man/systemd.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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   6   This file is part of systemd.
   7
   8   Copyright 2010 Lennart Poettering
   9
  10   systemd is free software; you can redistribute it and/or modify it
  11   under the terms of the GNU General Public License as published by
  12   the Free Software Foundation; either version 2 of the License, or
  13   (at your option) any later version.
  14
  15   systemd is distributed in the hope that it will be useful, but
  16   WITHOUT ANY WARRANTY; without even the implied warranty of
  17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  18   General Public License for more details.
  19
  20   You should have received a copy of the GNU General Public License
  21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  22 -->
  23
  24 <refentry id="systemd">
  25
  26         <refentryinfo>
  27                 <title>systemd</title>
  28                 <productname>systemd</productname>
  29
  30                 <authorgroup>
  31                         <author>
  32                                 <contrib>Developer</contrib>
  33                                 <firstname>Lennart</firstname>
  34                                 <surname>Poettering</surname>
  35                                 <email>lennart@poettering.net</email>
  36                         </author>
  37                 </authorgroup>
  38         </refentryinfo>
  39
  40         <refmeta>
  41                 <refentrytitle>systemd</refentrytitle>
  42                 <manvolnum>1</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>systemd</refname>
  47                 <refname>init</refname>
  48                 <refpurpose>systemd System and 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                 </variablelist>
 254         </refsect1>
 255
 256         <refsect1>
 257                 <title>Concepts</title>
 258
 259                 <para>systemd provides a dependency system between
 260                 various entities called "units". Units encapsulate
 261                 various objects that are relevant for system boot-up
 262                 and maintenance. The majority of units are configured
 263                 in unit configuration files, whose syntax and basic
 264                 set of options is described in
 265                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 266                 however some are created automatically from other
 267                 configuration or dynamically from system state. Units
 268                 may be 'active' (meaning started, bound, plugged in,
 269                 ...  depending on the unit type, see below), or
 270                 'inactive' (meaning stopped, unbound, unplugged, ...),
 271                 as well as in the process of being activated or
 272                 deactivated, i.e. between the two states (these states
 273                 are called 'activating', 'deactivating'). A special
 274                 'failed' state is available as well which is very
 275                 similar to 'inactive' and is entered when the service
 276                 failed in some way (process returned error code on
 277                 exit, or crashed, or an operation timed out). If this
 278                 state is entered the cause will be logged, for later
 279                 reference. Note that the various unit types may have a
 280                 number of additional substates, which are mapped to
 281                 the five generalized unit states described
 282                 here.</para>
 283
 284                 <para>The following unit types are available:</para>
 285
 286                 <orderedlist>
 287                         <listitem><para>Service units, which control
 288                         daemons and the processes they consist of. For
 289                         details see
 290                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 291
 292                         <listitem><para>Socket units, which
 293                         encapsulate local IPC or network sockets in
 294                         the system, useful for socket-based
 295                         activation. For details about socket units see
 296                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 297                         for details on socket-based activation and
 298                         other forms of activation, see
 299                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 300
 301                         <listitem><para>Target units are useful to
 302                         group units, or provide well-known
 303                         synchronization points during boot-up, see
 304                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 305
 306                         <listitem><para>Device units expose kernel
 307                         devices in systemd and may be used to
 308                         implement device-based activation. For details
 309                         see
 310                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 311
 312                         <listitem><para>Mount units control mount
 313                         points in the file system, for details see
 314                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 315
 316                         <listitem><para>Automount units provide
 317                         automount capabilities, for on-demand mounting
 318                         of file systems as well as parallelized
 319                         boot-up. See
 320                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 321
 322                         <listitem><para>Snapshot units can be used to
 323                         temporarily save the state of the set of
 324                         systemd units, which later may be restored by
 325                         activating the saved snapshot unit. For more
 326                         information see
 327                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 328
 329                         <listitem><para>Timer units are useful for
 330                         triggering activation of other units based on
 331                         timers. You may find details in
 332                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 333
 334                         <listitem><para>Swap units are very similar to
