man/systemd.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   This file is part of systemd.
   7
   8   Copyright 2010 Lennart Poettering
   9
  10   systemd is free software; you can redistribute it and/or modify it
  11   under the terms of the GNU Lesser General Public License as published by
  12   the Free Software Foundation; either version 2.1 of the License, or
  13   (at your option) any later version.
  14
  15   systemd is distributed in the hope that it will be useful, but
  16   WITHOUT ANY WARRANTY; without even the implied warranty of
  17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  18   Lesser General Public License for more details.
  19
  20   You should have received a copy of the GNU Lesser General Public License
  21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  22 -->
  23
  24 <refentry id="systemd"
  25           xmlns:xi="http://www.w3.org/2001/XInclude">
  26
  27         <refentryinfo>
  28                 <title>systemd</title>
  29                 <productname>systemd</productname>
  30
  31                 <authorgroup>
  32                         <author>
  33                                 <contrib>Developer</contrib>
  34                                 <firstname>Lennart</firstname>
  35                                 <surname>Poettering</surname>
  36                                 <email>lennart@poettering.net</email>
  37                         </author>
  38                 </authorgroup>
  39         </refentryinfo>
  40
  41         <refmeta>
  42                 <refentrytitle>systemd</refentrytitle>
  43                 <manvolnum>1</manvolnum>
  44         </refmeta>
  45
  46         <refnamediv>
  47                 <refname>systemd</refname>
  48                 <refname>init</refname>
  49                 <refpurpose>systemd system and service manager</refpurpose>
  50         </refnamediv>
  51
  52         <refsynopsisdiv>
  53                 <cmdsynopsis>
  54                         <command>systemd <arg choice="opt" rep="repeat">OPTIONS</arg></command>
  55                 </cmdsynopsis>
  56                 <cmdsynopsis>
  57                         <command>init <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="req">COMMAND</arg></command>
  58                 </cmdsynopsis>
  59         </refsynopsisdiv>
  60
  61         <refsect1>
  62                 <title>Description</title>
  63
  64                 <para>systemd is a system and service manager for
  65                 Linux operating systems. When run as first process on
  66                 boot (as PID 1), it acts as init system that brings
  67                 up and maintains userspace services.</para>
  68
  69                 <para>For compatibility with SysV, if systemd is called
  70                 as <command>init</command> and a PID that is not
  71                 1, it will execute <command>telinit</command> and pass
  72                 all command line arguments unmodified. That means
  73                 <command>init</command> and <command>telinit</command>
  74                 are mostly equivalent when invoked from 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
  80                 files in <filename>system.conf.d</filename> directories; when
  81                 run as a user instance, systemd interprets the configuration
  82                 file <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
  98                                 sequence, dump it and exit. This is an
  99                                 option useful for debugging
 100                                 only.</para></listitem>
 101                         </varlistentry>
 102                         <varlistentry>
 103                                 <term><option>--dump-configuration-items</option></term>
 104
 105                                 <listitem><para>Dump understood unit
 106                                 configuration items. This outputs a
 107                                 terse but complete list of
 108                                 configuration items understood in unit
 109                                 definition files.</para></listitem>
 110                         </varlistentry>
 111                         <varlistentry>
 112                                 <term><option>--unit=</option></term>
 113
 114                                 <listitem><para>Set default unit to
 115                                 activate on startup. If not specified,
 116                                 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>,
 124                                 tell systemd to run a
 125                                 system instance, even if the process ID is
 126                                 not 1, i.e. systemd is not run as init process.
 127                                 <option>--user</option> does the opposite,
 128                                 running a user instance even if the process
 129                                 ID is 1.
 130                                 Normally it should not be necessary to
 131                                 pass these options, as systemd
 132                                 automatically detects the mode it is
 133                                 started in. These options are hence of
 134                                 little use except for debugging. Note
 135                                 that it is not supported booting and
 136                                 maintaining a full system with systemd
 137                                 running in <option>--system</option>
 138                                 mode, but PID not 1. In practice,
 139                                 passing <option>--system</option> explicitly is
 140                                 only useful in conjunction with
 141                                 <option>--test</option>.</para></listitem>
 142                         </varlistentry>
 143                         <varlistentry>
 144                                 <term><option>--dump-core</option></term>
 145
 146                                 <listitem><para>Dump core on
 147                                 crash. This switch has no effect when
 148                                 run as user
 149                                 instance.</para></listitem>
 150                         </varlistentry>
 151                         <varlistentry>
 152                                 <term><option>--crash-shell</option></term>
 153
 154                                 <listitem><para>Run shell on
 155                                 crash. This switch has no effect when
 156                                 run as user
 157                                 instance.</para></listitem>
 158                         </varlistentry>
 159                         <varlistentry>
 160                                 <term><option>--confirm-spawn</option></term>
 161
 162                                 <listitem><para>Ask for confirmation
 163                                 when spawning processes. This switch
 164                                 has no effect when run as user
 165                                 instance.</para></listitem>
 166                         </varlistentry>
 167                         <varlistentry>
 168                                 <term><option>--show-status=</option></term>
 169
 170                                 <listitem><para>Show terse service
 171                                 status information while booting. This
 172                                 switch has no effect when run as user
 173                                 instance. Takes a boolean argument
 174                                 which may be omitted which is
 175                                 interpreted as
 176                                 <option>true</option>.</para></listitem>
 177                         </varlistentry>
 178                         <varlistentry>
 179                                 <term><option>--log-target=</option></term>
 180
 181                                 <listitem><para>Set log
 182                                 target. Argument must be one of
 183                                 <option>console</option>,
 184                                 <option>journal</option>,
 185                                 <option>kmsg</option>,
 186                                 <option>journal-or-kmsg</option>,
 187                                 <option>null</option>.</para></listitem>
 188                         </varlistentry>
 189                         <varlistentry>
 190                                 <term><option>--log-level=</option></term>
 191
 192                                 <listitem><para>Set log level. As
