man/systemd.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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   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
  77                 <para>When run as system instance, systemd interprets
  78                 the configuration file
  79                 <filename>system.conf</filename>, otherwise
  80                 <filename>session.conf</filename>. See
  81                 <citerefentry><refentrytitle>systemd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  82                 for more information.</para>
  83         </refsect1>
  84
  85         <refsect1>
  86                 <title>Options</title>
  87
  88                 <para>The following options are understood:</para>
  89
  90                 <variablelist>
  91                         <varlistentry>
  92                                 <term><option>-h</option></term>
  93                                 <term><option>--help</option></term>
  94
  95                                 <listitem><para>Prints a short help
  96                                 text and exits.</para></listitem>
  97                         </varlistentry>
  98                         <varlistentry>
  99                                 <term><option>--test</option></term>
 100
 101                                 <listitem><para>Determine startup
 102                                 sequence, dump it and exit. This is an
 103                                 option useful for debugging
 104                                 only.</para></listitem>
 105                         </varlistentry>
 106                         <varlistentry>
 107                                 <term><option>--dump-configuration-items</option></term>
 108
 109                                 <listitem><para>Dump understood unit
 110                                 configuration items. This outputs a
 111                                 terse but complete list of
 112                                 configuration items understood in unit
 113                                 definition files.</para></listitem>
 114                         </varlistentry>
 115                         <varlistentry>
 116                                 <term><option>--introspect=</option></term>
 117
 118                                 <listitem><para>Extract D-Bus
 119                                 interface introspection data. This is
 120                                 mostly useful at install time
 121                                 to generate data suitable for the
 122                                 D-Bus interfaces
 123                                 repository. Optionally the interface
 124                                 name for the introspection data may be
 125                                 specified. If omitted, the
 126                                 introspection data for all interfaces
 127                                 is dumped.</para></listitem>
 128                         </varlistentry>
 129                         <varlistentry>
 130                                 <term><option>--unit=</option></term>
 131
 132                                 <listitem><para>Set default unit to
 133                                 activate on startup. If not specified
 134                                 defaults to
 135                                 <filename>default.target</filename>.</para></listitem>
 136                         </varlistentry>
 137                         <varlistentry>
 138                                 <term><option>--system</option></term>
 139                                 <term><option>--session</option></term>
 140
 141                                 <listitem><para>Tell systemd to run a
 142                                 system instance (resp. session
 143                                 instance), even if the process ID is
 144                                 not 1 (resp. is 1), i.e. system is not
 145                                 (resp. is) run as init process.
 146                                 Normally it should not be necessary to
 147                                 pass these options, as systemd
 148                                 automatically detects the mode it is
 149                                 started in. These options are hence of
 150                                 little use except for
 151                                 debugging.</para></listitem>
 152                         </varlistentry>
 153                         <varlistentry>
 154                                 <term><option>--dump-core</option></term>
 155
 156                                 <listitem><para>Dump core on crash. This switch has no effect when run as session instance.</para></listitem>
 157                         </varlistentry>
 158                         <varlistentry>
 159                                 <term><option>--crash-shell</option></term>
 160
 161                                 <listitem><para>Run shell on crash. This switch has no effect when run as session instance.</para></listitem>
 162                         </varlistentry>
 163                         <varlistentry>
 164                                 <term><option>--confirm-spawn</option></term>
 165
 166                                 <listitem><para>Ask for confirmation when spawning processes. This switch has no effect when run as session instance.</para></listitem>
 167                         </varlistentry>
 168                         <varlistentry>
 169                                 <term><option>--show-status</option></term>
 170
 171                                 <listitem><para>Show terse service status information while booting. This switch has no effect when run as session instance.</para></listitem>
 172                         </varlistentry>
 173                         <varlistentry>
 174                                 <term><option>--log-target=</option></term>
 175
 176                                 <listitem><para>Set log
 177                                 target. Argument must be one of
 178                                 <option>console</option>,
 179                                 <option>syslog</option>,
 180                                 <option>kmsg</option>,
 181                                 <option>syslog-or-kmsg</option>,
 182                                 <option>null</option>.</para></listitem>
 183                         </varlistentry>
 184                         <varlistentry>
 185                                 <term><option>--log-level=</option></term>
