man/systemd.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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   5 <!--
   6   This file is part of systemd.
   7
   8   Copyright 2010 Lennart Poettering
   9
  10   systemd is free software; you can redistribute it and/or modify it
  11   under the terms of the GNU 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>--running-as=</option></term>
 139
 140                                 <listitem><para>Tell systemd to run in
 141                                 a particular mode. Argument is one of
 142                                 <option>system</option>,
 143                                 <option>session</option>. Normally it
 144                                 should not be necessary to pass this
 145                                 option, as systemd automatically
 146                                 detects the mode it is started
 147                                 in. This call is hence of little use
 148                                 except for
 149                                 debugging.</para></listitem>
 150                         </varlistentry>
 151                         <varlistentry>
 152                                 <term><option>--dump-core</option></term>
 153
 154                                 <listitem><para>Dump core on crash. This switch has no effect when run as session instance.</para></listitem>
 155                         </varlistentry>
 156                         <varlistentry>
 157                                 <term><option>--crash-shell</option></term>
 158
 159                                 <listitem><para>Run shell on crash. This switch has no effect when run as session instance.</para></listitem>
 160                         </varlistentry>
 161                         <varlistentry>
 162                                 <term><option>--confirm-spawn</option></term>
 163
 164                                 <listitem><para>Ask for confirmation when spawning processes. This switch has no effect when run as session instance.</para></listitem>
 165                         </varlistentry>
 166                         <varlistentry>
 167                                 <term><option>--show-status</option></term>
 168
 169                                 <listitem><para>Show terse service status information while booting. This switch has no effect when run as session instance.</para></listitem>
 170                         </varlistentry>
 171                         <varlistentry>
 172                                 <term><option>--log-target=</option></term>
 173
 174                                 <listitem><para>Set log
 175                                 target. Argument must be one of
 176                                 <option>console</option>,
 177                                 <option>syslog</option>,
 178                                 <option>kmsg</option>,
 179                                 <option>syslog-or-kmsg</option>,
 180                                 <option>null</option>.</para></listitem>
 181                         </varlistentry>
 182                         <varlistentry>
 183                                 <term><option>--log-level=</option></term>
 184
 185                                 <listitem><para>Set log level. As
 186                                 argument this accepts a numerical log
 187                                 level or the well-known <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 188                                 symbolic names (lowercase):
 189                                 <option>emerg</option>,
 190                                 <option>alert</option>,
 191                                 <option>crit</option>,
 192                                 <option>err</option>,
 193                                 <option>warning</option>,
 194                                 <option>notice</option>,
 195                                 <option>info</option>,
 196                                 <option>debug</option>.</para></listitem>
 197                         </varlistentry>
 198                         <varlistentry>
 199                                 <term><option>--log-color=</option></term>
 200
 201                                 <listitem><para>Highlight important
 202                                 log messages. Argument is a boolean
 203                                 value. If the argument is omitted it
 204                                 defaults to
 205                                 <option>true</option>.</para></listitem>
 206                         </varlistentry>
 207                         <varlistentry>
 208                                 <term><option>--log-location=</option></term>
 209
 210                                 <listitem><para>Include code location
 211                                 in log messages. This is mostly
 212                                 relevant for debugging
 213                                 purposes. Argument is a boolean
 214                                 value. If the argument is omitted
 215                                 it defaults to
 216                                 <option>true</option>.</para></listitem>
 217                         </varlistentry>
 218                 </variablelist>
 219         </refsect1>
 220
 221         <refsect1>
 222                 <title>Concepts</title>
 223
 224                 <para>systemd provides a dependency system between
 225                 various entities called "units". Units encapsulate
 226                 various objects that are relevant for system boot-up
 227                 and maintainance. The majority of units are configured
 228                 in unit configuration files, whose syntax and basic
 229                 set of options is described in
 230                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 231                 however some are created automatically from other
 232                 configuration or dynamically from system state. Units
 233                 may be active (meaning started, bound, plugged in, ...
