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 system instance, systemd interprets
  79                 the configuration file
  80                 <filename>system.conf</filename>, otherwise
  81                 <filename>user.conf</filename>. See
  82                 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  83                 for more information.</para>
  84         </refsect1>
  85
  86         <refsect1>
  87                 <title>Options</title>
  88
  89                 <para>The following options are understood:</para>
  90
  91                 <variablelist>
  92                         <varlistentry>
  93                                 <term><option>--test</option></term>
  94
  95                                 <listitem><para>Determine startup
  96                                 sequence, dump it and exit. This is an
  97                                 option useful for debugging
  98                                 only.</para></listitem>
  99                         </varlistentry>
 100                         <varlistentry>
 101                                 <term><option>--dump-configuration-items</option></term>
 102
 103                                 <listitem><para>Dump understood unit
 104                                 configuration items. This outputs a
 105                                 terse but complete list of
 106                                 configuration items understood in unit
 107                                 definition files.</para></listitem>
 108                         </varlistentry>
 109                         <varlistentry>
 110                                 <term><option>--unit=</option></term>
 111
 112                                 <listitem><para>Set default unit to
 113                                 activate on startup. If not specified,
 114                                 defaults to
 115                                 <filename>default.target</filename>.</para></listitem>
 116                         </varlistentry>
 117                         <varlistentry>
 118                                 <term><option>--system</option></term>
 119                                 <term><option>--user</option></term>
 120
 121                                 <listitem><para>For <option>--system</option>,
 122                                 tell systemd to run a
 123                                 system instance, even if the process ID is
 124                                 not 1, i.e. systemd is not run as init process.
 125                                 <option>--user</option> does the opposite,
 126                                 running a user instance even if the process
 127                                 ID is 1.
 128                                 Normally it should not be necessary to
 129                                 pass these options, as systemd
 130                                 automatically detects the mode it is
 131                                 started in. These options are hence of
 132                                 little use except for debugging. Note
 133                                 that it is not supported booting and
 134                                 maintaining a full system with systemd
 135                                 running in <option>--system</option>
 136                                 mode, but PID not 1. In practice,
 137                                 passing <option>--system</option> explicitly is
 138                                 only useful in conjunction with
 139                                 <option>--test</option>.</para></listitem>
 140                         </varlistentry>
 141                         <varlistentry>
 142                                 <term><option>--dump-core</option></term>
 143
 144                                 <listitem><para>Dump core on
 145                                 crash. This switch has no effect when
 146                                 run as user
 147                                 instance.</para></listitem>
 148                         </varlistentry>
 149                         <varlistentry>
 150                                 <term><option>--crash-shell</option></term>
 151
 152                                 <listitem><para>Run shell on
 153                                 crash. This switch has no effect when
 154                                 run as user
 155                                 instance.</para></listitem>
 156                         </varlistentry>
 157                         <varlistentry>
 158                                 <term><option>--confirm-spawn</option></term>
 159
 160                                 <listitem><para>Ask for confirmation
 161                                 when spawning processes. This switch
 162                                 has no effect when run as user
 163                                 instance.</para></listitem>
 164                         </varlistentry>
 165                         <varlistentry>
 166                                 <term><option>--show-status=</option></term>
 167
 168                                 <listitem><para>Show terse service
 169                                 status information while booting. This
 170                                 switch has no effect when run as user
 171                                 instance. Takes a boolean argument
 172                                 which may be omitted which is
 173                                 interpreted as
 174                                 <option>true</option>.</para></listitem>
 175                         </varlistentry>
 176                         <varlistentry>
 177                                 <term><option>--log-target=</option></term>
 178
 179                                 <listitem><para>Set log
 180                                 target. Argument must be one of
 181                                 <option>console</option>,
 182                                 <option>journal</option>,
 183                                 <option>kmsg</option>,
 184                                 <option>journal-or-kmsg</option>,
 185                                 <option>null</option>.</para></listitem>
 186                         </varlistentry>
 187                         <varlistentry>
 188                                 <term><option>--log-level=</option></term>
 189
 190                                 <listitem><para>Set log level. As
 191                                 argument this accepts a numerical log
 192                                 level or the well-known <citerefentry project='man-pages'><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 193                                 symbolic names (lowercase):
 194                                 <option>emerg</option>,
 195                                 <option>alert</option>,
 196                                 <option>crit</option>,
 197                                 <option>err</option>,
 198                                 <option>warning</option>,
 199                                 <option>notice</option>,
 200                                 <option>info</option>,
 201                                 <option>debug</option>.</para></listitem>
 202                         </varlistentry>
 203                         <varlistentry>
 204                                 <term><option>--log-color=</option></term>
 205
 206                                 <listitem><para>Highlight important
 207                                 log messages. Argument is a boolean
 208                                 value. If the argument is omitted, it
 209                                 defaults to
 210                                 <option>true</option>.</para></listitem>
 211                         </varlistentry>
 212                         <varlistentry>
 213                                 <term><option>--log-location=</option></term>
 214
 215                                 <listitem><para>Include code location
 216                                 in log messages. This is mostly
 217                                 relevant for debugging
 218                                 purposes. Argument is a boolean
 219                                 value. If the argument is omitted
 220                                 it defaults to
