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 General Public License as published by
  12   the Free Software Foundation; either version 2 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   General Public License for more details.
  19
  20   You should have received a copy of the GNU 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 Session 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 session 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         </refsect1>
  77
  78         <refsect1>
  79                 <title>Options</title>
  80
  81                 <para>The following options are understood:</para>
  82
  83                 <variablelist>
  84                         <varlistentry>
  85                                 <term><option>-h</option></term>
  86                                 <term><option>--help</option></term>
  87
  88                                 <listitem><para>Prints a short help
  89                                 text and exits.</para></listitem>
  90                         </varlistentry>
  91                         <varlistentry>
  92                                 <term><option>--unit=</option></term>
  93
  94                                 <listitem><para>Set default unit to
  95                                 activate on startup. If not specified
  96                                 defaults to
  97                                 <filename>default.target</filename>.</para></listitem>
  98                         </varlistentry>
  99                         <varlistentry>
 100                                 <term><option>--running-as=</option></term>
 101
 102                                 <listitem><para>Tell systemd to run in
 103                                 a particular mode. Argument is one of
 104                                 <option>system</option>,
 105                                 <option>session</option>. Normally it
 106                                 should not be necessary to pass this
 107                                 option, as systemd automatically
 108                                 detects the mode it is started
 109                                 in. This call is hence of little use
 110                                 except for
 111                                 debugging.</para></listitem>
 112                         </varlistentry>
 113                         <varlistentry>
 114                                 <term><option>--test</option></term>
 115
 116                                 <listitem><para>Determine startup
 117                                 sequence, dump it and exit. This is an
 118                                 option useful for debugging
 119                                 only.</para></listitem>
 120                         </varlistentry>
 121                         <varlistentry>
 122                                 <term><option>--dump-configuration-items</option></term>
 123
 124                                 <listitem><para>Dump understood unit
 125                                 configuration items. This outputs a
 126                                 terse but complete list of
 127                                 configuration items understood in unit
 128                                 definition files.</para></listitem>
 129                         </varlistentry>
 130                         <varlistentry>
 131                                 <term><option>--confirm-spawn</option></term>
 132
 133                                 <listitem><para>Ask for confirmation when spawning processes.</para></listitem>
 134                         </varlistentry>
 135                         <varlistentry>
 136                                 <term><option>--introspect=</option></term>
 137
 138                                 <listitem><para>Extract D-Bus
 139                                 interface introspection data. This is
 140                                 mostly useful at build at install time
 141                                 to generate data suitable for the
 142                                 D-Bus interfaces
 143                                 repository. Optionally the interface
 144                                 name for the introspection data may be
 145                                 specified. If omitted, the
 146                                 introspection data for all interfaces
 147                                 is dumped.</para></listitem>
 148                         </varlistentry>
 149                         <varlistentry>
 150                                 <term><option>--log-level=</option></term>
 151
 152                                 <listitem><para>Set log level. As
 153                                 argument this accepts a numerical log
 154                                 level or the well-known <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 155                                 symbolic names (lowercase):
 156                                 <option>emerg</option>,
 157                                 <option>alert</option>,
 158                                 <option>crit</option>,
 159                                 <option>err</option>,
 160                                 <option>warning</option>,
 161                                 <option>notice</option>,
 162                                 <option>info</option>,
 163                                 <option>debug</option>.</para></listitem>
 164                         </varlistentry>
 165                         <varlistentry>
 166                                 <term><option>--log-target=</option></term>
 167
 168                                 <listitem><para>Set log
 169                                 target. Argument must be one of
 170                                 <option>console</option>,
 171                                 <option>syslog</option>,
 172                                 <option>kmsg</option>,
 173                                 <option>syslog-or-kmsg</option>,
 174                                 <option>null</option>.</para></listitem>
 175                         </varlistentry>
 176                         <varlistentry>
 177                                 <term><option>--log-color=</option></term>
 178
 179                                 <listitem><para>Highlight important
 180                                 log messages. Argument is a boolean
 181                                 value. If the argument is omitted it
 182                                 defaults to
 183                                 <option>true</option>.</para></listitem>
 184                         </varlistentry>
 185                         <varlistentry>
 186                                 <term><option>--log-location=</option></term>
 187
 188                                 <listitem><para>Include code location
 189                                 in log messages. This is mostly
 190                                 relevant for debugging
 191                                 purposes. Argument is a boolean
 192                                 value. If the argument is omitted
 193                                 it defaults to
 194                                 <option>true</option>.</para></listitem>
 195                         </varlistentry>
 196                 </variablelist>
 197         </refsect1>
 198
 199         <refsect1>
 200                 <title>Concepts</title>
 201
 202                 <para>systemd provides a dependency system between
 203                 various entities called "units". Units encapsulate
 204                 various objects that are relevant for system boot-up
 205                 and maintainance. The majority of units are configured
 206                 in unit configuration files, whose syntax and basic
 207                 set of options is described in
 208                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 209                 however some are created automatically from other
 210                 configuration or dynamically from system state. Units
 211                 may be active (meaning started, bound, plugged in, ...