 193                                 argument this accepts a numerical log
 194                                 level or the well-known <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 195                                 symbolic names (lowercase):
 196                                 <option>emerg</option>,
 197                                 <option>alert</option>,
 198                                 <option>crit</option>,
 199                                 <option>err</option>,
 200                                 <option>warning</option>,
 201                                 <option>notice</option>,
 202                                 <option>info</option>,
 203                                 <option>debug</option>.</para></listitem>
 204                         </varlistentry>
 205                         <varlistentry>
 206                                 <term><option>--log-color=</option></term>
 207
 208                                 <listitem><para>Highlight important
 209                                 log messages. Argument is a boolean
 210                                 value. If the argument is omitted, it
 211                                 defaults to
 212                                 <option>true</option>.</para></listitem>
 213                         </varlistentry>
 214                         <varlistentry>
 215                                 <term><option>--log-location=</option></term>
 216
 217                                 <listitem><para>Include code location
 218                                 in log messages. This is mostly
 219                                 relevant for debugging
 220                                 purposes. Argument is a boolean
 221                                 value. If the argument is omitted
 222                                 it defaults to
 223                                 <option>true</option>.</para></listitem>
 224                         </varlistentry>
 225                         <varlistentry>
 226                                 <term><option>--default-standard-output=</option></term>
 227                                 <term><option>--default-standard-error=</option></term>
 228
 229                                 <listitem><para>Sets the default
 230                                 output or error output for all
 231                                 services and sockets, respectively. That is, controls
 232                                 the default for
 233                                 <option>StandardOutput=</option>
 234                                 and <option>StandardError=</option>
 235                                 (see
 236                                 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 237                                 for details). Takes one of
 238                                 <option>inherit</option>,
 239                                 <option>null</option>,
 240                                 <option>tty</option>,
 241                                 <option>journal</option>,
 242                                 <option>journal+console</option>,
 243                                 <option>syslog</option>,
 244                                 <option>syslog+console</option>,
 245                                 <option>kmsg</option>,
 246                                 <option>kmsg+console</option>.  If the
 247                                 argument is omitted
 248                                 <option>--default-standard-output=</option>
 249                                 defaults to <option>journal</option>
 250                                 and
 251                                 <option>--default-standard-error=</option>
 252                                 to
 253                                 <option>inherit</option>.</para></listitem>
 254                         </varlistentry>
 255
 256                         <xi:include href="standard-options.xml" xpointer="help" />
 257                         <xi:include href="standard-options.xml" xpointer="version" />
 258                 </variablelist>
 259         </refsect1>
 260
 261         <refsect1>
 262                 <title>Concepts</title>
 263
 264                 <para>systemd provides a dependency system between
 265                 various entities called "units" of 12 different
 266                 types. Units encapsulate various objects that are
 267                 relevant for system boot-up and maintenance. The
 268                 majority of units are configured in unit configuration
 269                 files, whose syntax and basic set of options is
 270                 described in
 271                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 272                 however some are created automatically from other
 273                 configuration, dynamically from system state or
 274                 programmatically at runtime. Units may be "active"
 275                 (meaning started, bound, plugged in, ..., depending on
 276                 the unit type, see below), or "inactive" (meaning
 277                 stopped, unbound, unplugged, ...), as well as in the
 278                 process of being activated or deactivated,
 279                 i.e. between the two states (these states are called
 280                 "activating", "deactivating"). A special "failed"
 281                 state is available as well, which is very similar to
 282                 "inactive" and is entered when the service failed in
 283                 some way (process returned error code on exit, or
 284                 crashed, or an operation timed out). If this state is
 285                 entered, the cause will be logged, for later
 286                 reference. Note that the various unit types may have a
 287                 number of additional substates, which are mapped to
 288                 the five generalized unit states described
 289                 here.</para>
 290
 291                 <para>The following unit types are available:</para>
 292
 293                 <orderedlist>
 294                         <listitem><para>Service units, which start and control
 295                         daemons and the processes they consist of. For
 296                         details see
 297                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 298
 299                         <listitem><para>Socket units, which
 300                         encapsulate local IPC or network sockets in
 301                         the system, useful for socket-based
 302                         activation. For details about socket units see
 303                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 304                         for details on socket-based activation and
 305                         other forms of activation, see
 306                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 307
 308                         <listitem><para>Target units are useful to
 309                         group units, or provide well-known
 310                         synchronization points during boot-up, see
 311                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 312
 313                         <listitem><para>Device units expose kernel
 314                         devices in systemd and may be used to
 315                         implement device-based activation. For details
 316                         see
 317                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 318
 319                         <listitem><para>Mount units control mount
 320                         points in the file system, for details see
 321                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 322
 323                         <listitem><para>Automount units provide
 324                         automount capabilities, for on-demand mounting
 325                         of file systems as well as parallelized
 326                         boot-up. See
 327                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 328
 329                         <listitem><para>Snapshot units can be used to
 330                         temporarily save the state of the set of
 331                         systemd units, which later may be restored by
 332                         activating the saved snapshot unit. For more
 333                         information see
 334                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 335
 336                         <listitem><para>Timer units are useful for
 337                         triggering activation of other units based on
 338                         timers. You may find details in
 339                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 340