 221                                 <option>true</option>.</para></listitem>
 222                         </varlistentry>
 223                         <varlistentry>
 224                                 <term><option>--default-standard-output=</option></term>
 225                                 <term><option>--default-standard-error=</option></term>
 226
 227                                 <listitem><para>Sets the default
 228                                 output or error output for all
 229                                 services and sockets, respectively. That is, controls
 230                                 the default for
 231                                 <option>StandardOutput=</option>
 232                                 and <option>StandardError=</option>
 233                                 (see
 234                                 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 235                                 for details). Takes one of
 236                                 <option>inherit</option>,
 237                                 <option>null</option>,
 238                                 <option>tty</option>,
 239                                 <option>journal</option>,
 240                                 <option>journal+console</option>,
 241                                 <option>syslog</option>,
 242                                 <option>syslog+console</option>,
 243                                 <option>kmsg</option>,
 244                                 <option>kmsg+console</option>.  If the
 245                                 argument is omitted
 246                                 <option>--default-standard-output=</option>
 247                                 defaults to <option>journal</option>
 248                                 and
 249                                 <option>--default-standard-error=</option>
 250                                 to
 251                                 <option>inherit</option>.</para></listitem>
 252                         </varlistentry>
 253
 254                         <xi:include href="standard-options.xml" xpointer="help" />
 255                         <xi:include href="standard-options.xml" xpointer="version" />
 256                 </variablelist>
 257         </refsect1>
 258
 259         <refsect1>
 260                 <title>Concepts</title>
 261
 262                 <para>systemd provides a dependency system between
 263                 various entities called "units" of 12 different
 264                 types. Units encapsulate various objects that are
 265                 relevant for system boot-up and maintenance. The
 266                 majority of units are configured in unit configuration
 267                 files, whose syntax and basic set of options is
 268                 described in
 269                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 270                 however some are created automatically from other
 271                 configuration, dynamically from system state or
 272                 programmatically at runtime. Units may be "active"
 273                 (meaning started, bound, plugged in, ..., depending on
 274                 the unit type, see below), or "inactive" (meaning
 275                 stopped, unbound, unplugged, ...), as well as in the
 276                 process of being activated or deactivated,
 277                 i.e. between the two states (these states are called
 278                 "activating", "deactivating"). A special "failed"
 279                 state is available as well, which is very similar to
 280                 "inactive" and is entered when the service failed in
 281                 some way (process returned error code on exit, or
 282                 crashed, or an operation timed out). If this state is
 283                 entered, the cause will be logged, for later
 284                 reference. Note that the various unit types may have a
 285                 number of additional substates, which are mapped to
 286                 the five generalized unit states described
 287                 here.</para>
 288
 289                 <para>The following unit types are available:</para>
 290
 291                 <orderedlist>
 292                         <listitem><para>Service units, which start and control
 293                         daemons and the processes they consist of. For
 294                         details see
 295                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 296
 297                         <listitem><para>Socket units, which
 298                         encapsulate local IPC or network sockets in
 299                         the system, useful for socket-based
 300                         activation. For details about socket units see
 301                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 302                         for details on socket-based activation and
 303                         other forms of activation, see
 304                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 305
 306                         <listitem><para>Target units are useful to
 307                         group units, or provide well-known
 308                         synchronization points during boot-up, see
 309                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 310
 311                         <listitem><para>Device units expose kernel
 312                         devices in systemd and may be used to
 313                         implement device-based activation. For details
 314                         see
 315                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 316
 317                         <listitem><para>Mount units control mount
 318                         points in the file system, for details see
 319                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 320
 321                         <listitem><para>Automount units provide
 322                         automount capabilities, for on-demand mounting
 323                         of file systems as well as parallelized
 324                         boot-up. See
 325                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 326
 327                         <listitem><para>Snapshot units can be used to
 328                         temporarily save the state of the set of
 329                         systemd units, which later may be restored by
 330                         activating the saved snapshot unit. For more
 331                         information see
 332                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 333
 334                         <listitem><para>Timer units are useful for
 335                         triggering activation of other units based on
 336                         timers. You may find details in
 337                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 338
 339                         <listitem><para>Swap units are very similar to
 340                         mount units and encapsulate memory swap
 341                         partitions or files of the operating
 342                         system. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 343
 344                         <listitem><para>Path units may be used
 345                         to activate other services when file system
 346                         objects change or are modified. See
 347                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 348
 349                         <listitem><para>Slice units may be used to
 350                         group units which manage system processes
 351                         (such as service and scope units) in a
 352                         hierarchical tree for resource management
 353                         purposes. See
 354                         <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 355
 356                         <listitem><para>Scope units are similar to
 357                         service units, but manage foreign processes
 358                         instead of starting them as well. See
 359                         <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 360
 361                 </orderedlist>
 362
 363                 <para>Units are named as their configuration
 364                 files. Some units have special semantics. A detailed
