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>--introspect=</option></term>
 123
 124                                 <listitem><para>Extract D-Bus
 125                                 interface introspection data. This is
 126                                 mostly useful at install time
 127                                 to generate data suitable for the
 128                                 D-Bus interfaces
 129                                 repository. Optionally the interface
 130                                 name for the introspection data may be
 131                                 specified. If omitted, the
 132                                 introspection data for all interfaces
 133                                 is dumped.</para></listitem>
 134                         </varlistentry>
 135                         <varlistentry>
 136                                 <term><option>--unit=</option></term>
 137
 138                                 <listitem><para>Set default unit to
 139                                 activate on startup. If not specified,
 140                                 defaults to
 141                                 <filename>default.target</filename>.</para></listitem>
 142                         </varlistentry>
 143                         <varlistentry>
 144                                 <term><option>--system</option></term>
 145                                 <term><option>--user</option></term>
 146
 147                                 <listitem><para>For <option>--system</option>,
 148                                 tell systemd to run a
 149                                 system instance, even if the process ID is
 150                                 not 1, i.e. systemd is not run as init process.
 151                                 <option>--user</option> does the opposite,
 152                                 running a user instance even if the process
 153                                 ID is 1.
 154                                 Normally it should not be necessary to
 155                                 pass these options, as systemd
 156                                 automatically detects the mode it is
 157                                 started in. These options are hence of
 158                                 little use except for debugging. Note
 159                                 that it is not supported booting and
 160                                 maintaining a full system with systemd
 161                                 running in <option>--system</option>
 162                                 mode, but PID not 1. In practice,
 163                                 passing <option>--system</option> explicitly is
 164                                 only useful in conjunction with
 165                                 <option>--test</option>.</para></listitem>
 166                         </varlistentry>
 167                         <varlistentry>
 168                                 <term><option>--dump-core</option></term>
 169
 170                                 <listitem><para>Dump core on
 171                                 crash. This switch has no effect when
 172                                 run as user
 173                                 instance.</para></listitem>
 174                         </varlistentry>
 175                         <varlistentry>
 176                                 <term><option>--crash-shell</option></term>
 177
 178                                 <listitem><para>Run shell on
 179                                 crash. This switch has no effect when
 180                                 run as user
 181                                 instance.</para></listitem>
 182                         </varlistentry>
 183                         <varlistentry>
 184                                 <term><option>--confirm-spawn</option></term>
 185
 186                                 <listitem><para>Ask for confirmation
 187                                 when spawning processes. This switch
 188                                 has no effect when run as user
 189                                 instance.</para></listitem>
 190                         </varlistentry>
 191                         <varlistentry>
 192                                 <term><option>--show-status=</option></term>
 193
 194                                 <listitem><para>Show terse service
 195                                 status information while booting. This
 196                                 switch has no effect when run as user
 197                                 instance. Takes a boolean argument
 198                                 which may be omitted which is
 199                                 interpreted as
 200                                 <option>true</option>.</para></listitem>
 201                         </varlistentry>
 202                         <varlistentry>
 203                                 <term><option>--log-target=</option></term>
 204
 205                                 <listitem><para>Set log
 206                                 target. Argument must be one of
 207                                 <option>console</option>,
 208                                 <option>journal</option>,
 209                                 <option>syslog</option>,
 210                                 <option>kmsg</option>,
 211                                 <option>journal-or-kmsg</option>,
 212                                 <option>syslog-or-kmsg</option>,
 213                                 <option>null</option>.</para></listitem>
 214                         </varlistentry>
 215                         <varlistentry>
 216                                 <term><option>--log-level=</option></term>
 217
 218                                 <listitem><para>Set log level. As
 219                                 argument this accepts a numerical log
 220                                 level or the well-known <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 221                                 symbolic names (lowercase):
 222                                 <option>emerg</option>,
 223                                 <option>alert</option>,
 224                                 <option>crit</option>,
 225                                 <option>err</option>,
 226                                 <option>warning</option>,
 227                                 <option>notice</option>,
 228                                 <option>info</option>,
 229                                 <option>debug</option>.</para></listitem>
 230                         </varlistentry>
 231                         <varlistentry>
 232                                 <term><option>--log-color=</option></term>
 233
 234                                 <listitem><para>Highlight important
 235                                 log messages. Argument is a boolean
 236                                 value. If the argument is omitted, it
 237                                 defaults to
 238                                 <option>true</option>.</para></listitem>
 239                         </varlistentry>
 240                         <varlistentry>
 241                                 <term><option>--log-location=</option></term>
 242
 243                                 <listitem><para>Include code location
 244                                 in log messages. This is mostly
 245                                 relevant for debugging
 246                                 purposes. Argument is a boolean
 247                                 value. If the argument is omitted
 248                                 it defaults to
 249                                 <option>true</option>.</para></listitem>
 250                         </varlistentry>
 251                         <varlistentry>
 252                                 <term><option>--default-standard-output=</option></term>
 253                                 <term><option>--default-standard-error=</option></term>
 254
 255                                 <listitem><para>Sets the default
 256                                 output or error output for all
 257                                 services and sockets, respectively. That is, controls
 258                                 the default for
