man/systemd.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   This file is part of systemd.
   7
   8   Copyright 2010 Lennart Poettering
   9
  10   systemd is free software; you can redistribute it and/or modify it
  11   under the terms of the GNU Lesser General Public License as published by
  12   the Free Software Foundation; either version 2.1 of the License, or
  13   (at your option) any later version.
  14
  15   systemd is distributed in the hope that it will be useful, but
  16   WITHOUT ANY WARRANTY; without even the implied warranty of
  17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  18   Lesser General Public License for more details.
  19
  20   You should have received a copy of the GNU Lesser General Public License
  21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  22 -->
  23
  24 <refentry id="systemd"
  25           xmlns:xi="http://www.w3.org/2001/XInclude">
  26
  27         <refentryinfo>
  28                 <title>systemd</title>
  29                 <productname>systemd</productname>
  30
  31                 <authorgroup>
  32                         <author>
  33                                 <contrib>Developer</contrib>
  34                                 <firstname>Lennart</firstname>
  35                                 <surname>Poettering</surname>
  36                                 <email>lennart@poettering.net</email>
  37                         </author>
  38                 </authorgroup>
  39         </refentryinfo>
  40
  41         <refmeta>
  42                 <refentrytitle>systemd</refentrytitle>
  43                 <manvolnum>1</manvolnum>
  44         </refmeta>
  45
  46         <refnamediv>
  47                 <refname>systemd</refname>
  48                 <refname>init</refname>
  49                 <refpurpose>systemd system and service manager</refpurpose>
  50         </refnamediv>
  51
  52         <refsynopsisdiv>
  53                 <cmdsynopsis>
  54                         <command>systemd <arg choice="opt" rep="repeat">OPTIONS</arg></command>
  55                 </cmdsynopsis>
  56                 <cmdsynopsis>
  57                         <command>init <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="req">COMMAND</arg></command>
  58                 </cmdsynopsis>
  59         </refsynopsisdiv>
  60
  61         <refsect1>
  62                 <title>Description</title>
  63
  64                 <para>systemd is a system and service manager for
  65                 Linux operating systems. When run as first process on
  66                 boot (as PID 1), it acts as init system that brings
  67                 up and maintains userspace services.</para>
  68
  69                 <para>For compatibility with SysV, if systemd is called
  70                 as <command>init</command> and a PID that is not
  71                 1, it will execute <command>telinit</command> and pass
  72                 all command line arguments unmodified. That means
  73                 <command>init</command> and <command>telinit</command>
  74                 are mostly equivalent when invoked from normal login sessions. See
  75                 <citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  76                 for more information.</para>
  77
  78                 <para>When run as system instance, systemd interprets
  79                 the configuration file
  80                 <filename>system.conf</filename>, otherwise
  81                 <filename>user.conf</filename>. See
  82                 <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  83                 for more information.</para>
  84         </refsect1>
  85
  86         <refsect1>
  87                 <title>Options</title>
  88
  89                 <para>The following options are understood:</para>
  90
  91                 <variablelist>
  92                         <varlistentry>
  93                                 <term><option>--test</option></term>
  94
  95                                 <listitem><para>Determine startup
  96                                 sequence, dump it and exit. This is an
  97                                 option useful for debugging
  98                                 only.</para></listitem>
  99                         </varlistentry>
 100                         <varlistentry>
 101                                 <term><option>--dump-configuration-items</option></term>
 102
 103                                 <listitem><para>Dump understood unit
 104                                 configuration items. This outputs a
 105                                 terse but complete list of
 106                                 configuration items understood in unit
 107                                 definition files.</para></listitem>
 108                         </varlistentry>
 109                         <varlistentry>
 110                                 <term><option>--unit=</option></term>
 111
 112                                 <listitem><para>Set default unit to
 113                                 activate on startup. If not specified,
 114                                 defaults to
 115                                 <filename>default.target</filename>.</para></listitem>
 116                         </varlistentry>
 117                         <varlistentry>
 118                                 <term><option>--system</option></term>
 119                                 <term><option>--user</option></term>
 120
 121                                 <listitem><para>For <option>--system</option>,
 122                                 tell systemd to run a
 123                                 system instance, even if the process ID is
 124                                 not 1, i.e. systemd is not run as init process.