 365                 list is available in
 366                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 367
 368                 <para>systemd knows various kinds of dependencies,
 369                 including positive and negative requirement
 370                 dependencies (i.e. <varname>Requires=</varname> and
 371                 <varname>Conflicts=</varname>) as well as ordering
 372                 dependencies (<varname>After=</varname> and
 373                 <varname>Before=</varname>). NB: ordering and
 374                 requirement dependencies are orthogonal. If only a
 375                 requirement dependency exists between two units
 376                 (e.g. <filename>foo.service</filename> requires
 377                 <filename>bar.service</filename>), but no ordering
 378                 dependency (e.g. <filename>foo.service</filename>
 379                 after <filename>bar.service</filename>) and both are
 380                 requested to start, they will be started in
 381                 parallel. It is a common pattern that both requirement
 382                 and ordering dependencies are placed between two
 383                 units. Also note that the majority of dependencies are
 384                 implicitly created and maintained by systemd. In most
 385                 cases, it should be unnecessary to declare additional
 386                 dependencies manually, however it is possible to do
 387                 this.</para>
 388
 389                 <para>Application programs and units (via
 390                 dependencies) may request state changes of units. In
 391                 systemd, these requests are encapsulated as 'jobs' and
 392                 maintained in a job queue. Jobs may succeed or can
 393                 fail, their execution is ordered based on the ordering
 394                 dependencies of the units they have been scheduled
 395                 for.</para>
 396
 397                 <para>On boot systemd activates the target unit
 398                 <filename>default.target</filename> whose job is to
 399                 activate on-boot services and other on-boot units by
 400                 pulling them in via dependencies. Usually the unit
 401                 name is just an alias (symlink) for either
 402                 <filename>graphical.target</filename> (for
 403                 fully-featured boots into the UI) or
 404                 <filename>multi-user.target</filename> (for limited
 405                 console-only boots for use in embedded or server
 406                 environments, or similar; a subset of
 407                 graphical.target). However, it is at the discretion of
 408                 the administrator to configure it as an alias to any
 409                 other target unit. See
 410                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 411                 for details about these target units.</para>
 412
 413                 <para>Processes systemd spawns are placed in
 414                 individual Linux control groups named after the unit
 415                 which they belong to in the private systemd
 416                 hierarchy. (see <ulink
 417                 url="https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 418                 for more information about control groups, or short
 419                 "cgroups"). systemd uses this to effectively keep
 420                 track of processes. Control group information is
 421                 maintained in the kernel, and is accessible via the
 422                 file system hierarchy (beneath
 423                 <filename>/sys/fs/cgroup/systemd/</filename>), or in tools
 424                 such as
 425                 <citerefentry project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 426                 (<command>ps xawf -eo pid,user,cgroup,args</command>
 427                 is particularly useful to list all processes and the
 428                 systemd units they belong to.).</para>
 429
 430                 <para>systemd is compatible with the SysV init system
 431                 to a large degree: SysV init scripts are supported and
 432                 simply read as an alternative (though limited)
 433                 configuration file format. The SysV
 434                 <filename>/dev/initctl</filename> interface is
 435                 provided, and compatibility implementations of the
 436                 various SysV client tools are available. In addition to
 437                 that, various established Unix functionality such as
 438                 <filename>/etc/fstab</filename> or the
 439                 <filename>utmp</filename> database are
 440                 supported.</para>
 441
 442                 <para>systemd has a minimal transaction system: if a
 443                 unit is requested to start up or shut down it will add
 444                 it and all its dependencies to a temporary
 445                 transaction. Then, it will verify if the transaction
 446                 is consistent (i.e. whether the ordering of all units
 447                 is cycle-free). If it is not, systemd will try to fix
 448                 it up, and removes non-essential jobs from the
 449                 transaction that might remove the loop. Also, systemd
 450                 tries to suppress non-essential jobs in the
 451                 transaction that would stop a running service. Finally
 452                 it is checked whether the jobs of the transaction
 453                 contradict jobs that have already been queued, and
 454                 optionally the transaction is aborted then. If all
 455                 worked out and the transaction is consistent and
 456                 minimized in its impact it is merged with all already
 457                 outstanding jobs and added to the run
 458                 queue. Effectively this means that before executing a
 459                 requested operation, systemd will verify that it makes
 460                 sense, fixing it if possible, and only failing if it
 461                 really cannot work.</para>
 462
 463                 <para>Systemd contains native implementations of
 464                 various tasks that need to be executed as part of the
 465                 boot process. For example, it sets the hostname or
 466                 configures the loopback network device. It also sets
 467                 up and mounts various API file systems, such as
 468                 <filename>/sys</filename> or
 469                 <filename>/proc</filename>.</para>
 470
 471                 <para>For more information about the concepts and
 472                 ideas behind systemd, please refer to the <ulink
 473                 url="http://0pointer.de/blog/projects/systemd.html">Original
 474                 Design Document</ulink>.</para>
 475
 476                 <para>Note that some but not all interfaces provided
 477                 by systemd are covered by the <ulink
 478                 url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 479                 Stability Promise</ulink>.</para>
 480
 481                 <para>Units may be generated dynamically at boot and
 482                 system manager reload time, for example based on other
 483                 configuration files or parameters passed on the kernel
 484                 command line. For details see the <ulink
 485                 url="http://www.freedesktop.org/wiki/Software/systemd/Generators">Generators
 486                 Specification</ulink>.</para>
 487
 488                 <para>Systems which invoke systemd in a container
 489                 or initrd environment should implement the
 490                 <ulink
 491                 url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container
 492                 Interface</ulink> or <ulink
 493                 url="http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd
 494                 Interface</ulink> specifications, respectively.</para>
 495         </refsect1>
 496
 497         <refsect1>
 498                 <title>Directories</title>
 499
 500                 <variablelist>
 501                         <varlistentry>
 502                                 <term>System unit directories</term>
 503