 234                 depending on the unit type), or inactive (meaning
 235                 stopped, unbound, unplugged, ...), as well is in the
 236                 process of being activated or deactivated,
 237                 i.e. between the two states. The following unit types
 238                 are available:</para>
 239
 240                 <orderedlist>
 241                         <listitem><para>Service units, which control
 242                         daemons and the processes they consist of. For
 243                         details see
 244                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 245
 246                         <listitem><para>Socket units, which
 247                         encapsulate local IPC or network sockets in
 248                         the system, useful for socket-based
 249                         activation. For details about socket units see
 250                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 251                         for details on socket-based activation and
 252                         other forms of activation, see
 253                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 254
 255                         <listitem><para>Target units are useful to
 256                         group units, or provide well-known
 257                         synchronization points during boot-up, see
 258                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 259
 260                         <listitem><para>Device units expose kernel
 261                         devices in systemd and may be used to
 262                         implement device-based activation. For details
 263                         see
 264                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 265
 266                         <listitem><para>Mount units control mount
 267                         points in the file system, for details see
 268                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 269
 270                         <listitem><para>Automount units provide
 271                         automount capabilities, for on-demand mounting
 272                         of file systems as well as parallelized
 273                         boot-up. See
 274                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 275
 276                         <listitem><para>Snapshot units can be used to
 277                         temporarily save the state of the set of
 278                         systemd units, which later may be restored by
 279                         activating the saved snapshot unit. For more
 280                         information see
 281                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 282
 283                         <listitem><para>Timer units are useful for
 284                         triggering activation of other units based on
 285                         timers. You may find details in
 286                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 287
 288                         <listitem><para>Swap units are very similar to
 289                         mount units and encapsulated memory swap
 290                         partitions or files of the operating
 291                         systemd. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 292
 293                         <listitem><para>Path units may be used
 294                         activate other services when file system
 295                         objects change or are modified. See
 296                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 297
 298                 </orderedlist>
 299
 300                 <para>Units are named as their configuration
 301                 files. Some units have special semantics. A detailed
 302                 list you may find in
 303                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 304
 305                 <para>On boot systemd activates the target unit
 306                 <filename>default.target</filename> whose job it is to
 307                 activate on-boot services and other on-boot units by
 308                 pulling them in via dependencies. Usually the unit
 309                 name is just an alias (symlink) for either
 310                 <filename>graphical.target</filename> (for
 311                 fully-featured boots into the UI) or
 312                 <filename>multi-user.target</filename> (for limited
 313                 console-only boots for use in embedded or server
 314                 environments, or similar; a subset of
 315                 graphical.target). However it is at the discretion of
 316                 the administrator to configure it as an alias to any
 317                 other target unit. See
 318                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 319                 for details about these target units.</para>
 320
 321                 <para>Processes systemd spawns ared placed in
 322                 individual Linux control groups named after the unit
 323                 which they belong to in the private systemd
 324                 hierarchy. (see <ulink
 325                 url="http://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 326                 for more information about control groups, or short
 327                 "cgroups"). systemd uses this to effectively keep
 328                 track of processes. Control group information is
 329                 maintained in the kernel, and is accessible via the
 330                 file system hierarchy (beneath
 331                 <filename>/cgroup/systemd/</filename>), or in tools
 332                 such as
 333                 <citerefentry><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 334                 (<command>ps xawf -eo pid,user,cgroup,args</command>
 335                 is particularly useful to list all processes and the
 336                 systemd units they belong to.).</para>
 337
 338                 <para>systemd is compatible with the SysV init system
 339                 to a large degree: SysV init scripts are supported and
 340                 simply read as an alternative (though limited)
 341                 configuration file format. The SysV
 342                 <filename>/dev/initctl</filename> interface is
 343                 provided, and comaptibility implementations of the
 344                 various SysV client tools available. In addition to
 345                 that various established Unix functionality such as
 346                 <filename>/etc/fstab</filename> or the
 347                 <filename>utmp</filename> database are
 348                 supported.</para>
 349
 350                 <para>systemd has a minimal transaction system: if a
 351                 unit is requested to start up or shut down it will add
 352                 it and all its dependencies to a temporary
