man/systemd.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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   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
  26         <refentryinfo>
  27                 <title>systemd</title>
  28                 <productname>systemd</productname>
  29
  30                 <authorgroup>
  31                         <author>
  32                                 <contrib>Developer</contrib>
  33                                 <firstname>Lennart</firstname>
  34                                 <surname>Poettering</surname>
  35                                 <email>lennart@poettering.net</email>
  36                         </author>
  37                 </authorgroup>
  38         </refentryinfo>
  39
  40         <refmeta>
  41                 <refentrytitle>systemd</refentrytitle>
  42                 <manvolnum>1</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>systemd</refname>
  47                 <refname>init</refname>
  48                 <refpurpose>systemd system and service manager</refpurpose>
  49         </refnamediv>
  50
  51         <refsynopsisdiv>
  52                 <cmdsynopsis>
  53                         <command>systemd <arg choice="opt" rep="repeat">OPTIONS</arg></command>
  54                 </cmdsynopsis>
  55                 <cmdsynopsis>
  56                         <command>init <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="req">COMMAND</arg></command>
  57                 </cmdsynopsis>
  58         </refsynopsisdiv>
  59
  60         <refsect1>
  61                 <title>Description</title>
  62
  63                 <para>systemd is a system and service manager for
  64                 Linux operating systems. When run as first process on
  65                 boot (as PID 1), it acts as init system that brings
  66                 up and maintains userspace services.</para>
  67
  68                 <para>For compatibility with SysV, if systemd is called
  69                 as <command>init</command> and a PID that is not
  70                 1, it will execute <command>telinit</command> and pass
  71                 all command line arguments unmodified. That means
  72                 <command>init</command> and <command>telinit</command>
  73                 are mostly equivalent when invoked from normal login sessions. See
  74                 <citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  75                 for more information.</para>
  76
  77                 <para>When run as system instance, systemd interprets
  78                 the configuration file
  79                 <filename>system.conf</filename>, otherwise
  80                 <filename>user.conf</filename>. See
  81                 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  82                 for more information.</para>
  83         </refsect1>
  84
  85         <refsect1>
  86                 <title>Options</title>
  87
  88                 <para>The following options are understood:</para>
  89
  90                 <variablelist>
  91                         <varlistentry>
  92                                 <term><option>-h</option></term>
  93                                 <term><option>--help</option></term>
  94
  95                                 <listitem><para>Prints a short help
  96                                 text and exits.</para></listitem>
  97                         </varlistentry>
  98                         <varlistentry>
  99                                 <term><option>--version</option></term>
 100
 101                                 <listitem><para>Prints a systemd version
 102                                 identifier and exits.</para></listitem>
 103                         </varlistentry>
 104                         <varlistentry>
 105                                 <term><option>--test</option></term>
 106
 107                                 <listitem><para>Determine startup
 108                                 sequence, dump it and exit. This is an
 109                                 option useful for debugging
 110                                 only.</para></listitem>
 111                         </varlistentry>
 112                         <varlistentry>
 113                                 <term><option>--dump-configuration-items</option></term>
 114
 115                                 <listitem><para>Dump understood unit
 116                                 configuration items. This outputs a
 117                                 terse but complete list of
 118                                 configuration items understood in unit
 119                                 definition files.</para></listitem>
 120                         </varlistentry>
 121                         <varlistentry>
 122                                 <term><option>--unit=</option></term>
 123
 124                                 <listitem><para>Set default unit to
 125                                 activate on startup. If not specified,
 126                                 defaults to
 127                                 <filename>default.target</filename>.</para></listitem>
 128                         </varlistentry>
 129                         <varlistentry>
 130                                 <term><option>--system</option></term>
 131                                 <term><option>--user</option></term>
 132
 133                                 <listitem><para>For <option>--system</option>,
 134                                 tell systemd to run a
 135                                 system instance, even if the process ID is
 136                                 not 1, i.e. systemd is not run as init process.
 137                                 <option>--user</option> does the opposite,
 138                                 running a user instance even if the process
 139                                 ID is 1.
 140                                 Normally it should not be necessary to
 141                                 pass these options, as systemd
 142                                 automatically detects the mode it is
 143                                 started in. These options are hence of
 144                                 little use except for debugging. Note
 145                                 that it is not supported booting and
 146                                 maintaining a full system with systemd
 147                                 running in <option>--system</option>
 148                                 mode, but PID not 1. In practice,
 149                                 passing <option>--system</option> explicitly is
 150                                 only useful in conjunction with
 151                                 <option>--test</option>.</para></listitem>
 152                         </varlistentry>
 153                         <varlistentry>
 154                                 <term><option>--dump-core</option></term>
 155
 156                                 <listitem><para>Dump core on
 157                                 crash. This switch has no effect when
 158                                 run as user
 159                                 instance.</para></listitem>
 160                         </varlistentry>
 161                         <varlistentry>
 162                                 <term><option>--crash-shell</option></term>
 163
 164                                 <listitem><para>Run shell on
 165                                 crash. This switch has no effect when
 166                                 run as user
 167                                 instance.</para></listitem>
 168                         </varlistentry>
 169                         <varlistentry>
 170                                 <term><option>--confirm-spawn</option></term>
 171
 172                                 <listitem><para>Ask for confirmation
 173                                 when spawning processes. This switch
 174                                 has no effect when run as user
 175                                 instance.</para></listitem>
 176                         </varlistentry>
 177                         <varlistentry>
 178                                 <term><option>--show-status=</option></term>
 179
 180                                 <listitem><para>Show terse service
 181                                 status information while booting. This
 182                                 switch has no effect when run as user
 183                                 instance. Takes a boolean argument
 184                                 which may be omitted which is
 185                                 interpreted as
 186                                 <option>true</option>.</para></listitem>
 187                         </varlistentry>
 188                         <varlistentry>
 189                                 <term><option>--log-target=</option></term>
 190