 504                                 <listitem><para>The systemd system
 505                                 manager reads unit configuration from
 506                                 various directories. Packages that
 507                                 want to install unit files shall place
 508                                 them in the directory returned by
 509                                 <command>pkg-config systemd
 510                                 --variable=systemdsystemunitdir</command>. Other
 511                                 directories checked are
 512                                 <filename>/usr/local/lib/systemd/system</filename>
 513                                 and
 514                                 <filename>/usr/lib/systemd/system</filename>. User
 515                                 configuration always takes
 516                                 precedence. <command>pkg-config
 517                                 systemd
 518                                 --variable=systemdsystemconfdir</command>
 519                                 returns the path of the system
 520                                 configuration directory. Packages
 521                                 should alter the content of these
 522                                 directories only with the
 523                                 <command>enable</command> and
 524                                 <command>disable</command> commands of
 525                                 the
 526                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 527                                 tool. Full list of directories is provided in
 528                                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 529                                 </para></listitem>
 530                         </varlistentry>
 531                 </variablelist>
 532
 533                 <variablelist>
 534                         <varlistentry>
 535                                 <term>User unit directories</term>
 536
 537                                 <listitem><para>Similar rules apply
 538                                 for the user unit
 539                                 directories. However, here the <ulink
 540                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 541                                 Base Directory specification</ulink>
 542                                 is followed to find
 543                                 units. Applications should place their
 544                                 unit files in the directory returned
 545                                 by <command>pkg-config systemd
 546                                 --variable=systemduserunitdir</command>. Global
 547                                 configuration is done in the directory
 548                                 reported by <command>pkg-config
 549                                 systemd
 550                                 --variable=systemduserconfdir</command>. The
 551                                 <command>enable</command> and
 552                                 <command>disable</command> commands of
 553                                 the
 554                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 555                                 tool can handle both global (i.e. for
 556                                 all users) and private (for one user)
 557                                 enabling/disabling of
 558                                 units. Full list of directories is provided in
 559                                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 560                                 </para></listitem>
 561                         </varlistentry>
 562                 </variablelist>
 563
 564                 <variablelist>
 565                         <varlistentry>
 566                                 <term>SysV init scripts directory</term>
 567
 568                                 <listitem><para>The location of the
 569                                 SysV init script directory varies
 570                                 between distributions. If systemd
 571                                 cannot find a native unit file for a
 572                                 requested service, it will look for a
 573                                 SysV init script of the same name
 574                                 (with the
 575                                 <filename>.service</filename> suffix
 576                                 removed).</para></listitem>
 577                         </varlistentry>
 578                 </variablelist>
 579
 580                 <variablelist>
 581                         <varlistentry>
 582                                 <term>SysV runlevel link farm directory</term>
 583
 584                                 <listitem><para>The location of the
 585                                 SysV runlevel link farm directory
 586                                 varies between distributions. systemd
 587                                 will take the link farm into account
 588                                 when figuring out whether a service
 589                                 shall be enabled. Note that a service
 590                                 unit with a native unit configuration
 591                                 file cannot be started by activating it
 592                                 in the SysV runlevel link
 593                                 farm.</para></listitem>
 594                         </varlistentry>
 595                 </variablelist>
 596         </refsect1>
 597
 598         <refsect1>
 599                 <title>Signals</title>
 600
 601                 <variablelist>
 602                         <varlistentry>
 603                                 <term><constant>SIGTERM</constant></term>
 604
 605                                 <listitem><para>Upon receiving this
 606                                 signal the systemd system manager
 607                                 serializes its state, reexecutes
 608                                 itself and deserializes the saved
 609                                 state again. This is mostly equivalent
 610                                 to <command>systemctl
 611                                 daemon-reexec</command>.</para>
 612
 613                                 <para>systemd user managers will
 614                                 start the
 615                                 <filename>exit.target</filename> unit
 616                                 when this signal is received. This is
 617                                 mostly equivalent to
 618                                 <command>systemctl --user start
 619                                 exit.target</command>.</para></listitem>
 620                         </varlistentry>
 621
 622                         <varlistentry>
 623                                 <term><constant>SIGINT</constant></term>
 624
 625                                 <listitem><para>Upon receiving this
 626                                 signal the systemd system manager will
 627                                 start the
 628                                 <filename>ctrl-alt-del.target</filename> unit. This
 629                                 is mostly equivalent to
 630                                 <command>systemctl start
 631                                 ctl-alt-del.target</command>.</para>
 632
 633                                 <para>systemd user managers
 634                                 treat this signal the same way as
 635                                 <constant>SIGTERM</constant>.</para></listitem>
 636                         </varlistentry>
 637
 638                         <varlistentry>
 639                                 <term><constant>SIGWINCH</constant></term>
 640
 641                                 <listitem><para>When this signal is
 642                                 received the systemd system manager
 643                                 will start the
 644                                 <filename>kbrequest.target</filename>
 645                                 unit. This is mostly equivalent to
 646                                 <command>systemctl start
 647                                 kbrequest.target</command>.</para>
 648