 212                 depending on the unit type), or inactive (meaning
 213                 stopped, unbound, unplugged, ...), as well is in the
 214                 process of being activated or deactivated,
 215                 i.e. between the two states. The following unit types
 216                 are available:</para>
 217
 218                 <orderedlist>
 219                         <listitem><para>Service units, which control
 220                         daemons and the processes they consist of. For
 221                         details see
 222                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 223
 224                         <listitem><para>Socket units, which
 225                         encapsulate local IPC or network sockets in
 226                         the system, useful for socket-based
 227                         activation. For details about socket units see
 228                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 229                         for details on socket-based activation and
 230                         other forms of activation, see
 231                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 232
 233                         <listitem><para>Target units are useful to
 234                         group units, or provide well-known
 235                         synchronization points during boot-up, see
 236                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 237
 238                         <listitem><para>Device units expose kernel
 239                         devices in systemd and may be used to
 240                         implement device-based activation. For details
 241                         see
 242                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 243
 244                         <listitem><para>Mount units control mount
 245                         points in the file system, for details see
 246                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 247
 248                         <listitem><para>Automount units provide
 249                         automount capabilities, for on-demand mounting
 250                         of file systems as well as parallelized
 251                         boot-up. See
 252                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 253
 254                         <listitem><para>Snapshot units can be used to
 255                         temporarily save the state of the set of
 256                         systemd units, which later may be restored by
 257                         activating the saved snapshot unit. For more
 258                         information see
 259                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 260
 261                         <listitem><para>Timer units are useful for
 262                         triggering activation of other units based on
 263                         timers. You may find details in
 264                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 265
 266                         <listitem><para>Swap units are very similar to
 267                         mount units and encapsulated memory swap
 268                         partitions or files of the operating
 269                         systemd. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 270
 271                         <listitem><para>Path units may be used
 272                         activate other services when file system
 273                         objects change or are modified. See
 274                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 275
 276                 </orderedlist>
 277
 278                 <para>Units are named as their configuration
 279                 files. Some units have special semantics. A detailed
 280                 list you may find in
 281                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 282
 283                 <para>On boot systemd activates the target unit
 284                 <filename>default.target</filename> whose job it is to
 285                 activate on-boot services and other on-boot units by
 286                 pulling them in via dependencies. Usually the unit
 287                 name is just an alias (symlink) for either
 288                 <filename>graphical.target</filename> (for
 289                 fully-featured boots into the UI) or
 290                 <filename>multi-user.target</filename> (for limited
 291                 console-only boots for use in embedded or server
 292                 environments, or similar; a subset of
 293                 graphical.target). However it is at the discretion of
 294                 the administrator to configure it as an alias to any
 295                 other target unit. See
 296                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 297                 for details about these target units.</para>
 298
 299                 <para>Processes systemd spawns ared placed in
 300                 individual Linux control groups named after the unit
 301                 which they belong to in the private systemd
 302                 hierarchy. (see <ulink
 303                 url="http://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 304                 for more information about control groups, or short
 305                 "cgroups"). systemd uses this to effectively keep
 306                 track of processes. Control group information is
 307                 maintained in the kernel, and is accessible via the
 308                 file system hierarchy (beneath
 309                 <filename>/cgroup/systemd/</filename>), or in tools
 310                 such as
 311                 <citerefentry><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 312                 (<command>ps xawf -eo pid,user,cgroup,args</command>
 313                 is particularly useful to list all processes and the
 314                 systemd units they belong to.).</para>
 315
 316                 <para>systemd is compatible with the SysV init system
 317                 to a large degree: SysV init scripts are supported and
 318                 simply read as an alternative (though limited)
 319                 configuration file format. The SysV
 320                 <filename>/dev/initctl</filename> interface is
 321                 provided, and comaptibility implementations of the