 125                                 <option>--user</option> does the opposite,
 126                                 running a user instance even if the process
 127                                 ID is 1.
 128                                 Normally it should not be necessary to
 129                                 pass these options, as systemd
 130                                 automatically detects the mode it is
 131                                 started in. These options are hence of
 132                                 little use except for debugging. Note
 133                                 that it is not supported booting and
 134                                 maintaining a full system with systemd
 135                                 running in <option>--system</option>
 136                                 mode, but PID not 1. In practice,
 137                                 passing <option>--system</option> explicitly is
 138                                 only useful in conjunction with
 139                                 <option>--test</option>.</para></listitem>
 140                         </varlistentry>
 141                         <varlistentry>
 142                                 <term><option>--dump-core</option></term>
 143
 144                                 <listitem><para>Dump core on
 145                                 crash. This switch has no effect when
 146                                 run as user
 147                                 instance.</para></listitem>
 148                         </varlistentry>
 149                         <varlistentry>
 150                                 <term><option>--crash-shell</option></term>
 151
 152                                 <listitem><para>Run shell on
 153                                 crash. This switch has no effect when
 154                                 run as user
 155                                 instance.</para></listitem>
 156                         </varlistentry>
 157                         <varlistentry>
 158                                 <term><option>--confirm-spawn</option></term>
 159
 160                                 <listitem><para>Ask for confirmation
 161                                 when spawning processes. This switch
 162                                 has no effect when run as user
 163                                 instance.</para></listitem>
 164                         </varlistentry>
 165                         <varlistentry>
 166                                 <term><option>--show-status=</option></term>
 167
 168                                 <listitem><para>Show terse service
 169                                 status information while booting. This
 170                                 switch has no effect when run as user
 171                                 instance. Takes a boolean argument
 172                                 which may be omitted which is
 173                                 interpreted as
 174                                 <option>true</option>.</para></listitem>
 175                         </varlistentry>
 176                         <varlistentry>
 177                                 <term><option>--log-target=</option></term>
 178
 179                                 <listitem><para>Set log
 180                                 target. Argument must be one of
 181                                 <option>console</option>,
 182                                 <option>journal</option>,
 183                                 <option>syslog</option>,
 184                                 <option>kmsg</option>,
 185                                 <option>journal-or-kmsg</option>,
 186                                 <option>syslog-or-kmsg</option>,
 187                                 <option>null</option>.</para></listitem>
 188                         </varlistentry>
 189                         <varlistentry>
 190                                 <term><option>--log-level=</option></term>
 191
 192                                 <listitem><para>Set log level. As
 193                                 argument this accepts a numerical log
 194                                 level or the well-known <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 195                                 symbolic names (lowercase):
 196                                 <option>emerg</option>,
 197                                 <option>alert</option>,
 198                                 <option>crit</option>,
 199                                 <option>err</option>,
 200                                 <option>warning</option>,
 201                                 <option>notice</option>,
 202                                 <option>info</option>,
 203                                 <option>debug</option>.</para></listitem>
 204                         </varlistentry>
 205                         <varlistentry>
 206                                 <term><option>--log-color=</option></term>
 207
 208                                 <listitem><para>Highlight important
 209                                 log messages. Argument is a boolean
 210                                 value. If the argument is omitted, it
 211                                 defaults to
 212                                 <option>true</option>.</para></listitem>
 213                         </varlistentry>
 214                         <varlistentry>
 215                                 <term><option>--log-location=</option></term>
 216
 217                                 <listitem><para>Include code location
 218                                 in log messages. This is mostly
 219                                 relevant for debugging
 220                                 purposes. Argument is a boolean
 221                                 value. If the argument is omitted
 222                                 it defaults to
 223                                 <option>true</option>.</para></listitem>
 224                         </varlistentry>
 225                         <varlistentry>
 226                                 <term><option>--default-standard-output=</option></term>
 227                                 <term><option>--default-standard-error=</option></term>
 228
 229                                 <listitem><para>Sets the default
 230                                 output or error output for all
 231                                 services and sockets, respectively. That is, controls
 232                                 the default for
 233                                 <option>StandardOutput=</option>
 234                                 and <option>StandardError=</option>
 235                                 (see
 236                                 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 237                                 for details). Takes one of
 238                                 <option>inherit</option>,
 239                                 <option>null</option>,
 240                                 <option>tty</option>,
 241                                 <option>journal</option>,
 242                                 <option>journal+console</option>,
 243                                 <option>syslog</option>,
 244                                 <option>syslog+console</option>,
 245                                 <option>kmsg</option>,
 246                                 <option>kmsg+console</option>.  If the
 247                                 argument is omitted
 248                                 <option>--default-standard-output=</option>
 249                                 defaults to <option>journal</option>
 250                                 and
 251                                 <option>--default-standard-error=</option>
 252                                 to
 253                                 <option>inherit</option>.</para></listitem>
 254                         </varlistentry>
 255
 256                         <xi:include href="standard-options.xml" xpointer="help" />
 257                         <xi:include href="standard-options.xml" xpointer="version" />
 258                 </variablelist>
 259         </refsect1>
 260
 261         <refsect1>
 262                 <title>Concepts</title>
 263
 264                 <para>systemd provides a dependency system between
 265                 various entities called "units" of 12 different
 266                 types. Units encapsulate various objects that are
 267                 relevant for system boot-up and maintenance. The
 268                 majority of units are configured in unit configuration
 269                 files, whose syntax and basic set of options is
 270                 described in
 271                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 272                 however some are created automatically from other
 273                 configuration, dynamically from system state or
 274                 programmatically at runtime. Units may be "active"
 275                 (meaning started, bound, plugged in, ..., depending on
 276                 the unit type, see below), or "inactive" (meaning
 277                 stopped, unbound, unplugged, ...), as well as in the
 278                 process of being activated or deactivated,
 279                 i.e. between the two states (these states are called
 280                 "activating", "deactivating"). A special "failed"
 281                 state is available as well, which is very similar to
 282                 "inactive" and is entered when the service failed in
 283                 some way (process returned error code on exit, or