 259                                 <option>StandardOutput=</option>
 260                                 and <option>StandardError=</option>
 261                                 (see
 262                                 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 263                                 for details). Takes one of
 264                                 <option>inherit</option>,
 265                                 <option>null</option>,
 266                                 <option>tty</option>,
 267                                 <option>journal</option>,
 268                                 <option>journal+console</option>,
 269                                 <option>syslog</option>,
 270                                 <option>syslog+console</option>,
 271                                 <option>kmsg</option>,
 272                                 <option>kmsg+console</option>.  If the
 273                                 argument is omitted
 274                                 <option>--default-standard-output=</option>
 275                                 defaults to <option>journal</option>
 276                                 and
 277                                 <option>--default-standard-error=</option>
 278                                 to
 279                                 <option>inherit</option>.</para></listitem>
 280                         </varlistentry>
 281                 </variablelist>
 282         </refsect1>
 283
 284         <refsect1>
 285                 <title>Concepts</title>
 286
 287                 <para>systemd provides a dependency system between
 288                 various entities called "units" of 12 different
 289                 types. Units encapsulate various objects that are
 290                 relevant for system boot-up and maintenance. The
 291                 majority of units are configured in unit configuration
 292                 files, whose syntax and basic set of options is
 293                 described in
 294                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 295                 however some are created automatically from other
 296                 configuration, dynamically from system state or
 297                 programmatically at runtime. Units may be "active"
 298                 (meaning started, bound, plugged in, ..., depending on
 299                 the unit type, see below), or "inactive" (meaning
 300                 stopped, unbound, unplugged, ...), as well as in the
 301                 process of being activated or deactivated,
 302                 i.e. between the two states (these states are called
 303                 "activating", "deactivating"). A special "failed"
 304                 state is available as well, which is very similar to
 305                 "inactive" and is entered when the service failed in
 306                 some way (process returned error code on exit, or
 307                 crashed, or an operation timed out). If this state is
 308                 entered, the cause will be logged, for later
 309                 reference. Note that the various unit types may have a
 310                 number of additional substates, which are mapped to
 311                 the five generalized unit states described
 312                 here.</para>
 313
 314                 <para>The following unit types are available:</para>
 315
 316                 <orderedlist>
 317                         <listitem><para>Service units, which start and control
 318                         daemons and the processes they consist of. For
 319                         details see
 320                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 321
 322                         <listitem><para>Socket units, which
 323                         encapsulate local IPC or network sockets in
 324                         the system, useful for socket-based
 325                         activation. For details about socket units see
 326                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 327                         for details on socket-based activation and
 328                         other forms of activation, see
 329                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 330
 331                         <listitem><para>Target units are useful to
 332                         group units, or provide well-known
 333                         synchronization points during boot-up, see
 334                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 335
 336                         <listitem><para>Device units expose kernel
 337                         devices in systemd and may be used to
 338                         implement device-based activation. For details
 339                         see
 340                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 341
 342                         <listitem><para>Mount units control mount
 343                         points in the file system, for details see
 344                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 345
 346                         <listitem><para>Automount units provide
 347                         automount capabilities, for on-demand mounting
 348                         of file systems as well as parallelized
 349                         boot-up. See
 350                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 351
 352                         <listitem><para>Snapshot units can be used to
 353                         temporarily save the state of the set of
 354                         systemd units, which later may be restored by
 355                         activating the saved snapshot unit. For more
 356                         information see
 357                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 358
 359                         <listitem><para>Timer units are useful for
 360                         triggering activation of other units based on
 361                         timers. You may find details in
 362                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 363
 364                         <listitem><para>Swap units are very similar to
 365                         mount units and encapsulate memory swap
 366                         partitions or files of the operating
 367                         system. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 368
 369                         <listitem><para>Path units may be used
 370                         to activate other services when file system
 371                         objects change or are modified. See
 372                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 373
 374                         <listitem><para>Slice units may be used to
 375                         group units which manage system processes
 376                         (such as service and scope units) in a
 377                         hierarchical tree for resource management
 378                         purposes. See
 379                         <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 380
 381                         <listitem><para>Scope units are similar to
 382                         service units, but manage foreign processes
 383                         instead of starting them as well. See
 384                         <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 385
 386                 </orderedlist>
 387
 388                 <para>Units are named as their configuration
 389                 files. Some units have special semantics. A detailed
 390                 list is available in
 391                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 392
 393                 <para>systemd knows various kinds of dependencies,
 394                 including positive and negative requirement
 395                 dependencies (i.e. <varname>Requires=</varname> and
 396                 <varname>Conflicts=</varname>) as well as ordering
 397                 dependencies (<varname>After=</varname> and
 398                 <varname>Before=</varname>). NB: ordering and
 399                 requirement dependencies are orthogonal. If only a
 400                 requirement dependency exists between two units