 186
 187                                 <listitem><para>Set log level. As
 188                                 argument this accepts a numerical log
 189                                 level or the well-known <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 190                                 symbolic names (lowercase):
 191                                 <option>emerg</option>,
 192                                 <option>alert</option>,
 193                                 <option>crit</option>,
 194                                 <option>err</option>,
 195                                 <option>warning</option>,
 196                                 <option>notice</option>,
 197                                 <option>info</option>,
 198                                 <option>debug</option>.</para></listitem>
 199                         </varlistentry>
 200                         <varlistentry>
 201                                 <term><option>--log-color=</option></term>
 202
 203                                 <listitem><para>Highlight important
 204                                 log messages. Argument is a boolean
 205                                 value. If the argument is omitted it
 206                                 defaults to
 207                                 <option>true</option>.</para></listitem>
 208                         </varlistentry>
 209                         <varlistentry>
 210                                 <term><option>--log-location=</option></term>
 211
 212                                 <listitem><para>Include code location
 213                                 in log messages. This is mostly
 214                                 relevant for debugging
 215                                 purposes. Argument is a boolean
 216                                 value. If the argument is omitted
 217                                 it defaults to
 218                                 <option>true</option>.</para></listitem>
 219                         </varlistentry>
 220                 </variablelist>
 221         </refsect1>
 222
 223         <refsect1>
 224                 <title>Concepts</title>
 225
 226                 <para>systemd provides a dependency system between
 227                 various entities called "units". Units encapsulate
 228                 various objects that are relevant for system boot-up
 229                 and maintainance. The majority of units are configured
 230                 in unit configuration files, whose syntax and basic
 231                 set of options is described in
 232                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 233                 however some are created automatically from other
 234                 configuration or dynamically from system state. Units
 235                 may be active (meaning started, bound, plugged in, ...
 236                 depending on the unit type), or inactive (meaning
 237                 stopped, unbound, unplugged, ...), as well as in the
 238                 process of being activated or deactivated,
 239                 i.e. between the two states. The following unit types
 240                 are available:</para>
 241
 242                 <orderedlist>
 243                         <listitem><para>Service units, which control
 244                         daemons and the processes they consist of. For
 245                         details see
 246                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 247
 248                         <listitem><para>Socket units, which
 249                         encapsulate local IPC or network sockets in
 250                         the system, useful for socket-based
 251                         activation. For details about socket units see
 252                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 253                         for details on socket-based activation and
 254                         other forms of activation, see
 255                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 256
 257                         <listitem><para>Target units are useful to
 258                         group units, or provide well-known
 259                         synchronization points during boot-up, see
 260                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 261
 262                         <listitem><para>Device units expose kernel
 263                         devices in systemd and may be used to
 264                         implement device-based activation. For details
 265                         see
 266                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 267
 268                         <listitem><para>Mount units control mount
 269                         points in the file system, for details see
 270                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 271
 272                         <listitem><para>Automount units provide
 273                         automount capabilities, for on-demand mounting
 274                         of file systems as well as parallelized
 275                         boot-up. See
 276                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 277
 278                         <listitem><para>Snapshot units can be used to
 279                         temporarily save the state of the set of
 280                         systemd units, which later may be restored by
 281                         activating the saved snapshot unit. For more
 282                         information see
 283                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 284
 285                         <listitem><para>Timer units are useful for
 286                         triggering activation of other units based on
 287                         timers. You may find details in
 288                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 289
 290                         <listitem><para>Swap units are very similar to
 291                         mount units and encapsulated memory swap
 292                         partitions or files of the operating
 293                         systemd. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 294
 295                         <listitem><para>Path units may be used
 296                         to activate other services when file system
 297                         objects change or are modified. See
 298                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 299
 300                 </orderedlist>
 301