 284                 crashed, or an operation timed out). If this state is
 285                 entered, the cause will be logged, for later
 286                 reference. Note that the various unit types may have a
 287                 number of additional substates, which are mapped to
 288                 the five generalized unit states described
 289                 here.</para>
 290
 291                 <para>The following unit types are available:</para>
 292
 293                 <orderedlist>
 294                         <listitem><para>Service units, which start and control
 295                         daemons and the processes they consist of. For
 296                         details see
 297                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 298
 299                         <listitem><para>Socket units, which
 300                         encapsulate local IPC or network sockets in
 301                         the system, useful for socket-based
 302                         activation. For details about socket units see
 303                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 304                         for details on socket-based activation and
 305                         other forms of activation, see
 306                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 307
 308                         <listitem><para>Target units are useful to
 309                         group units, or provide well-known
 310                         synchronization points during boot-up, see
 311                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 312
 313                         <listitem><para>Device units expose kernel
 314                         devices in systemd and may be used to
 315                         implement device-based activation. For details
 316                         see
 317                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 318
 319                         <listitem><para>Mount units control mount
 320                         points in the file system, for details see
 321                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 322
 323                         <listitem><para>Automount units provide
 324                         automount capabilities, for on-demand mounting
 325                         of file systems as well as parallelized
 326                         boot-up. See
 327                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 328
 329                         <listitem><para>Snapshot units can be used to
 330                         temporarily save the state of the set of
 331                         systemd units, which later may be restored by
 332                         activating the saved snapshot unit. For more
 333                         information see
 334                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 335
 336                         <listitem><para>Timer units are useful for
 337                         triggering activation of other units based on
 338                         timers. You may find details in
 339                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 340
 341                         <listitem><para>Swap units are very similar to
 342                         mount units and encapsulate memory swap
 343                         partitions or files of the operating
 344                         system. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 345
 346                         <listitem><para>Path units may be used
 347                         to activate other services when file system
 348                         objects change or are modified. See
 349                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 350
 351                         <listitem><para>Slice units may be used to
 352                         group units which manage system processes
 353                         (such as service and scope units) in a
 354                         hierarchical tree for resource management
 355                         purposes. See
 356                         <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 357
 358                         <listitem><para>Scope units are similar to
 359                         service units, but manage foreign processes
 360                         instead of starting them as well. See
 361                         <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 362
 363                 </orderedlist>
 364
 365                 <para>Units are named as their configuration
 366                 files. Some units have special semantics. A detailed
 367                 list is available in
 368                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 369
 370                 <para>systemd knows various kinds of dependencies,
 371                 including positive and negative requirement
 372                 dependencies (i.e. <varname>Requires=</varname> and
 373                 <varname>Conflicts=</varname>) as well as ordering
 374                 dependencies (<varname>After=</varname> and
 375                 <varname>Before=</varname>). NB: ordering and
 376                 requirement dependencies are orthogonal. If only a
 377                 requirement dependency exists between two units
 378                 (e.g. <filename>foo.service</filename> requires
 379                 <filename>bar.service</filename>), but no ordering
 380                 dependency (e.g. <filename>foo.service</filename>
 381                 after <filename>bar.service</filename>) and both are
 382                 requested to start, they will be started in
 383                 parallel. It is a common pattern that both requirement
 384                 and ordering dependencies are placed between two
 385                 units. Also note that the majority of dependencies are
 386                 implicitly created and maintained by systemd. In most
 387                 cases, it should be unnecessary to declare additional
 388                 dependencies manually, however it is possible to do
 389                 this.</para>
 390
 391                 <para>Application programs and units (via
 392                 dependencies) may request state changes of units. In
 393                 systemd, these requests are encapsulated as 'jobs' and
 394                 maintained in a job queue. Jobs may succeed or can
 395                 fail, their execution is ordered based on the ordering
 396                 dependencies of the units they have been scheduled
 397                 for.</para>
 398
 399                 <para>On boot systemd activates the target unit
 400                 <filename>default.target</filename> whose job is to
 401                 activate on-boot services and other on-boot units by
 402                 pulling them in via dependencies. Usually the unit
 403                 name is just an alias (symlink) for either
 404                 <filename>graphical.target</filename> (for
 405                 fully-featured boots into the UI) or
 406                 <filename>multi-user.target</filename> (for limited
 407                 console-only boots for use in embedded or server
 408                 environments, or similar; a subset of
 409                 graphical.target). However, it is at the discretion of
 410                 the administrator to configure it as an alias to any
 411                 other target unit. See
 412                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 413                 for details about these target units.</para>
 414
 415                 <para>Processes systemd spawns are placed in
 416                 individual Linux control groups named after the unit
 417                 which they belong to in the private systemd
 418                 hierarchy. (see <ulink
 419                 url="https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 420                 for more information about control groups, or short
 421                 "cgroups"). systemd uses this to effectively keep
 422                 track of processes. Control group information is
 423                 maintained in the kernel, and is accessible via the
 424                 file system hierarchy (beneath
 425                 <filename>/sys/fs/cgroup/systemd/</filename>), or in tools
 426                 such as
 427                 <citerefentry><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 428                 (<command>ps xawf -eo pid,user,cgroup,args</command>
 429                 is particularly useful to list all processes and the
 430                 systemd units they belong to.).</para>
 431
 432                 <para>systemd is compatible with the SysV init system
 433                 to a large degree: SysV init scripts are supported and
 434                 simply read as an alternative (though limited)
 435                 configuration file format. The SysV
 436                 <filename>/dev/initctl</filename> interface is
 437                 provided, and compatibility implementations of the
 438                 various SysV client tools are available. In addition to
 439                 that, various established Unix functionality such as
 440                 <filename>/etc/fstab</filename> or the
 441                 <filename>utmp</filename> database are
 442                 supported.</para>
 443
 444                 <para>systemd has a minimal transaction system: if a
 445                 unit is requested to start up or shut down it will add
 446                 it and all its dependencies to a temporary
