man/systemd.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   This file is part of systemd.
   7
   8   Copyright 2010 Lennart Poettering
   9
  10   systemd is free software; you can redistribute it and/or modify it
  11   under the terms of the GNU Lesser General Public License as published by
  12   the Free Software Foundation; either version 2.1 of the License, or
  13   (at your option) any later version.
  14
  15   systemd is distributed in the hope that it will be useful, but
  16   WITHOUT ANY WARRANTY; without even the implied warranty of
  17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  18   Lesser General Public License for more details.
  19
  20   You should have received a copy of the GNU Lesser General Public License
  21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  22 -->
  23
  24 <refentry id="systemd">
  25
  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". Units encapsulate
 289                 various objects that are relevant for system boot-up
 290                 and maintenance. The majority of units are configured
 291                 in unit configuration files, whose syntax and basic
 292                 set of options is described in
 293                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 294                 however some are created automatically from other
 295                 configuration or dynamically from system state. Units
 296                 may be 'active' (meaning started, bound, plugged in,
 297                 ...  depending on the unit type, see below), or
 298                 'inactive' (meaning stopped, unbound, unplugged, ...),
 299                 as well as in the process of being activated or
 300                 deactivated, i.e. between the two states (these states
 301                 are called 'activating', 'deactivating'). A special
 302                 'failed' state is available as well which is very
 303                 similar to 'inactive' and is entered when the service
 304                 failed in some way (process returned error code on
 305                 exit, or crashed, or an operation timed out). If this
 306                 state is entered the cause will be logged, for later
 307                 reference. Note that the various unit types may have a
 308                 number of additional substates, which are mapped to
 309                 the five generalized unit states described
 310                 here.</para>
 311
 312                 <para>The following unit types are available:</para>
 313
 314                 <orderedlist>
 315                         <listitem><para>Service units, which control
 316                         daemons and the processes they consist of. For
 317                         details see
 318                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 319
 320                         <listitem><para>Socket units, which
 321                         encapsulate local IPC or network sockets in
 322                         the system, useful for socket-based
 323                         activation. For details about socket units see
 324                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 325                         for details on socket-based activation and
 326                         other forms of activation, see
 327                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 328
 329                         <listitem><para>Target units are useful to
 330                         group units, or provide well-known
 331                         synchronization points during boot-up, see
 332                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 333
 334                         <listitem><para>Device units expose kernel
 335                         devices in systemd and may be used to
 336                         implement device-based activation. For details
 337                         see
 338                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 339
 340                         <listitem><para>Mount units control mount
 341                         points in the file system, for details see
 342                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 343
 344                         <listitem><para>Automount units provide
 345                         automount capabilities, for on-demand mounting
 346                         of file systems as well as parallelized
 347                         boot-up. See
 348                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 349
 350                         <listitem><para>Snapshot units can be used to
 351                         temporarily save the state of the set of
 352                         systemd units, which later may be restored by
 353                         activating the saved snapshot unit. For more
 354                         information see
 355                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 356
 357                         <listitem><para>Timer units are useful for
 358                         triggering activation of other units based on
 359                         timers. You may find details in
 360                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 361
 362                         <listitem><para>Swap units are very similar to
 363                         mount units and encapsulate memory swap
 364                         partitions or files of the operating
 365                         system. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 366
 367                         <listitem><para>Path units may be used
 368                         to activate other services when file system
 369                         objects change or are modified. See
 370                         <citerefentry><refentrytitle>systemd.path</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="http://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 host name 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 class='unit-directives'>
 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>SIGTERM</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>SIGINT</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                                 SIGTERM.</para></listitem>
 647                         </varlistentry>
 648
 649                         <varlistentry>
 650                                 <term>SIGWINCH</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>SIGPWR</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>SIGUSR1</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>SIGUSR2</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>SIGHUP</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>SIGRTMIN+0</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>SIGRTMIN+1</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>SIGRTMIN+2</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>SIGRTMIN+3</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>SIGRTMIN+4</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>SIGRTMIN+5</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>SIGRTMIN+6</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>SIGRTMIN+13</term>
 784
 785                                 <listitem><para>Immediately halts the machine.</para></listitem>
 786                         </varlistentry>
 787
 788                         <varlistentry>
 789                                 <term>SIGRTMIN+14</term>
 790
 791                                 <listitem><para>Immediately powers off the machine.</para></listitem>
 792                         </varlistentry>
 793
 794                         <varlistentry>
 795                                 <term>SIGRTMIN+15</term>
 796
 797                                 <listitem><para>Immediately reboots the machine.</para></listitem>
 798                         </varlistentry>
 799