 302                 <para>Units are named as their configuration
 303                 files. Some units have special semantics. A detailed
 304                 list you may find in
 305                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 306
 307                 <para>On boot systemd activates the target unit
 308                 <filename>default.target</filename> whose job is to
 309                 activate on-boot services and other on-boot units by
 310                 pulling them in via dependencies. Usually the unit
 311                 name is just an alias (symlink) for either
 312                 <filename>graphical.target</filename> (for
 313                 fully-featured boots into the UI) or
 314                 <filename>multi-user.target</filename> (for limited
 315                 console-only boots for use in embedded or server
 316                 environments, or similar; a subset of
 317                 graphical.target). However it is at the discretion of
 318                 the administrator to configure it as an alias to any
 319                 other target unit. See
 320                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 321                 for details about these target units.</para>
 322
 323                 <para>Processes systemd spawns are placed in
 324                 individual Linux control groups named after the unit
 325                 which they belong to in the private systemd
 326                 hierarchy. (see <ulink
 327                 url="http://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 328                 for more information about control groups, or short
 329                 "cgroups"). systemd uses this to effectively keep
 330                 track of processes. Control group information is
 331                 maintained in the kernel, and is accessible via the
 332                 file system hierarchy (beneath
 333                 <filename>/cgroup/systemd/</filename>), or in tools
 334                 such as
 335                 <citerefentry><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 336                 (<command>ps xawf -eo pid,user,cgroup,args</command>
 337                 is particularly useful to list all processes and the
 338                 systemd units they belong to.).</para>
 339
 340                 <para>systemd is compatible with the SysV init system
 341                 to a large degree: SysV init scripts are supported and
 342                 simply read as an alternative (though limited)
 343                 configuration file format. The SysV
 344                 <filename>/dev/initctl</filename> interface is
 345                 provided, and compatibility implementations of the
 346                 various SysV client tools are available. In addition to
 347                 that, various established Unix functionality such as
 348                 <filename>/etc/fstab</filename> or the
 349                 <filename>utmp</filename> database are
 350                 supported.</para>
 351
 352                 <para>systemd has a minimal transaction system: if a
 353                 unit is requested to start up or shut down it will add
 354                 it and all its dependencies to a temporary
 355                 transaction. Then, it will verify if the transaction
 356                 is consistent (i.e. whether the ordering of all units
 357                 is cycle-free). If it is not, systemd will try to fix
 358                 it up, and removes non-essential jobs from the
 359                 transaction that might remove the loop. Also, systemd
 360                 tries to suppress non-essential jobs in the
 361                 transaction that would stop a running service. Finally
 362                 it is checked whether the jobs of the transaction
 363                 contradict jobs that have already been queued, and
 364                 optionally the transaction is aborted then. If all
 365                 worked out and the transaction is consistent and
 366                 minimized in its impact it is merged with all already
 367                 outstanding jobs and added to the run
 368                 queue. Effectively this means that before executing a
 369                 requested operation, systemd will verify that it makes
 370                 sense, fixing it if possible, and only failing if it
 371                 really cannot work.</para>
 372
 373                 <para>Systemd contains native implementations of
 374                 various tasks that need to be executed as part of the
 375                 boot process. For example, it sets the host name or
 376                 configures the loopback network device. It also sets
 377                 up and mounts various API file systems, such as
 378                 <filename>/sys</filename> or
 379                 <filename>/proc</filename>.</para>
 380
 381                 <para>For more information about the concepts and
 382                 ideas behind systemd please refer to the <ulink
 383                 url="http://0pointer.de/blog/projects/systemd.html">Original
 384                 Design Document</ulink>.</para>
 385         </refsect1>
 386
 387         <refsect1>
 388                 <title>Directories</title>
 389
 390                 <variablelist>
 391                         <varlistentry>
 392                                 <term>System unit directories</term>
 393
 394                                 <listitem><para>The systemd system
 395                                 manager reads unit configuration from
 396                                 various directories. Packages that
 397                                 want to install unit files shall place
 398                                 them in the directory returned by
 399                                 <command>pkg-config systemd
 400                                 --variable=systemdsystemunitdir</command>. Other
 401                                 directories checked are
 402                                 <filename>/usr/local/share/systemd/system</filename>
 403                                 and
 404                                 <filename>/usr/share/systemd/system</filename>. User
 405                                 configuration always takes
 406                                 precedence. <command>pkg-config
 407                                 systemd
 408                                 --variable=systemdsystemconfdir</command>
 409                                 returns the path of the system
