man/systemd.xml

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