 341                         <listitem><para>Swap units are very similar to
 342                         mount units and encapsulate memory swap
 343                         partitions or files of the operating
 344                         system. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 345
 346                         <listitem><para>Path units may be used
 347                         to activate other services when file system
 348                         objects change or are modified. See
 349                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 350
 351                         <listitem><para>Slice units may be used to
 352                         group units which manage system processes
 353                         (such as service and scope units) in a
 354                         hierarchical tree for resource management
 355                         purposes. See
 356                         <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 357
 358                         <listitem><para>Scope units are similar to
 359                         service units, but manage foreign processes
 360                         instead of starting them as well. See
 361                         <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 362
 363                 </orderedlist>
 364
 365                 <para>Units are named as their configuration
 366                 files. Some units have special semantics. A detailed
 367                 list is available in
 368                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 369
 370                 <para>systemd knows various kinds of dependencies,
 371                 including positive and negative requirement
 372                 dependencies (i.e. <varname>Requires=</varname> and
 373                 <varname>Conflicts=</varname>) as well as ordering
 374                 dependencies (<varname>After=</varname> and
 375                 <varname>Before=</varname>). NB: ordering and
 376                 requirement dependencies are orthogonal. If only a
 377                 requirement dependency exists between two units
 378                 (e.g. <filename>foo.service</filename> requires
 379                 <filename>bar.service</filename>), but no ordering
 380                 dependency (e.g. <filename>foo.service</filename>
 381                 after <filename>bar.service</filename>) and both are
 382                 requested to start, they will be started in
 383                 parallel. It is a common pattern that both requirement
 384                 and ordering dependencies are placed between two
 385                 units. Also note that the majority of dependencies are
 386                 implicitly created and maintained by systemd. In most
 387                 cases, it should be unnecessary to declare additional
 388                 dependencies manually, however it is possible to do
 389                 this.</para>
 390
 391                 <para>Application programs and units (via
 392                 dependencies) may request state changes of units. In
 393                 systemd, these requests are encapsulated as 'jobs' and
 394                 maintained in a job queue. Jobs may succeed or can
 395                 fail, their execution is ordered based on the ordering
 396                 dependencies of the units they have been scheduled
 397                 for.</para>
 398
 399                 <para>On boot systemd activates the target unit
 400                 <filename>default.target</filename> whose job is to
 401                 activate on-boot services and other on-boot units by
 402                 pulling them in via dependencies. Usually the unit
 403                 name is just an alias (symlink) for either
 404                 <filename>graphical.target</filename> (for
 405                 fully-featured boots into the UI) or
 406                 <filename>multi-user.target</filename> (for limited
 407                 console-only boots for use in embedded or server
 408                 environments, or similar; a subset of
 409                 graphical.target). However, it is at the discretion of
 410                 the administrator to configure it as an alias to any
 411                 other target unit. See
 412                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 413                 for details about these target units.</para>
 414
 415                 <para>Processes systemd spawns are placed in
 416                 individual Linux control groups named after the unit
 417                 which they belong to in the private systemd
 418                 hierarchy. (see <ulink
 419                 url="https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 420                 for more information about control groups, or short
 421                 "cgroups"). systemd uses this to effectively keep
 422                 track of processes. Control group information is
 423                 maintained in the kernel, and is accessible via the
 424                 file system hierarchy (beneath
 425                 <filename>/sys/fs/cgroup/systemd/</filename>), or in tools
 426                 such as
 427                 <citerefentry project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 428                 (<command>ps xawf -eo pid,user,cgroup,args</command>
 429                 is particularly useful to list all processes and the
 430                 systemd units they belong to.).</para>
 431
 432                 <para>systemd is compatible with the SysV init system
 433                 to a large degree: SysV init scripts are supported and
 434                 simply read as an alternative (though limited)
 435                 configuration file format. The SysV
 436                 <filename>/dev/initctl</filename> interface is
 437                 provided, and compatibility implementations of the
 438                 various SysV client tools are available. In addition to
 439                 that, various established Unix functionality such as
 440                 <filename>/etc/fstab</filename> or the
 441                 <filename>utmp</filename> database are
 442                 supported.</para>
 443
 444                 <para>systemd has a minimal transaction system: if a
 445                 unit is requested to start up or shut down it will add
 446                 it and all its dependencies to a temporary
 447                 transaction. Then, it will verify if the transaction
 448                 is consistent (i.e. whether the ordering of all units
 449                 is cycle-free). If it is not, systemd will try to fix
 450                 it up, and removes non-essential jobs from the
 451                 transaction that might remove the loop. Also, systemd
 452                 tries to suppress non-essential jobs in the
 453                 transaction that would stop a running service. Finally
 454                 it is checked whether the jobs of the transaction
 455                 contradict jobs that have already been queued, and
 456                 optionally the transaction is aborted then. If all
 457                 worked out and the transaction is consistent and
 458                 minimized in its impact it is merged with all already
 459                 outstanding jobs and added to the run
 460                 queue. Effectively this means that before executing a
 461                 requested operation, systemd will verify that it makes
 462                 sense, fixing it if possible, and only failing if it
 463                 really cannot work.</para>
 464
 465                 <para>Systemd contains native implementations of
 466                 various tasks that need to be executed as part of the
 467                 boot process. For example, it sets the hostname or
 468                 configures the loopback network device. It also sets
 469                 up and mounts various API file systems, such as
 470                 <filename>/sys</filename> or
 471                 <filename>/proc</filename>.</para>
 472
 473                 <para>For more information about the concepts and
 474                 ideas behind systemd, please refer to the <ulink
 475                 url="http://0pointer.de/blog/projects/systemd.html">Original
 476                 Design Document</ulink>.</para>
 477
 478                 <para>Note that some but not all interfaces provided
 479                 by systemd are covered by the <ulink
 480                 url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 481                 Stability Promise</ulink>.</para>
 482
 483                 <para>Units may be generated dynamically at boot and