 447                 transaction. Then, it will verify if the transaction
 448                 is consistent (i.e. whether the ordering of all units
 449                 is cycle-free). If it is not, systemd will try to fix
 450                 it up, and removes non-essential jobs from the
 451                 transaction that might remove the loop. Also, systemd
 452                 tries to suppress non-essential jobs in the
 453                 transaction that would stop a running service. Finally
 454                 it is checked whether the jobs of the transaction
 455                 contradict jobs that have already been queued, and
 456                 optionally the transaction is aborted then. If all
 457                 worked out and the transaction is consistent and
 458                 minimized in its impact it is merged with all already
 459                 outstanding jobs and added to the run
 460                 queue. Effectively this means that before executing a
 461                 requested operation, systemd will verify that it makes
 462                 sense, fixing it if possible, and only failing if it
 463                 really cannot work.</para>
 464
 465                 <para>Systemd contains native implementations of
 466                 various tasks that need to be executed as part of the
 467                 boot process. For example, it sets the hostname or
 468                 configures the loopback network device. It also sets
 469                 up and mounts various API file systems, such as
 470                 <filename>/sys</filename> or
 471                 <filename>/proc</filename>.</para>
 472
 473                 <para>For more information about the concepts and
 474                 ideas behind systemd, please refer to the <ulink
 475                 url="http://0pointer.de/blog/projects/systemd.html">Original
 476                 Design Document</ulink>.</para>
 477
 478                 <para>Note that some but not all interfaces provided
 479                 by systemd are covered by the <ulink
 480                 url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 481                 Stability Promise</ulink>.</para>
 482
 483                 <para>Units may be generated dynamically at boot and
 484                 system manager reload time, for example based on other
 485                 configuration files or parameters passed on the kernel
 486                 command line. For details see the <ulink
 487                 url="http://www.freedesktop.org/wiki/Software/systemd/Generators">Generators
 488                 Specification</ulink>.</para>
 489
 490                 <para>Systems which invoke systemd in a container
 491                 or initrd environment should implement the
 492                 <ulink
 493                 url="http://www.freedesktop.org/wiki/Software/systemd/ContainerInterface">Container
 494                 Interface</ulink> or <ulink
 495                 url="http://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd
 496                 Interface</ulink> specifications, respectively.</para>
 497         </refsect1>
 498
 499         <refsect1>
 500                 <title>Directories</title>
 501
 502                 <variablelist>
 503                         <varlistentry>
 504                                 <term>System unit directories</term>
 505
 506                                 <listitem><para>The systemd system
 507                                 manager reads unit configuration from
 508                                 various directories. Packages that
 509                                 want to install unit files shall place
 510                                 them in the directory returned by
 511                                 <command>pkg-config systemd
 512                                 --variable=systemdsystemunitdir</command>. Other
 513                                 directories checked are
 514                                 <filename>/usr/local/lib/systemd/system</filename>
 515                                 and
 516                                 <filename>/usr/lib/systemd/system</filename>. User
 517                                 configuration always takes
 518                                 precedence. <command>pkg-config
 519                                 systemd
 520                                 --variable=systemdsystemconfdir</command>
 521                                 returns the path of the system
 522                                 configuration directory. Packages
 523                                 should alter the content of these
 524                                 directories only with the
 525                                 <command>enable</command> and
 526                                 <command>disable</command> commands of
 527                                 the
 528                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 529                                 tool. Full list of directories is provided in
 530                                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 531                                 </para></listitem>
 532                         </varlistentry>
 533                 </variablelist>
 534
 535                 <variablelist>
 536                         <varlistentry>
 537                                 <term>User unit directories</term>
 538
 539                                 <listitem><para>Similar rules apply
 540                                 for the user unit
 541                                 directories. However, here the <ulink
 542                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 543                                 Base Directory specification</ulink>
 544                                 is followed to find
 545                                 units. Applications should place their
 546                                 unit files in the directory returned
 547                                 by <command>pkg-config systemd
 548                                 --variable=systemduserunitdir</command>. Global
 549                                 configuration is done in the directory
 550                                 reported by <command>pkg-config
 551                                 systemd
 552                                 --variable=systemduserconfdir</command>. The
 553                                 <command>enable</command> and
 554                                 <command>disable</command> commands of
 555                                 the
 556                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 557                                 tool can handle both global (i.e. for
 558                                 all users) and private (for one user)
 559                                 enabling/disabling of
 560                                 units. Full list of directories is provided in
 561                                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 562                                 </para></listitem>
 563                         </varlistentry>
 564                 </variablelist>
 565
 566                 <variablelist>
 567                         <varlistentry>
 568                                 <term>SysV init scripts directory</term>
 569
 570                                 <listitem><para>The location of the
 571                                 SysV init script directory varies
 572                                 between distributions. If systemd
 573                                 cannot find a native unit file for a
 574                                 requested service, it will look for a
 575                                 SysV init script of the same name
 576                                 (with the
 577                                 <filename>.service</filename> suffix
 578                                 removed).</para></listitem>
 579                         </varlistentry>
 580                 </variablelist>
 581
 582                 <variablelist>
 583                         <varlistentry>
 584                                 <term>SysV runlevel link farm directory</term>
 585
 586                                 <listitem><para>The location of the
 587                                 SysV runlevel link farm directory
 588                                 varies between distributions. systemd
 589                                 will take the link farm into account
 590                                 when figuring out whether a service
 591                                 shall be enabled. Note that a service
 592                                 unit with a native unit configuration
 593                                 file cannot be started by activating it
 594                                 in the SysV runlevel link
 595                                 farm.</para></listitem>
 596                         </varlistentry>
 597                 </variablelist>
 598         </refsect1>
 599
 600         <refsect1>
 601                 <title>Signals</title>
 602
 603                 <variablelist>
 604                         <varlistentry>
 605                                 <term><constant>SIGTERM</constant></term>
 606
 607                                 <listitem><para>Upon receiving this
 608                                 signal the systemd system manager
 609                                 serializes its state, reexecutes
 610                                 itself and deserializes the saved
 611                                 state again. This is mostly equivalent