 335                         mount units and encapsulate memory swap
 336                         partitions or files of the operating
 337                         system. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 338
 339                         <listitem><para>Path units may be used
 340                         to activate other services when file system
 341                         objects change or are modified. See
 342                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 343
 344                 </orderedlist>
 345
 346                 <para>Units are named as their configuration
 347                 files. Some units have special semantics. A detailed
 348                 list is available in
 349                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 350
 351                 <para>systemd knows various kinds of dependencies,
 352                 including positive and negative requirement
 353                 dependencies (i.e. <varname>Requires=</varname> and
 354                 <varname>Conflicts=</varname>) as well as ordering
 355                 dependencies (<varname>After=</varname> and
 356                 <varname>Before=</varname>). NB: ordering and
 357                 requirement dependencies are orthogonal. If only a
 358                 requirement dependency exists between two units
 359                 (e.g. <filename>foo.service</filename> requires
 360                 <filename>bar.service</filename>), but no ordering
 361                 dependency (e.g. <filename>foo.service</filename>
 362                 after <filename>bar.service</filename>) and both are
 363                 requested to start, they will be started in
 364                 parallel. It is a common pattern that both requirement
 365                 and ordering dependencies are placed between two
 366                 units. Also note that the majority of dependencies are
 367                 implicitly created and maintained by systemd. In most
 368                 cases it should be unnecessary to declare additional
 369                 dependencies manually, however it is possible to do
 370                 this.</para>
 371
 372                 <para>Application programs and units (via
 373                 dependencies) may request state changes of units. In
 374                 systemd, these requests are encapsulated as 'jobs' and
 375                 maintained in a job queue. Jobs may succeed or can
 376                 fail, their execution is ordered based on the ordering
 377                 dependencies of the units they have been scheduled
 378                 for.</para>
 379
 380                 <para>On boot systemd activates the target unit
 381                 <filename>default.target</filename> whose job is to
 382                 activate on-boot services and other on-boot units by
 383                 pulling them in via dependencies. Usually the unit
 384                 name is just an alias (symlink) for either
 385                 <filename>graphical.target</filename> (for
 386                 fully-featured boots into the UI) or
 387                 <filename>multi-user.target</filename> (for limited
 388                 console-only boots for use in embedded or server
 389                 environments, or similar; a subset of
 390                 graphical.target). However it is at the discretion of
 391                 the administrator to configure it as an alias to any
 392                 other target unit. See
 393                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 394                 for details about these target units.</para>
 395
 396                 <para>Processes systemd spawns are placed in
 397                 individual Linux control groups named after the unit
 398                 which they belong to in the private systemd
 399                 hierarchy. (see <ulink
 400                 url="http://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 401                 for more information about control groups, or short
 402                 "cgroups"). systemd uses this to effectively keep
 403                 track of processes. Control group information is
 404                 maintained in the kernel, and is accessible via the
 405                 file system hierarchy (beneath
 406                 <filename>/sys/fs/cgroup/systemd/</filename>), or in tools
 407                 such as
 408                 <citerefentry><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 409                 (<command>ps xawf -eo pid,user,cgroup,args</command>
 410                 is particularly useful to list all processes and the
 411                 systemd units they belong to.).</para>
 412
 413                 <para>systemd is compatible with the SysV init system
 414                 to a large degree: SysV init scripts are supported and
 415                 simply read as an alternative (though limited)
 416                 configuration file format. The SysV
 417                 <filename>/dev/initctl</filename> interface is
 418                 provided, and compatibility implementations of the
 419                 various SysV client tools are available. In addition to
 420                 that, various established Unix functionality such as
 421                 <filename>/etc/fstab</filename> or the
 422                 <filename>utmp</filename> database are
 423                 supported.</para>
 424
 425                 <para>systemd has a minimal transaction system: if a
 426                 unit is requested to start up or shut down it will add
 427                 it and all its dependencies to a temporary
 428                 transaction. Then, it will verify if the transaction
 429                 is consistent (i.e. whether the ordering of all units
 430                 is cycle-free). If it is not, systemd will try to fix
 431                 it up, and removes non-essential jobs from the
 432                 transaction that might remove the loop. Also, systemd
 433                 tries to suppress non-essential jobs in the
 434                 transaction that would stop a running service. Finally
 435                 it is checked whether the jobs of the transaction
 436                 contradict jobs that have already been queued, and
 437                 optionally the transaction is aborted then. If all
 438                 worked out and the transaction is consistent and
 439                 minimized in its impact it is merged with all already
