man/systemd.xml

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