 612                                 to <command>systemctl
 613                                 daemon-reexec</command>.</para>
 614
 615                                 <para>systemd user managers will
 616                                 start the
 617                                 <filename>exit.target</filename> unit
 618                                 when this signal is received. This is
 619                                 mostly equivalent to
 620                                 <command>systemctl --user start
 621                                 exit.target</command>.</para></listitem>
 622                         </varlistentry>
 623
 624                         <varlistentry>
 625                                 <term><constant>SIGINT</constant></term>
 626
 627                                 <listitem><para>Upon receiving this
 628                                 signal the systemd system manager will
 629                                 start the
 630                                 <filename>ctrl-alt-del.target</filename> unit. This
 631                                 is mostly equivalent to
 632                                 <command>systemctl start
 633                                 ctl-alt-del.target</command>.</para>
 634
 635                                 <para>systemd user managers
 636                                 treat this signal the same way as
 637                                 <constant>SIGTERM</constant>.</para></listitem>
 638                         </varlistentry>
 639
 640                         <varlistentry>
 641                                 <term><constant>SIGWINCH</constant></term>
 642
 643                                 <listitem><para>When this signal is
 644                                 received the systemd system manager
 645                                 will start the
 646                                 <filename>kbrequest.target</filename>
 647                                 unit. This is mostly equivalent to
 648                                 <command>systemctl start
 649                                 kbrequest.target</command>.</para>
 650
 651                                 <para>This signal is ignored by
 652                                 systemd user
 653                                 managers.</para></listitem>
 654                         </varlistentry>
 655
 656                         <varlistentry>
 657                                 <term><constant>SIGPWR</constant></term>
 658
 659                                 <listitem><para>When this signal is
 660                                 received the systemd manager
 661                                 will start the
 662                                 <filename>sigpwr.target</filename>
 663                                 unit. This is mostly equivalent to
 664                                 <command>systemctl start
 665                                 sigpwr.target</command>.</para></listitem>
 666                         </varlistentry>
 667
 668                         <varlistentry>
 669                                 <term><constant>SIGUSR1</constant></term>
 670
 671                                 <listitem><para>When this signal is
 672                                 received the systemd manager will try
 673                                 to reconnect to the D-Bus
 674                                 bus.</para></listitem>
 675                         </varlistentry>
 676
 677                         <varlistentry>
 678                                 <term><constant>SIGUSR2</constant></term>
 679
 680                                 <listitem><para>When this signal is
 681                                 received the systemd manager will log
 682                                 its complete state in human readable
 683                                 form. The data logged is the same as
 684                                 printed by <command>systemctl
 685                                 dump</command>.</para></listitem>
 686                         </varlistentry>
 687
 688                         <varlistentry>
 689                                 <term><constant>SIGHUP</constant></term>
 690
 691                                 <listitem><para>Reloads the complete
 692                                 daemon configuration. This is mostly
 693                                 equivalent to <command>systemctl
 694                                 daemon-reload</command>.</para></listitem>
 695                         </varlistentry>
 696
 697                         <varlistentry>
 698                                 <term><constant>SIGRTMIN+0</constant></term>
 699
 700                                 <listitem><para>Enters default mode, starts the
 701                                 <filename>default.target</filename>
 702                                 unit. This is mostly equivalent to
 703                                 <command>systemctl start
 704                                 default.target</command>.</para></listitem>
 705                         </varlistentry>
 706
 707                         <varlistentry>
 708                                 <term><constant>SIGRTMIN+1</constant></term>
 709
 710                                 <listitem><para>Enters rescue mode,
 711                                 starts the
 712                                 <filename>rescue.target</filename>
 713                                 unit. This is mostly equivalent to
 714                                 <command>systemctl isolate
 715                                 rescue.target</command>.</para></listitem>
 716                         </varlistentry>
 717
 718                         <varlistentry>
 719                                 <term><constant>SIGRTMIN+2</constant></term>
 720
 721                                 <listitem><para>Enters emergency mode,
 722                                 starts the
 723                                 <filename>emergency.service</filename>
 724                                 unit. This is mostly equivalent to
 725                                 <command>systemctl isolate
 726                                 emergency.service</command>.</para></listitem>
 727                         </varlistentry>
 728
 729                         <varlistentry>
 730                                 <term><constant>SIGRTMIN+3</constant></term>
 731
 732                                 <listitem><para>Halts the machine,
 733                                 starts the
 734                                 <filename>halt.target</filename>
 735                                 unit. This is mostly equivalent to
 736                                 <command>systemctl start
 737                                 halt.target</command>.</para></listitem>
 738                         </varlistentry>
 739
 740                         <varlistentry>
 741                                 <term><constant>SIGRTMIN+4</constant></term>
 742
 743                                 <listitem><para>Powers off the machine,
 744                                 starts the
 745                                 <filename>poweroff.target</filename>
 746                                 unit. This is mostly equivalent to
 747                                 <command>systemctl start
 748                                 poweroff.target</command>.</para></listitem>
 749                         </varlistentry>
 750
 751                         <varlistentry>
 752                                 <term><constant>SIGRTMIN+5</constant></term>
 753
 754                                 <listitem><para>Reboots the machine,
 755                                 starts the
 756                                 <filename>reboot.target</filename>
 757                                 unit. This is mostly equivalent to
 758                                 <command>systemctl start
 759                                 reboot.target</command>.</para></listitem>
 760                         </varlistentry>
 761
 762                         <varlistentry>
 763                                 <term><constant>SIGRTMIN+6</constant></term>
 764
 765                                 <listitem><para>Reboots the machine via kexec,
 766                                 starts the
 767                                 <filename>kexec.target</filename>
 768                                 unit. This is mostly equivalent to
 769                                 <command>systemctl start
 770                                 kexec.target</command>.</para></listitem>
 771                         </varlistentry>
 772
 773                         <varlistentry>
 774                                 <term><constant>SIGRTMIN+13</constant></term>
 775
 776                                 <listitem><para>Immediately halts the machine.</para></listitem>
 777                         </varlistentry>
 778
 779                         <varlistentry>
 780                                 <term><constant>SIGRTMIN+14</constant></term>
 781
 782                                 <listitem><para>Immediately powers off the machine.</para></listitem>
 783                         </varlistentry>
 784
 785                         <varlistentry>
 786                                 <term><constant>SIGRTMIN+15</constant></term>
 787
 788                                 <listitem><para>Immediately reboots the machine.</para></listitem>
 789                         </varlistentry>
 790
 791                         <varlistentry>
 792                                 <term><constant>SIGRTMIN+16</constant></term>
 793
 794                                 <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