 649                                 <para>This signal is ignored by
 650                                 systemd user
 651                                 managers.</para></listitem>
 652                         </varlistentry>
 653
 654                         <varlistentry>
 655                                 <term><constant>SIGPWR</constant></term>
 656
 657                                 <listitem><para>When this signal is
 658                                 received the systemd manager
 659                                 will start the
 660                                 <filename>sigpwr.target</filename>
 661                                 unit. This is mostly equivalent to
 662                                 <command>systemctl start
 663                                 sigpwr.target</command>.</para></listitem>
 664                         </varlistentry>
 665
 666                         <varlistentry>
 667                                 <term><constant>SIGUSR1</constant></term>
 668
 669                                 <listitem><para>When this signal is
 670                                 received the systemd manager will try
 671                                 to reconnect to the D-Bus
 672                                 bus.</para></listitem>
 673                         </varlistentry>
 674
 675                         <varlistentry>
 676                                 <term><constant>SIGUSR2</constant></term>
 677
 678                                 <listitem><para>When this signal is
 679                                 received the systemd manager will log
 680                                 its complete state in human readable
 681                                 form. The data logged is the same as
 682                                 printed by <command>systemctl
 683                                 dump</command>.</para></listitem>
 684                         </varlistentry>
 685
 686                         <varlistentry>
 687                                 <term><constant>SIGHUP</constant></term>
 688
 689                                 <listitem><para>Reloads the complete
 690                                 daemon configuration. This is mostly
 691                                 equivalent to <command>systemctl
 692                                 daemon-reload</command>.</para></listitem>
 693                         </varlistentry>
 694
 695                         <varlistentry>
 696                                 <term><constant>SIGRTMIN+0</constant></term>
 697
 698                                 <listitem><para>Enters default mode, starts the
 699                                 <filename>default.target</filename>
 700                                 unit. This is mostly equivalent to
 701                                 <command>systemctl start
 702                                 default.target</command>.</para></listitem>
 703                         </varlistentry>
 704
 705                         <varlistentry>
 706                                 <term><constant>SIGRTMIN+1</constant></term>
 707
 708                                 <listitem><para>Enters rescue mode,
 709                                 starts the
 710                                 <filename>rescue.target</filename>
 711                                 unit. This is mostly equivalent to
 712                                 <command>systemctl isolate
 713                                 rescue.target</command>.</para></listitem>
 714                         </varlistentry>
 715
 716                         <varlistentry>
 717                                 <term><constant>SIGRTMIN+2</constant></term>
 718
 719                                 <listitem><para>Enters emergency mode,
 720                                 starts the
 721                                 <filename>emergency.service</filename>
 722                                 unit. This is mostly equivalent to
 723                                 <command>systemctl isolate
 724                                 emergency.service</command>.</para></listitem>
 725                         </varlistentry>
 726
 727                         <varlistentry>
 728                                 <term><constant>SIGRTMIN+3</constant></term>
 729
 730                                 <listitem><para>Halts the machine,
 731                                 starts the
 732                                 <filename>halt.target</filename>
 733                                 unit. This is mostly equivalent to
 734                                 <command>systemctl start
 735                                 halt.target</command>.</para></listitem>
 736                         </varlistentry>
 737
 738                         <varlistentry>
 739                                 <term><constant>SIGRTMIN+4</constant></term>
 740
 741                                 <listitem><para>Powers off the machine,
 742                                 starts the
 743                                 <filename>poweroff.target</filename>
 744                                 unit. This is mostly equivalent to
 745                                 <command>systemctl start
 746                                 poweroff.target</command>.</para></listitem>
 747                         </varlistentry>
 748
 749                         <varlistentry>
 750                                 <term><constant>SIGRTMIN+5</constant></term>
 751
 752                                 <listitem><para>Reboots the machine,
 753                                 starts the
 754                                 <filename>reboot.target</filename>
 755                                 unit. This is mostly equivalent to
 756                                 <command>systemctl start
 757                                 reboot.target</command>.</para></listitem>
 758                         </varlistentry>
 759
 760                         <varlistentry>
 761                                 <term><constant>SIGRTMIN+6</constant></term>
 762
 763                                 <listitem><para>Reboots the machine via kexec,
 764                                 starts the
 765                                 <filename>kexec.target</filename>
 766                                 unit. This is mostly equivalent to
 767                                 <command>systemctl start
 768                                 kexec.target</command>.</para></listitem>
 769                         </varlistentry>
 770
 771                         <varlistentry>
 772                                 <term><constant>SIGRTMIN+13</constant></term>
 773
 774                                 <listitem><para>Immediately halts the machine.</para></listitem>
 775                         </varlistentry>
 776
 777                         <varlistentry>
 778                                 <term><constant>SIGRTMIN+14</constant></term>
 779
 780                                 <listitem><para>Immediately powers off the machine.</para></listitem>
 781                         </varlistentry>
 782
 783                         <varlistentry>
 784                                 <term><constant>SIGRTMIN+15</constant></term>
 785
 786                                 <listitem><para>Immediately reboots the machine.</para></listitem>
 787                         </varlistentry>
 788
 789                         <varlistentry>
 790                                 <term><constant>SIGRTMIN+16</constant></term>
 791
 792                                 <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
 793                         </varlistentry>
 794
 795                         <varlistentry>
 796                                 <term><constant>SIGRTMIN+20</constant></term>
 797
 798                                 <listitem><para>Enables display of
 799                                 status messages on the console, as
 800                                 controlled via
 801                                 <varname>systemd.show_status=1</varname>
 802                                 on the kernel command
 803                                 line.</para></listitem>
 804                         </varlistentry>
 805
 806                         <varlistentry>
 807                                 <term><constant>SIGRTMIN+21</constant></term>
 808
 809                                 <listitem><para>Disables display of