 322                 various SysV client tools available. In addition to
 323                 that various established Unix functionality such as
 324                 <filename>/etc/fstab</filename> or the
 325                 <filename>utmp</filename> database are
 326                 supported.</para>
 327
 328                 <para>systemd has a minimal transaction system: if a
 329                 unit is requested to start up or shut down it will add
 330                 it and all its dependencies to a temporary
 331                 transaction. Then, it will verify if the transaction
 332                 is consistent (i.e. whether the ordering of all units
 333                 is cycle-free). If it is not, systemd will try to fix
 334                 it up, and removes non-essential jobs from the
 335                 transaction that might remove the loop. Also, systemd
 336                 tries to suppress non-essential jobs in the
 337                 transaction that would stop a running service. Finally
 338                 it is checked whether the jobs of the transaction
 339                 contradict jobs that have already been queued, and
 340                 optionally the transaction is aborted then. If all
 341                 worked out and the transaction is consistent and
 342                 minimized in its impact it is merged with all already
 343                 outstanding jobs and added to the run
 344                 queue. Effectively this means that before executing a
 345                 requested operation, systemd will verify that it makes
 346                 sense, fixing it if possible, and only failing if it
 347                 really cannot work.</para>
 348
 349                 <para>Systemd contains native implementations of
 350                 various tasks that need to be executed as part of the
 351                 boot process. For example, it sets the host name or
 352                 configures the loopback network device. It also sets
 353                 up and mounts various API file systems, such as
 354                 <filename>/sys</filename> or
 355                 <filename>/proc</filename>.</para>
 356
 357                 <para>For more information about the concepts and
 358                 ideas behind systemd please refer to the <ulink
 359                 url="http://0pointer.de/blog/projects/systemd.html">Original
 360                 Design Document</ulink>.</para>
 361         </refsect1>
 362
 363         <refsect1>
 364                 <title>Directories</title>
 365
 366                 <variablelist>
 367                         <varlistentry>
 368                                 <term>System unit directories</term>
 369
 370                                 <listitem><para>The systemd system
 371                                 manager reads unit configuration from
 372                                 various directories. Packages that
 373                                 want to install unit files shall place
 374                                 them in the directory returned by
 375                                 <command>pkg-config systemd
 376                                 --variable=systemdsystemunitdir</command>. Other
 377                                 directories checked are
 378                                 <filename>/usr/local/share/systemd/system</filename>
 379                                 and
 380                                 <filename>/usr/share/systemd/system</filename>. User
 381                                 configuration always takes
 382                                 precedence. <command>pkg-config
 383                                 systemd
 384                                 --variable=systemdsystemconfdir</command>
 385                                 returns the path of the system
 386                                 configuration directory. Packages
 387                                 should alter the content of these directories
 388                                 only with the
 389                                 <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 390                                 tool.</para></listitem>
 391                         </varlistentry>
 392                 </variablelist>
 393
 394                 <variablelist>
 395                         <varlistentry>
 396                                 <term>Session unit directories</term>
 397
 398                                 <listitem><para>Similar rules apply
 399                                 for the session unit
 400                                 directories. However, here the <ulink
 401                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 402                                 Base Directory specification</ulink>
 403                                 is followed to find
 404                                 units. Applications should place their
 405                                 unit files in the directory returned
 406                                 by <command>pkg-config systemd
 407                                 --variable=systemdsessionunitdir</command>. Global
 408                                 configuration is done in the
 409                                 directory reported by
 410                                 <command>pkg-config systemd
 411                                 --variable=systemdsessionconfdir</command>. The
 412                                 <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 413                                 tool can handle both global (i.e. for
 414                                 all users) and private (for one user)
 415                                 enabling/disabling of
 416                                 units.</para></listitem>
 417                         </varlistentry>
 418                 </variablelist>
 419
 420                 <variablelist>
 421                         <varlistentry>
 422                                 <term>SysV init scripts directory</term>
 423
 424                                 <listitem><para>The location of the
 425                                 SysV init script directory varies
 426                                 between distributions. If systemd
 427                                 cannot find a native unit file for a
 428                                 requested service, it will look for a