 484                 system manager reload time, for example based on other
 485                 configuration files or parameters passed on the kernel
 486                 command line. For details see the <ulink
 487                 url="http://www.freedesktop.org/wiki/Software/systemd/Generators">Generators
 488                 Specification</ulink>.</para>
 489
 490                 <para>Systems which invoke systemd in a container
 491                 or initrd environment should implement the
 492                 <ulink
 493                 url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container
 494                 Interface</ulink> or <ulink
 495                 url="http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd
 496                 Interface</ulink> specifications, respectively.</para>
 497         </refsect1>
 498
 499         <refsect1>
 500                 <title>Directories</title>
 501
 502                 <variablelist>
 503                         <varlistentry>
 504                                 <term>System unit directories</term>
 505
 506                                 <listitem><para>The systemd system
 507                                 manager reads unit configuration from
 508                                 various directories. Packages that
 509                                 want to install unit files shall place
 510                                 them in the directory returned by
 511                                 <command>pkg-config systemd
 512                                 --variable=systemdsystemunitdir</command>. Other
 513                                 directories checked are
 514                                 <filename>/usr/local/lib/systemd/system</filename>
 515                                 and
 516                                 <filename>/usr/lib/systemd/system</filename>. User
 517                                 configuration always takes
 518                                 precedence. <command>pkg-config
 519                                 systemd
 520                                 --variable=systemdsystemconfdir</command>
 521                                 returns the path of the system
 522                                 configuration directory. Packages
 523                                 should alter the content of these
 524                                 directories only with the
 525                                 <command>enable</command> and
 526                                 <command>disable</command> commands of
 527                                 the
 528                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 529                                 tool. Full list of directories is provided in
 530                                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 531                                 </para></listitem>
 532                         </varlistentry>
 533                 </variablelist>
 534
 535                 <variablelist>
 536                         <varlistentry>
 537                                 <term>User unit directories</term>
 538
 539                                 <listitem><para>Similar rules apply
 540                                 for the user unit
 541                                 directories. However, here the <ulink
 542                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 543                                 Base Directory specification</ulink>
 544                                 is followed to find
 545                                 units. Applications should place their
 546                                 unit files in the directory returned
 547                                 by <command>pkg-config systemd
 548                                 --variable=systemduserunitdir</command>. Global
 549                                 configuration is done in the directory
 550                                 reported by <command>pkg-config
 551                                 systemd
 552                                 --variable=systemduserconfdir</command>. The
 553                                 <command>enable</command> and
 554                                 <command>disable</command> commands of
 555                                 the
 556                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 557                                 tool can handle both global (i.e. for
 558                                 all users) and private (for one user)
 559                                 enabling/disabling of
 560                                 units. Full list of directories is provided in
 561                                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 562                                 </para></listitem>
 563                         </varlistentry>
 564                 </variablelist>
 565
 566                 <variablelist>
 567                         <varlistentry>
 568                                 <term>SysV init scripts directory</term>
 569
 570                                 <listitem><para>The location of the
 571                                 SysV init script directory varies
 572                                 between distributions. If systemd
 573                                 cannot find a native unit file for a
 574                                 requested service, it will look for a
 575                                 SysV init script of the same name
 576                                 (with the
 577                                 <filename>.service</filename> suffix
 578                                 removed).</para></listitem>
 579                         </varlistentry>
 580                 </variablelist>
 581
 582                 <variablelist>
 583                         <varlistentry>
 584                                 <term>SysV runlevel link farm directory</term>
 585
 586                                 <listitem><para>The location of the
 587                                 SysV runlevel link farm directory
 588                                 varies between distributions. systemd
 589                                 will take the link farm into account
 590                                 when figuring out whether a service
 591                                 shall be enabled. Note that a service
 592                                 unit with a native unit configuration
 593                                 file cannot be started by activating it
 594                                 in the SysV runlevel link
 595                                 farm.</para></listitem>
 596                         </varlistentry>
 597                 </variablelist>
 598         </refsect1>
 599
 600         <refsect1>
 601                 <title>Signals</title>
 602
 603                 <variablelist>
 604                         <varlistentry>
 605                                 <term><constant>SIGTERM</constant></term>
 606
 607                                 <listitem><para>Upon receiving this
 608                                 signal the systemd system manager
 609                                 serializes its state, reexecutes
 610                                 itself and deserializes the saved
 611                                 state again. This is mostly equivalent
 612                                 to <command>systemctl
 613                                 daemon-reexec</command>.</para>
 614
 615                                 <para>systemd user managers will
 616                                 start the
 617                                 <filename>exit.target</filename> unit
 618                                 when this signal is received. This is
 619                                 mostly equivalent to
 620                                 <command>systemctl --user start
 621                                 exit.target</command>.</para></listitem>
 622                         </varlistentry>
 623
 624                         <varlistentry>
 625                                 <term><constant>SIGINT</constant></term>
 626
 627                                 <listitem><para>Upon receiving this
 628                                 signal the systemd system manager will
 629                                 start the
 630                                 <filename>ctrl-alt-del.target</filename> unit. This
 631                                 is mostly equivalent to
 632                                 <command>systemctl start
 633                                 ctl-alt-del.target</command>.</para>
 634
 635                                 <para>systemd user managers
 636                                 treat this signal the same way as