 353                 transaction. Then, it will verify if the transaction
 354                 is consistent (i.e. whether the ordering of all units
 355                 is cycle-free). If it is not, systemd will try to fix
 356                 it up, and removes non-essential jobs from the
 357                 transaction that might remove the loop. Also, systemd
 358                 tries to suppress non-essential jobs in the
 359                 transaction that would stop a running service. Finally
 360                 it is checked whether the jobs of the transaction
 361                 contradict jobs that have already been queued, and
 362                 optionally the transaction is aborted then. If all
 363                 worked out and the transaction is consistent and
 364                 minimized in its impact it is merged with all already
 365                 outstanding jobs and added to the run
 366                 queue. Effectively this means that before executing a
 367                 requested operation, systemd will verify that it makes
 368                 sense, fixing it if possible, and only failing if it
 369                 really cannot work.</para>
 370
 371                 <para>Systemd contains native implementations of
 372                 various tasks that need to be executed as part of the
 373                 boot process. For example, it sets the host name or
 374                 configures the loopback network device. It also sets
 375                 up and mounts various API file systems, such as
 376                 <filename>/sys</filename> or
 377                 <filename>/proc</filename>.</para>
 378
 379                 <para>For more information about the concepts and
 380                 ideas behind systemd please refer to the <ulink
 381                 url="http://0pointer.de/blog/projects/systemd.html">Original
 382                 Design Document</ulink>.</para>
 383         </refsect1>
 384
 385         <refsect1>
 386                 <title>Directories</title>
 387
 388                 <variablelist>
 389                         <varlistentry>
 390                                 <term>System unit directories</term>
 391
 392                                 <listitem><para>The systemd system
 393                                 manager reads unit configuration from
 394                                 various directories. Packages that
 395                                 want to install unit files shall place
 396                                 them in the directory returned by
 397                                 <command>pkg-config systemd
 398                                 --variable=systemdsystemunitdir</command>. Other
 399                                 directories checked are
 400                                 <filename>/usr/local/share/systemd/system</filename>
 401                                 and
 402                                 <filename>/usr/share/systemd/system</filename>. User
 403                                 configuration always takes
 404                                 precedence. <command>pkg-config
 405                                 systemd
 406                                 --variable=systemdsystemconfdir</command>
 407                                 returns the path of the system
 408                                 configuration directory. Packages
 409                                 should alter the content of these directories
 410                                 only with the
 411                                 <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 412                                 tool.</para></listitem>
 413                         </varlistentry>
 414                 </variablelist>
 415
 416                 <variablelist>
 417                         <varlistentry>
 418                                 <term>Session unit directories</term>
 419
 420                                 <listitem><para>Similar rules apply
 421                                 for the session unit
 422                                 directories. However, here the <ulink
 423                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 424                                 Base Directory specification</ulink>
 425                                 is followed to find
 426                                 units. Applications should place their
 427                                 unit files in the directory returned
 428                                 by <command>pkg-config systemd
 429                                 --variable=systemdsessionunitdir</command>. Global
 430                                 configuration is done in the
 431                                 directory reported by
 432                                 <command>pkg-config systemd
 433                                 --variable=systemdsessionconfdir</command>. The
 434                                 <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 435                                 tool can handle both global (i.e. for
 436                                 all users) and private (for one user)
 437                                 enabling/disabling of
 438                                 units.</para></listitem>
 439                         </varlistentry>
 440                 </variablelist>
 441
 442                 <variablelist>
 443                         <varlistentry>
 444                                 <term>SysV init scripts directory</term>
 445
 446                                 <listitem><para>The location of the
 447                                 SysV init script directory varies
 448                                 between distributions. If systemd
 449                                 cannot find a native unit file for a
 450                                 requested service, it will look for a
 451                                 SysV init script of the same name
 452                                 (with the
 453                                 <filename>.service</filename> suffix
 454                                 removed).</para></listitem>
 455                         </varlistentry>
 456                 </variablelist>
 457
 458                 <variablelist>
 459                         <varlistentry>
 460                                 <term>SysV runlevel link farm directory</term>
 461
 462                                 <listitem><para>The location of the
 463                                 SysV runlevel link farm directory
 464                                 varies between distributions. systemd
 465                                 will take the link farm into account
 466                                 when figuring out whether a service
 467                                 shall be enabled. Note that a service
 468                                 unit with a native unit configuration
 469                                 file can be started by activating it