 401                 (e.g. <filename>foo.service</filename> requires
 402                 <filename>bar.service</filename>), but no ordering
 403                 dependency (e.g. <filename>foo.service</filename>
 404                 after <filename>bar.service</filename>) and both are
 405                 requested to start, they will be started in
 406                 parallel. It is a common pattern that both requirement
 407                 and ordering dependencies are placed between two
 408                 units. Also note that the majority of dependencies are
 409                 implicitly created and maintained by systemd. In most
 410                 cases it should be unnecessary to declare additional
 411                 dependencies manually, however it is possible to do
 412                 this.</para>
 413
 414                 <para>Application programs and units (via
 415                 dependencies) may request state changes of units. In
 416                 systemd, these requests are encapsulated as 'jobs' and
 417                 maintained in a job queue. Jobs may succeed or can
 418                 fail, their execution is ordered based on the ordering
 419                 dependencies of the units they have been scheduled
 420                 for.</para>
 421
 422                 <para>On boot systemd activates the target unit
 423                 <filename>default.target</filename> whose job is to
 424                 activate on-boot services and other on-boot units by
 425                 pulling them in via dependencies. Usually the unit
 426                 name is just an alias (symlink) for either
 427                 <filename>graphical.target</filename> (for
 428                 fully-featured boots into the UI) or
 429                 <filename>multi-user.target</filename> (for limited
 430                 console-only boots for use in embedded or server
 431                 environments, or similar; a subset of
 432                 graphical.target). However, it is at the discretion of
 433                 the administrator to configure it as an alias to any
 434                 other target unit. See
 435                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 436                 for details about these target units.</para>
 437
 438                 <para>Processes systemd spawns are placed in
 439                 individual Linux control groups named after the unit
 440                 which they belong to in the private systemd
 441                 hierarchy. (see <ulink
 442                 url="https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 443                 for more information about control groups, or short
 444                 "cgroups"). systemd uses this to effectively keep
 445                 track of processes. Control group information is
 446                 maintained in the kernel, and is accessible via the
 447                 file system hierarchy (beneath
 448                 <filename>/sys/fs/cgroup/systemd/</filename>), or in tools
 449                 such as
 450                 <citerefentry><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 451                 (<command>ps xawf -eo pid,user,cgroup,args</command>
 452                 is particularly useful to list all processes and the
 453                 systemd units they belong to.).</para>
 454
 455                 <para>systemd is compatible with the SysV init system
 456                 to a large degree: SysV init scripts are supported and
 457                 simply read as an alternative (though limited)
 458                 configuration file format. The SysV
 459                 <filename>/dev/initctl</filename> interface is
 460                 provided, and compatibility implementations of the
 461                 various SysV client tools are available. In addition to
 462                 that, various established Unix functionality such as
 463                 <filename>/etc/fstab</filename> or the
 464                 <filename>utmp</filename> database are
 465                 supported.</para>
 466
 467                 <para>systemd has a minimal transaction system: if a
 468                 unit is requested to start up or shut down it will add
 469                 it and all its dependencies to a temporary
 470                 transaction. Then, it will verify if the transaction
 471                 is consistent (i.e. whether the ordering of all units
 472                 is cycle-free). If it is not, systemd will try to fix
 473                 it up, and removes non-essential jobs from the
 474                 transaction that might remove the loop. Also, systemd
 475                 tries to suppress non-essential jobs in the
 476                 transaction that would stop a running service. Finally
 477                 it is checked whether the jobs of the transaction
 478                 contradict jobs that have already been queued, and
 479                 optionally the transaction is aborted then. If all
 480                 worked out and the transaction is consistent and
 481                 minimized in its impact it is merged with all already
 482                 outstanding jobs and added to the run
 483                 queue. Effectively this means that before executing a
 484                 requested operation, systemd will verify that it makes
 485                 sense, fixing it if possible, and only failing if it
 486                 really cannot work.</para>
 487
 488                 <para>Systemd contains native implementations of
 489                 various tasks that need to be executed as part of the
 490                 boot process. For example, it sets the hostname or
 491                 configures the loopback network device. It also sets
 492                 up and mounts various API file systems, such as
 493                 <filename>/sys</filename> or
 494                 <filename>/proc</filename>.</para>
 495
 496                 <para>For more information about the concepts and
 497                 ideas behind systemd please refer to the <ulink
 498                 url="http://0pointer.de/blog/projects/systemd.html">Original
 499                 Design Document</ulink>.</para>
 500
 501                 <para>Note that some but not all interfaces provided
 502                 by systemd are covered by the <ulink
 503                 url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 504                 Stability Promise</ulink>.</para>
 505
 506                 <para>Units may be generated dynamically at boot and
 507                 system manager reload time, for example based on other
 508                 configuration files or parameters passed on the kernel
 509                 command line. For details see the <ulink
 510                 url="http://www.freedesktop.org/wiki/Software/systemd/Generators">Generators
 511                 Specification</ulink>.</para>
 512
 513                 <para>Systems which invoke systemd in a container
 514                 or initrd environment should implement the
 515                 <ulink
 516                 url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container
 517                 Interface</ulink> or <ulink
 518                 url="http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd
 519                 Interface</ulink> specifications, respectively.</para>
 520         </refsect1>
 521
 522         <refsect1>
 523                 <title>Directories</title>
 524
 525                 <variablelist>
 526                         <varlistentry>
 527                                 <term>System unit directories</term>
 528
 529                                 <listitem><para>The systemd system
 530                                 manager reads unit configuration from
 531                                 various directories. Packages that
 532                                 want to install unit files shall place
 533                                 them in the directory returned by
 534                                 <command>pkg-config systemd
 535                                 --variable=systemdsystemunitdir</command>. Other
 536                                 directories checked are
 537                                 <filename>/usr/local/lib/systemd/system</filename>