 800                         <varlistentry>
 801                                 <term>SIGRTMIN+16</term>
 802
 803                                 <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
 804                         </varlistentry>
 805
 806                         <varlistentry>
 807                                 <term>SIGRTMIN+20</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>SIGRTMIN+21</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>SIGRTMIN+22</term>
 830                                 <term>SIGRTMIN+23</term>
 831
 832                                 <listitem><para>Sets the log level to
 833                                 <literal>debug</literal>
 834                                 (or <literal>info</literal> on
 835                                 <literal>SIGRTMIN+23</literal>), as
 836                                 controlled via
 837                                 <varname>systemd.log_level=debug</varname>
 838                                 (or <varname>systemd.log_level=info</varname>
 839                                 on <literal>SIGRTMIN+23</literal>) on
 840                                 the kernel command
 841                                 line.</para></listitem>
 842                         </varlistentry>
 843
 844                         <varlistentry>
 845                                 <term>SIGRTMIN+24</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>SIGRTMIN+26</term>
 854                                 <term>SIGRTMIN+27</term>
 855                                 <term>SIGRTMIN+28</term>
 856                                 <term>SIGRTMIN+29</term>
 857
 858                                 <listitem><para>Sets the log level to
 859                                 <literal>journal-or-kmsg</literal>
 860                                 (or <literal>console</literal> on
 861                                 <literal>SIGRTMIN+27</literal>,
 862                                 <literal>kmsg</literal> on
 863                                 <literal>SIGRTMIN+28</literal>,
 864                                 or <literal>syslog-or-kmsg</literal>
 865                                 on <literal>SIGRTMIN+29</literal>), as
 866                                 controlled via
 867                                 <varname>systemd.log_target=journal-or-kmsg</varname>
 868                                 (or <varname>systemd.log_target=console</varname>
 869                                 on <literal>SIGRTMIN+27</literal>,
 870                                 <varname>systemd.log_target=kmsg</varname>
 871                                 on <literal>SIGRTMIN+28</literal>,
 872                                 or
 873                                 <varname>systemd.log_target=syslog-or-kmsg</varname>
 874                                 on <literal>SIGRTMIN+29</literal>) 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 isn't 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                                 <literal>-1</literal>.</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. If <option>true</option>
1065                                 shows terse service status updates on
1066                                 the console during bootup. Defaults to
1067                                 <option>true</option>, unless
1068                                 <option>quiet</option> is passed as
1069                                 kernel command line option in which
1070                                 case it defaults to
1071                                 <option>false</option>.</para></listitem>
1072                         </varlistentry>
1073
1074                         <varlistentry>
1075                                 <term><varname>systemd.log_target=</varname></term>
1076                                 <term><varname>systemd.log_level=</varname></term>
1077                                 <term><varname>systemd.log_color=</varname></term>
1078                                 <term><varname>systemd.log_location=</varname></term>
1079
1080                                 <listitem><para>Controls log output,
1081                                 with the same effect as the
1082                                 <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
1083                                 environment variables described above.</para></listitem>
1084                         </varlistentry>
1085
1086                         <varlistentry>
1087                                 <term><varname>systemd.default_standard_output=</varname></term>
1088                                 <term><varname>systemd.default_standard_error=</varname></term>
1089                                 <listitem><para>Controls default
1090                                 standard output and error output for
1091                                 services, with the same effect as the
1092                                 <option>--default-standard-output=</option>
1093                                 and <option>--default-standard-error=</option>
1094                                 command line arguments described
1095                                 above, respectively.</para></listitem>
1096                         </varlistentry>
1097
1098                         <varlistentry>
1099                                 <term><varname>systemd.setenv=</varname></term>
1100
1101                                 <listitem><para>Takes a string
1102                                 argument in the form
1103                                 VARIABLE=VALUE. May be used to set
1104                                 environment variables for the init
1105                                 process and all its children at boot
1106                                 time. May be used more than once to
1107                                 set multiple variables. If the equal
1108                                 sign and variable are missing it unsets
1109                                 an environment variable which might be
1110                                 passed in from the initial ram
1111                                 disk.</para></listitem>
1112                         </varlistentry>
1113
1114                         <varlistentry>
1115                                 <term><varname>quiet</varname></term>
1116
1117                                 <listitem><para>If passed turns off
1118                                 status output at boot, much like
1119                                 <varname>systemd.show_status=false</varname>
1120                                 would. Note that this option is also
1121                                 read by the kernel itself and disables
1122                                 kernel log output to the
1123                                 kernel. Passing this option hence
1124                                 turns off the usual output from both
1125                                 the system manager and the
1126                                 kernel.</para></listitem>
1127                         </varlistentry>
1128
1129                         <varlistentry>
1130                                 <term><varname>emergency</varname></term>
1131
1132                                 <listitem><para>Boot into emergency
1133                                 mode. This is equivalent to
1134                                 <varname>systemd.unit=emergency.target</varname>
1135                                 and provided for compatibility
1136                                 reasons and to be easier to type.</para></listitem>
1137                         </varlistentry>
1138
1139                         <varlistentry>
1140                                 <term><varname>single</varname></term>
1141                                 <term><varname>s</varname></term>
1142                                 <term><varname>S</varname></term>