 470                                 in the SysV runlevel link
 471                                 farm.</para></listitem>
 472                         </varlistentry>
 473                 </variablelist>
 474         </refsect1>
 475
 476         <refsect1>
 477                 <title>Signals</title>
 478
 479                 <variablelist>
 480                         <varlistentry>
 481                                 <term>SIGTERM</term>
 482
 483                                 <listitem><para>Upon receiving this
 484                                 signal the systemd system manager
 485                                 serializes its state, reexecutes
 486                                 itself and deserializes the saved
 487                                 state again. This is mostly equivalent
 488                                 to <command>systemctl
 489                                 daemon-reexec</command>.</para>
 490
 491                                 <para>systemd session managers will
 492                                 start the
 493                                 <filename>exit.target</filename> unit
 494                                 when this signal is received. This is
 495                                 mostly equivalent to
 496                                 <command>systemctl --session start
 497                                 exit.target</command>.</para></listitem>
 498                         </varlistentry>
 499
 500                         <varlistentry>
 501                                 <term>SIGINT</term>
 502
 503                                 <listitem><para>Upon receiving this
 504                                 signal the systemd system manager will
 505                                 start the
 506                                 <filename>ctrl-alt-del.target</filename> unit. This
 507                                 is mostly equivalent to
 508                                 <command>systemctl start
 509                                 ctl-alt-del.target</command>.</para>
 510
 511                                 <para>systemd session managers
 512                                 treat this signal the same way as
 513                                 SIGTERM.</para></listitem>
 514                         </varlistentry>
 515
 516                         <varlistentry>
 517                                 <term>SIGWINCH</term>
 518
 519                                 <listitem><para>When this signal is
 520                                 received the systemd system manager
 521                                 will start the
 522                                 <filename>kbrequest.target</filename>
 523                                 unit. This is mostly equivalent to
 524                                 <command>systemctl start
 525                                 kbrequest.target</command>.</para>
 526
 527                                 <para>This signal is ignored by
 528                                 systemd session
 529                                 managers.</para></listitem>
 530                         </varlistentry>
 531
 532                         <varlistentry>
 533                                 <term>SIGPWR</term>
 534
 535                                 <listitem><para>When this signal is
 536                                 received the systemd manager
 537                                 will start the
 538                                 <filename>sigpwr.target</filename>
 539                                 unit. This is mostly equivalent to
 540                                 <command>systemctl start
 541                                 sigpwr.target</command>.</para></listitem>
 542                         </varlistentry>
 543
 544                         <varlistentry>
 545                                 <term>SIGUSR1</term>
 546
 547                                 <listitem><para>When this signal is
 548                                 received the systemd manager will try
 549                                 to reconnect to the D-Bus
 550                                 bus.</para></listitem>
 551                         </varlistentry>
 552
 553                         <varlistentry>
 554                                 <term>SIGUSR2</term>
 555
 556                                 <listitem><para>When this signal is
 557                                 received the systemd manager will log
 558                                 its complete state in human readable
 559                                 form. The data logged is the same as
 560                                 printed by <command>systemctl
 561                                 dump</command>.</para></listitem>
 562                         </varlistentry>
 563
 564                         <varlistentry>
 565                                 <term>SIGHUP</term>
 566
 567                                 <listitem><para>Reloads the complete
 568                                 daemon configuration. This is mostly
 569                                 equivalent to <command>systemctl
 570                                 daemon-reload</command>.</para></listitem>
 571                         </varlistentry>
 572
 573                         <varlistentry>
 574                                 <term>SIGRTMIN+0</term>
 575
 576                                 <listitem><para>Enters default mode, starts the
 577                                 <filename>default.target</filename>
 578                                 unit. This is mostly equivalent to
 579                                 <command>systemctl start
 580                                 default.target</command>.</para></listitem>
 581                         </varlistentry>
 582
 583                         <varlistentry>
 584                                 <term>SIGRTMIN+1</term>
 585
 586                                 <listitem><para>Enters rescue mode,
 587                                 starts the
 588                                 <filename>rescue.target</filename>
 589                                 unit. This is mostly equivalent to
 590                                 <command>systemctl isolate
 591                                 rescue.target</command>.</para></listitem>
 592                         </varlistentry>
 593
 594                         <varlistentry>
 595                                 <term>SIGRTMIN+2</term>
 596
 597                                 <listitem><para>Enters emergency mode,
 598                                 starts the
 599                                 <filename>emergency.service</filename>
 600                                 unit. This is mostly equivalent to
 601                                 <command>systemctl isolate
 602                                 emergency.service</command>.</para></listitem>
 603                         </varlistentry>
 604
 605                         <varlistentry>