 538                                 and
 539                                 <filename>/usr/lib/systemd/system</filename>. User
 540                                 configuration always takes
 541                                 precedence. <command>pkg-config
 542                                 systemd
 543                                 --variable=systemdsystemconfdir</command>
 544                                 returns the path of the system
 545                                 configuration directory. Packages
 546                                 should alter the content of these
 547                                 directories only with the
 548                                 <command>enable</command> and
 549                                 <command>disable</command> commands of
 550                                 the
 551                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 552                                 tool. Full list of directories is provided in
 553                                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 554                                 </para></listitem>
 555                         </varlistentry>
 556                 </variablelist>
 557
 558                 <variablelist>
 559                         <varlistentry>
 560                                 <term>User unit directories</term>
 561
 562                                 <listitem><para>Similar rules apply
 563                                 for the user unit
 564                                 directories. However, here the <ulink
 565                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 566                                 Base Directory specification</ulink>
 567                                 is followed to find
 568                                 units. Applications should place their
 569                                 unit files in the directory returned
 570                                 by <command>pkg-config systemd
 571                                 --variable=systemduserunitdir</command>. Global
 572                                 configuration is done in the directory
 573                                 reported by <command>pkg-config
 574                                 systemd
 575                                 --variable=systemduserconfdir</command>. The
 576                                 <command>enable</command> and
 577                                 <command>disable</command> commands of
 578                                 the
 579                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 580                                 tool can handle both global (i.e. for
 581                                 all users) and private (for one user)
 582                                 enabling/disabling of
 583                                 units. Full list of directories is provided in
 584                                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 585                                 </para></listitem>
 586                         </varlistentry>
 587                 </variablelist>
 588
 589                 <variablelist>
 590                         <varlistentry>
 591                                 <term>SysV init scripts directory</term>
 592
 593                                 <listitem><para>The location of the
 594                                 SysV init script directory varies
 595                                 between distributions. If systemd
 596                                 cannot find a native unit file for a
 597                                 requested service, it will look for a
 598                                 SysV init script of the same name
 599                                 (with the
 600                                 <filename>.service</filename> suffix
 601                                 removed).</para></listitem>
 602                         </varlistentry>
 603                 </variablelist>
 604
 605                 <variablelist>
 606                         <varlistentry>
 607                                 <term>SysV runlevel link farm directory</term>
 608
 609                                 <listitem><para>The location of the
 610                                 SysV runlevel link farm directory
 611                                 varies between distributions. systemd
 612                                 will take the link farm into account
 613                                 when figuring out whether a service
 614                                 shall be enabled. Note that a service
 615                                 unit with a native unit configuration
 616                                 file cannot be started by activating it
 617                                 in the SysV runlevel link
 618                                 farm.</para></listitem>
 619                         </varlistentry>
 620                 </variablelist>
 621         </refsect1>
 622
 623         <refsect1>
 624                 <title>Signals</title>
 625
 626                 <variablelist>
 627                         <varlistentry>
 628                                 <term><constant>SIGTERM</constant></term>
 629
 630                                 <listitem><para>Upon receiving this
 631                                 signal the systemd system manager
 632                                 serializes its state, reexecutes
 633                                 itself and deserializes the saved
 634                                 state again. This is mostly equivalent
 635                                 to <command>systemctl
 636                                 daemon-reexec</command>.</para>
 637
 638                                 <para>systemd user managers will
 639                                 start the
 640                                 <filename>exit.target</filename> unit
 641                                 when this signal is received. This is
 642                                 mostly equivalent to
 643                                 <command>systemctl --user start
 644                                 exit.target</command>.</para></listitem>
 645                         </varlistentry>
 646
 647                         <varlistentry>
 648                                 <term><constant>SIGINT</constant></term>
 649
 650                                 <listitem><para>Upon receiving this
 651                                 signal the systemd system manager will
 652                                 start the
 653                                 <filename>ctrl-alt-del.target</filename> unit. This
 654                                 is mostly equivalent to
 655                                 <command>systemctl start
 656                                 ctl-alt-del.target</command>.</para>
 657
 658                                 <para>systemd user managers
 659                                 treat this signal the same way as
 660                                 <constant>SIGTERM</constant>.</para></listitem>
 661                         </varlistentry>
 662
 663                         <varlistentry>
 664                                 <term><constant>SIGWINCH</constant></term>
 665
 666                                 <listitem><para>When this signal is
 667                                 received the systemd system manager
 668                                 will start the
 669                                 <filename>kbrequest.target</filename>
 670                                 unit. This is mostly equivalent to
 671                                 <command>systemctl start
 672                                 kbrequest.target</command>.</para>
 673
 674                                 <para>This signal is ignored by
 675                                 systemd user
 676                                 managers.</para></listitem>
 677                         </varlistentry>
 678
 679                         <varlistentry>
 680                                 <term><constant>SIGPWR</constant></term>
 681
 682                                 <listitem><para>When this signal is
 683                                 received the systemd manager
 684                                 will start the