 795                         </varlistentry>
 796
 797                         <varlistentry>
 798                                 <term><constant>SIGRTMIN+20</constant></term>
 799
 800                                 <listitem><para>Enables display of
 801                                 status messages on the console, as
 802                                 controlled via
 803                                 <varname>systemd.show_status=1</varname>
 804                                 on the kernel command
 805                                 line.</para></listitem>
 806                         </varlistentry>
 807
 808                         <varlistentry>
 809                                 <term><constant>SIGRTMIN+21</constant></term>
 810
 811                                 <listitem><para>Disables display of
 812                                 status messages on the console, as
 813                                 controlled via
 814                                 <varname>systemd.show_status=0</varname>
 815                                 on the kernel command
 816                                 line.</para></listitem>
 817                         </varlistentry>
 818
 819                         <varlistentry>
 820                                 <term><constant>SIGRTMIN+22</constant></term>
 821                                 <term><constant>SIGRTMIN+23</constant></term>
 822
 823                                 <listitem><para>Sets the log level to
 824                                 <literal>debug</literal>
 825                                 (or <literal>info</literal> on
 826                                 <constant>SIGRTMIN+23</constant>), as
 827                                 controlled via
 828                                 <varname>systemd.log_level=debug</varname>
 829                                 (or <varname>systemd.log_level=info</varname>
 830                                 on <constant>SIGRTMIN+23</constant>) on
 831                                 the kernel command
 832                                 line.</para></listitem>
 833                         </varlistentry>
 834
 835                         <varlistentry>
 836                                 <term><constant>SIGRTMIN+24</constant></term>
 837
 838                                 <listitem><para>Immediately exits the
 839                                 manager (only available for --user
 840                                 instances).</para></listitem>
 841                         </varlistentry>
 842
 843                         <varlistentry>
 844                                 <term><constant>SIGRTMIN+26</constant></term>
 845                                 <term><constant>SIGRTMIN+27</constant></term>
 846                                 <term><constant>SIGRTMIN+28</constant></term>
 847                                 <term><constant>SIGRTMIN+29</constant></term>
 848
 849                                 <listitem><para>Sets the log level to
 850                                 <literal>journal-or-kmsg</literal>
 851                                 (or <literal>console</literal> on
 852                                 <constant>SIGRTMIN+27</constant>,
 853                                 <literal>kmsg</literal> on
 854                                 <constant>SIGRTMIN+28</constant>,
 855                                 or <literal>syslog-or-kmsg</literal>
 856                                 on <constant>SIGRTMIN+29</constant>), as
 857                                 controlled via
 858                                 <varname>systemd.log_target=journal-or-kmsg</varname>
 859                                 (or <varname>systemd.log_target=console</varname>
 860                                 on <constant>SIGRTMIN+27</constant>,
 861                                 <varname>systemd.log_target=kmsg</varname>
 862                                 on <constant>SIGRTMIN+28</constant>,
 863                                 or
 864                                 <varname>systemd.log_target=syslog-or-kmsg</varname>
 865                                 on <constant>SIGRTMIN+29</constant>) on
 866                                 the kernel command
 867                                 line.</para></listitem>
 868                         </varlistentry>
 869                 </variablelist>
 870         </refsect1>
 871
 872         <refsect1>
 873                 <title>Environment</title>
 874
 875                 <variablelist class='environment-variables'>
 876                         <varlistentry>
 877                                 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 878                                 <listitem><para>systemd reads the
 879                                 log level from this environment
 880                                 variable. This can be overridden with
 881                                 <option>--log-level=</option>.</para></listitem>
 882                         </varlistentry>
 883
 884                         <varlistentry>
 885                                 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 886                                 <listitem><para>systemd reads the
 887                                 log target from this environment
 888                                 variable. This can be overridden with
 889                                 <option>--log-target=</option>.</para></listitem>
 890                         </varlistentry>
 891
 892                         <varlistentry>
 893                                 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 894                                 <listitem><para>Controls whether
 895                                 systemd highlights important log
 896                                 messages. This can be overridden with
 897                                 <option>--log-color=</option>.</para></listitem>
 898                         </varlistentry>
 899
 900                         <varlistentry>
 901                                 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 902                                 <listitem><para>Controls whether
 903                                 systemd prints the code location along
 904                                 with log messages. This can be
 905                                 overridden with
 906                                 <option>--log-location=</option>.</para></listitem>
 907                         </varlistentry>
 908
 909                         <varlistentry>
 910                                 <term><varname>$XDG_CONFIG_HOME</varname></term>
 911                                 <term><varname>$XDG_CONFIG_DIRS</varname></term>
 912                                 <term><varname>$XDG_DATA_HOME</varname></term>
 913                                 <term><varname>$XDG_DATA_DIRS</varname></term>
 914
 915                                 <listitem><para>The systemd user
 916                                 manager uses these variables in
 917                                 accordance to the <ulink
 918                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 919                                 Base Directory specification</ulink>
 920                                 to find its configuration.</para></listitem>
 921                         </varlistentry>
 922
 923                         <varlistentry>
 924                                 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 925
 926                                 <listitem><para>Controls where systemd
 927                                 looks for unit
 928                                 files.</para></listitem>
 929                         </varlistentry>
 930
 931                         <varlistentry>
 932                                 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 933
 934                                 <listitem><para>Controls where systemd
 935                                 looks for SysV init scripts.</para></listitem>
 936                         </varlistentry>
 937
 938                         <varlistentry>
 939                                 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 940
 941                                 <listitem><para>Controls where systemd
 942                                 looks for SysV init script runlevel link
 943                                 farms.</para></listitem>
 944                         </varlistentry>
 945
 946                         <varlistentry>
 947                                 <term><varname>$LISTEN_PID</varname></term>
 948                                 <term><varname>$LISTEN_FDS</varname></term>
 949
 950                                 <listitem><para>Set by systemd for
 951                                 supervised processes during
 952                                 socket-based activation. See
 953                                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 954                                 for more information.
 955                                 </para></listitem>
 956                         </varlistentry>
 957
 958                         <varlistentry>
 959                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 960
 961                                 <listitem><para>Set by systemd for
 962                                 supervised processes for status and
 963                                 start-up completion notification. See
 964                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 965                                 for more information.