 440                 outstanding jobs and added to the run
 441                 queue. Effectively this means that before executing a
 442                 requested operation, systemd will verify that it makes
 443                 sense, fixing it if possible, and only failing if it
 444                 really cannot work.</para>
 445
 446                 <para>Systemd contains native implementations of
 447                 various tasks that need to be executed as part of the
 448                 boot process. For example, it sets the host name or
 449                 configures the loopback network device. It also sets
 450                 up and mounts various API file systems, such as
 451                 <filename>/sys</filename> or
 452                 <filename>/proc</filename>.</para>
 453
 454                 <para>For more information about the concepts and
 455                 ideas behind systemd please refer to the <ulink
 456                 url="http://0pointer.de/blog/projects/systemd.html">Original
 457                 Design Document</ulink>.</para>
 458
 459                 <para>Note that some but not all interfaces provided
 460                 by systemd are covered by the <ulink
 461                 url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 462                 Stability Promise</ulink>.</para>
 463         </refsect1>
 464
 465         <refsect1>
 466                 <title>Directories</title>
 467
 468                 <variablelist>
 469                         <varlistentry>
 470                                 <term>System unit directories</term>
 471
 472                                 <listitem><para>The systemd system
 473                                 manager reads unit configuration from
 474                                 various directories. Packages that
 475                                 want to install unit files shall place
 476                                 them in the directory returned by
 477                                 <command>pkg-config systemd
 478                                 --variable=systemdsystemunitdir</command>. Other
 479                                 directories checked are
 480                                 <filename>/usr/local/share/systemd/system</filename>
 481                                 and
 482                                 <filename>/usr/share/systemd/system</filename>. User
 483                                 configuration always takes
 484                                 precedence. <command>pkg-config
 485                                 systemd
 486                                 --variable=systemdsystemconfdir</command>
 487                                 returns the path of the system
 488                                 configuration directory. Packages
 489                                 should alter the content of these
 490                                 directories only with the
 491                                 <command>enable</command> and
 492                                 <command>disable</command> commands of
 493                                 the
 494                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 495                                 tool.</para></listitem>
 496                         </varlistentry>
 497                 </variablelist>
 498
 499                 <variablelist>
 500                         <varlistentry>
 501                                 <term>User unit directories</term>
 502
 503                                 <listitem><para>Similar rules apply
 504                                 for the user unit
 505                                 directories. However, here the <ulink
 506                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 507                                 Base Directory specification</ulink>
 508                                 is followed to find
 509                                 units. Applications should place their
 510                                 unit files in the directory returned
 511                                 by <command>pkg-config systemd
 512                                 --variable=systemduserunitdir</command>. Global
 513                                 configuration is done in the directory
 514                                 reported by <command>pkg-config
 515                                 systemd
 516                                 --variable=systemduserconfdir</command>. The
 517                                 <command>enable</command> and
 518                                 <command>disable</command> commands of
 519                                 the
 520                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 521                                 tool can handle both global (i.e. for
 522                                 all users) and private (for one user)
 523                                 enabling/disabling of
 524                                 units.</para></listitem>
 525                         </varlistentry>
 526                 </variablelist>
 527
 528                 <variablelist>
 529                         <varlistentry>
 530                                 <term>SysV init scripts directory</term>
 531
 532                                 <listitem><para>The location of the
 533                                 SysV init script directory varies
 534                                 between distributions. If systemd
 535                                 cannot find a native unit file for a
 536                                 requested service, it will look for a
 537                                 SysV init script of the same name
 538                                 (with the
 539                                 <filename>.service</filename> suffix
 540                                 removed).</para></listitem>
 541                         </varlistentry>
 542                 </variablelist>
 543
 544                 <variablelist>
 545                         <varlistentry>
 546                                 <term>SysV runlevel link farm directory</term>
 547
 548                                 <listitem><para>The location of the
 549                                 SysV runlevel link farm directory
 550                                 varies between distributions. systemd
 551                                 will take the link farm into account
 552                                 when figuring out whether a service