 810                                 status messages on the console, as
 811                                 controlled via
 812                                 <varname>systemd.show_status=0</varname>
 813                                 on the kernel command
 814                                 line.</para></listitem>
 815                         </varlistentry>
 816
 817                         <varlistentry>
 818                                 <term><constant>SIGRTMIN+22</constant></term>
 819                                 <term><constant>SIGRTMIN+23</constant></term>
 820
 821                                 <listitem><para>Sets the log level to
 822                                 <literal>debug</literal>
 823                                 (or <literal>info</literal> on
 824                                 <constant>SIGRTMIN+23</constant>), as
 825                                 controlled via
 826                                 <varname>systemd.log_level=debug</varname>
 827                                 (or <varname>systemd.log_level=info</varname>
 828                                 on <constant>SIGRTMIN+23</constant>) on
 829                                 the kernel command
 830                                 line.</para></listitem>
 831                         </varlistentry>
 832
 833                         <varlistentry>
 834                                 <term><constant>SIGRTMIN+24</constant></term>
 835
 836                                 <listitem><para>Immediately exits the
 837                                 manager (only available for --user
 838                                 instances).</para></listitem>
 839                         </varlistentry>
 840
 841                         <varlistentry>
 842                                 <term><constant>SIGRTMIN+26</constant></term>
 843                                 <term><constant>SIGRTMIN+27</constant></term>
 844                                 <term><constant>SIGRTMIN+28</constant></term>
 845
 846                                 <listitem><para>Sets the log level to
 847                                 <literal>journal-or-kmsg</literal> (or
 848                                 <literal>console</literal> on
 849                                 <constant>SIGRTMIN+27</constant>,
 850                                 <literal>kmsg</literal> on
 851                                 <constant>SIGRTMIN+28</constant>), as
 852                                 controlled via
 853                                 <varname>systemd.log_target=journal-or-kmsg</varname>
 854                                 (or
 855                                 <varname>systemd.log_target=console</varname>
 856                                 on <constant>SIGRTMIN+27</constant> or
 857                                 <varname>systemd.log_target=kmsg</varname>
 858                                 on <constant>SIGRTMIN+28</constant>)
 859                                 on the kernel command
 860                                 line.</para></listitem>
 861                         </varlistentry>
 862                 </variablelist>
 863         </refsect1>
 864
 865         <refsect1>
 866                 <title>Environment</title>
 867
 868                 <variablelist class='environment-variables'>
 869                         <varlistentry>
 870                                 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 871                                 <listitem><para>systemd reads the
 872                                 log level from this environment
 873                                 variable. This can be overridden with
 874                                 <option>--log-level=</option>.</para></listitem>
 875                         </varlistentry>
 876
 877                         <varlistentry>
 878                                 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 879                                 <listitem><para>systemd reads the
 880                                 log target from this environment
 881                                 variable. This can be overridden with
 882                                 <option>--log-target=</option>.</para></listitem>
 883                         </varlistentry>
 884
 885                         <varlistentry>
 886                                 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 887                                 <listitem><para>Controls whether
 888                                 systemd highlights important log
 889                                 messages. This can be overridden with
 890                                 <option>--log-color=</option>.</para></listitem>
 891                         </varlistentry>
 892
 893                         <varlistentry>
 894                                 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 895                                 <listitem><para>Controls whether
 896                                 systemd prints the code location along
 897                                 with log messages. This can be
 898                                 overridden with
 899                                 <option>--log-location=</option>.</para></listitem>
 900                         </varlistentry>
 901
 902                         <varlistentry>
 903                                 <term><varname>$XDG_CONFIG_HOME</varname></term>
 904                                 <term><varname>$XDG_CONFIG_DIRS</varname></term>
 905                                 <term><varname>$XDG_DATA_HOME</varname></term>
 906                                 <term><varname>$XDG_DATA_DIRS</varname></term>
 907
 908                                 <listitem><para>The systemd user
 909                                 manager uses these variables in
 910                                 accordance to the <ulink
 911                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 912                                 Base Directory specification</ulink>
 913                                 to find its configuration.</para></listitem>
 914                         </varlistentry>
 915
 916                         <varlistentry>
 917                                 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 918
 919                                 <listitem><para>Controls where systemd
 920                                 looks for unit
 921                                 files.</para></listitem>
 922                         </varlistentry>
 923
 924                         <varlistentry>
 925                                 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 926
 927                                 <listitem><para>Controls where systemd
 928                                 looks for SysV init scripts.</para></listitem>
 929                         </varlistentry>
 930
 931                         <varlistentry>
 932                                 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 933
 934                                 <listitem><para>Controls where systemd
 935                                 looks for SysV init script runlevel link
 936                                 farms.</para></listitem>
 937                         </varlistentry>
 938
 939                         <varlistentry>
 940                                 <term><varname>$LISTEN_PID</varname></term>
 941                                 <term><varname>$LISTEN_FDS</varname></term>
 942
 943                                 <listitem><para>Set by systemd for
 944                                 supervised processes during
 945                                 socket-based activation. See
 946                                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 947                                 for more information.
 948                                 </para></listitem>
 949                         </varlistentry>
 950
 951                         <varlistentry>
 952                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 953
 954                                 <listitem><para>Set by systemd for
 955                                 supervised processes for status and
 956                                 start-up completion notification. See
 957                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 958                                 for more information.