 685                                 <filename>sigpwr.target</filename>
 686                                 unit. This is mostly equivalent to
 687                                 <command>systemctl start
 688                                 sigpwr.target</command>.</para></listitem>
 689                         </varlistentry>
 690
 691                         <varlistentry>
 692                                 <term><constant>SIGUSR1</constant></term>
 693
 694                                 <listitem><para>When this signal is
 695                                 received the systemd manager will try
 696                                 to reconnect to the D-Bus
 697                                 bus.</para></listitem>
 698                         </varlistentry>
 699
 700                         <varlistentry>
 701                                 <term><constant>SIGUSR2</constant></term>
 702
 703                                 <listitem><para>When this signal is
 704                                 received the systemd manager will log
 705                                 its complete state in human readable
 706                                 form. The data logged is the same as
 707                                 printed by <command>systemctl
 708                                 dump</command>.</para></listitem>
 709                         </varlistentry>
 710
 711                         <varlistentry>
 712                                 <term><constant>SIGHUP</constant></term>
 713
 714                                 <listitem><para>Reloads the complete
 715                                 daemon configuration. This is mostly
 716                                 equivalent to <command>systemctl
 717                                 daemon-reload</command>.</para></listitem>
 718                         </varlistentry>
 719
 720                         <varlistentry>
 721                                 <term><constant>SIGRTMIN+0</constant></term>
 722
 723                                 <listitem><para>Enters default mode, starts the
 724                                 <filename>default.target</filename>
 725                                 unit. This is mostly equivalent to
 726                                 <command>systemctl start
 727                                 default.target</command>.</para></listitem>
 728                         </varlistentry>
 729
 730                         <varlistentry>
 731                                 <term><constant>SIGRTMIN+1</constant></term>
 732
 733                                 <listitem><para>Enters rescue mode,
 734                                 starts the
 735                                 <filename>rescue.target</filename>
 736                                 unit. This is mostly equivalent to
 737                                 <command>systemctl isolate
 738                                 rescue.target</command>.</para></listitem>
 739                         </varlistentry>
 740
 741                         <varlistentry>
 742                                 <term><constant>SIGRTMIN+2</constant></term>
 743
 744                                 <listitem><para>Enters emergency mode,
 745                                 starts the
 746                                 <filename>emergency.service</filename>
 747                                 unit. This is mostly equivalent to
 748                                 <command>systemctl isolate
 749                                 emergency.service</command>.</para></listitem>
 750                         </varlistentry>
 751
 752                         <varlistentry>
 753                                 <term><constant>SIGRTMIN+3</constant></term>
 754
 755                                 <listitem><para>Halts the machine,
 756                                 starts the
 757                                 <filename>halt.target</filename>
 758                                 unit. This is mostly equivalent to
 759                                 <command>systemctl start
 760                                 halt.target</command>.</para></listitem>
 761                         </varlistentry>
 762
 763                         <varlistentry>
 764                                 <term><constant>SIGRTMIN+4</constant></term>
 765
 766                                 <listitem><para>Powers off the machine,
 767                                 starts the
 768                                 <filename>poweroff.target</filename>
 769                                 unit. This is mostly equivalent to
 770                                 <command>systemctl start
 771                                 poweroff.target</command>.</para></listitem>
 772                         </varlistentry>
 773
 774                         <varlistentry>
 775                                 <term><constant>SIGRTMIN+5</constant></term>
 776
 777                                 <listitem><para>Reboots the machine,
 778                                 starts the
 779                                 <filename>reboot.target</filename>
 780                                 unit. This is mostly equivalent to
 781                                 <command>systemctl start
 782                                 reboot.target</command>.</para></listitem>
 783                         </varlistentry>
 784
 785                         <varlistentry>
 786                                 <term><constant>SIGRTMIN+6</constant></term>
 787
 788                                 <listitem><para>Reboots the machine via kexec,
 789                                 starts the
 790                                 <filename>kexec.target</filename>
 791                                 unit. This is mostly equivalent to
 792                                 <command>systemctl start
 793                                 kexec.target</command>.</para></listitem>
 794                         </varlistentry>
 795
 796                         <varlistentry>
 797                                 <term><constant>SIGRTMIN+13</constant></term>
 798
 799                                 <listitem><para>Immediately halts the machine.</para></listitem>
 800                         </varlistentry>
 801
 802                         <varlistentry>
 803                                 <term><constant>SIGRTMIN+14</constant></term>
 804
 805                                 <listitem><para>Immediately powers off the machine.</para></listitem>
 806                         </varlistentry>
 807
 808                         <varlistentry>
 809                                 <term><constant>SIGRTMIN+15</constant></term>
 810
 811                                 <listitem><para>Immediately reboots the machine.</para></listitem>
 812                         </varlistentry>
 813
 814                         <varlistentry>
 815                                 <term><constant>SIGRTMIN+16</constant></term>
 816
 817                                 <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
 818                         </varlistentry>
 819
 820                         <varlistentry>
 821                                 <term><constant>SIGRTMIN+20</constant></term>
 822
 823                                 <listitem><para>Enables display of
 824                                 status messages on the console, as
 825                                 controlled via
 826                                 <varname>systemd.show_status=1</varname>
 827                                 on the kernel command
 828                                 line.</para></listitem>
 829                         </varlistentry>
 830
 831                         <varlistentry>
 832                                 <term><constant>SIGRTMIN+21</constant></term>
 833
 834                                 <listitem><para>Disables display of
 835                                 status messages on the console, as
 836                                 controlled via
 837                                 <varname>systemd.show_status=0</varname>
 838                                 on the kernel command
 839                                 line.</para></listitem>
 840                         </varlistentry>
 841
 842                         <varlistentry>
 843                                 <term><constant>SIGRTMIN+22</constant></term>