 637                                 <constant>SIGTERM</constant>.</para></listitem>
 638                         </varlistentry>
 639
 640                         <varlistentry>
 641                                 <term><constant>SIGWINCH</constant></term>
 642
 643                                 <listitem><para>When this signal is
 644                                 received the systemd system manager
 645                                 will start the
 646                                 <filename>kbrequest.target</filename>
 647                                 unit. This is mostly equivalent to
 648                                 <command>systemctl start
 649                                 kbrequest.target</command>.</para>
 650
 651                                 <para>This signal is ignored by
 652                                 systemd user
 653                                 managers.</para></listitem>
 654                         </varlistentry>
 655
 656                         <varlistentry>
 657                                 <term><constant>SIGPWR</constant></term>
 658
 659                                 <listitem><para>When this signal is
 660                                 received the systemd manager
 661                                 will start the
 662                                 <filename>sigpwr.target</filename>
 663                                 unit. This is mostly equivalent to
 664                                 <command>systemctl start
 665                                 sigpwr.target</command>.</para></listitem>
 666                         </varlistentry>
 667
 668                         <varlistentry>
 669                                 <term><constant>SIGUSR1</constant></term>
 670
 671                                 <listitem><para>When this signal is
 672                                 received the systemd manager will try
 673                                 to reconnect to the D-Bus
 674                                 bus.</para></listitem>
 675                         </varlistentry>
 676
 677                         <varlistentry>
 678                                 <term><constant>SIGUSR2</constant></term>
 679
 680                                 <listitem><para>When this signal is
 681                                 received the systemd manager will log
 682                                 its complete state in human readable
 683                                 form. The data logged is the same as
 684                                 printed by <command>systemd-analyze
 685                                 dump</command>.</para></listitem>
 686                         </varlistentry>
 687
 688                         <varlistentry>
 689                                 <term><constant>SIGHUP</constant></term>
 690
 691                                 <listitem><para>Reloads the complete
 692                                 daemon configuration. This is mostly
 693                                 equivalent to <command>systemctl
 694                                 daemon-reload</command>.</para></listitem>
 695                         </varlistentry>
 696
 697                         <varlistentry>
 698                                 <term><constant>SIGRTMIN+0</constant></term>
 699
 700                                 <listitem><para>Enters default mode, starts the
 701                                 <filename>default.target</filename>
 702                                 unit. This is mostly equivalent to
 703                                 <command>systemctl start
 704                                 default.target</command>.</para></listitem>
 705                         </varlistentry>
 706
 707                         <varlistentry>
 708                                 <term><constant>SIGRTMIN+1</constant></term>
 709
 710                                 <listitem><para>Enters rescue mode,
 711                                 starts the
 712                                 <filename>rescue.target</filename>
 713                                 unit. This is mostly equivalent to
 714                                 <command>systemctl isolate
 715                                 rescue.target</command>.</para></listitem>
 716                         </varlistentry>
 717
 718                         <varlistentry>
 719                                 <term><constant>SIGRTMIN+2</constant></term>
 720
 721                                 <listitem><para>Enters emergency mode,
 722                                 starts the
 723                                 <filename>emergency.service</filename>
 724                                 unit. This is mostly equivalent to
 725                                 <command>systemctl isolate
 726                                 emergency.service</command>.</para></listitem>
 727                         </varlistentry>
 728
 729                         <varlistentry>
 730                                 <term><constant>SIGRTMIN+3</constant></term>
 731
 732                                 <listitem><para>Halts the machine,
 733                                 starts the
 734                                 <filename>halt.target</filename>
 735                                 unit. This is mostly equivalent to
 736                                 <command>systemctl start
 737                                 halt.target</command>.</para></listitem>
 738                         </varlistentry>
 739
 740                         <varlistentry>
 741                                 <term><constant>SIGRTMIN+4</constant></term>
 742
 743                                 <listitem><para>Powers off the machine,
 744                                 starts the
 745                                 <filename>poweroff.target</filename>
 746                                 unit. This is mostly equivalent to
 747                                 <command>systemctl start
 748                                 poweroff.target</command>.</para></listitem>
 749                         </varlistentry>
 750
 751                         <varlistentry>
 752                                 <term><constant>SIGRTMIN+5</constant></term>
 753
 754                                 <listitem><para>Reboots the machine,
 755                                 starts the
 756                                 <filename>reboot.target</filename>
 757                                 unit. This is mostly equivalent to
 758                                 <command>systemctl start
 759                                 reboot.target</command>.</para></listitem>
 760                         </varlistentry>
 761
 762                         <varlistentry>
 763                                 <term><constant>SIGRTMIN+6</constant></term>
 764
 765                                 <listitem><para>Reboots the machine via kexec,
 766                                 starts the
 767                                 <filename>kexec.target</filename>
 768                                 unit. This is mostly equivalent to
 769                                 <command>systemctl start
 770                                 kexec.target</command>.</para></listitem>
 771                         </varlistentry>
 772
 773                         <varlistentry>
 774                                 <term><constant>SIGRTMIN+13</constant></term>
 775
 776                                 <listitem><para>Immediately halts the machine.</para></listitem>
 777                         </varlistentry>
 778
 779                         <varlistentry>
 780                                 <term><constant>SIGRTMIN+14</constant></term>
 781
 782                                 <listitem><para>Immediately powers off the machine.</para></listitem>
 783                         </varlistentry>
 784
 785                         <varlistentry>
 786                                 <term><constant>SIGRTMIN+15</constant></term>
 787
 788                                 <listitem><para>Immediately reboots the machine.</para></listitem>
 789                         </varlistentry>
 790
 791                         <varlistentry>
 792                                 <term><constant>SIGRTMIN+16</constant></term>
 793
 794                                 <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
 795                         </varlistentry>
 796
 797                         <varlistentry>
 798                                 <term><constant>SIGRTMIN+20</constant></term>
 799
 800                                 <listitem><para>Enables display of
 801                                 status messages on the console, as
 802                                 controlled via
 803                                 <varname>systemd.show_status=1</varname>