 429                                 SysV init script of the same name
 430                                 (with the
 431                                 <filename>.service</filename> suffix
 432                                 removed).</para></listitem>
 433                         </varlistentry>
 434                 </variablelist>
 435
 436                 <variablelist>
 437                         <varlistentry>
 438                                 <term>SysV runlevel link farm directory</term>
 439
 440                                 <listitem><para>The location of the
 441                                 SysV runlevel link farm directory
 442                                 varies between distributions. systemd
 443                                 will take the link farm into account
 444                                 when figuring out whether a service
 445                                 shall be enabled. Note that a service
 446                                 unit with a native unit configuration
 447                                 file can be started by activating it
 448                                 in the SysV runlevel link
 449                                 farm.</para></listitem>
 450                         </varlistentry>
 451                 </variablelist>
 452         </refsect1>
 453
 454         <refsect1>
 455                 <title>Signals</title>
 456
 457                 <variablelist>
 458                         <varlistentry>
 459                                 <term>SIGTERM</term>
 460
 461                                 <listitem><para>Upon receiving this
 462                                 signal the systemd system manager
 463                                 serializes its state, reexecutes
 464                                 itself and deserializes the saved
 465                                 state again. This is mostly equivalent
 466                                 to <command>systemctl
 467                                 daemon-reexec</command>.</para>
 468
 469                                 <para>systemd session managers will
 470                                 start the
 471                                 <filename>exit.target</filename> unit
 472                                 when this signal is received. This is
 473                                 mostly equivalent to
 474                                 <command>systemctl --session start
 475                                 exit.target</command>.</para></listitem>
 476                         </varlistentry>
 477
 478                         <varlistentry>
 479                                 <term>SIGINT</term>
 480
 481                                 <listitem><para>Upon receiving this
 482                                 signal the systemd system manager will
 483                                 start the
 484                                 <filename>ctrl-alt-del.target</filename> unit. This
 485                                 is mostly equivalent to
 486                                 <command>systemctl start
 487                                 ctl-alt-del.target</command>.</para>
 488
 489                                 <para>systemd session managers
 490                                 treat this signal the same way as
 491                                 SIGTERM.</para></listitem>
 492                         </varlistentry>
 493
 494                         <varlistentry>
 495                                 <term>SIGWINCH</term>
 496
 497                                 <listitem><para>When this signal is
 498                                 received the systemd system manager
 499                                 will start the
 500                                 <filename>kbrequest.target</filename>
 501                                 unit. This is mostly equivalent to
 502                                 <command>systemctl start
 503                                 kbrequest.target</command>.</para>
 504
 505                                 <para>This signal is ignored by
 506                                 systemd session
 507                                 managers.</para></listitem>
 508                         </varlistentry>
 509
 510                         <varlistentry>
 511                                 <term>SIGPWR</term>
 512
 513                                 <listitem><para>When this signal is
 514                                 received the systemd manager
 515                                 will start the
 516                                 <filename>sigpwr.target</filename>
 517                                 unit. This is mostly equivalent to
 518                                 <command>systemctl start
 519                                 sigpwr.target</command>.</para></listitem>
 520                         </varlistentry>
 521
 522                         <varlistentry>
 523                                 <term>SIGUSR1</term>
 524
 525                                 <listitem><para>When this signal is
 526                                 received the systemd manager will try
 527                                 to reconnect to the D-Bus
 528                                 bus.</para></listitem>
 529                         </varlistentry>
 530
 531                         <varlistentry>
 532                                 <term>SIGUSR2</term>
 533
 534                                 <listitem><para>When this signal is
 535                                 received the systemd manager will log
 536                                 its complete state in human readable
 537                                 form. The data logged is the same as
 538                                 printed by <command>systemctl
 539                                 dump</command>.</para></listitem>
 540                         </varlistentry>
 541
 542                         <varlistentry>
 543                                 <term>SIGHUP</term>
 544
 545                                 <listitem><para>Reloads the complete
 546                                 daemon configuration. This is mostly
 547                                 equivalent to <command>systemctl
 548                                 daemon-reload</command>.</para></listitem>
 549                         </varlistentry>
 550
 551                         <varlistentry>
 552                                 <term>SIGRTMIN+0</term>
 553