 410                                 configuration directory. Packages
 411                                 should alter the content of these directories
 412                                 only with the
 413                                 <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 414                                 tool.</para></listitem>
 415                         </varlistentry>
 416                 </variablelist>
 417
 418                 <variablelist>
 419                         <varlistentry>
 420                                 <term>Session unit directories</term>
 421
 422                                 <listitem><para>Similar rules apply
 423                                 for the session unit
 424                                 directories. However, here the <ulink
 425                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 426                                 Base Directory specification</ulink>
 427                                 is followed to find
 428                                 units. Applications should place their
 429                                 unit files in the directory returned
 430                                 by <command>pkg-config systemd
 431                                 --variable=systemdsessionunitdir</command>. Global
 432                                 configuration is done in the
 433                                 directory reported by
 434                                 <command>pkg-config systemd
 435                                 --variable=systemdsessionconfdir</command>. The
 436                                 <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 437                                 tool can handle both global (i.e. for
 438                                 all users) and private (for one user)
 439                                 enabling/disabling of
 440                                 units.</para></listitem>
 441                         </varlistentry>
 442                 </variablelist>
 443
 444                 <variablelist>
 445                         <varlistentry>
 446                                 <term>SysV init scripts directory</term>
 447
 448                                 <listitem><para>The location of the
 449                                 SysV init script directory varies
 450                                 between distributions. If systemd
 451                                 cannot find a native unit file for a
 452                                 requested service, it will look for a
 453                                 SysV init script of the same name
 454                                 (with the
 455                                 <filename>.service</filename> suffix
 456                                 removed).</para></listitem>
 457                         </varlistentry>
 458                 </variablelist>
 459
 460                 <variablelist>
 461                         <varlistentry>
 462                                 <term>SysV runlevel link farm directory</term>
 463
 464                                 <listitem><para>The location of the
 465                                 SysV runlevel link farm directory
 466                                 varies between distributions. systemd
 467                                 will take the link farm into account
 468                                 when figuring out whether a service
 469                                 shall be enabled. Note that a service
 470                                 unit with a native unit configuration
 471                                 file cannot be started by activating it
 472                                 in the SysV runlevel link
 473                                 farm.</para></listitem>
 474                         </varlistentry>
 475                 </variablelist>
 476         </refsect1>
 477
 478         <refsect1>
 479                 <title>Signals</title>
 480
 481                 <variablelist>
 482                         <varlistentry>
 483                                 <term>SIGTERM</term>
 484
 485                                 <listitem><para>Upon receiving this
 486                                 signal the systemd system manager
 487                                 serializes its state, reexecutes
 488                                 itself and deserializes the saved
 489                                 state again. This is mostly equivalent
 490                                 to <command>systemctl
 491                                 daemon-reexec</command>.</para>
 492
 493                                 <para>systemd session managers will
 494                                 start the
 495                                 <filename>exit.target</filename> unit
 496                                 when this signal is received. This is
 497                                 mostly equivalent to
 498                                 <command>systemctl --session start
 499                                 exit.target</command>.</para></listitem>
 500                         </varlistentry>
 501
 502                         <varlistentry>
 503                                 <term>SIGINT</term>
 504
 505                                 <listitem><para>Upon receiving this
 506                                 signal the systemd system manager will
 507                                 start the
 508                                 <filename>ctrl-alt-del.target</filename> unit. This
 509                                 is mostly equivalent to
 510                                 <command>systemctl start
 511                                 ctl-alt-del.target</command>.</para>
 512
 513                                 <para>systemd session managers
 514                                 treat this signal the same way as
 515                                 SIGTERM.</para></listitem>
 516                         </varlistentry>
 517
 518                         <varlistentry>
 519                                 <term>SIGWINCH</term>
 520
 521                                 <listitem><para>When this signal is
 522                                 received the systemd system manager
 523                                 will start the
 524                                 <filename>kbrequest.target</filename>
 525                                 unit. This is mostly equivalent to
 526                                 <command>systemctl start
 527                                 kbrequest.target</command>.</para>
 528
 529                                 <para>This signal is ignored by