 191                                 <listitem><para>Set log
 192                                 target. Argument must be one of
 193                                 <option>console</option>,
 194                                 <option>journal</option>,
 195                                 <option>syslog</option>,
 196                                 <option>kmsg</option>,
 197                                 <option>journal-or-kmsg</option>,
 198                                 <option>syslog-or-kmsg</option>,
 199                                 <option>null</option>.</para></listitem>
 200                         </varlistentry>
 201                         <varlistentry>
 202                                 <term><option>--log-level=</option></term>
 203
 204                                 <listitem><para>Set log level. As
 205                                 argument this accepts a numerical log
 206                                 level or the well-known <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 207                                 symbolic names (lowercase):
 208                                 <option>emerg</option>,
 209                                 <option>alert</option>,
 210                                 <option>crit</option>,
 211                                 <option>err</option>,
 212                                 <option>warning</option>,
 213                                 <option>notice</option>,
 214                                 <option>info</option>,
 215                                 <option>debug</option>.</para></listitem>
 216                         </varlistentry>
 217                         <varlistentry>
 218                                 <term><option>--log-color=</option></term>
 219
 220                                 <listitem><para>Highlight important
 221                                 log messages. Argument is a boolean
 222                                 value. If the argument is omitted, it
 223                                 defaults to
 224                                 <option>true</option>.</para></listitem>
 225                         </varlistentry>
 226                         <varlistentry>
 227                                 <term><option>--log-location=</option></term>
 228
 229                                 <listitem><para>Include code location
 230                                 in log messages. This is mostly
 231                                 relevant for debugging
 232                                 purposes. Argument is a boolean
 233                                 value. If the argument is omitted
 234                                 it defaults to
 235                                 <option>true</option>.</para></listitem>
 236                         </varlistentry>
 237                         <varlistentry>
 238                                 <term><option>--default-standard-output=</option></term>
 239                                 <term><option>--default-standard-error=</option></term>
 240
 241                                 <listitem><para>Sets the default
 242                                 output or error output for all
 243                                 services and sockets, respectively. That is, controls
 244                                 the default for
 245                                 <option>StandardOutput=</option>
 246                                 and <option>StandardError=</option>
 247                                 (see
 248                                 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 249                                 for details). Takes one of
 250                                 <option>inherit</option>,
 251                                 <option>null</option>,
 252                                 <option>tty</option>,
 253                                 <option>journal</option>,
 254                                 <option>journal+console</option>,
 255                                 <option>syslog</option>,
 256                                 <option>syslog+console</option>,
 257                                 <option>kmsg</option>,
 258                                 <option>kmsg+console</option>.  If the
 259                                 argument is omitted
 260                                 <option>--default-standard-output=</option>
 261                                 defaults to <option>journal</option>
 262                                 and
 263                                 <option>--default-standard-error=</option>
 264                                 to
 265                                 <option>inherit</option>.</para></listitem>
 266                         </varlistentry>
 267                 </variablelist>
 268         </refsect1>
 269
 270         <refsect1>
 271                 <title>Concepts</title>
 272
 273                 <para>systemd provides a dependency system between
 274                 various entities called "units" of 12 different
 275                 types. Units encapsulate various objects that are
 276                 relevant for system boot-up and maintenance. The
 277                 majority of units are configured in unit configuration
 278                 files, whose syntax and basic set of options is
 279                 described in
 280                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 281                 however some are created automatically from other
 282                 configuration, dynamically from system state or
 283                 programmatically at runtime. Units may be "active"
 284                 (meaning started, bound, plugged in, ..., depending on
 285                 the unit type, see below), or "inactive" (meaning
 286                 stopped, unbound, unplugged, ...), as well as in the
 287                 process of being activated or deactivated,
 288                 i.e. between the two states (these states are called
 289                 "activating", "deactivating"). A special "failed"
 290                 state is available as well, which is very similar to
 291                 "inactive" and is entered when the service failed in
 292                 some way (process returned error code on exit, or
 293                 crashed, or an operation timed out). If this state is
 294                 entered, the cause will be logged, for later
 295                 reference. Note that the various unit types may have a
 296                 number of additional substates, which are mapped to
 297                 the five generalized unit states described
 298                 here.</para>
 299
 300                 <para>The following unit types are available:</para>
 301
 302                 <orderedlist>
 303                         <listitem><para>Service units, which start and control
 304                         daemons and the processes they consist of. For
 305                         details see
 306                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 307
 308                         <listitem><para>Socket units, which
 309                         encapsulate local IPC or network sockets in
 310                         the system, useful for socket-based
 311                         activation. For details about socket units see
 312                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 313                         for details on socket-based activation and
 314                         other forms of activation, see
 315                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 316
 317                         <listitem><para>Target units are useful to
 318                         group units, or provide well-known
 319                         synchronization points during boot-up, see
 320                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 321
 322                         <listitem><para>Device units expose kernel
 323                         devices in systemd and may be used to
 324                         implement device-based activation. For details
 325                         see
 326                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 327
 328                         <listitem><para>Mount units control mount
 329                         points in the file system, for details see
 330                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 331
 332                         <listitem><para>Automount units provide
 333                         automount capabilities, for on-demand mounting
 334                         of file systems as well as parallelized
 335                         boot-up. See
 336                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 337
 338                         <listitem><para>Snapshot units can be used to
 339                         temporarily save the state of the set of
 340                         systemd units, which later may be restored by