 844                                 <term><constant>SIGRTMIN+23</constant></term>
 845
 846                                 <listitem><para>Sets the log level to
 847                                 <literal>debug</literal>
 848                                 (or <literal>info</literal> on
 849                                 <constant>SIGRTMIN+23</constant>), as
 850                                 controlled via
 851                                 <varname>systemd.log_level=debug</varname>
 852                                 (or <varname>systemd.log_level=info</varname>
 853                                 on <constant>SIGRTMIN+23</constant>) on
 854                                 the kernel command
 855                                 line.</para></listitem>
 856                         </varlistentry>
 857
 858                         <varlistentry>
 859                                 <term><constant>SIGRTMIN+24</constant></term>
 860
 861                                 <listitem><para>Immediately exits the
 862                                 manager (only available for --user
 863                                 instances).</para></listitem>
 864                         </varlistentry>
 865
 866                         <varlistentry>
 867                                 <term><constant>SIGRTMIN+26</constant></term>
 868                                 <term><constant>SIGRTMIN+27</constant></term>
 869                                 <term><constant>SIGRTMIN+28</constant></term>
 870                                 <term><constant>SIGRTMIN+29</constant></term>
 871
 872                                 <listitem><para>Sets the log level to
 873                                 <literal>journal-or-kmsg</literal>
 874                                 (or <literal>console</literal> on
 875                                 <constant>SIGRTMIN+27</constant>,
 876                                 <literal>kmsg</literal> on
 877                                 <constant>SIGRTMIN+28</constant>,
 878                                 or <literal>syslog-or-kmsg</literal>
 879                                 on <constant>SIGRTMIN+29</constant>), as
 880                                 controlled via
 881                                 <varname>systemd.log_target=journal-or-kmsg</varname>
 882                                 (or <varname>systemd.log_target=console</varname>
 883                                 on <constant>SIGRTMIN+27</constant>,
 884                                 <varname>systemd.log_target=kmsg</varname>
 885                                 on <constant>SIGRTMIN+28</constant>,
 886                                 or
 887                                 <varname>systemd.log_target=syslog-or-kmsg</varname>
 888                                 on <constant>SIGRTMIN+29</constant>) on
 889                                 the kernel command
 890                                 line.</para></listitem>
 891                         </varlistentry>
 892                 </variablelist>
 893         </refsect1>
 894
 895         <refsect1>
 896                 <title>Environment</title>
 897
 898                 <variablelist class='environment-variables'>
 899                         <varlistentry>
 900                                 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 901                                 <listitem><para>systemd reads the
 902                                 log level from this environment
 903                                 variable. This can be overridden with
 904                                 <option>--log-level=</option>.</para></listitem>
 905                         </varlistentry>
 906
 907                         <varlistentry>
 908                                 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 909                                 <listitem><para>systemd reads the
 910                                 log target from this environment
 911                                 variable. This can be overridden with
 912                                 <option>--log-target=</option>.</para></listitem>
 913                         </varlistentry>
 914
 915                         <varlistentry>
 916                                 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 917                                 <listitem><para>Controls whether
 918                                 systemd highlights important log
 919                                 messages. This can be overridden with
 920                                 <option>--log-color=</option>.</para></listitem>
 921                         </varlistentry>
 922
 923                         <varlistentry>
 924                                 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 925                                 <listitem><para>Controls whether
 926                                 systemd prints the code location along
 927                                 with log messages. This can be
 928                                 overridden with
 929                                 <option>--log-location=</option>.</para></listitem>
 930                         </varlistentry>
 931
 932                         <varlistentry>
 933                                 <term><varname>$XDG_CONFIG_HOME</varname></term>
 934                                 <term><varname>$XDG_CONFIG_DIRS</varname></term>
 935                                 <term><varname>$XDG_DATA_HOME</varname></term>
 936                                 <term><varname>$XDG_DATA_DIRS</varname></term>
 937
 938                                 <listitem><para>The systemd user
 939                                 manager uses these variables in
 940                                 accordance to the <ulink
 941                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 942                                 Base Directory specification</ulink>
 943                                 to find its configuration.</para></listitem>
 944                         </varlistentry>
 945
 946                         <varlistentry>
 947                                 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 948
 949                                 <listitem><para>Controls where systemd
 950                                 looks for unit
 951                                 files.</para></listitem>
 952                         </varlistentry>
 953
 954                         <varlistentry>
 955                                 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 956
 957                                 <listitem><para>Controls where systemd
 958                                 looks for SysV init scripts.</para></listitem>
 959                         </varlistentry>
 960
 961                         <varlistentry>
 962                                 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 963
 964                                 <listitem><para>Controls where systemd
 965                                 looks for SysV init script runlevel link
 966                                 farms.</para></listitem>
 967                         </varlistentry>
 968
 969                         <varlistentry>
 970                                 <term><varname>$LISTEN_PID</varname></term>
 971                                 <term><varname>$LISTEN_FDS</varname></term>
 972
 973                                 <listitem><para>Set by systemd for
 974                                 supervised processes during
 975                                 socket-based activation. See
 976                                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 977                                 for more information.
 978                                 </para></listitem>
 979                         </varlistentry>
 980
 981                         <varlistentry>
 982                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 983
 984                                 <listitem><para>Set by systemd for
 985                                 supervised processes for status and
 986                                 start-up completion notification. See
 987                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 988                                 for more information.