 530                                 systemd session
 531                                 managers.</para></listitem>
 532                         </varlistentry>
 533
 534                         <varlistentry>
 535                                 <term>SIGPWR</term>
 536
 537                                 <listitem><para>When this signal is
 538                                 received the systemd manager
 539                                 will start the
 540                                 <filename>sigpwr.target</filename>
 541                                 unit. This is mostly equivalent to
 542                                 <command>systemctl start
 543                                 sigpwr.target</command>.</para></listitem>
 544                         </varlistentry>
 545
 546                         <varlistentry>
 547                                 <term>SIGUSR1</term>
 548
 549                                 <listitem><para>When this signal is
 550                                 received the systemd manager will try
 551                                 to reconnect to the D-Bus
 552                                 bus.</para></listitem>
 553                         </varlistentry>
 554
 555                         <varlistentry>
 556                                 <term>SIGUSR2</term>
 557
 558                                 <listitem><para>When this signal is
 559                                 received the systemd manager will log
 560                                 its complete state in human readable
 561                                 form. The data logged is the same as
 562                                 printed by <command>systemctl
 563                                 dump</command>.</para></listitem>
 564                         </varlistentry>
 565
 566                         <varlistentry>
 567                                 <term>SIGHUP</term>
 568
 569                                 <listitem><para>Reloads the complete
 570                                 daemon configuration. This is mostly
 571                                 equivalent to <command>systemctl
 572                                 daemon-reload</command>.</para></listitem>
 573                         </varlistentry>
 574
 575                         <varlistentry>
 576                                 <term>SIGRTMIN+0</term>
 577
 578                                 <listitem><para>Enters default mode, starts the
 579                                 <filename>default.target</filename>
 580                                 unit. This is mostly equivalent to
 581                                 <command>systemctl start
 582                                 default.target</command>.</para></listitem>
 583                         </varlistentry>
 584
 585                         <varlistentry>
 586                                 <term>SIGRTMIN+1</term>
 587
 588                                 <listitem><para>Enters rescue mode,
 589                                 starts the
 590                                 <filename>rescue.target</filename>
 591                                 unit. This is mostly equivalent to
 592                                 <command>systemctl isolate
 593                                 rescue.target</command>.</para></listitem>
 594                         </varlistentry>
 595
 596                         <varlistentry>
 597                                 <term>SIGRTMIN+2</term>
 598
 599                                 <listitem><para>Enters emergency mode,
 600                                 starts the
 601                                 <filename>emergency.service</filename>
 602                                 unit. This is mostly equivalent to
 603                                 <command>systemctl isolate
 604                                 emergency.service</command>.</para></listitem>
 605                         </varlistentry>
 606
 607                         <varlistentry>
 608                                 <term>SIGRTMIN+3</term>
 609
 610                                 <listitem><para>Halts the machine,
 611                                 starts the
 612                                 <filename>halt.target</filename>
 613                                 unit. This is mostly equivalent to
 614                                 <command>systemctl start
 615                                 halt.target</command>.</para></listitem>
 616                         </varlistentry>
 617
 618                         <varlistentry>
 619                                 <term>SIGRTMIN+4</term>
 620
 621                                 <listitem><para>Powers off the machine,
 622                                 starts the
 623                                 <filename>poweroff.target</filename>
 624                                 unit. This is mostly equivalent to
 625                                 <command>systemctl start
 626                                 poweroff.target</command>.</para></listitem>
 627                         </varlistentry>
 628
 629                         <varlistentry>
 630                                 <term>SIGRTMIN+5</term>
 631
 632                                 <listitem><para>Reboots the machine,
 633                                 starts the
 634                                 <filename>reboot.target</filename>
 635                                 unit. This is mostly equivalent to
 636                                 <command>systemctl start
 637                                 reboot.target</command>.</para></listitem>
 638                         </varlistentry>
 639                 </variablelist>
 640         </refsect1>
 641
 642         <refsect1>
 643                 <title>Environment</title>
 644
 645                 <variablelist>
 646                         <varlistentry>
 647                                 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 648                                 <listitem><para>systemd reads the
 649                                 log level from this environment
 650                                 variable. This can be overridden with
 651                                 <option>--log-level=</option>.</para></listitem>
 652                         </varlistentry>
 653
 654                         <varlistentry>
 655                                 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 656                                 <listitem><para>systemd reads the
 657                                 log target from this environment