 341                         activating the saved snapshot unit. For more
 342                         information see
 343                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 344
 345                         <listitem><para>Timer units are useful for
 346                         triggering activation of other units based on
 347                         timers. You may find details in
 348                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 349
 350                         <listitem><para>Swap units are very similar to
 351                         mount units and encapsulate memory swap
 352                         partitions or files of the operating
 353                         system. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 354
 355                         <listitem><para>Path units may be used
 356                         to activate other services when file system
 357                         objects change or are modified. See
 358                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 359
 360                         <listitem><para>Slice units may be used to
 361                         group units which manage system processes
 362                         (such as service and scope units) in a
 363                         hierarchical tree for resource management
 364                         purposes. See
 365                         <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 366
 367                         <listitem><para>Scope units are similar to
 368                         service units, but manage foreign processes
 369                         instead of starting them as well. See
 370                         <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 371
 372                 </orderedlist>
 373
 374                 <para>Units are named as their configuration
 375                 files. Some units have special semantics. A detailed
 376                 list is available in
 377                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 378
 379                 <para>systemd knows various kinds of dependencies,
 380                 including positive and negative requirement
 381                 dependencies (i.e. <varname>Requires=</varname> and
 382                 <varname>Conflicts=</varname>) as well as ordering
 383                 dependencies (<varname>After=</varname> and
 384                 <varname>Before=</varname>). NB: ordering and
 385                 requirement dependencies are orthogonal. If only a
 386                 requirement dependency exists between two units
 387                 (e.g. <filename>foo.service</filename> requires
 388                 <filename>bar.service</filename>), but no ordering
 389                 dependency (e.g. <filename>foo.service</filename>
 390                 after <filename>bar.service</filename>) and both are
 391                 requested to start, they will be started in
 392                 parallel. It is a common pattern that both requirement
 393                 and ordering dependencies are placed between two
 394                 units. Also note that the majority of dependencies are
 395                 implicitly created and maintained by systemd. In most
 396                 cases it should be unnecessary to declare additional
 397                 dependencies manually, however it is possible to do
 398                 this.</para>
 399
 400                 <para>Application programs and units (via
 401                 dependencies) may request state changes of units. In
 402                 systemd, these requests are encapsulated as 'jobs' and
 403                 maintained in a job queue. Jobs may succeed or can
 404                 fail, their execution is ordered based on the ordering
 405                 dependencies of the units they have been scheduled
 406                 for.</para>
 407
 408                 <para>On boot systemd activates the target unit
 409                 <filename>default.target</filename> whose job is to
 410                 activate on-boot services and other on-boot units by
 411                 pulling them in via dependencies. Usually the unit
 412                 name is just an alias (symlink) for either
 413                 <filename>graphical.target</filename> (for
 414                 fully-featured boots into the UI) or
 415                 <filename>multi-user.target</filename> (for limited
 416                 console-only boots for use in embedded or server
 417                 environments, or similar; a subset of
 418                 graphical.target). However, it is at the discretion of
 419                 the administrator to configure it as an alias to any
 420                 other target unit. See
 421                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 422                 for details about these target units.</para>
 423
 424                 <para>Processes systemd spawns are placed in
 425                 individual Linux control groups named after the unit
 426                 which they belong to in the private systemd
 427                 hierarchy. (see <ulink
 428                 url="https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 429                 for more information about control groups, or short
 430                 "cgroups"). systemd uses this to effectively keep
 431                 track of processes. Control group information is
 432                 maintained in the kernel, and is accessible via the
 433                 file system hierarchy (beneath
 434                 <filename>/sys/fs/cgroup/systemd/</filename>), or in tools
 435                 such as
 436                 <citerefentry><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 437                 (<command>ps xawf -eo pid,user,cgroup,args</command>
 438                 is particularly useful to list all processes and the
 439                 systemd units they belong to.).</para>
 440
 441                 <para>systemd is compatible with the SysV init system
 442                 to a large degree: SysV init scripts are supported and
 443                 simply read as an alternative (though limited)
 444                 configuration file format. The SysV
 445                 <filename>/dev/initctl</filename> interface is
 446                 provided, and compatibility implementations of the
 447                 various SysV client tools are available. In addition to
 448                 that, various established Unix functionality such as
 449                 <filename>/etc/fstab</filename> or the
 450                 <filename>utmp</filename> database are
 451                 supported.</para>
 452
 453                 <para>systemd has a minimal transaction system: if a
 454                 unit is requested to start up or shut down it will add
 455                 it and all its dependencies to a temporary
 456                 transaction. Then, it will verify if the transaction
 457                 is consistent (i.e. whether the ordering of all units
 458                 is cycle-free). If it is not, systemd will try to fix
 459                 it up, and removes non-essential jobs from the
 460                 transaction that might remove the loop. Also, systemd
 461                 tries to suppress non-essential jobs in the
 462                 transaction that would stop a running service. Finally
 463                 it is checked whether the jobs of the transaction
 464                 contradict jobs that have already been queued, and
 465                 optionally the transaction is aborted then. If all
 466                 worked out and the transaction is consistent and
 467                 minimized in its impact it is merged with all already
 468                 outstanding jobs and added to the run
 469                 queue. Effectively this means that before executing a
 470                 requested operation, systemd will verify that it makes
 471                 sense, fixing it if possible, and only failing if it
 472                 really cannot work.</para>
 473
 474                 <para>Systemd contains native implementations of
 475                 various tasks that need to be executed as part of the
 476                 boot process. For example, it sets the hostname or
 477                 configures the loopback network device. It also sets
 478                 up and mounts various API file systems, such as
 479                 <filename>/sys</filename> or
 480                 <filename>/proc</filename>.</para>
 481
 482                 <para>For more information about the concepts and
 483                 ideas behind systemd, please refer to the <ulink
 484                 url="http://0pointer.de/blog/projects/systemd.html">Original
 485                 Design Document</ulink>.</para>
 486
 487                 <para>Note that some but not all interfaces provided