 554                                 <listitem><para>Enters default mode, starts the
 555                                 <filename>default.target</filename>
 556                                 unit. This is mostly equivalent to
 557                                 <command>systemctl start
 558                                 default.target</command>.</para></listitem>
 559                         </varlistentry>
 560
 561                         <varlistentry>
 562                                 <term>SIGRTMIN+1</term>
 563
 564                                 <listitem><para>Enters rescue mode,
 565                                 starts the
 566                                 <filename>rescue.target</filename>
 567                                 unit. This is mostly equivalent to
 568                                 <command>systemctl isolate
 569                                 rescue.target</command>.</para></listitem>
 570                         </varlistentry>
 571
 572                         <varlistentry>
 573                                 <term>SIGRTMIN+2</term>
 574
 575                                 <listitem><para>Enters emergency mode,
 576                                 starts the
 577                                 <filename>emergency.service</filename>
 578                                 unit. This is mostly equivalent to
 579                                 <command>systemctl isolate
 580                                 emergency.service</command>.</para></listitem>
 581                         </varlistentry>
 582
 583                         <varlistentry>
 584                                 <term>SIGRTMIN+3</term>
 585
 586                                 <listitem><para>Halts the machine,
 587                                 starts the
 588                                 <filename>halt.target</filename>
 589                                 unit. This is mostly equivalent to
 590                                 <command>systemctl start
 591                                 halt.target</command>.</para></listitem>
 592                         </varlistentry>
 593
 594                         <varlistentry>
 595                                 <term>SIGRTMIN+4</term>
 596
 597                                 <listitem><para>Powers off the machine,
 598                                 starts the
 599                                 <filename>poweroff.target</filename>
 600                                 unit. This is mostly equivalent to
 601                                 <command>systemctl start
 602                                 poweroff.target</command>.</para></listitem>
 603                         </varlistentry>
 604
 605                         <varlistentry>
 606                                 <term>SIGRTMIN+5</term>
 607
 608                                 <listitem><para>Reboots the machine,
 609                                 starts the
 610                                 <filename>reboot.target</filename>
 611                                 unit. This is mostly equivalent to
 612                                 <command>systemctl start
 613                                 reboot.target</command>.</para></listitem>
 614                         </varlistentry>
 615                 </variablelist>
 616         </refsect1>
 617
 618         <refsect1>
 619                 <title>Environment</title>
 620
 621                 <variablelist>
 622                         <varlistentry>
 623                                 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 624                                 <listitem><para>systemd reads the
 625                                 log level from this environment
 626                                 variable. This can be overridden with
 627                                 <option>--log-level=</option>.</para></listitem>
 628                         </varlistentry>
 629
 630                         <varlistentry>
 631                                 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 632                                 <listitem><para>systemd reads the
 633                                 log target from this environment
 634                                 variable. This can be overridden with
 635                                 <option>--log-target=</option>.</para></listitem>
 636                         </varlistentry>
 637
 638                         <varlistentry>
 639                                 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 640                                 <listitem><para>Controls whether
 641                                 systemd highlights important log
 642                                 messages. This can be overridden with
 643                                 <option>--log-color=</option>.</para></listitem>
 644                         </varlistentry>
 645
 646                         <varlistentry>
 647                                 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 648                                 <listitem><para>Controls whether
 649                                 systemd prints the code location along
 650                                 with log messages. This can be
 651                                 overridden with
 652                                 <option>--log-location=</option>.</para></listitem>
 653                         </varlistentry>
 654
 655                         <varlistentry>
 656                                 <term><varname>$XDG_CONFIG_HOME</varname></term>
 657                                 <term><varname>$XDG_CONFIG_DIRS</varname></term>
 658                                 <term><varname>$XDG_DATA_HOME</varname></term>
 659                                 <term><varname>$XDG_DATA_DIRS</varname></term>
 660
 661                                 <listitem><para>The systemd session
 662                                 manager uses these variables in
 663                                 accordance to the <ulink
 664                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 665                                 Base Directory specification</ulink>
 666                                 to find its configuration.</para></listitem>
 667                         </varlistentry>
 668
 669                         <varlistentry>
 670                                 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 671