 804                                 on the kernel command
 805                                 line.</para></listitem>
 806                         </varlistentry>
 807
 808                         <varlistentry>
 809                                 <term><constant>SIGRTMIN+21</constant></term>
 810
 811                                 <listitem><para>Disables display of
 812                                 status messages on the console, as
 813                                 controlled via
 814                                 <varname>systemd.show_status=0</varname>
 815                                 on the kernel command
 816                                 line.</para></listitem>
 817                         </varlistentry>
 818
 819                         <varlistentry>
 820                                 <term><constant>SIGRTMIN+22</constant></term>
 821                                 <term><constant>SIGRTMIN+23</constant></term>
 822
 823                                 <listitem><para>Sets the log level to
 824                                 <literal>debug</literal>
 825                                 (or <literal>info</literal> on
 826                                 <constant>SIGRTMIN+23</constant>), as
 827                                 controlled via
 828                                 <varname>systemd.log_level=debug</varname>
 829                                 (or <varname>systemd.log_level=info</varname>
 830                                 on <constant>SIGRTMIN+23</constant>) on
 831                                 the kernel command
 832                                 line.</para></listitem>
 833                         </varlistentry>
 834
 835                         <varlistentry>
 836                                 <term><constant>SIGRTMIN+24</constant></term>
 837
 838                                 <listitem><para>Immediately exits the
 839                                 manager (only available for --user
 840                                 instances).</para></listitem>
 841                         </varlistentry>
 842
 843                         <varlistentry>
 844                                 <term><constant>SIGRTMIN+26</constant></term>
 845                                 <term><constant>SIGRTMIN+27</constant></term>
 846                                 <term><constant>SIGRTMIN+28</constant></term>
 847
 848                                 <listitem><para>Sets the log level to
 849                                 <literal>journal-or-kmsg</literal> (or
 850                                 <literal>console</literal> on
 851                                 <constant>SIGRTMIN+27</constant>,
 852                                 <literal>kmsg</literal> on
 853                                 <constant>SIGRTMIN+28</constant>), as
 854                                 controlled via
 855                                 <varname>systemd.log_target=journal-or-kmsg</varname>
 856                                 (or
 857                                 <varname>systemd.log_target=console</varname>
 858                                 on <constant>SIGRTMIN+27</constant> or
 859                                 <varname>systemd.log_target=kmsg</varname>
 860                                 on <constant>SIGRTMIN+28</constant>)
 861                                 on the kernel command
 862                                 line.</para></listitem>
 863                         </varlistentry>
 864                 </variablelist>
 865         </refsect1>
 866
 867         <refsect1>
 868                 <title>Environment</title>
 869
 870                 <variablelist class='environment-variables'>
 871                         <varlistentry>
 872                                 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 873                                 <listitem><para>systemd reads the
 874                                 log level from this environment
 875                                 variable. This can be overridden with
 876                                 <option>--log-level=</option>.</para></listitem>
 877                         </varlistentry>
 878
 879                         <varlistentry>
 880                                 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 881                                 <listitem><para>systemd reads the
 882                                 log target from this environment
 883                                 variable. This can be overridden with
 884                                 <option>--log-target=</option>.</para></listitem>
 885                         </varlistentry>
 886
 887                         <varlistentry>
 888                                 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 889                                 <listitem><para>Controls whether
 890                                 systemd highlights important log
 891                                 messages. This can be overridden with
 892                                 <option>--log-color=</option>.</para></listitem>
 893                         </varlistentry>
 894
 895                         <varlistentry>
 896                                 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 897                                 <listitem><para>Controls whether
 898                                 systemd prints the code location along
 899                                 with log messages. This can be
 900                                 overridden with
 901                                 <option>--log-location=</option>.</para></listitem>
 902                         </varlistentry>
 903
 904                         <varlistentry>
 905                                 <term><varname>$XDG_CONFIG_HOME</varname></term>
 906                                 <term><varname>$XDG_CONFIG_DIRS</varname></term>
 907                                 <term><varname>$XDG_DATA_HOME</varname></term>
 908                                 <term><varname>$XDG_DATA_DIRS</varname></term>
 909
 910                                 <listitem><para>The systemd user
 911                                 manager uses these variables in
 912                                 accordance to the <ulink
 913                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 914                                 Base Directory specification</ulink>
 915                                 to find its configuration.</para></listitem>
 916                         </varlistentry>
 917
 918                         <varlistentry>
 919                                 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 920
 921                                 <listitem><para>Controls where systemd
 922                                 looks for unit
 923                                 files.</para></listitem>
 924                         </varlistentry>
 925
 926                         <varlistentry>
 927                                 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 928
 929                                 <listitem><para>Controls where systemd
 930                                 looks for SysV init scripts.</para></listitem>
 931                         </varlistentry>
 932
 933                         <varlistentry>
 934                                 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 935
 936                                 <listitem><para>Controls where systemd
 937                                 looks for SysV init script runlevel link
 938                                 farms.</para></listitem>
 939                         </varlistentry>
 940
 941                         <varlistentry>
 942                                 <term><varname>$LISTEN_PID</varname></term>
 943                                 <term><varname>$LISTEN_FDS</varname></term>
 944
 945                                 <listitem><para>Set by systemd for
 946                                 supervised processes during
 947                                 socket-based activation. See
 948                                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 949                                 for more information.
 950                                 </para></listitem>
 951                         </varlistentry>
 952
 953                         <varlistentry>
 954                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 955
 956                                 <listitem><para>Set by systemd for
 957                                 supervised processes for status and
 958                                 start-up completion notification. See
 959                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 960                                 for more information.