 488                 by systemd are covered by the <ulink
 489                 url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 490                 Stability Promise</ulink>.</para>
 491
 492                 <para>Units may be generated dynamically at boot and
 493                 system manager reload time, for example based on other
 494                 configuration files or parameters passed on the kernel
 495                 command line. For details see the <ulink
 496                 url="http://www.freedesktop.org/wiki/Software/systemd/Generators">Generators
 497                 Specification</ulink>.</para>
 498
 499                 <para>Systems which invoke systemd in a container
 500                 or initrd environment should implement the
 501                 <ulink
 502                 url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container
 503                 Interface</ulink> or <ulink
 504                 url="http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd
 505                 Interface</ulink> specifications, respectively.</para>
 506         </refsect1>
 507
 508         <refsect1>
 509                 <title>Directories</title>
 510
 511                 <variablelist>
 512                         <varlistentry>
 513                                 <term>System unit directories</term>
 514
 515                                 <listitem><para>The systemd system
 516                                 manager reads unit configuration from
 517                                 various directories. Packages that
 518                                 want to install unit files shall place
 519                                 them in the directory returned by
 520                                 <command>pkg-config systemd
 521                                 --variable=systemdsystemunitdir</command>. Other
 522                                 directories checked are
 523                                 <filename>/usr/local/lib/systemd/system</filename>
 524                                 and
 525                                 <filename>/usr/lib/systemd/system</filename>. User
 526                                 configuration always takes
 527                                 precedence. <command>pkg-config
 528                                 systemd
 529                                 --variable=systemdsystemconfdir</command>
 530                                 returns the path of the system
 531                                 configuration directory. Packages
 532                                 should alter the content of these
 533                                 directories only with the
 534                                 <command>enable</command> and
 535                                 <command>disable</command> commands of
 536                                 the
 537                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 538                                 tool. Full list of directories is provided in
 539                                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 540                                 </para></listitem>
 541                         </varlistentry>
 542                 </variablelist>
 543
 544                 <variablelist>
 545                         <varlistentry>
 546                                 <term>User unit directories</term>
 547
 548                                 <listitem><para>Similar rules apply
 549                                 for the user unit
 550                                 directories. However, here the <ulink
 551                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 552                                 Base Directory specification</ulink>
 553                                 is followed to find
 554                                 units. Applications should place their
 555                                 unit files in the directory returned
 556                                 by <command>pkg-config systemd
 557                                 --variable=systemduserunitdir</command>. Global
 558                                 configuration is done in the directory
 559                                 reported by <command>pkg-config
 560                                 systemd
 561                                 --variable=systemduserconfdir</command>. The
 562                                 <command>enable</command> and
 563                                 <command>disable</command> commands of
 564                                 the
 565                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 566                                 tool can handle both global (i.e. for
 567                                 all users) and private (for one user)
 568                                 enabling/disabling of
 569                                 units. Full list of directories is provided in
 570                                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 571                                 </para></listitem>
 572                         </varlistentry>
 573                 </variablelist>
 574
 575                 <variablelist>
 576                         <varlistentry>
 577                                 <term>SysV init scripts directory</term>
 578
 579                                 <listitem><para>The location of the
 580                                 SysV init script directory varies
 581                                 between distributions. If systemd
 582                                 cannot find a native unit file for a
 583                                 requested service, it will look for a
 584                                 SysV init script of the same name
 585                                 (with the
 586                                 <filename>.service</filename> suffix
 587                                 removed).</para></listitem>
 588                         </varlistentry>
 589                 </variablelist>
 590
 591                 <variablelist>
 592                         <varlistentry>
 593                                 <term>SysV runlevel link farm directory</term>
 594
 595                                 <listitem><para>The location of the
 596                                 SysV runlevel link farm directory
 597                                 varies between distributions. systemd
 598                                 will take the link farm into account
 599                                 when figuring out whether a service
 600                                 shall be enabled. Note that a service
 601                                 unit with a native unit configuration
 602                                 file cannot be started by activating it
 603                                 in the SysV runlevel link
 604                                 farm.</para></listitem>
 605                         </varlistentry>
 606                 </variablelist>
 607         </refsect1>
 608
 609         <refsect1>
 610                 <title>Signals</title>
 611
 612                 <variablelist>
 613                         <varlistentry>
 614                                 <term><constant>SIGTERM</constant></term>
 615
 616                                 <listitem><para>Upon receiving this
 617                                 signal the systemd system manager
 618                                 serializes its state, reexecutes
 619                                 itself and deserializes the saved
 620                                 state again. This is mostly equivalent
 621                                 to <command>systemctl
 622                                 daemon-reexec</command>.</para>
 623
 624                                 <para>systemd user managers will
 625                                 start the
 626                                 <filename>exit.target</filename> unit
 627                                 when this signal is received. This is
 628                                 mostly equivalent to
 629                                 <command>systemctl --user start
 630                                 exit.target</command>.</para></listitem>
 631                         </varlistentry>
 632
 633                         <varlistentry>
 634                                 <term><constant>SIGINT</constant></term>
 635
 636                                 <listitem><para>Upon receiving this
 637                                 signal the systemd system manager will
 638                                 start the
 639                                 <filename>ctrl-alt-del.target</filename> unit. This
 640                                 is mostly equivalent to
 641                                 <command>systemctl start
 642                                 ctl-alt-del.target</command>.</para>
 643
 644                                 <para>systemd user managers
 645                                 treat this signal the same way as