 658                                 variable. This can be overridden with
 659                                 <option>--log-target=</option>.</para></listitem>
 660                         </varlistentry>
 661
 662                         <varlistentry>
 663                                 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 664                                 <listitem><para>Controls whether
 665                                 systemd highlights important log
 666                                 messages. This can be overridden with
 667                                 <option>--log-color=</option>.</para></listitem>
 668                         </varlistentry>
 669
 670                         <varlistentry>
 671                                 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 672                                 <listitem><para>Controls whether
 673                                 systemd prints the code location along
 674                                 with log messages. This can be
 675                                 overridden with
 676                                 <option>--log-location=</option>.</para></listitem>
 677                         </varlistentry>
 678
 679                         <varlistentry>
 680                                 <term><varname>$XDG_CONFIG_HOME</varname></term>
 681                                 <term><varname>$XDG_CONFIG_DIRS</varname></term>
 682                                 <term><varname>$XDG_DATA_HOME</varname></term>
 683                                 <term><varname>$XDG_DATA_DIRS</varname></term>
 684
 685                                 <listitem><para>The systemd session
 686                                 manager uses these variables in
 687                                 accordance to the <ulink
 688                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 689                                 Base Directory specification</ulink>
 690                                 to find its configuration.</para></listitem>
 691                         </varlistentry>
 692
 693                         <varlistentry>
 694                                 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 695
 696                                 <listitem><para>Controls where systemd
 697                                 looks for unit
 698                                 files.</para></listitem>
 699                         </varlistentry>
 700
 701                         <varlistentry>
 702                                 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 703
 704                                 <listitem><para>Controls where systemd
 705                                 looks for SysV init scripts.</para></listitem>
 706                         </varlistentry>
 707
 708                         <varlistentry>
 709                                 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 710
 711                                 <listitem><para>Controls where systemd
 712                                 looks for SysV init script runlevel link
 713                                 farms.</para></listitem>
 714                         </varlistentry>
 715
 716                         <varlistentry>
 717                                 <term><varname>$LISTEN_PID</varname></term>
 718                                 <term><varname>$LISTEN_FDS</varname></term>
 719
 720                                 <listitem><para>Set by systemd for
 721                                 supervised processes during
 722                                 socket-based activation. See
 723                                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 724                                 for more information.
 725                                 </para></listitem>
 726                         </varlistentry>
 727
 728                         <varlistentry>
 729                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 730
 731                                 <listitem><para>Set by systemd for
 732                                 supervised processes for status and
 733                                 start-up completion notification. See
 734                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 735                                 for more information.
 736                                 </para></listitem>
 737                         </varlistentry>
 738                 </variablelist>
 739         </refsect1>
 740
 741         <refsect1>
 742                 <title>Kernel Command Line</title>
 743
 744                 <para>When run as system instance systemd parses a few kernel command line arguments:</para>
 745
 746                 <variablelist>
 747                         <varlistentry>
 748                                 <term><varname>systemd.unit=</varname></term>
 749
 750                                 <listitem><para>Overrides the unit to
 751                                 activate on boot. Defaults to
 752                                 <filename>default.target</filename>. This
 753                                 may be used to temporarily boot into a
 754                                 different boot unit, for example
 755                                 <filename>rescue.target</filename> or
 756                                 <filename>emergency.service</filename>. See
 757                                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 758                                 for details about these
 759                                 units.</para></listitem>
 760                         </varlistentry>
 761
 762                         <varlistentry>
 763                                 <term><varname>systemd.log_target=</varname></term>
 764                                 <term><varname>systemd.log_level=</varname></term>
 765                                 <term><varname>systemd.log_color=</varname></term>
 766                                 <term><varname>systemd.log_location=</varname></term>
 767
 768                                 <listitem><para>Controls log output,
 769                                 with the same effect as the
 770                                 <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
 771                                 environment variables described above.</para></listitem>
 772                         </varlistentry>
 773
 774                         <varlistentry>
 775                                 <term><varname>systemd.dump_core=</varname></term>