 961                                 </para></listitem>
 962                         </varlistentry>
 963                 </variablelist>
 964         </refsect1>
 965
 966         <refsect1>
 967                 <title>Kernel Command Line</title>
 968
 969                 <para>When run as system instance systemd parses a
 970                 number of kernel command line
 971                 arguments<footnote><para>If run inside a Linux
 972                 container these arguments may be passed as command
 973                 line arguments to systemd itself, next to any of the
 974                 command line options listed in the Options section
 975                 above. If run outside of Linux containers, these
 976                 arguments are parsed from
 977                 <filename>/proc/cmdline</filename>
 978                 instead.</para></footnote>:</para>
 979
 980                 <variablelist class='kernel-commandline-options'>
 981                         <varlistentry>
 982                                 <term><varname>systemd.unit=</varname></term>
 983                                 <term><varname>rd.systemd.unit=</varname></term>
 984
 985                                 <listitem><para>Overrides the unit to
 986                                 activate on boot. Defaults to
 987                                 <filename>default.target</filename>. This
 988                                 may be used to temporarily boot into a
 989                                 different boot unit, for example
 990                                 <filename>rescue.target</filename> or
 991                                 <filename>emergency.service</filename>. See
 992                                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 993                                 for details about these units. The
 994                                 option prefixed with
 995                                 <literal>rd.</literal> is honored
 996                                 only in the initial RAM disk (initrd),
 997                                 while the one that is not prefixed only
 998                                 in the main system.</para></listitem>
 999                         </varlistentry>
1000
1001                         <varlistentry>
1002                                 <term><varname>systemd.dump_core=</varname></term>
1003
1004                                 <listitem><para>Takes a boolean
1005                                 argument. If <option>true</option>,
1006                                 systemd dumps core when it
1007                                 crashes. Otherwise, no core dump is
1008                                 created. Defaults to
1009                                 <option>true</option>.</para></listitem>
1010                         </varlistentry>
1011
1012                         <varlistentry>
1013                                 <term><varname>systemd.crash_shell=</varname></term>
1014
1015                                 <listitem><para>Takes a boolean
1016                                 argument. If <option>true</option>,
1017                                 systemd spawns a shell when it
1018                                 crashes. Otherwise, no shell is
1019                                 spawned. Defaults to
1020                                 <option>false</option>, for security
1021                                 reasons, as the shell is not protected
1022                                 by any password
1023                                 authentication.</para></listitem>
1024                         </varlistentry>
1025
1026                         <varlistentry>
1027                                 <term><varname>systemd.crash_chvt=</varname></term>
1028
1029                                 <listitem><para>Takes an integer
1030                                 argument. If positive systemd
1031                                 activates the specified virtual
1032                                 terminal when it crashes. Defaults to
1033                                 <constant>-1</constant>.</para></listitem>
1034                         </varlistentry>
1035
1036                         <varlistentry>
1037                                 <term><varname>systemd.confirm_spawn=</varname></term>
1038
1039                                 <listitem><para>Takes a boolean
1040                                 argument. If <option>true</option>,
1041                                 asks for confirmation when spawning
1042                                 processes. Defaults to
1043                                 <option>false</option>.</para></listitem>
1044                         </varlistentry>
1045
1046                         <varlistentry>
1047                                 <term><varname>systemd.show_status=</varname></term>
1048
1049                                 <listitem><para>Takes a boolean
1050                                 argument or the constant
1051                                 <constant>auto</constant>. If
1052                                 <option>true</option>, shows terse
1053                                 service status updates on the console
1054                                 during bootup.
1055                                 <constant>auto</constant> behaves like
1056                                 <option>false</option> until a service
1057                                 fails or there is a significant delay
1058                                 in boot. Defaults to
1059                                 <option>true</option>, unless
1060                                 <option>quiet</option> is passed as
1061                                 kernel command line option in which
1062                                 case it defaults to
1063                                 <constant>auto</constant>.</para></listitem>
1064                         </varlistentry>
1065
1066                         <varlistentry>
1067                                 <term><varname>systemd.log_target=</varname></term>
1068                                 <term><varname>systemd.log_level=</varname></term>
1069                                 <term><varname>systemd.log_color=</varname></term>
1070                                 <term><varname>systemd.log_location=</varname></term>
1071
1072                                 <listitem><para>Controls log output,
1073                                 with the same effect as the
1074                                 <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
1075                                 environment variables described above.</para></listitem>
1076                         </varlistentry>
1077
1078                         <varlistentry>
1079                                 <term><varname>systemd.default_standard_output=</varname></term>
1080                                 <term><varname>systemd.default_standard_error=</varname></term>
1081                                 <listitem><para>Controls default
1082                                 standard output and error output for
1083                                 services, with the same effect as the
1084                                 <option>--default-standard-output=</option>
1085                                 and <option>--default-standard-error=</option>
1086                                 command line arguments described
1087                                 above, respectively.</para></listitem>
1088                         </varlistentry>
1089
1090                         <varlistentry>
1091                                 <term><varname>systemd.setenv=</varname></term>
1092
1093                                 <listitem><para>Takes a string
1094                                 argument in the form VARIABLE=VALUE.
1095                                 May be used to set default environment
1096                                 variables to add to forked child processes.
1097                                 May be used more than once to set multiple
1098                                 variables.</para></listitem>
1099                         </varlistentry>
1100
1101                         <varlistentry>
1102                                 <term><varname>quiet</varname></term>
1103
1104                                 <listitem><para>Turn off
1105                                 status output at boot, much like
1106                                 <varname>systemd.show_status=false</varname>
1107                                 would. Note that this option is also
1108                                 read by the kernel itself and disables
1109                                 kernel log output. Passing this option
1110                                 hence turns off the usual output from
1111                                 both the system manager and the kernel.
1112                                 </para></listitem>
1113                         </varlistentry>
1114
1115                         <varlistentry>
1116                                 <term><varname>debug</varname></term>
1117
1118                                 <listitem><para>Turn on debugging
1119                                 output. This is equivalent to
1120                                 <varname>systemd.log_level=debug</varname>.