 606                                 <term>SIGRTMIN+3</term>
 607
 608                                 <listitem><para>Halts the machine,
 609                                 starts the
 610                                 <filename>halt.target</filename>
 611                                 unit. This is mostly equivalent to
 612                                 <command>systemctl start
 613                                 halt.target</command>.</para></listitem>
 614                         </varlistentry>
 615
 616                         <varlistentry>
 617                                 <term>SIGRTMIN+4</term>
 618
 619                                 <listitem><para>Powers off the machine,
 620                                 starts the
 621                                 <filename>poweroff.target</filename>
 622                                 unit. This is mostly equivalent to
 623                                 <command>systemctl start
 624                                 poweroff.target</command>.</para></listitem>
 625                         </varlistentry>
 626
 627                         <varlistentry>
 628                                 <term>SIGRTMIN+5</term>
 629
 630                                 <listitem><para>Reboots the machine,
 631                                 starts the
 632                                 <filename>reboot.target</filename>
 633                                 unit. This is mostly equivalent to
 634                                 <command>systemctl start
 635                                 reboot.target</command>.</para></listitem>
 636                         </varlistentry>
 637                 </variablelist>
 638         </refsect1>
 639
 640         <refsect1>
 641                 <title>Environment</title>
 642
 643                 <variablelist>
 644                         <varlistentry>
 645                                 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 646                                 <listitem><para>systemd reads the
 647                                 log level from this environment
 648                                 variable. This can be overridden with
 649                                 <option>--log-level=</option>.</para></listitem>
 650                         </varlistentry>
 651
 652                         <varlistentry>
 653                                 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 654                                 <listitem><para>systemd reads the
 655                                 log target from this environment
 656                                 variable. This can be overridden with
 657                                 <option>--log-target=</option>.</para></listitem>
 658                         </varlistentry>
 659
 660                         <varlistentry>
 661                                 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 662                                 <listitem><para>Controls whether
 663                                 systemd highlights important log
 664                                 messages. This can be overridden with
 665                                 <option>--log-color=</option>.</para></listitem>
 666                         </varlistentry>
 667
 668                         <varlistentry>
 669                                 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 670                                 <listitem><para>Controls whether
 671                                 systemd prints the code location along
 672                                 with log messages. This can be
 673                                 overridden with
 674                                 <option>--log-location=</option>.</para></listitem>
 675                         </varlistentry>
 676
 677                         <varlistentry>
 678                                 <term><varname>$XDG_CONFIG_HOME</varname></term>
 679                                 <term><varname>$XDG_CONFIG_DIRS</varname></term>
 680                                 <term><varname>$XDG_DATA_HOME</varname></term>
 681                                 <term><varname>$XDG_DATA_DIRS</varname></term>
 682
 683                                 <listitem><para>The systemd session
 684                                 manager uses these variables in
 685                                 accordance to the <ulink
 686                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 687                                 Base Directory specification</ulink>
 688                                 to find its configuration.</para></listitem>
 689                         </varlistentry>
 690
 691                         <varlistentry>
 692                                 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 693
 694                                 <listitem><para>Controls where systemd
 695                                 looks for unit
 696                                 files.</para></listitem>
 697                         </varlistentry>
 698
 699                         <varlistentry>
 700                                 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 701
 702                                 <listitem><para>Controls where systemd
 703                                 looks for SysV init scripts.</para></listitem>
 704                         </varlistentry>
 705
 706                         <varlistentry>
 707                                 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 708
 709                                 <listitem><para>Controls where systemd
 710                                 looks for SysV init script runlevel link
 711                                 farms.</para></listitem>
 712                         </varlistentry>
 713
 714                         <varlistentry>
 715                                 <term><varname>$LISTEN_PID</varname></term>
 716                                 <term><varname>$LISTEN_FDS</varname></term>
 717
 718                                 <listitem><para>Set by systemd for
 719                                 supervised processes during
 720                                 socket-based activation. See
 721                                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 722                                 for more information.
 723                                 </para></listitem>
 724                         </varlistentry>
 725
 726                         <varlistentry>
 727                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 728
 729                                 <listitem><para>Set by systemd for
 730                                 supervised processes for status and
 731                                 start-up completion notification. See
 732                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 733                                 for more information.