 646                                 <constant>SIGTERM</constant>.</para></listitem>
 647                         </varlistentry>
 648
 649                         <varlistentry>
 650                                 <term><constant>SIGWINCH</constant></term>
 651
 652                                 <listitem><para>When this signal is
 653                                 received the systemd system manager
 654                                 will start the
 655                                 <filename>kbrequest.target</filename>
 656                                 unit. This is mostly equivalent to
 657                                 <command>systemctl start
 658                                 kbrequest.target</command>.</para>
 659
 660                                 <para>This signal is ignored by
 661                                 systemd user
 662                                 managers.</para></listitem>
 663                         </varlistentry>
 664
 665                         <varlistentry>
 666                                 <term><constant>SIGPWR</constant></term>
 667
 668                                 <listitem><para>When this signal is
 669                                 received the systemd manager
 670                                 will start the
 671                                 <filename>sigpwr.target</filename>
 672                                 unit. This is mostly equivalent to
 673                                 <command>systemctl start
 674                                 sigpwr.target</command>.</para></listitem>
 675                         </varlistentry>
 676
 677                         <varlistentry>
 678                                 <term><constant>SIGUSR1</constant></term>
 679
 680                                 <listitem><para>When this signal is
 681                                 received the systemd manager will try
 682                                 to reconnect to the D-Bus
 683                                 bus.</para></listitem>
 684                         </varlistentry>
 685
 686                         <varlistentry>
 687                                 <term><constant>SIGUSR2</constant></term>
 688
 689                                 <listitem><para>When this signal is
 690                                 received the systemd manager will log
 691                                 its complete state in human readable
 692                                 form. The data logged is the same as
 693                                 printed by <command>systemctl
 694                                 dump</command>.</para></listitem>
 695                         </varlistentry>
 696
 697                         <varlistentry>
 698                                 <term><constant>SIGHUP</constant></term>
 699
 700                                 <listitem><para>Reloads the complete
 701                                 daemon configuration. This is mostly
 702                                 equivalent to <command>systemctl
 703                                 daemon-reload</command>.</para></listitem>
 704                         </varlistentry>
 705
 706                         <varlistentry>
 707                                 <term><constant>SIGRTMIN+0</constant></term>
 708
 709                                 <listitem><para>Enters default mode, starts the
 710                                 <filename>default.target</filename>
 711                                 unit. This is mostly equivalent to
 712                                 <command>systemctl start
 713                                 default.target</command>.</para></listitem>
 714                         </varlistentry>
 715
 716                         <varlistentry>
 717                                 <term><constant>SIGRTMIN+1</constant></term>
 718
 719                                 <listitem><para>Enters rescue mode,
 720                                 starts the
 721                                 <filename>rescue.target</filename>
 722                                 unit. This is mostly equivalent to
 723                                 <command>systemctl isolate
 724                                 rescue.target</command>.</para></listitem>
 725                         </varlistentry>
 726
 727                         <varlistentry>
 728                                 <term><constant>SIGRTMIN+2</constant></term>
 729
 730                                 <listitem><para>Enters emergency mode,
 731                                 starts the
 732                                 <filename>emergency.service</filename>
 733                                 unit. This is mostly equivalent to
 734                                 <command>systemctl isolate
 735                                 emergency.service</command>.</para></listitem>
 736                         </varlistentry>
 737
 738                         <varlistentry>
 739                                 <term><constant>SIGRTMIN+3</constant></term>
 740
 741                                 <listitem><para>Halts the machine,
 742                                 starts the
 743                                 <filename>halt.target</filename>
 744                                 unit. This is mostly equivalent to
 745                                 <command>systemctl start
 746                                 halt.target</command>.</para></listitem>
 747                         </varlistentry>
 748
 749                         <varlistentry>
 750                                 <term><constant>SIGRTMIN+4</constant></term>
 751
 752                                 <listitem><para>Powers off the machine,
 753                                 starts the
 754                                 <filename>poweroff.target</filename>
 755                                 unit. This is mostly equivalent to
 756                                 <command>systemctl start
 757                                 poweroff.target</command>.</para></listitem>
 758                         </varlistentry>
 759
 760                         <varlistentry>
 761                                 <term><constant>SIGRTMIN+5</constant></term>
 762
 763                                 <listitem><para>Reboots the machine,
 764                                 starts the
 765                                 <filename>reboot.target</filename>
 766                                 unit. This is mostly equivalent to
 767                                 <command>systemctl start
 768                                 reboot.target</command>.</para></listitem>
 769                         </varlistentry>
 770
 771                         <varlistentry>
 772                                 <term><constant>SIGRTMIN+6</constant></term>
 773
 774                                 <listitem><para>Reboots the machine via kexec,
 775                                 starts the
 776                                 <filename>kexec.target</filename>
 777                                 unit. This is mostly equivalent to
 778                                 <command>systemctl start
 779                                 kexec.target</command>.</para></listitem>
 780                         </varlistentry>
 781
 782                         <varlistentry>
 783                                 <term><constant>SIGRTMIN+13</constant></term>
 784
 785                                 <listitem><para>Immediately halts the machine.</para></listitem>
 786                         </varlistentry>
 787
 788                         <varlistentry>
 789                                 <term><constant>SIGRTMIN+14</constant></term>
 790
 791                                 <listitem><para>Immediately powers off the machine.</para></listitem>
 792                         </varlistentry>
 793
 794                         <varlistentry>
 795                                 <term><constant>SIGRTMIN+15</constant></term>
 796
 797                                 <listitem><para>Immediately reboots the machine.</para></listitem>
 798                         </varlistentry>
 799
 800                         <varlistentry>
 801                                 <term><constant>SIGRTMIN+16</constant></term>
 802
 803                                 <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
 804                         </varlistentry>
 805
 806                         <varlistentry>
 807                                 <term><constant>SIGRTMIN+20</constant></term>
 808
 809                                 <listitem><para>Enables display of
 810                                 status messages on the console, as
 811                                 controlled via
 812                                 <varname>systemd.show_status=1</varname>
 813                                 on the kernel command
 814                                 line.</para></listitem>
 815                         </varlistentry>
 816
 817                         <varlistentry>