 966                                 </para></listitem>
 967                         </varlistentry>
 968                 </variablelist>
 969         </refsect1>
 970
 971         <refsect1>
 972                 <title>Kernel Command Line</title>
 973
 974                 <para>When run as system instance systemd parses a
 975                 number of kernel command line
 976                 arguments<footnote><para>If run inside a Linux
 977                 container these arguments may be passed as command
 978                 line arguments to systemd itself, next to any of the
 979                 command line options listed in the Options section
 980                 above. If run outside of Linux containers, these
 981                 arguments are parsed from
 982                 <filename>/proc/cmdline</filename>
 983                 instead.</para></footnote>:</para>
 984
 985                 <variablelist class='kernel-commandline-options'>
 986                         <varlistentry>
 987                                 <term><varname>systemd.unit=</varname></term>
 988                                 <term><varname>rd.systemd.unit=</varname></term>
 989
 990                                 <listitem><para>Overrides the unit to
 991                                 activate on boot. Defaults to
 992                                 <filename>default.target</filename>. This
 993                                 may be used to temporarily boot into a
 994                                 different boot unit, for example
 995                                 <filename>rescue.target</filename> or
 996                                 <filename>emergency.service</filename>. See
 997                                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 998                                 for details about these units. The
 999                                 option prefixed with
1000                                 <literal>rd.</literal> is honored
1001                                 only in the initial RAM disk (initrd),
1002                                 while the one that is not prefixed only
1003                                 in the main system.</para></listitem>
1004                         </varlistentry>
1005
1006                         <varlistentry>
1007                                 <term><varname>systemd.dump_core=</varname></term>
1008
1009                                 <listitem><para>Takes a boolean
1010                                 argument. If <option>true</option>,
1011                                 systemd dumps core when it
1012                                 crashes. Otherwise, no core dump is
1013                                 created. Defaults to
1014                                 <option>true</option>.</para></listitem>
1015                         </varlistentry>
1016
1017                         <varlistentry>
1018                                 <term><varname>systemd.crash_shell=</varname></term>
1019
1020                                 <listitem><para>Takes a boolean
1021                                 argument. If <option>true</option>,
1022                                 systemd spawns a shell when it
1023                                 crashes. Otherwise, no shell is
1024                                 spawned. Defaults to
1025                                 <option>false</option>, for security
1026                                 reasons, as the shell is not protected
1027                                 by any password
1028                                 authentication.</para></listitem>
1029                         </varlistentry>
1030
1031                         <varlistentry>
1032                                 <term><varname>systemd.crash_chvt=</varname></term>
1033
1034                                 <listitem><para>Takes an integer
1035                                 argument. If positive systemd
1036                                 activates the specified virtual
1037                                 terminal when it crashes. Defaults to
1038                                 <constant>-1</constant>.</para></listitem>
1039                         </varlistentry>
1040
1041                         <varlistentry>
1042                                 <term><varname>systemd.confirm_spawn=</varname></term>
1043
1044                                 <listitem><para>Takes a boolean
1045                                 argument. If <option>true</option>,
1046                                 asks for confirmation when spawning
1047                                 processes. Defaults to
1048                                 <option>false</option>.</para></listitem>
1049                         </varlistentry>
1050
1051                         <varlistentry>
1052                                 <term><varname>systemd.show_status=</varname></term>
1053
1054                                 <listitem><para>Takes a boolean
1055                                 argument or the constant
1056                                 <constant>auto</constant>. If
1057                                 <option>true</option>, shows terse
1058                                 service status updates on the console
1059                                 during bootup.
1060                                 <constant>auto</constant> behaves like
1061                                 <option>false</option> until a service
1062                                 fails or there is a significant delay
1063                                 in boot. Defaults to
1064                                 <option>true</option>, unless
1065                                 <option>quiet</option> is passed as
1066                                 kernel command line option in which
1067                                 case it defaults to
1068                                 <constant>auto</constant>.</para></listitem>
1069                         </varlistentry>
1070
1071                         <varlistentry>
1072                                 <term><varname>systemd.log_target=</varname></term>
1073                                 <term><varname>systemd.log_level=</varname></term>
1074                                 <term><varname>systemd.log_color=</varname></term>
1075                                 <term><varname>systemd.log_location=</varname></term>
1076
1077                                 <listitem><para>Controls log output,
1078                                 with the same effect as the
1079                                 <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
1080                                 environment variables described above.</para></listitem>
1081                         </varlistentry>
1082
1083                         <varlistentry>
1084                                 <term><varname>systemd.default_standard_output=</varname></term>
1085                                 <term><varname>systemd.default_standard_error=</varname></term>
1086                                 <listitem><para>Controls default
1087                                 standard output and error output for
1088                                 services, with the same effect as the
1089                                 <option>--default-standard-output=</option>
1090                                 and <option>--default-standard-error=</option>
1091                                 command line arguments described
1092                                 above, respectively.</para></listitem>
1093                         </varlistentry>
1094
1095                         <varlistentry>
1096                                 <term><varname>systemd.setenv=</varname></term>
1097
1098                                 <listitem><para>Takes a string
1099                                 argument in the form VARIABLE=VALUE.
1100                                 May be used to set default environment
1101                                 variables to add to forked child processes.
1102                                 May be used more than once to set multiple
1103                                 variables.</para></listitem>
1104                         </varlistentry>
1105
1106                         <varlistentry>
1107                                 <term><varname>quiet</varname></term>
1108
1109                                 <listitem><para>Turn off
1110                                 status output at boot, much like
1111                                 <varname>systemd.show_status=false</varname>
1112                                 would. Note that this option is also
1113                                 read by the kernel itself and disables
1114                                 kernel log output. Passing this option
1115                                 hence turns off the usual output from
1116                                 both the system manager and the kernel.
1117                                 </para></listitem>
1118                         </varlistentry>
1119
1120                         <varlistentry>
1121                                 <term><varname>debug</varname></term>
1122
1123                                 <listitem><para>Turn on debugging
1124                                 output. This is equivalent to
1125                                 <varname>systemd.log_level=debug</varname>.