 959                                 </para></listitem>
 960                         </varlistentry>
 961                 </variablelist>
 962         </refsect1>
 963
 964         <refsect1>
 965                 <title>Kernel Command Line</title>
 966
 967                 <para>When run as system instance systemd parses a
 968                 number of kernel command line
 969                 arguments<footnote><para>If run inside a Linux
 970                 container these arguments may be passed as command
 971                 line arguments to systemd itself, next to any of the
 972                 command line options listed in the Options section
 973                 above. If run outside of Linux containers, these
 974                 arguments are parsed from
 975                 <filename>/proc/cmdline</filename>
 976                 instead.</para></footnote>:</para>
 977
 978                 <variablelist class='kernel-commandline-options'>
 979                         <varlistentry>
 980                                 <term><varname>systemd.unit=</varname></term>
 981                                 <term><varname>rd.systemd.unit=</varname></term>
 982
 983                                 <listitem><para>Overrides the unit to
 984                                 activate on boot. Defaults to
 985                                 <filename>default.target</filename>. This
 986                                 may be used to temporarily boot into a
 987                                 different boot unit, for example
 988                                 <filename>rescue.target</filename> or
 989                                 <filename>emergency.service</filename>. See
 990                                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 991                                 for details about these units. The
 992                                 option prefixed with
 993                                 <literal>rd.</literal> is honored
 994                                 only in the initial RAM disk (initrd),
 995                                 while the one that is not prefixed only
 996                                 in the main system.</para></listitem>
 997                         </varlistentry>
 998
 999                         <varlistentry>
1000                                 <term><varname>systemd.dump_core=</varname></term>
1001
1002                                 <listitem><para>Takes a boolean
1003                                 argument. If <option>true</option>,
1004                                 systemd dumps core when it
1005                                 crashes. Otherwise, no core dump is
1006                                 created. Defaults to
1007                                 <option>true</option>.</para></listitem>
1008                         </varlistentry>
1009
1010                         <varlistentry>
1011                                 <term><varname>systemd.crash_shell=</varname></term>
1012
1013                                 <listitem><para>Takes a boolean
1014                                 argument. If <option>true</option>,
1015                                 systemd spawns a shell when it
1016                                 crashes. Otherwise, no shell is
1017                                 spawned. Defaults to
1018                                 <option>false</option>, for security
1019                                 reasons, as the shell is not protected
1020                                 by any password
1021                                 authentication.</para></listitem>
1022                         </varlistentry>
1023
1024                         <varlistentry>
1025                                 <term><varname>systemd.crash_chvt=</varname></term>
1026
1027                                 <listitem><para>Takes an integer
1028                                 argument. If positive systemd
1029                                 activates the specified virtual
1030                                 terminal when it crashes. Defaults to
1031                                 <constant>-1</constant>.</para></listitem>
1032                         </varlistentry>
1033
1034                         <varlistentry>
1035                                 <term><varname>systemd.confirm_spawn=</varname></term>
1036
1037                                 <listitem><para>Takes a boolean
1038                                 argument. If <option>true</option>,
1039                                 asks for confirmation when spawning
1040                                 processes. Defaults to
1041                                 <option>false</option>.</para></listitem>
1042                         </varlistentry>
1043
1044                         <varlistentry>
1045                                 <term><varname>systemd.show_status=</varname></term>
1046
1047                                 <listitem><para>Takes a boolean
1048                                 argument or the constant
1049                                 <constant>auto</constant>. If
1050                                 <option>true</option>, shows terse
1051                                 service status updates on the console
1052                                 during bootup.
1053                                 <constant>auto</constant> behaves like
1054                                 <option>false</option> until a service
1055                                 fails or there is a significant delay
1056                                 in boot. Defaults to
1057                                 <option>true</option>, unless
1058                                 <option>quiet</option> is passed as
1059                                 kernel command line option in which
1060                                 case it defaults to
1061                                 <constant>auto</constant>.</para></listitem>
1062                         </varlistentry>
1063
1064                         <varlistentry>
1065                                 <term><varname>systemd.log_target=</varname></term>
1066                                 <term><varname>systemd.log_level=</varname></term>
1067                                 <term><varname>systemd.log_color=</varname></term>
1068                                 <term><varname>systemd.log_location=</varname></term>
1069
1070                                 <listitem><para>Controls log output,
1071                                 with the same effect as the
1072                                 <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
1073                                 environment variables described above.</para></listitem>
1074                         </varlistentry>
1075
1076                         <varlistentry>
1077                                 <term><varname>systemd.default_standard_output=</varname></term>
1078                                 <term><varname>systemd.default_standard_error=</varname></term>
1079                                 <listitem><para>Controls default
1080                                 standard output and error output for
1081                                 services, with the same effect as the
1082                                 <option>--default-standard-output=</option>
1083                                 and <option>--default-standard-error=</option>
1084                                 command line arguments described
1085                                 above, respectively.</para></listitem>
1086                         </varlistentry>
1087
1088                         <varlistentry>
1089                                 <term><varname>systemd.setenv=</varname></term>
1090
1091                                 <listitem><para>Takes a string
1092                                 argument in the form VARIABLE=VALUE.
1093                                 May be used to set default environment
1094                                 variables to add to forked child processes.
1095                                 May be used more than once to set multiple
1096                                 variables.</para></listitem>
1097                         </varlistentry>
1098
1099                         <varlistentry>
1100                                 <term><varname>quiet</varname></term>
1101
1102                                 <listitem><para>Turn off
1103                                 status output at boot, much like
1104                                 <varname>systemd.show_status=false</varname>
1105                                 would. Note that this option is also
1106                                 read by the kernel itself and disables
1107                                 kernel log output. Passing this option
1108                                 hence turns off the usual output from
1109                                 both the system manager and the kernel.
1110                                 </para></listitem>
1111                         </varlistentry>
1112
1113                         <varlistentry>
1114                                 <term><varname>debug</varname></term>
1115
1116                                 <listitem><para>Turn on debugging
1117                                 output. This is equivalent to
1118                                 <varname>systemd.log_level=debug</varname>.