1121                                 Note that this option is also read by
1122                                 the kernel itself and enables kernel
1123                                 debug output.  Passing this option
1124                                 hence turns on the debug output from
1125                                 both the system manager and the
1126                                 kernel.</para></listitem>
1127                         </varlistentry>
1128
1129                         <varlistentry>
1130                                 <term><varname>emergency</varname></term>
1131                                 <term><varname>-b</varname></term>
1132
1133                                 <listitem><para>Boot into emergency
1134                                 mode. This is equivalent to
1135                                 <varname>systemd.unit=emergency.target</varname>
1136                                 and provided for compatibility reasons
1137                                 and to be easier to
1138                                 type.</para></listitem>
1139                         </varlistentry>
1140
1141                         <varlistentry>
1142                                 <term><varname>rescue</varname></term>
1143                                 <term><varname>single</varname></term>
1144                                 <term><varname>s</varname></term>
1145                                 <term><varname>S</varname></term>
1146                                 <term><varname>1</varname></term>
1147
1148                                 <listitem><para>Boot into rescue
1149                                 mode. This is equivalent to
1150                                 <varname>systemd.unit=rescue.target</varname>
1151                                 and provided for compatibility reasons
1152                                 and to be easier to
1153                                 type.</para></listitem>
1154                         </varlistentry>
1155
1156                         <varlistentry>
1157                                 <term><varname>2</varname></term>
1158                                 <term><varname>3</varname></term>
1159                                 <term><varname>4</varname></term>
1160                                 <term><varname>5</varname></term>
1161
1162                                 <listitem><para>Boot into the
1163                                 specified legacy SysV runlevel. These
1164                                 are equivalent to
1165                                 <varname>systemd.unit=runlevel2.target</varname>,
1166                                 <varname>systemd.unit=runlevel3.target</varname>,
1167                                 <varname>systemd.unit=runlevel4.target</varname>,
1168                                 and <varname>systemd.unit=runlevel5.target</varname>, respectively,
1169                                 and provided for compatibility reasons
1170                                 and to be easier to
1171                                 type.</para></listitem>
1172                         </varlistentry>
1173
1174                         <varlistentry>
1175                                 <term><varname>locale.LANG=</varname></term>
1176                                 <term><varname>locale.LANGUAGE=</varname></term>
1177                                 <term><varname>locale.LC_CTYPE=</varname></term>
1178                                 <term><varname>locale.LC_NUMERIC=</varname></term>
1179                                 <term><varname>locale.LC_TIME=</varname></term>
1180                                 <term><varname>locale.LC_COLLATE=</varname></term>
1181                                 <term><varname>locale.LC_MONETARY=</varname></term>
1182                                 <term><varname>locale.LC_MESSAGES=</varname></term>
1183                                 <term><varname>locale.LC_PAPER=</varname></term>
1184                                 <term><varname>locale.LC_NAME=</varname></term>
1185                                 <term><varname>locale.LC_ADDRESS=</varname></term>
1186                                 <term><varname>locale.LC_TELEPHONE=</varname></term>
1187                                 <term><varname>locale.LC_MEASUREMENT=</varname></term>
1188                                 <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1189
1190                                 <listitem><para>Set the system locale
1191                                 to use. This overrides the settings in
1192                                 <filename>/etc/locale.conf</filename>. For
1193                                 more information see
1194                                 <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1195                                 and
1196                                 <citerefentry><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1197                                 </para></listitem>
1198                         </varlistentry>
1199                 </variablelist>
1200
1201                 <para>For other kernel command line parameters
1202                 understood by components of the core OS, please refer
1203                 to
1204                 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1205         </refsect1>
1206
1207         <refsect1>
1208                 <title>Sockets and FIFOs</title>
1209
1210                 <variablelist>
1211                         <varlistentry>
1212                                 <term><filename>/run/systemd/notify</filename></term>
1213
1214                                 <listitem><para>Daemon status
1215                                 notification socket. This is an
1216                                 <constant>AF_UNIX</constant> datagram socket and is used to
1217                                 implement the daemon notification
1218                                 logic as implemented by
1219                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1220
1221                         </varlistentry>
1222
1223                         <varlistentry>
1224                                 <term><filename>/run/systemd/shutdownd</filename></term>
1225
1226                                 <listitem><para>Used internally by the
1227                                 <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1228                                 tool to implement delayed
1229                                 shutdowns. This is an <constant>AF_UNIX</constant> datagram
1230                                 socket.</para></listitem>
1231                         </varlistentry>
1232
1233                         <varlistentry>
1234                                 <term><filename>/run/systemd/private</filename></term>
1235
1236                                 <listitem><para>Used internally as
1237                                 communication channel between
1238                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1239                                 and the systemd process. This is an
1240                                 <constant>AF_UNIX</constant> stream socket. This interface
1241                                 is private to systemd and should not
1242                                 be used in external
1243                                 projects.</para></listitem>
1244                         </varlistentry>
1245
1246                         <varlistentry>
1247                                 <term><filename>/dev/initctl</filename></term>
1248
1249                                 <listitem><para>Limited compatibility
1250                                 support for the SysV client interface,
1251                                 as implemented by the
1252                                 <filename>systemd-initctl.service</filename>
1253                                 unit. This is a named pipe in the file
1254                                 system. This interface is obsolete and
1255                                 should not be used in new
1256                                 applications.</para></listitem>
1257                         </varlistentry>
1258                 </variablelist>
1259         </refsect1>
1260
1261         <refsect1>
1262                 <title>See Also</title>
1263                 <para>
1264                         The <ulink url="http://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
1265                         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1266                         <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1267                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1268                         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1269                         <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1270                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1271                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1272                         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1273                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1274                         <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1275                         <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1276                         <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1277                         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1278                 </para>
1279         </refsect1>
1280
1281 </refentry>