistentry>
 922         <term><varname>systemd.dump_core</varname></term>
 923
 924         <listitem><para>Takes a boolean argument or enables the option if specified
 925         without an argument. If enabled, the systemd manager (PID 1) dumps core when
 926         it crashes. Otherwise, no core dump is created. Defaults to enabled.</para>
 927         </listitem>
 928       </varlistentry>
 929
 930       <varlistentry>
 931         <term><varname>systemd.crash_chvt</varname></term>
 932
 933         <listitem><para>Takes a positive integer, or a boolean argument. Can be also
 934         specified without an argument, with the same effect as a positive boolean. If
 935         a positive integer (in the range 1–63) is specified, the system manager (PID
 936         1) will activate the specified virtual terminal (VT) when it
 937         crashes. Defaults to disabled, meaning that no such switch is attempted. If
 938         set to enabled, the VT the kernel messages are written to is selected.
 939         </para></listitem>
 940       </varlistentry>
 941
 942       <varlistentry>
 943         <term><varname>systemd.crash_shell</varname></term>
 944
 945         <listitem><para>Takes a boolean argument or enables the option if specified
 946         without an argument. If enabled, the system manager (PID 1) spawns a shell
 947         when it crashes, after a 10s delay. Otherwise, no shell is spawned. Defaults
 948         to disabled, for security reasons, as the shell is not protected by password
 949         authentication.</para></listitem>
 950       </varlistentry>
 951
 952       <varlistentry>
 953         <term><varname>systemd.crash_reboot</varname></term>
 954
 955         <listitem><para>Takes a boolean argument or enables the option if specified
 956         without an argument. If enabled, the system manager (PID 1) will reboot the
 957         machine automatically when it crashes, after a 10s delay.  Otherwise, the
 958         system will hang indefinitely. Defaults to disabled, in order to avoid a
 959         reboot loop. If combined with <varname>systemd.crash_shell</varname>, the
 960         system is rebooted after the shell exits.</para></listitem>
 961       </varlistentry>
 962
 963       <varlistentry>
 964         <term><varname>systemd.confirm_spawn</varname></term>
 965
 966         <listitem><para>Takes a boolean argument or a path to the virtual console
 967         where the confirmation messages should be emitted. Can be also specified
 968         without an argument, with the same effect as a positive boolean. If enabled,
 969         the system manager (PID 1) asks for confirmation when spawning processes
 970         using <option>/dev/console</option>. If a path or a console name (such as
 971         <literal>ttyS0</literal>) is provided, the virtual console pointed to by this
 972         path or described by the give name will be used instead. Defaults to disabled.
 973         </para></listitem>
 974       </varlistentry>
 975
 976       <varlistentry>
 977         <term><varname>systemd.service_watchdogs=</varname></term>
 978
 979         <listitem><para>Takes a boolean argument. If disabled, all service runtime
 980         watchdogs (<option>WatchdogSec=</option>) and emergency actions (e.g.
 981         <option>OnFailure=</option> or <option>StartLimitAction=</option>) are
 982         ignored by the system manager (PID 1); see
 983         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 984         Defaults to enabled, i.e. watchdogs and failure actions are processed
 985         normally. The hardware watchdog is not affected by this
 986         option.</para></listitem>
 987       </varlistentry>
 988
 989       <varlistentry>
 990         <term><varname>systemd.show_status</varname></term>
 991
 992         <listitem><para>Takes a boolean argument or the constant
 993         <constant>auto</constant>. Can be also specified without an argument, with
 994         the same effect as a positive boolean.  If enabled, the systemd manager (PID
 995         1) shows terse service status updates on the console during bootup.
 996         <constant>auto</constant> behaves like <option>false</option> until a unit
 997         fails or there is a significant delay in boot. Defaults to enabled, unless
 998         <option>quiet</option> is passed as kernel command line option, in which case
 999         it defaults to <constant>auto</constant>. If specified overrides the system
1000         manager configuration file option <option>ShowStatus=</option>, see
1001         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
1002         However, the process command line option <option>--show-status=</option>
1003         takes precedence over both this kernel command line option and the
1004         configuration file option.</para></listitem>
1005       </varlistentry>
1006
1007       <varlistentry>
1008         <term><varname>systemd.log_target=</varname></term>
1009         <term><varname>systemd.log_level=</varname></term>
1010         <term><varname>systemd.log_location=</varname></term>
1011         <term><varname>systemd.log_color</varname></term>
1012
1013         <listitem><para>Controls log output, with the same effect as the
1014         <varname>$SYSTEMD_LOG_TARGET</varname>,
1015         <varname>$SYSTEMD_LOG_LEVEL</varname>,
1016         <varname>$SYSTEMD_LOG_LOCATION</varname>,
1017         <varname>$SYSTEMD_LOG_COLOR</varname> environment variables described above.