 818                                 <term><constant>SIGRTMIN+21</constant></term>
 819
 820                                 <listitem><para>Disables display of
 821                                 status messages on the console, as
 822                                 controlled via
 823                                 <varname>systemd.show_status=0</varname>
 824                                 on the kernel command
 825                                 line.</para></listitem>
 826                         </varlistentry>
 827
 828                         <varlistentry>
 829                                 <term><constant>SIGRTMIN+22</constant></term>
 830                                 <term><constant>SIGRTMIN+23</constant></term>
 831
 832                                 <listitem><para>Sets the log level to
 833                                 <literal>debug</literal>
 834                                 (or <literal>info</literal> on
 835                                 <constant>SIGRTMIN+23</constant>), as
 836                                 controlled via
 837                                 <varname>systemd.log_level=debug</varname>
 838                                 (or <varname>systemd.log_level=info</varname>
 839                                 on <constant>SIGRTMIN+23</constant>) on
 840                                 the kernel command
 841                                 line.</para></listitem>
 842                         </varlistentry>
 843
 844                         <varlistentry>
 845                                 <term><constant>SIGRTMIN+24</constant></term>
 846
 847                                 <listitem><para>Immediately exits the
 848                                 manager (only available for --user
 849                                 instances).</para></listitem>
 850                         </varlistentry>
 851
 852                         <varlistentry>
 853                                 <term><constant>SIGRTMIN+26</constant></term>
 854                                 <term><constant>SIGRTMIN+27</constant></term>
 855                                 <term><constant>SIGRTMIN+28</constant></term>
 856                                 <term><constant>SIGRTMIN+29</constant></term>
 857
 858                                 <listitem><para>Sets the log level to
 859                                 <literal>journal-or-kmsg</literal>
 860                                 (or <literal>console</literal> on
 861                                 <constant>SIGRTMIN+27</constant>,
 862                                 <literal>kmsg</literal> on
 863                                 <constant>SIGRTMIN+28</constant>,
 864                                 or <literal>syslog-or-kmsg</literal>
 865                                 on <constant>SIGRTMIN+29</constant>), as
 866                                 controlled via
 867                                 <varname>systemd.log_target=journal-or-kmsg</varname>
 868                                 (or <varname>systemd.log_target=console</varname>
 869                                 on <constant>SIGRTMIN+27</constant>,
 870                                 <varname>systemd.log_target=kmsg</varname>
 871                                 on <constant>SIGRTMIN+28</constant>,
 872                                 or
 873                                 <varname>systemd.log_target=syslog-or-kmsg</varname>
 874                                 on <constant>SIGRTMIN+29</constant>) on
 875                                 the kernel command
 876                                 line.</para></listitem>
 877                         </varlistentry>
 878                 </variablelist>
 879         </refsect1>
 880
 881         <refsect1>
 882                 <title>Environment</title>
 883
 884                 <variablelist class='environment-variables'>
 885                         <varlistentry>
 886                                 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 887                                 <listitem><para>systemd reads the
 888                                 log level from this environment
 889                                 variable. This can be overridden with
 890                                 <option>--log-level=</option>.</para></listitem>
 891                         </varlistentry>
 892
 893                         <varlistentry>
 894                                 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 895                                 <listitem><para>systemd reads the
 896                                 log target from this environment
 897                                 variable. This can be overridden with
 898                                 <option>--log-target=</option>.</para></listitem>
 899                         </varlistentry>
 900
 901                         <varlistentry>
 902                                 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 903                                 <listitem><para>Controls whether
 904                                 systemd highlights important log
 905                                 messages. This can be overridden with
 906                                 <option>--log-color=</option>.</para></listitem>
 907                         </varlistentry>
 908
 909                         <varlistentry>
 910                                 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 911                                 <listitem><para>Controls whether
 912                                 systemd prints the code location along
 913                                 with log messages. This can be
 914                                 overridden with
 915                                 <option>--log-location=</option>.</para></listitem>
 916                         </varlistentry>
 917
 918                         <varlistentry>
 919                                 <term><varname>$XDG_CONFIG_HOME</varname></term>
 920                                 <term><varname>$XDG_CONFIG_DIRS</varname></term>
 921                                 <term><varname>$XDG_DATA_HOME</varname></term>
 922                                 <term><varname>$XDG_DATA_DIRS</varname></term>
 923
 924                                 <listitem><para>The systemd user
 925                                 manager uses these variables in
 926                                 accordance to the <ulink
 927                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 928                                 Base Directory specification</ulink>
 929                                 to find its configuration.</para></listitem>
 930                         </varlistentry>
 931
 932                         <varlistentry>
 933                                 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 934
 935                                 <listitem><para>Controls where systemd
 936                                 looks for unit
 937                                 files.</para></listitem>
 938                         </varlistentry>
 939
 940                         <varlistentry>
 941                                 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 942
 943                                 <listitem><para>Controls where systemd
 944                                 looks for SysV init scripts.</para></listitem>
 945                         </varlistentry>
 946
 947                         <varlistentry>
 948                                 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 949
 950                                 <listitem><para>Controls where systemd
 951                                 looks for SysV init script runlevel link
 952                                 farms.</para></listitem>
 953                         </varlistentry>
 954
 955                         <varlistentry>
 956                                 <term><varname>$LISTEN_PID</varname></term>
 957                                 <term><varname>$LISTEN_FDS</varname></term>
 958
 959                                 <listitem><para>Set by systemd for
 960                                 supervised processes during
 961                                 socket-based activation. See
 962                                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 963                                 for more information.
 964                                 </para></listitem>
 965                         </varlistentry>
 966
 967                         <varlistentry>
 968                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 969
 970                                 <listitem><para>Set by systemd for
 971                                 supervised processes for status and
 972                                 start-up completion notification. See
 973                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 974                                 for more information.