1126                                 Note that this option is also read by
1127                                 the kernel itself and enables kernel
1128                                 debug output.  Passing this option
1129                                 hence turns on the debug output from
1130                                 both the system manager and the
1131                                 kernel.</para></listitem>
1132                         </varlistentry>
1133
1134                         <varlistentry>
1135                                 <term><varname>-b</varname></term>
1136                                 <term><varname>emergency</varname></term>
1137
1138                                 <listitem><para>Boot into emergency
1139                                 mode. This is equivalent to
1140                                 <varname>systemd.unit=emergency.target</varname>
1141                                 and provided for compatibility
1142                                 reasons and to be easier to type.</para></listitem>
1143                         </varlistentry>
1144
1145                         <varlistentry>
1146                                 <term><varname>single</varname></term>
1147                                 <term><varname>s</varname></term>
1148                                 <term><varname>S</varname></term>
1149                                 <term><varname>1</varname></term>
1150
1151                                 <listitem><para>Boot into rescue
1152                                 mode. This is equivalent to
1153                                 <varname>systemd.unit=rescue.target</varname>
1154                                 and provided for compatibility reasons
1155                                 and to be easier to
1156                                 type.</para></listitem>
1157                         </varlistentry>
1158
1159                         <varlistentry>
1160                                 <term><varname>2</varname></term>
1161                                 <term><varname>3</varname></term>
1162                                 <term><varname>4</varname></term>
1163                                 <term><varname>5</varname></term>
1164
1165                                 <listitem><para>Boot into the
1166                                 specified legacy SysV runlevel. These
1167                                 are equivalent to
1168                                 <varname>systemd.unit=runlevel2.target</varname>,
1169                                 <varname>systemd.unit=runlevel3.target</varname>,
1170                                 <varname>systemd.unit=runlevel4.target</varname>,
1171                                 and <varname>systemd.unit=runlevel5.target</varname>, respectively,
1172                                 and provided for compatibility reasons
1173                                 and to be easier to
1174                                 type.</para></listitem>
1175                         </varlistentry>
1176
1177                         <varlistentry>
1178                                 <term><varname>locale.LANG=</varname></term>
1179                                 <term><varname>locale.LANGUAGE=</varname></term>
1180                                 <term><varname>locale.LC_CTYPE=</varname></term>
1181                                 <term><varname>locale.LC_NUMERIC=</varname></term>
1182                                 <term><varname>locale.LC_TIME=</varname></term>
1183                                 <term><varname>locale.LC_COLLATE=</varname></term>
1184                                 <term><varname>locale.LC_MONETARY=</varname></term>
1185                                 <term><varname>locale.LC_MESSAGES=</varname></term>
1186                                 <term><varname>locale.LC_PAPER=</varname></term>
1187                                 <term><varname>locale.LC_NAME=</varname></term>
1188                                 <term><varname>locale.LC_ADDRESS=</varname></term>
1189                                 <term><varname>locale.LC_TELEPHONE=</varname></term>
1190                                 <term><varname>locale.LC_MEASUREMENT=</varname></term>
1191                                 <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1192
1193                                 <listitem><para>Set the system locale
1194                                 to use. This overrides the settings in
1195                                 <filename>/etc/locale.conf</filename>. For
1196                                 more information see
1197                                 <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1198                                 and
1199                                 <citerefentry><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1200                                 </para></listitem>
1201                         </varlistentry>
1202                 </variablelist>
1203
1204                 <para>For other kernel command line parameters
1205                 understood by components of the core OS, please refer
1206                 to
1207                 <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1208         </refsect1>
1209
1210         <refsect1>
1211                 <title>Sockets and FIFOs</title>
1212
1213                 <variablelist>
1214                         <varlistentry>
1215                                 <term><filename>/run/systemd/notify</filename></term>
1216
1217                                 <listitem><para>Daemon status
1218                                 notification socket. This is an
1219                                 <constant>AF_UNIX</constant> datagram socket and is used to
1220                                 implement the daemon notification
1221                                 logic as implemented by
1222                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1223
1224                         </varlistentry>
1225
1226                         <varlistentry>
1227                                 <term><filename>/run/systemd/shutdownd</filename></term>
1228
1229                                 <listitem><para>Used internally by the
1230                                 <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1231                                 tool to implement delayed
1232                                 shutdowns. This is an <constant>AF_UNIX</constant> datagram
1233                                 socket.</para></listitem>
1234                         </varlistentry>
1235
1236                         <varlistentry>
1237                                 <term><filename>/run/systemd/private</filename></term>
1238
1239                                 <listitem><para>Used internally as
1240                                 communication channel between
1241                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1242                                 and the systemd process. This is an
1243                                 <constant>AF_UNIX</constant> stream socket. This interface
1244                                 is private to systemd and should not
1245                                 be used in external
1246                                 projects.</para></listitem>
1247                         </varlistentry>
1248
1249                         <varlistentry>
1250                                 <term><filename>/dev/initctl</filename></term>
1251
1252                                 <listitem><para>Limited compatibility
1253                                 support for the SysV client interface,
1254                                 as implemented by the
1255                                 <filename>systemd-initctl.service</filename>
1256                                 unit. This is a named pipe in the file
1257                                 system. This interface is obsolete and
1258                                 should not be used in new
1259                                 applications.</para></listitem>
1260                         </varlistentry>
1261                 </variablelist>
1262         </refsect1>
1263
1264         <refsect1>
1265                 <title>See Also</title>
1266                 <para>
1267                         The <ulink url="http://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
1268                         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1269                         <citerefentry><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1270                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1271                         <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1272                         <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1273                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1274                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1275                         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1276                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1277                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1278                         <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1279                         <citerefentry><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1280                         <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1281                 </para>
1282         </refsect1>
1283
1284 </refentry>