1018         <varname>systemd.log_color</varname> can be specified without an argument,
1019         with the same effect as a positive boolean.</para></listitem>
1020       </varlistentry>
1021
1022       <varlistentry>
1023         <term><varname>systemd.default_standard_output=</varname></term>
1024         <term><varname>systemd.default_standard_error=</varname></term>
1025         <listitem><para>Controls default standard output and error
1026         output for services, with the same effect as the
1027         <option>--default-standard-output=</option> and
1028         <option>--default-standard-error=</option> command line
1029         arguments described above, respectively.</para></listitem>
1030       </varlistentry>
1031
1032       <varlistentry>
1033         <term><varname>systemd.setenv=</varname></term>
1034
1035         <listitem><para>Takes a string argument in the form
1036         VARIABLE=VALUE. May be used to set default environment
1037         variables to add to forked child processes. May be used more
1038         than once to set multiple variables.</para></listitem>
1039       </varlistentry>
1040
1041       <varlistentry>
1042         <term><varname>systemd.machine_id=</varname></term>
1043
1044         <listitem><para>Takes a 32 character hex value to be
1045         used for setting the machine-id. Intended mostly for
1046         network booting where the same machine-id is desired
1047         for every boot.</para></listitem>
1048       </varlistentry>
1049
1050       <varlistentry>
1051         <term><varname>systemd.unified_cgroup_hierarchy</varname></term>
1052
1053         <listitem><para>When specified without an argument or with a true argument,
1054         enables the usage of
1055         <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v2.txt">unified cgroup hierarchy</ulink>
1056         (a.k.a. cgroups-v2). When specified with a false argument, fall back to
1057         hybrid or full legacy cgroup hierarchy.</para>
1058
1059         <para>If this option is not specified, the default behaviour is determined
1060         during compilation (the <option>--with-default-hierarchy=</option>
1061         option). If the kernel does not support unified cgroup hierarchy, the legacy
1062         hierarchy will be used even if this option is specified.</para>
1063         </listitem>
1064       </varlistentry>
1065
1066       <varlistentry>
1067         <term><varname>systemd.legacy_systemd_cgroup_controller</varname></term>
1068
1069         <listitem><para>Takes effect if the full unified cgroup hierarchy is not used
1070         (see previous option). When specified without an argument or with a true
1071         argument, disables the use of "hybrid" cgroup hierarchy (i.e. a cgroups-v2
1072         tree used for systemd, and
1073         <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v1/">legacy
1074         cgroup hierarchy</ulink>, a.k.a. cgroups-v1, for other controllers), and
1075         forces a full "legacy" mode. When specified with a false argument, enables
1076         the use of "hybrid" hierarchy.</para>
1077
1078         <para>If this option is not specified, the default behaviour is determined
1079         during compilation (the <option>--with-default-hierarchy=</option>
1080         option). If the kernel does not support unified cgroup hierarchy, the legacy
1081         hierarchy will be used  even if this option is specified.</para>
1082         </listitem>
1083       </varlistentry>
1084
1085       <varlistentry>
1086         <term><varname>quiet</varname></term>
1087
1088         <listitem><para>Turn off status output at boot, much like
1089         <varname>systemd.show_status=false</varname> would. Note that
1090         this option is also read by the kernel itself and disables
1091         kernel log output. Passing this option hence turns off the
1092         usual output from both the system manager and the kernel.