 734                                 </para></listitem>
 735                         </varlistentry>
 736                 </variablelist>
 737         </refsect1>
 738
 739         <refsect1>
 740                 <title>Kernel Command Line</title>
 741
 742                 <para>When run as system instance systemd parses a few kernel command line arguments:</para>
 743
 744                 <variablelist>
 745                         <varlistentry>
 746                                 <term><varname>systemd.unit=</varname></term>
 747
 748                                 <listitem><para>Overrides the unit to
 749                                 activate on boot. Defaults to
 750                                 <filename>default.target</filename>. This
 751                                 may be used to temporarily boot into a
 752                                 different boot unit, for example
 753                                 <filename>rescue.target</filename> or
 754                                 <filename>emergency.service</filename>. See
 755                                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 756                                 for details about these
 757                                 units.</para></listitem>
 758                         </varlistentry>
 759
 760                         <varlistentry>
 761                                 <term><varname>systemd.log_target=</varname></term>
 762                                 <term><varname>systemd.log_level=</varname></term>
 763                                 <term><varname>systemd.log_color=</varname></term>
 764                                 <term><varname>systemd.log_location=</varname></term>
 765
 766                                 <listitem><para>Controls log output,
 767                                 with the same effect as the
 768                                 <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
 769                                 environment variables described above.</para></listitem>
 770                         </varlistentry>
 771
 772                         <varlistentry>
 773                                 <term><varname>systemd.dump_core=</varname></term>
 774
 775                                 <listitem><para>Takes a boolean
 776                                 argument. If <option>true</option>
 777                                 systemd dumps core when it
 778                                 crashes. Otherwise no core dump is
 779                                 created. Defaults to
 780                                 <option>true</option>.</para></listitem>
 781                         </varlistentry>
 782
 783                         <varlistentry>
 784                                 <term><varname>systemd.crash_shell=</varname></term>
 785
 786                                 <listitem><para>Takes a boolean
 787                                 argument. If <option>true</option>
 788                                 systemd spawns a shell when it
 789                                 crashes. Otherwise no core dump is
 790                                 created. Defaults to
 791                                 <option>false</option>, for security
 792                                 reasons, as the shell is not protected
 793                                 by any password
 794                                 authentication.</para></listitem>
 795                         </varlistentry>
 796
 797                         <varlistentry>
 798                                 <term><varname>systemd.crash_chvt=</varname></term>
 799
 800                                 <listitem><para>Takes an integer
 801                                 argument. If positive systemd
 802                                 activates the specified virtual
 803                                 terminal when it crashes. Defaults to
 804                                 <literal>-1</literal>.</para></listitem>
 805                         </varlistentry>
 806
 807                         <varlistentry>
 808                                 <term><varname>systemd.show_status=</varname></term>
 809
 810                                 <listitem><para>Takes a boolean
 811                                 argument. If <option>true</option>
 812                                 shows terse service status updates on
 813                                 the console during bootup. Defaults to
 814                                 <option>true</option>.</para></listitem>
 815                         </varlistentry>
 816
 817                 </variablelist>
 818         </refsect1>
 819
 820         <refsect1>
 821                 <title>Sockets and FIFOs</title>
 822
 823                 <variablelist>
 824                         <varlistentry>
 825                                 <term><filename>@/org/freedesktop/systemd1/notify</filename></term>
 826
 827                                 <listitem><para>Daemon status
 828                                 notification socket. This is an AF_UNIX
 829                                 datagram socket in the Linux abstract
 830                                 namespace, and is used to implement
 831                                 the daemon notification logic as
 832                                 implemented by
 833                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 834
 835                         </varlistentry>
 836
 837                         <varlistentry>
 838                                 <term><filename>@/org/freedesktop/systemd1/logger</filename></term>
 839
 840                                 <listitem><para>Used internally by the
 841                                 <filename>systemd-logger.service</filename>
 842                                 unit to connect STDOUT and/or STDERR
 843                                 of spawned processes to
 844                                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 845                                 or the kernel log buffer. This is an
 846                                 AF_UNIX stream socket in the Linux
 847                                 abstract namespace.</para></listitem>
 848                         </varlistentry>
 849
 850                         <varlistentry>
 851                                 <term><filename>@/org/freedesktop/systemd1/private</filename></term>
 852
 853                                 <listitem><para>Used internally as
 854                                 communication channel between
 855                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 856                                 and the systemd process. This is an
 857                                 AF_UNIX stream socket in the Linux
 858                                 abstract namespace. This interface is
 859                                 private to systemd and should not be
 860                                 used in external
 861                                 projects.</para></listitem>
 862                         </varlistentry>
 863
 864                         <varlistentry>
 865                                 <term><filename>/dev/initctl</filename></term>
 866
 867                                 <listitem><para>Limited compatibility
 868                                 support for the SysV client interface,
 869                                 as implemented by the
 870                                 <filename>systemd-initctl.service</filename>
 871                                 unit. This is a named pipe in the file
 872                                 system. This interface is obsolete and
 873                                 should not be used in new
 874                                 applications.</para></listitem>
 875                         </varlistentry>
 876                 </variablelist>
 877         </refsect1>
 878
 879         <refsect1>
 880                 <title>See Also</title>
 881                 <para>
 882                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 883                         <citerefentry><refentrytitle>systemadm</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 884                         <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 885                         <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 886                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 887                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 888                         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 889                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 890                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 891                 </para>
 892         </refsect1>
 893
 894 </refentry>