 553                                 shall be enabled. Note that a service
 554                                 unit with a native unit configuration
 555                                 file cannot be started by activating it
 556                                 in the SysV runlevel link
 557                                 farm.</para></listitem>
 558                         </varlistentry>
 559                 </variablelist>
 560         </refsect1>
 561
 562         <refsect1>
 563                 <title>Signals</title>
 564
 565                 <variablelist>
 566                         <varlistentry>
 567                                 <term>SIGTERM</term>
 568
 569                                 <listitem><para>Upon receiving this
 570                                 signal the systemd system manager
 571                                 serializes its state, reexecutes
 572                                 itself and deserializes the saved
 573                                 state again. This is mostly equivalent
 574                                 to <command>systemctl
 575                                 daemon-reexec</command>.</para>
 576
 577                                 <para>systemd user managers will
 578                                 start the
 579                                 <filename>exit.target</filename> unit
 580                                 when this signal is received. This is
 581                                 mostly equivalent to
 582                                 <command>systemctl --user start
 583                                 exit.target</command>.</para></listitem>
 584                         </varlistentry>
 585
 586                         <varlistentry>
 587                                 <term>SIGINT</term>
 588
 589                                 <listitem><para>Upon receiving this
 590                                 signal the systemd system manager will
 591                                 start the
 592                                 <filename>ctrl-alt-del.target</filename> unit. This
 593                                 is mostly equivalent to
 594                                 <command>systemctl start
 595                                 ctl-alt-del.target</command>.</para>
 596
 597                                 <para>systemd user managers
 598                                 treat this signal the same way as
 599                                 SIGTERM.</para></listitem>
 600                         </varlistentry>
 601
 602                         <varlistentry>
 603                                 <term>SIGWINCH</term>
 604
 605                                 <listitem><para>When this signal is
 606                                 received the systemd system manager
 607                                 will start the
 608                                 <filename>kbrequest.target</filename>
 609                                 unit. This is mostly equivalent to
 610                                 <command>systemctl start
 611                                 kbrequest.target</command>.</para>
 612
 613                                 <para>This signal is ignored by
 614                                 systemd user
 615                                 managers.</para></listitem>
 616                         </varlistentry>
 617
 618                         <varlistentry>
 619                                 <term>SIGPWR</term>
 620
 621                                 <listitem><para>When this signal is
 622                                 received the systemd manager
 623                                 will start the
 624                                 <filename>sigpwr.target</filename>
 625                                 unit. This is mostly equivalent to
 626                                 <command>systemctl start
 627                                 sigpwr.target</command>.</para></listitem>
 628                         </varlistentry>
 629
 630                         <varlistentry>
 631                                 <term>SIGUSR1</term>
 632
 633                                 <listitem><para>When this signal is
 634                                 received the systemd manager will try
 635                                 to reconnect to the D-Bus
 636                                 bus.</para></listitem>
 637                         </varlistentry>
 638
 639                         <varlistentry>
 640                                 <term>SIGUSR2</term>
 641
 642                                 <listitem><para>When this signal is
 643                                 received the systemd manager will log
 644                                 its complete state in human readable
 645                                 form. The data logged is the same as
 646                                 printed by <command>systemctl
 647                                 dump</command>.</para></listitem>
 648                         </varlistentry>
 649
 650                         <varlistentry>
 651                                 <term>SIGHUP</term>
 652
 653                                 <listitem><para>Reloads the complete
 654                                 daemon configuration. This is mostly
 655                                 equivalent to <command>systemctl
 656                                 daemon-reload</command>.</para></listitem>
 657                         </varlistentry>
 658
 659                         <varlistentry>
 660                                 <term>SIGRTMIN+0</term>
 661
 662                                 <listitem><para>Enters default mode, starts the
 663                                 <filename>default.target</filename>
 664                                 unit. This is mostly equivalent to
 665                                 <command>systemctl start
 666                                 default.target</command>.</para></listitem>
 667                         </varlistentry>
 668
 669                         <varlistentry>
 670                                 <term>SIGRTMIN+1</term>
 671
 672                                 <listitem><para>Enters rescue mode,
 673                                 starts the
 674                                 <filename>rescue.target</filename>
 675                                 unit. This is mostly equivalent to
 676                                 <command>systemctl isolate
 677                                 rescue.target</command>.</para></listitem>
 678                         </varlistentry>
 679
 680                         <varlistentry>