 776
 777                                 <listitem><para>Takes a boolean
 778                                 argument. If <option>true</option>
 779                                 systemd dumps core when it
 780                                 crashes. Otherwise no core dump is
 781                                 created. Defaults to
 782                                 <option>true</option>.</para></listitem>
 783                         </varlistentry>
 784
 785                         <varlistentry>
 786                                 <term><varname>systemd.crash_shell=</varname></term>
 787
 788                                 <listitem><para>Takes a boolean
 789                                 argument. If <option>true</option>
 790                                 systemd spawns a shell when it
 791                                 crashes. Otherwise no core dump is
 792                                 created. Defaults to
 793                                 <option>false</option>, for security
 794                                 reasons, as the shell is not protected
 795                                 by any password
 796                                 authentication.</para></listitem>
 797                         </varlistentry>
 798
 799                         <varlistentry>
 800                                 <term><varname>systemd.crash_chvt=</varname></term>
 801
 802                                 <listitem><para>Takes an integer
 803                                 argument. If positive systemd
 804                                 activates the specified virtual
 805                                 terminal when it crashes. Defaults to
 806                                 <literal>-1</literal>.</para></listitem>
 807                         </varlistentry>
 808
 809                         <varlistentry>
 810                                 <term><varname>systemd.show_status=</varname></term>
 811
 812                                 <listitem><para>Takes a boolean
 813                                 argument. If <option>true</option>
 814                                 shows terse service status updates on
 815                                 the console during bootup. Defaults to
 816                                 <option>true</option>.</para></listitem>
 817                         </varlistentry>
 818
 819                 </variablelist>
 820         </refsect1>
 821
 822         <refsect1>
 823                 <title>Sockets and FIFOs</title>
 824
 825                 <variablelist>
 826                         <varlistentry>
 827                                 <term><filename>@/org/freedesktop/systemd1/notify</filename></term>
 828
 829                                 <listitem><para>Daemon status
 830                                 notification socket. This is an AF_UNIX
 831                                 datagram socket in the Linux abstract
 832                                 namespace, and is used to implement
 833                                 the daemon notification logic as
 834                                 implemented by
 835                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 836
 837                         </varlistentry>
 838
 839                         <varlistentry>
 840                                 <term><filename>@/org/freedesktop/systemd1/logger</filename></term>
 841
 842                                 <listitem><para>Used internally by the
 843                                 <filename>systemd-logger.service</filename>
 844                                 unit to connect STDOUT and/or STDERR
 845                                 of spawned processes to
 846                                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 847                                 or the kernel log buffer. This is an
 848                                 AF_UNIX stream socket in the Linux
 849                                 abstract namespace.</para></listitem>
 850                         </varlistentry>
 851
 852                         <varlistentry>
 853                                 <term><filename>@/org/freedesktop/systemd1/private</filename></term>
 854
 855                                 <listitem><para>Used internally as
 856                                 communication channel between
 857                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 858                                 and the systemd process. This is an
 859                                 AF_UNIX stream socket in the Linux
 860                                 abstract namespace. This interface is
 861                                 private to systemd and should not be
 862                                 used in external
 863                                 projects.</para></listitem>
 864                         </varlistentry>
 865
 866                         <varlistentry>
 867                                 <term><filename>/dev/initctl</filename></term>
 868
 869                                 <listitem><para>Limited compatibility
 870                                 support for the SysV client interface,
 871                                 as implemented by the
 872                                 <filename>systemd-initctl.service</filename>
 873                                 unit. This is a named pipe in the file
 874                                 system. This interface is obsolete and
 875                                 should not be used in new
 876                                 applications.</para></listitem>
 877                         </varlistentry>
 878                 </variablelist>
 879         </refsect1>
 880
 881         <refsect1>
 882                 <title>See Also</title>
 883                 <para>
 884                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 885                         <citerefentry><refentrytitle>systemadm</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 886                         <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 887                         <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 888                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 889                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 890                         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 891                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 892                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 893                 </para>
 894         </refsect1>
 895
 896 </refentry>