1119                                 Note that this option is also read by
1120                                 the kernel itself and enables kernel
1121                                 debug output.  Passing this option
1122                                 hence turns on the debug output from
1123                                 both the system manager and the
1124                                 kernel.</para></listitem>
1125                         </varlistentry>
1126
1127                         <varlistentry>
1128                                 <term><varname>emergency</varname></term>
1129                                 <term><varname>-b</varname></term>
1130
1131                                 <listitem><para>Boot into emergency
1132                                 mode. This is equivalent to
1133                                 <varname>systemd.unit=emergency.target</varname>
1134                                 and provided for compatibility reasons
1135                                 and to be easier to
1136                                 type.</para></listitem>
1137                         </varlistentry>
1138
1139                         <varlistentry>
1140                                 <term><varname>rescue</varname></term>
1141                                 <term><varname>single</varname></term>
1142                                 <term><varname>s</varname></term>
1143                                 <term><varname>S</varname></term>
1144                                 <term><varname>1</varname></term>
1145
1146                                 <listitem><para>Boot into rescue
1147                                 mode. This is equivalent to
1148                                 <varname>systemd.unit=rescue.target</varname>
1149                                 and provided for compatibility reasons
1150                                 and to be easier to
1151                                 type.</para></listitem>
1152                         </varlistentry>
1153
1154                         <varlistentry>
1155                                 <term><varname>2</varname></term>
1156                                 <term><varname>3</varname></term>
1157                                 <term><varname>4</varname></term>
1158                                 <term><varname>5</varname></term>
1159
1160                                 <listitem><para>Boot into the
1161                                 specified legacy SysV runlevel. These
1162                                 are equivalent to
1163                                 <varname>systemd.unit=runlevel2.target</varname>,
1164                                 <varname>systemd.unit=runlevel3.target</varname>,
1165                                 <varname>systemd.unit=runlevel4.target</varname>,
1166                                 and <varname>systemd.unit=runlevel5.target</varname>, respectively,
1167                                 and provided for compatibility reasons
1168                                 and to be easier to
1169                                 type.</para></listitem>
1170                         </varlistentry>
1171
1172                         <varlistentry>
1173                                 <term><varname>locale.LANG=</varname></term>
1174                                 <term><varname>locale.LANGUAGE=</varname></term>
1175                                 <term><varname>locale.LC_CTYPE=</varname></term>
1176                                 <term><varname>locale.LC_NUMERIC=</varname></term>
1177                                 <term><varname>locale.LC_TIME=</varname></term>
1178                                 <term><varname>locale.LC_COLLATE=</varname></term>
1179                                 <term><varname>locale.LC_MONETARY=</varname></term>
1180                                 <term><varname>locale.LC_MESSAGES=</varname></term>
1181                                 <term><varname>locale.LC_PAPER=</varname></term>
1182                                 <term><varname>locale.LC_NAME=</varname></term>
1183                                 <term><varname>locale.LC_ADDRESS=</varname></term>
1184                                 <term><varname>locale.LC_TELEPHONE=</varname></term>
1185                                 <term><varname>locale.LC_MEASUREMENT=</varname></term>
1186                                 <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1187
1188                                 <listitem><para>Set the system locale
1189                                 to use. This overrides the settings in
1190                                 <filename>/etc/locale.conf</filename>. For
1191                                 more information see
1192                                 <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1193                                 and
1194                                 <citerefentry><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1195                                 </para></listitem>
1196                         </varlistentry>
1197                 </variablelist>
1198
1199                 <para>For other kernel command line parameters
1200                 understood by components of the core OS, please refer
1201                 to
1202                 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1203         </refsect1>
1204
1205         <refsect1>
1206                 <title>Sockets and FIFOs</title>
1207
1208                 <variablelist>
1209                         <varlistentry>
1210                                 <term><filename>/run/systemd/notify</filename></term>
1211
1212                                 <listitem><para>Daemon status
1213                                 notification socket. This is an
1214                                 <constant>AF_UNIX</constant> datagram socket and is used to
1215                                 implement the daemon notification
1216                                 logic as implemented by
1217                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1218
1219                         </varlistentry>
1220
1221                         <varlistentry>
1222                                 <term><filename>/run/systemd/shutdownd</filename></term>
1223
1224                                 <listitem><para>Used internally by the
1225                                 <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1226                                 tool to implement delayed
1227                                 shutdowns. This is an <constant>AF_UNIX</constant> datagram
1228                                 socket.</para></listitem>
1229                         </varlistentry>
1230
1231                         <varlistentry>
1232                                 <term><filename>/run/systemd/private</filename></term>
1233
1234                                 <listitem><para>Used internally as
1235                                 communication channel between
1236                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1237                                 and the systemd process. This is an
1238                                 <constant>AF_UNIX</constant> stream socket. This interface
1239                                 is private to systemd and should not
1240                                 be used in external
1241                                 projects.</para></listitem>
1242                         </varlistentry>
1243
1244                         <varlistentry>
1245                                 <term><filename>/dev/initctl</filename></term>
1246
1247                                 <listitem><para>Limited compatibility
1248                                 support for the SysV client interface,
1249                                 as implemented by the
1250                                 <filename>systemd-initctl.service</filename>
1251                                 unit. This is a named pipe in the file
1252                                 system. This interface is obsolete and
1253                                 should not be used in new
1254                                 applications.</para></listitem>
1255                         </varlistentry>
1256                 </variablelist>
1257         </refsect1>
1258
1259         <refsect1>
1260                 <title>See Also</title>
1261                 <para>
1262                         The <ulink url="http://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
1263                         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1264                         <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1265                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1266                         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1267                         <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1268                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1269                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1270                         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1271                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1272                         <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1273                         <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1274                         <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1275                         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1276                 </para>
1277         </refsect1>
1278
1279 </refentry>