 672                                 <listitem><para>Controls where systemd
 673                                 looks for unit
 674                                 files.</para></listitem>
 675                         </varlistentry>
 676
 677                         <varlistentry>
 678                                 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 679
 680                                 <listitem><para>Controls where systemd
 681                                 looks for SysV init scripts.</para></listitem>
 682                         </varlistentry>
 683
 684                         <varlistentry>
 685                                 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 686
 687                                 <listitem><para>Controls where systemd
 688                                 looks for SysV init script runlevel link
 689                                 farms.</para></listitem>
 690                         </varlistentry>
 691
 692                         <varlistentry>
 693                                 <term><varname>$LISTEN_PID</varname></term>
 694                                 <term><varname>$LISTEN_FDS</varname></term>
 695
 696                                 <listitem><para>Set by systemd for
 697                                 supervised processes during
 698                                 socket-based activation. See
 699                                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 700                                 for more information.
 701                                 </para></listitem>
 702                         </varlistentry>
 703
 704                         <varlistentry>
 705                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 706
 707                                 <listitem><para>Set by systemd for
 708                                 supervised processes for status and
 709                                 start-up completion notification. See
 710                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 711                                 for more information.
 712                                 </para></listitem>
 713                         </varlistentry>
 714                 </variablelist>
 715         </refsect1>
 716
 717         <refsect1>
 718                 <title>Sockets and FIFOs</title>
 719
 720                 <variablelist>
 721                         <varlistentry>
 722                                 <term><filename>@/org/freedesktop/systemd1/notify</filename></term>
 723
 724                                 <listitem><para>Daemon status
 725                                 notification socket. This is an AF_UNIX
 726                                 datagram socket in the Linux abstract
 727                                 namespace, and is used to implement
 728                                 the daemon notification logic as
 729                                 implemented by
 730                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 731
 732                         </varlistentry>
 733
 734                         <varlistentry>
 735                                 <term><filename>@/org/freedesktop/systemd1/logger</filename></term>
 736
 737                                 <listitem><para>Used internally by the
 738                                 <filename>systemd-logger.service</filename>
 739                                 unit to connect STDOUT and/or STDERR
 740                                 of spawned processes to
 741                                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 742                                 or the kernel log buffer. This is an
 743                                 AF_UNIX stream socket in the Linux
 744                                 abstract namespace.</para></listitem>
 745                         </varlistentry>
 746
 747                         <varlistentry>
 748                                 <term><filename>@/org/freedesktop/systemd1/private</filename></term>
 749
 750                                 <listitem><para>Used internally as
 751                                 communication channel between
 752                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 753                                 and the systemd process. This is an
 754                                 AF_UNIX stream socket in the Linux
 755                                 abstract namespace. This interface is
 756                                 private to systemd and should not be
 757                                 used in external
 758                                 projects.</para></listitem>
 759                         </varlistentry>
 760
 761                         <varlistentry>
 762                                 <term><filename>/dev/initctl</filename></term>
 763
 764                                 <listitem><para>Limited compatibility
 765                                 support for the SysV client interface,
 766                                 as implemented by the
 767                                 <filename>systemd-initctl.service</filename>
 768                                 unit. This is a named pipe in the file
 769                                 system. This interface is obsolete and
 770                                 should not be used in new
 771                                 applications.</para></listitem>
 772                         </varlistentry>
 773                 </variablelist>
 774         </refsect1>
 775
 776         <refsect1>
 777                 <title>See Also</title>
 778                 <para>
 779                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 780                         <citerefentry><refentrytitle>systemadm</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 781                         <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 782                         <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 783                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 784                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 785                         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 786                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 787                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 788                 </para>
 789         </refsect1>
 790
 791 </refentry>