 989                                 </para></listitem>
 990                         </varlistentry>
 991                 </variablelist>
 992         </refsect1>
 993
 994         <refsect1>
 995                 <title>Kernel Command Line</title>
 996
 997                 <para>When run as system instance systemd parses a
 998                 number of kernel command line
 999                 arguments<footnote><para>If run inside a Linux
1000                 container these arguments may be passed as command
1001                 line arguments to systemd itself, next to any of the
1002                 command line options listed in the Options section
1003                 above. If run outside of Linux containers, these
1004                 arguments are parsed from
1005                 <filename>/proc/cmdline</filename>
1006                 instead.</para></footnote>:</para>
1007
1008                 <variablelist class='kernel-commandline-options'>
1009                         <varlistentry>
1010                                 <term><varname>systemd.unit=</varname></term>
1011                                 <term><varname>rd.systemd.unit=</varname></term>
1012
1013                                 <listitem><para>Overrides the unit to
1014                                 activate on boot. Defaults to
1015                                 <filename>default.target</filename>. This
1016                                 may be used to temporarily boot into a
1017                                 different boot unit, for example
1018                                 <filename>rescue.target</filename> or
1019                                 <filename>emergency.service</filename>. See
1020                                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1021                                 for details about these units. The
1022                                 option prefixed with
1023                                 <literal>rd.</literal> is honored
1024                                 only in the initial RAM disk (initrd),
1025                                 while the one that is not prefixed only
1026                                 in the main system.</para></listitem>
1027                         </varlistentry>
1028
1029                         <varlistentry>
1030                                 <term><varname>systemd.dump_core=</varname></term>
1031
1032                                 <listitem><para>Takes a boolean
1033                                 argument. If <option>true</option>,
1034                                 systemd dumps core when it
1035                                 crashes. Otherwise, no core dump is
1036                                 created. Defaults to
1037                                 <option>true</option>.</para></listitem>
1038                         </varlistentry>
1039
1040                         <varlistentry>
1041                                 <term><varname>systemd.crash_shell=</varname></term>
1042
1043                                 <listitem><para>Takes a boolean
1044                                 argument. If <option>true</option>,
1045                                 systemd spawns a shell when it
1046                                 crashes. Otherwise, no shell is
1047                                 spawned. Defaults to
1048                                 <option>false</option>, for security
1049                                 reasons, as the shell is not protected
1050                                 by any password
1051                                 authentication.</para></listitem>
1052                         </varlistentry>
1053
1054                         <varlistentry>
1055                                 <term><varname>systemd.crash_chvt=</varname></term>
1056
1057                                 <listitem><para>Takes an integer
1058                                 argument. If positive systemd
1059                                 activates the specified virtual
1060                                 terminal when it crashes. Defaults to
1061                                 <constant>-1</constant>.</para></listitem>
1062                         </varlistentry>
1063
1064                         <varlistentry>
1065                                 <term><varname>systemd.confirm_spawn=</varname></term>
1066
1067                                 <listitem><para>Takes a boolean
1068                                 argument. If <option>true</option>,
1069                                 asks for confirmation when spawning
1070                                 processes. Defaults to
1071                                 <option>false</option>.</para></listitem>
1072                         </varlistentry>
1073
1074                         <varlistentry>
1075                                 <term><varname>systemd.show_status=</varname></term>
1076
1077                                 <listitem><para>Takes a boolean
1078                                 argument. If <option>true</option>,
1079                                 shows terse service status updates on
1080                                 the console during bootup. Defaults to
1081                                 <option>true</option>, unless
1082                                 <option>quiet</option> is passed as
1083                                 kernel command line option in which
1084                                 case it defaults to
1085                                 <option>false</option>.</para></listitem>
1086                         </varlistentry>
1087
1088                         <varlistentry>
1089                                 <term><varname>systemd.log_target=</varname></term>
1090                                 <term><varname>systemd.log_level=</varname></term>
1091                                 <term><varname>systemd.log_color=</varname></term>
1092                                 <term><varname>systemd.log_location=</varname></term>
1093
1094                                 <listitem><para>Controls log output,
1095                                 with the same effect as the
1096                                 <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
1097                                 environment variables described above.</para></listitem>
1098                         </varlistentry>
1099
1100                         <varlistentry>
1101                                 <term><varname>systemd.default_standard_output=</varname></term>
1102                                 <term><varname>systemd.default_standard_error=</varname></term>
1103                                 <listitem><para>Controls default
1104                                 standard output and error output for
1105                                 services, with the same effect as the
1106                                 <option>--default-standard-output=</option>
1107                                 and <option>--default-standard-error=</option>
1108                                 command line arguments described
1109                                 above, respectively.</para></listitem>
1110                         </varlistentry>
1111
1112                         <varlistentry>
1113                                 <term><varname>systemd.setenv=</varname></term>
1114
1115                                 <listitem><para>Takes a string
1116                                 argument in the form VARIABLE=VALUE.
1117                                 May be used to set default environment
1118                                 variables to add to forked child processes.
1119                                 May be used more than once to set multiple
1120                                 variables.</para></listitem>
1121                         </varlistentry>
1122
1123                         <varlistentry>
1124                                 <term><varname>quiet</varname></term>
1125
1126                                 <listitem><para>Turn off
1127                                 status output at boot, much like
1128                                 <varname>systemd.show_status=false</varname>
1129                                 would. Note that this option is also
1130                                 read by the kernel itself and disables
1131                                 kernel log output. Passing this option
1132                                 hence turns off the usual output from
1133                                 both the system manager and the kernel.
1134                                 </para></listitem>
1135                         </varlistentry>
1136
1137                         <varlistentry>
1138                                 <term><varname>debug</varname></term>
1139
1140                                 <listitem><para>Turn on debugging
1141                                 output. This is equivalent to
1142                                 <varname>systemd.log_level=debug</varname>.