1093         </para></listitem>
1094       </varlistentry>
1095
1096       <varlistentry>
1097         <term><varname>debug</varname></term>
1098
1099         <listitem><para>Turn on debugging output. This is equivalent
1100         to <varname>systemd.log_level=debug</varname>. Note that this
1101         option is also read by the kernel itself and enables kernel
1102         debug output. Passing this option hence turns on the debug
1103         output from both the system manager and the
1104         kernel.</para></listitem>
1105       </varlistentry>
1106
1107       <varlistentry>
1108         <term><varname>emergency</varname></term>
1109         <term><varname>rd.emergency</varname></term>
1110         <term><varname>-b</varname></term>
1111
1112         <listitem><para>Boot into emergency mode. This is equivalent
1113         to <varname>systemd.unit=emergency.target</varname> or
1114         <varname>rd.systemd.unit=emergency.target</varname>, respectively, and
1115         provided for compatibility reasons and to be easier to type.</para></listitem>
1116       </varlistentry>
1117
1118       <varlistentry>
1119         <term><varname>rescue</varname></term>
1120         <term><varname>rd.rescue</varname></term>
1121         <term><varname>single</varname></term>
1122         <term><varname>s</varname></term>
1123         <term><varname>S</varname></term>
1124         <term><varname>1</varname></term>
1125
1126         <listitem><para>Boot into rescue mode. This is equivalent to
1127         <varname>systemd.unit=rescue.target</varname> or
1128         <varname>rd.systemd.unit=rescue.target</varname>, respectively, and
1129         provided for compatibility reasons and to be easier to type.</para></listitem>
1130       </varlistentry>
1131
1132       <varlistentry>
1133         <term><varname>2</varname></term>
1134         <term><varname>3</varname></term>
1135         <term><varname>4</varname></term>
1136         <term><varname>5</varname></term>
1137
1138         <listitem><para>Boot into the specified legacy SysV runlevel.
1139         These are equivalent to
1140         <varname>systemd.unit=runlevel2.target</varname>,
1141         <varname>systemd.unit=runlevel3.target</varname>,
1142         <varname>systemd.unit=runlevel4.target</varname>, and
1143         <varname>systemd.unit=runlevel5.target</varname>,
1144         respectively, and provided for compatibility reasons and to be
1145         easier to type.</para></listitem>
1146       </varlistentry>
1147
1148       <varlistentry>
1149         <term><varname>locale.LANG=</varname></term>
1150         <term><varname>locale.LANGUAGE=</varname></term>
1151         <term><varname>locale.LC_CTYPE=</varname></term>
1152         <term><varname>locale.LC_NUMERIC=</varname></term>
1153         <term><varname>locale.LC_TIME=</varname></term>
1154         <term><varname>locale.LC_COLLATE=</varname></term>
1155         <term><varname>locale.LC_MONETARY=</varname></term>
1156         <term><varname>locale.LC_MESSAGES=</varname></term>
1157         <term><varname>locale.LC_PAPER=</varname></term>
1158         <term><varname>locale.LC_NAME=</varname></term>
1159         <term><varname>locale.LC_ADDRESS=</varname></term>
1160         <term><varname>locale.LC_TELEPHONE=</varname></term>
1161         <term><varname>locale.LC_MEASUREMENT=</varname></term>
1162         <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1163
1164         <listitem><para>Set the system locale to use. This overrides
1165         the settings in <filename>/etc/locale.conf</filename>. For
1166         more information, see
1167         <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1168         and
1169         <citerefentry project='man-pages'><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1170         </para></listitem>
1171       </varlistentry>
1172     </variablelist>
1173
1174     <para>For other kernel command line parameters understood by
1175     components of the core OS, please refer to
1176     <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1177   </refsect1>
1178
1179   <refsect1>
1180     <title>Sockets and FIFOs</title>
1181
1182     <variablelist>
1183       <varlistentry>
1184         <term><filename>/run/systemd/notify</filename></term>
1185
1186         <listitem><para>Daemon status notification socket. This is an
1187         <constant>AF_UNIX</constant> datagram socket and is used to
1188         implement the daemon notification logic as implemented by
1189         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1190
1191       </varlistentry>
1192
1193       <varlistentry>
1194         <term><filename>/run/systemd/private</filename></term>
1195
1196         <listitem><para>Used internally as communication channel
1197         between
1198         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1199         and the systemd process. This is an
1200         <constant>AF_UNIX</constant> stream socket. This interface is
1201         private to systemd and should not be used in external
1202         projects.</para></listitem>
1203       </varlistentry>
1204
1205       <varlistentry>
1206         <term><filename>/dev/initctl</filename></term>
1207
1208         <listitem><para>Limited compatibility support for the SysV
1209         client interface, as implemented by the
1210         <filename>systemd-initctl.service</filename> unit. This is a
1211         named pipe in the file system. This interface is obsolete and
1212         should not be used in new applications.</para></listitem>
1213       </varlistentry>
1214     </variablelist>
1215   </refsect1>
1216
1217   <refsect1>
1218     <title>See Also</title>
1219     <para>
1220       The <ulink url="https://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
1221       <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1222       <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1223       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1224       <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1225       <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1226       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1227       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1228       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1229       <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1230       <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1231       <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1232       <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1233       <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1234     </para>
1235   </refsect1>
1236
1237 </refentry>