1143                                 <term><varname>1</varname></term>
1144
1145                                 <listitem><para>Boot into rescue
1146                                 mode. This is equivalent to
1147                                 <varname>systemd.unit=rescue.target</varname>
1148                                 and provided for compatibility reasons
1149                                 and to be easier to
1150                                 type.</para></listitem>
1151                         </varlistentry>
1152
1153                         <varlistentry>
1154                                 <term><varname>2</varname></term>
1155                                 <term><varname>3</varname></term>
1156                                 <term><varname>4</varname></term>
1157                                 <term><varname>5</varname></term>
1158
1159                                 <listitem><para>Boot into the
1160                                 specified legacy SysV runlevel. These
1161                                 are equivalent to
1162                                 <varname>systemd.unit=runlevel2.target</varname>,
1163                                 <varname>systemd.unit=runlevel3.target</varname>,
1164                                 <varname>systemd.unit=runlevel4.target</varname>,
1165                                 and <varname>systemd.unit=runlevel5.target</varname>, respectively,
1166                                 and provided for compatibility reasons
1167                                 and to be easier to
1168                                 type.</para></listitem>
1169                         </varlistentry>
1170
1171                         <varlistentry>
1172                                 <term><varname>locale.LANG=</varname></term>
1173                                 <term><varname>locale.LANGUAGE=</varname></term>
1174                                 <term><varname>locale.LC_CTYPE=</varname></term>
1175                                 <term><varname>locale.LC_NUMERIC=</varname></term>
1176                                 <term><varname>locale.LC_TIME=</varname></term>
1177                                 <term><varname>locale.LC_COLLATE=</varname></term>
1178                                 <term><varname>locale.LC_MONETARY=</varname></term>
1179                                 <term><varname>locale.LC_MESSAGES=</varname></term>
1180                                 <term><varname>locale.LC_PAPER=</varname></term>
1181                                 <term><varname>locale.LC_NAME=</varname></term>
1182                                 <term><varname>locale.LC_ADDRESS=</varname></term>
1183                                 <term><varname>locale.LC_TELEPHONE=</varname></term>
1184                                 <term><varname>locale.LC_MEASUREMENT=</varname></term>
1185                                 <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1186
1187                                 <listitem><para>Set the system locale
1188                                 to use. This overrides the settings in
1189                                 <filename>/etc/locale.conf</filename>. For
1190                                 more information see
1191                                 <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1192                                 and
1193                                 <citerefentry><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1194                                 </para></listitem>
1195                         </varlistentry>
1196                 </variablelist>
1197
1198                 <para>For other kernel command line parameters
1199                 understood by components of the core OS, please refer
1200                 to
1201                 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1202         </refsect1>
1203
1204         <refsect1>
1205                 <title>Sockets and FIFOs</title>
1206
1207                 <variablelist>
1208                         <varlistentry>
1209                                 <term><filename>/run/systemd/notify</filename></term>
1210
1211                                 <listitem><para>Daemon status
1212                                 notification socket. This is an
1213                                 AF_UNIX datagram socket and is used to
1214                                 implement the daemon notification
1215                                 logic as implemented by
1216                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1217
1218                         </varlistentry>
1219
1220                         <varlistentry>
1221                                 <term><filename>/run/systemd/shutdownd</filename></term>
1222
1223                                 <listitem><para>Used internally by the
1224                                 <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1225                                 tool to implement delayed
1226                                 shutdowns. This is an AF_UNIX datagram
1227                                 socket.</para></listitem>
1228                         </varlistentry>
1229
1230                         <varlistentry>
1231                                 <term><filename>/run/systemd/private</filename></term>
1232
1233                                 <listitem><para>Used internally as
1234                                 communication channel between
1235                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1236                                 and the systemd process. This is an
1237                                 AF_UNIX stream socket. This interface
1238                                 is private to systemd and should not
1239                                 be used in external
1240                                 projects.</para></listitem>
1241                         </varlistentry>
1242
1243                         <varlistentry>
1244                                 <term><filename>/dev/initctl</filename></term>
1245
1246                                 <listitem><para>Limited compatibility
1247                                 support for the SysV client interface,
1248                                 as implemented by the
1249                                 <filename>systemd-initctl.service</filename>
1250                                 unit. This is a named pipe in the file
1251                                 system. This interface is obsolete and
1252                                 should not be used in new
1253                                 applications.</para></listitem>
1254                         </varlistentry>
1255                 </variablelist>
1256         </refsect1>
1257
1258         <refsect1>
1259                 <title>See Also</title>
1260                 <para>
1261                         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1262                         <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1263                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1264                         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1265                         <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1266                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1267                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1268                         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1269                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1270                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1271                         <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1272                         <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1273                         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1274                 </para>
1275         </refsect1>
1276
1277 </refentry>