1143                                 Note that this option is also read by
1144                                 the kernel itself and enables kernel
1145                                 debug output.  Passing this option
1146                                 hence turns on the debug output from
1147                                 both the system manager and the
1148                                 kernel.</para></listitem>
1149                         </varlistentry>
1150
1151                         <varlistentry>
1152                                 <term><varname>emergency</varname></term>
1153
1154                                 <listitem><para>Boot into emergency
1155                                 mode. This is equivalent to
1156                                 <varname>systemd.unit=emergency.target</varname>
1157                                 and provided for compatibility
1158                                 reasons and to be easier to type.</para></listitem>
1159                         </varlistentry>
1160
1161                         <varlistentry>
1162                                 <term><varname>single</varname></term>
1163                                 <term><varname>s</varname></term>
1164                                 <term><varname>S</varname></term>
1165                                 <term><varname>1</varname></term>
1166
1167                                 <listitem><para>Boot into rescue
1168                                 mode. This is equivalent to
1169                                 <varname>systemd.unit=rescue.target</varname>
1170                                 and provided for compatibility reasons
1171                                 and to be easier to
1172                                 type.</para></listitem>
1173                         </varlistentry>
1174
1175                         <varlistentry>
1176                                 <term><varname>2</varname></term>
1177                                 <term><varname>3</varname></term>
1178                                 <term><varname>4</varname></term>
1179                                 <term><varname>5</varname></term>
1180
1181                                 <listitem><para>Boot into the
1182                                 specified legacy SysV runlevel. These
1183                                 are equivalent to
1184                                 <varname>systemd.unit=runlevel2.target</varname>,
1185                                 <varname>systemd.unit=runlevel3.target</varname>,
1186                                 <varname>systemd.unit=runlevel4.target</varname>,
1187                                 and <varname>systemd.unit=runlevel5.target</varname>, respectively,
1188                                 and provided for compatibility reasons
1189                                 and to be easier to
1190                                 type.</para></listitem>
1191                         </varlistentry>
1192
1193                         <varlistentry>
1194                                 <term><varname>locale.LANG=</varname></term>
1195                                 <term><varname>locale.LANGUAGE=</varname></term>
1196                                 <term><varname>locale.LC_CTYPE=</varname></term>
1197                                 <term><varname>locale.LC_NUMERIC=</varname></term>
1198                                 <term><varname>locale.LC_TIME=</varname></term>
1199                                 <term><varname>locale.LC_COLLATE=</varname></term>
1200                                 <term><varname>locale.LC_MONETARY=</varname></term>
1201                                 <term><varname>locale.LC_MESSAGES=</varname></term>
1202                                 <term><varname>locale.LC_PAPER=</varname></term>
1203                                 <term><varname>locale.LC_NAME=</varname></term>
1204                                 <term><varname>locale.LC_ADDRESS=</varname></term>
1205                                 <term><varname>locale.LC_TELEPHONE=</varname></term>
1206                                 <term><varname>locale.LC_MEASUREMENT=</varname></term>
1207                                 <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1208
1209                                 <listitem><para>Set the system locale
1210                                 to use. This overrides the settings in
1211                                 <filename>/etc/locale.conf</filename>. For
1212                                 more information see
1213                                 <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1214                                 and
1215                                 <citerefentry><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1216                                 </para></listitem>
1217                         </varlistentry>
1218                 </variablelist>
1219
1220                 <para>For other kernel command line parameters
1221                 understood by components of the core OS, please refer
1222                 to
1223                 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1224         </refsect1>
1225
1226         <refsect1>
1227                 <title>Sockets and FIFOs</title>
1228
1229                 <variablelist>
1230                         <varlistentry>
1231                                 <term><filename>/run/systemd/notify</filename></term>
1232
1233                                 <listitem><para>Daemon status
1234                                 notification socket. This is an
1235                                 <constant>AF_UNIX</constant> datagram socket and is used to
1236                                 implement the daemon notification
1237                                 logic as implemented by
1238                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1239
1240                         </varlistentry>
1241
1242                         <varlistentry>
1243                                 <term><filename>/run/systemd/shutdownd</filename></term>
1244
1245                                 <listitem><para>Used internally by the
1246                                 <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1247                                 tool to implement delayed
1248                                 shutdowns. This is an <constant>AF_UNIX</constant> datagram
1249                                 socket.</para></listitem>
1250                         </varlistentry>
1251
1252                         <varlistentry>
1253                                 <term><filename>/run/systemd/private</filename></term>
1254
1255                                 <listitem><para>Used internally as
1256                                 communication channel between
1257                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1258                                 and the systemd process. This is an
1259                                 <constant>AF_UNIX</constant> stream socket. This interface
1260                                 is private to systemd and should not
1261                                 be used in external
1262                                 projects.</para></listitem>
1263                         </varlistentry>
1264
1265                         <varlistentry>
1266                                 <term><filename>/dev/initctl</filename></term>
1267
1268                                 <listitem><para>Limited compatibility
1269                                 support for the SysV client interface,
1270                                 as implemented by the
1271                                 <filename>systemd-initctl.service</filename>
1272                                 unit. This is a named pipe in the file
1273                                 system. This interface is obsolete and
1274                                 should not be used in new
1275                                 applications.</para></listitem>
1276                         </varlistentry>
1277                 </variablelist>
1278         </refsect1>
1279
1280         <refsect1>
1281                 <title>See Also</title>
1282                 <para>
1283                         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1284                         <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1285                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1286                         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1287                         <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1288                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1289                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1290                         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1291                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1292                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1293                         <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1294                         <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1295                         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1296                 </para>
1297         </refsect1>
1298
1299 </refentry>