 975                                 </para></listitem>
 976                         </varlistentry>
 977                 </variablelist>
 978         </refsect1>
 979
 980         <refsect1>
 981                 <title>Kernel Command Line</title>
 982
 983                 <para>When run as system instance systemd parses a
 984                 number of kernel command line
 985                 arguments<footnote><para>If run inside a Linux
 986                 container these arguments may be passed as command
 987                 line arguments to systemd itself, next to any of the
 988                 command line options listed in the Options section
 989                 above. If run outside of Linux containers, these
 990                 arguments are parsed from
 991                 <filename>/proc/cmdline</filename>
 992                 instead.</para></footnote>:</para>
 993
 994                 <variablelist class='kernel-commandline-options'>
 995                         <varlistentry>
 996                                 <term><varname>systemd.unit=</varname></term>
 997                                 <term><varname>rd.systemd.unit=</varname></term>
 998
 999                                 <listitem><para>Overrides the unit to
1000                                 activate on boot. Defaults to
1001                                 <filename>default.target</filename>. This
1002                                 may be used to temporarily boot into a
1003                                 different boot unit, for example
1004                                 <filename>rescue.target</filename> or
1005                                 <filename>emergency.service</filename>. See
1006                                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1007                                 for details about these units. The
1008                                 option prefixed with
1009                                 <literal>rd.</literal> is honored
1010                                 only in the initial RAM disk (initrd),
1011                                 while the one that is not prefixed only
1012                                 in the main system.</para></listitem>
1013                         </varlistentry>
1014
1015                         <varlistentry>
1016                                 <term><varname>systemd.dump_core=</varname></term>
1017
1018                                 <listitem><para>Takes a boolean
1019                                 argument. If <option>true</option>,
1020                                 systemd dumps core when it
1021                                 crashes. Otherwise, no core dump is
1022                                 created. Defaults to
1023                                 <option>true</option>.</para></listitem>
1024                         </varlistentry>
1025
1026                         <varlistentry>
1027                                 <term><varname>systemd.crash_shell=</varname></term>
1028
1029                                 <listitem><para>Takes a boolean
1030                                 argument. If <option>true</option>,
1031                                 systemd spawns a shell when it
1032                                 crashes. Otherwise, no shell is
1033                                 spawned. Defaults to
1034                                 <option>false</option>, for security
1035                                 reasons, as the shell is not protected
1036                                 by any password
1037                                 authentication.</para></listitem>
1038                         </varlistentry>
1039
1040                         <varlistentry>
1041                                 <term><varname>systemd.crash_chvt=</varname></term>
1042
1043                                 <listitem><para>Takes an integer
1044                                 argument. If positive systemd
1045                                 activates the specified virtual
1046                                 terminal when it crashes. Defaults to
1047                                 <constant>-1</constant>.</para></listitem>
1048                         </varlistentry>
1049
1050                         <varlistentry>
1051                                 <term><varname>systemd.confirm_spawn=</varname></term>
1052
1053                                 <listitem><para>Takes a boolean
1054                                 argument. If <option>true</option>,
1055                                 asks for confirmation when spawning
1056                                 processes. Defaults to
1057                                 <option>false</option>.</para></listitem>
1058                         </varlistentry>
1059
1060                         <varlistentry>
1061                                 <term><varname>systemd.show_status=</varname></term>
1062
1063                                 <listitem><para>Takes a boolean
1064                                 argument or the constant
1065                                 <constant>auto</constant>. If
1066                                 <option>true</option>, shows terse
1067                                 service status updates on the console
1068                                 during bootup.
1069                                 <constant>auto</constant> behaves like
1070                                 <option>false</option> until a service
1071                                 fails or there is a significant delay
1072                                 in boot. Defaults to
1073                                 <option>true</option>, unless
1074                                 <option>quiet</option> is passed as
1075                                 kernel command line option in which
1076                                 case it defaults to
1077                                 <constant>auto</constant>.</para></listitem>
1078                         </varlistentry>
1079
1080                         <varlistentry>
1081                                 <term><varname>systemd.log_target=</varname></term>
1082                                 <term><varname>systemd.log_level=</varname></term>
1083                                 <term><varname>systemd.log_color=</varname></term>
1084                                 <term><varname>systemd.log_location=</varname></term>
1085
1086                                 <listitem><para>Controls log output,
1087                                 with the same effect as the
1088                                 <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
1089                                 environment variables described above.</para></listitem>
1090                         </varlistentry>
1091
1092                         <varlistentry>
1093                                 <term><varname>systemd.default_standard_output=</varname></term>
1094                                 <term><varname>systemd.default_standard_error=</varname></term>
1095                                 <listitem><para>Controls default
1096                                 standard output and error output for
1097                                 services, with the same effect as the
1098                                 <option>--default-standard-output=</option>
1099                                 and <option>--default-standard-error=</option>
1100                                 command line arguments described
1101                                 above, respectively.</para></listitem>
1102                         </varlistentry>
1103
1104                         <varlistentry>
1105                                 <term><varname>systemd.setenv=</varname></term>
1106
1107                                 <listitem><para>Takes a string
1108                                 argument in the form VARIABLE=VALUE.
1109                                 May be used to set default environment
1110                                 variables to add to forked child processes.
1111                                 May be used more than once to set multiple
1112                                 variables.</para></listitem>
1113                         </varlistentry>
1114
1115                         <varlistentry>
1116                                 <term><varname>quiet</varname></term>
1117
1118                                 <listitem><para>Turn off
1119                                 status output at boot, much like
1120                                 <varname>systemd.show_status=false</varname>
1121                                 would. Note that this option is also
1122                                 read by the kernel itself and disables
1123                                 kernel log output. Passing this option
1124                                 hence turns off the usual output from
1125                                 both the system manager and the kernel.
1126                                 </para></listitem>
1127                         </varlistentry>
1128
1129                         <varlistentry>
1130                                 <term><varname>debug</varname></term>
1131
1132                                 <listitem><para>Turn on debugging
1133                                 output. This is equivalent to
1134                                 <varname>systemd.log_level=debug</varname>.
1135                                 Note that this option is also read by
1136                                 the kernel itself and enables kernel
1137                                 debug output.  Passing this option
1138                                 hence turns on the debug output from
1139                                 both the system manager and the
1140                                 kernel.</para></listitem>
1141                         </varlistentry>
1142
1143                         <varlistentry>
1144                                 <term><varname>-b</varname></term>
1145                                 <term><varname>emergency</varname></term>
1146
1147                                 <listitem><para>Boot into emergency
1148                                 mode. This is equivalent to
1149                                 <varname>systemd.unit=emergency.target</varname>
1150                                 and provided for compatibility
1151                                 reasons and to be easier to type.</para></listitem>
1152                         </varlistentry>
1153
1154                         <varlistentry>
1155                                 <term><varname>single</varname></term>
1156                                 <term><varname>s</varname></term>
1157                                 <term><varname>S</varname></term>
1158                                 <term><varname>1</varname></term>
1159
1160                                 <listitem><para>Boot into rescue
1161                                 mode. This is equivalent to
1162                                 <varname>systemd.unit=rescue.target</varname>
1163                                 and provided for compatibility reasons
1164                                 and to be easier to
1165                                 type.</para></listitem>
1166                         </varlistentry>
1167
1168                         <varlistentry>
1169                                 <term><varname>2</varname></term>
1170                                 <term><varname>3</varname></term>
1171                                 <term><varname>4</varname></term>
1172                                 <term><varname>5</varname></term>
1173
1174                                 <listitem><para>Boot into the
1175                                 specified legacy SysV runlevel. These
1176                                 are equivalent to
1177                                 <varname>systemd.unit=runlevel2.target</varname>,
1178                                 <varname>systemd.unit=runlevel3.target</varname>,
1179                                 <varname>systemd.unit=runlevel4.target</varname>,
1180                                 and <varname>systemd.unit=runlevel5.target</varname>, respectively,
1181                                 and provided for compatibility reasons
1182                                 and to be easier to
1183                                 type.</para></listitem>
1184                         </varlistentry>
1185
1186                         <varlistentry>
1187                                 <term><varname>locale.LANG=</varname></term>
1188                                 <term><varname>locale.LANGUAGE=</varname></term>
1189                                 <term><varname>locale.LC_CTYPE=</varname></term>
1190                                 <term><varname>locale.LC_NUMERIC=</varname></term>
1191                                 <term><varname>locale.LC_TIME=</varname></term>
1192                                 <term><varname>locale.LC_COLLATE=</varname></term>
1193                                 <term><varname>locale.LC_MONETARY=</varname></term>
1194                                 <term><varname>locale.LC_MESSAGES=</varname></term>
1195                                 <term><varname>locale.LC_PAPER=</varname></term>
1196                                 <term><varname>locale.LC_NAME=</varname></term>
1197                                 <term><varname>locale.LC_ADDRESS=</varname></term>
1198                                 <term><varname>locale.LC_TELEPHONE=</varname></term>
1199                                 <term><varname>locale.LC_MEASUREMENT=</varname></term>
1200                                 <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1201
1202                                 <listitem><para>Set the system locale
1203                                 to use. This overrides the settings in
1204                                 <filename>/etc/locale.conf</filename>. For
1205                                 more information see
1206                                 <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1207                                 and
1208                                 <citerefentry><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1209                                 </para></listitem>
1210                         </varlistentry>
1211                 </variablelist>
1212
1213                 <para>For other kernel command line parameters
1214                 understood by components of the core OS, please refer
1215                 to
1216                 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1217         </refsect1>
1218
1219         <refsect1>
1220                 <title>Sockets and FIFOs</title>
1221
1222                 <variablelist>
1223                         <varlistentry>
1224                                 <term><filename>/run/systemd/notify</filename></term>
1225
1226                                 <listitem><para>Daemon status
1227                                 notification socket. This is an
1228                                 <constant>AF_UNIX</constant> datagram socket and is used to
1229                                 implement the daemon notification
1230                                 logic as implemented by
1231                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1232
1233                         </varlistentry>
1234
1235                         <varlistentry>
1236                                 <term><filename>/run/systemd/shutdownd</filename></term>
1237
1238                                 <listitem><para>Used internally by the
1239                                 <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1240                                 tool to implement delayed
1241                                 shutdowns. This is an <constant>AF_UNIX</constant> datagram
1242                                 socket.</para></listitem>
1243                         </varlistentry>
1244
1245                         <varlistentry>
1246                                 <term><filename>/run/systemd/private</filename></term>
1247
1248                                 <listitem><para>Used internally as
1249                                 communication channel between
1250                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1251                                 and the systemd process. This is an
1252                                 <constant>AF_UNIX</constant> stream socket. This interface
1253                                 is private to systemd and should not
1254                                 be used in external
1255                                 projects.</para></listitem>
1256                         </varlistentry>
1257
1258                         <varlistentry>
1259                                 <term><filename>/dev/initctl</filename></term>
1260
1261                                 <listitem><para>Limited compatibility
1262                                 support for the SysV client interface,
1263                                 as implemented by the
1264                                 <filename>systemd-initctl.service</filename>
1265                                 unit. This is a named pipe in the file
1266                                 system. This interface is obsolete and
1267                                 should not be used in new
1268                                 applications.</para></listitem>
1269                         </varlistentry>
1270                 </variablelist>
1271         </refsect1>
1272
1273         <refsect1>
1274                 <title>See Also</title>
1275                 <para>
1276                         The <ulink url="http://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
1277                         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1278                         <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1279                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1280                         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1281                         <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1282                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1283                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1284                         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1285                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1286                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1287                         <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1288                         <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1289                         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1290                 </para>
1291         </refsect1>
1292
1293 </refentry>