 681                                 <term>SIGRTMIN+2</term>
 682
 683                                 <listitem><para>Enters emergency mode,
 684                                 starts the
 685                                 <filename>emergency.service</filename>
 686                                 unit. This is mostly equivalent to
 687                                 <command>systemctl isolate
 688                                 emergency.service</command>.</para></listitem>
 689                         </varlistentry>
 690
 691                         <varlistentry>
 692                                 <term>SIGRTMIN+3</term>
 693
 694                                 <listitem><para>Halts the machine,
 695                                 starts the
 696                                 <filename>halt.target</filename>
 697                                 unit. This is mostly equivalent to
 698                                 <command>systemctl start
 699                                 halt.target</command>.</para></listitem>
 700                         </varlistentry>
 701
 702                         <varlistentry>
 703                                 <term>SIGRTMIN+4</term>
 704
 705                                 <listitem><para>Powers off the machine,
 706                                 starts the
 707                                 <filename>poweroff.target</filename>
 708                                 unit. This is mostly equivalent to
 709                                 <command>systemctl start
 710                                 poweroff.target</command>.</para></listitem>
 711                         </varlistentry>
 712
 713                         <varlistentry>
 714                                 <term>SIGRTMIN+5</term>
 715
 716                                 <listitem><para>Reboots the machine,
 717                                 starts the
 718                                 <filename>reboot.target</filename>
 719                                 unit. This is mostly equivalent to
 720                                 <command>systemctl start
 721                                 reboot.target</command>.</para></listitem>
 722                         </varlistentry>
 723                 </variablelist>
 724         </refsect1>
 725
 726         <refsect1>
 727                 <title>Environment</title>
 728
 729                 <variablelist>
 730                         <varlistentry>
 731                                 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 732                                 <listitem><para>systemd reads the
 733                                 log level from this environment
 734                                 variable. This can be overridden with
 735                                 <option>--log-level=</option>.</para></listitem>
 736                         </varlistentry>
 737
 738                         <varlistentry>
 739                                 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 740                                 <listitem><para>systemd reads the
 741                                 log target from this environment
 742                                 variable. This can be overridden with
 743                                 <option>--log-target=</option>.</para></listitem>
 744                         </varlistentry>
 745
 746                         <varlistentry>
 747                                 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 748                                 <listitem><para>Controls whether
 749                                 systemd highlights important log
 750                                 messages. This can be overridden with
 751                                 <option>--log-color=</option>.</para></listitem>
 752                         </varlistentry>
 753
 754                         <varlistentry>
 755                                 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 756                                 <listitem><para>Controls whether
 757                                 systemd prints the code location along
 758                                 with log messages. This can be
 759                                 overridden with
 760                                 <option>--log-location=</option>.</para></listitem>
 761                         </varlistentry>
 762
 763                         <varlistentry>
 764                                 <term><varname>$XDG_CONFIG_HOME</varname></term>
 765                                 <term><varname>$XDG_CONFIG_DIRS</varname></term>
 766                                 <term><varname>$XDG_DATA_HOME</varname></term>
 767                                 <term><varname>$XDG_DATA_DIRS</varname></term>
 768
 769                                 <listitem><para>The systemd user
 770                                 manager uses these variables in
 771                                 accordance to the <ulink
 772                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 773                                 Base Directory specification</ulink>
 774                                 to find its configuration.</para></listitem>
 775                         </varlistentry>
 776
 777                         <varlistentry>
 778                                 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 779
 780                                 <listitem><para>Controls where systemd
 781                                 looks for unit
 782                                 files.</para></listitem>
 783                         </varlistentry>
 784
 785                         <varlistentry>
 786                                 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 787
 788                                 <listitem><para>Controls where systemd
 789                                 looks for SysV init scripts.</para></listitem>
 790                         </varlistentry>
 791
 792                         <varlistentry>
 793                                 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 794
 795                                 <listitem><para>Controls where systemd
 796                                 looks for SysV init script runlevel link
 797                                 farms.</para></listitem>
 798                         </varlistentry>
 799
 800                         <varlistentry>
 801                                 <term><varname>$LISTEN_PID</varname></term>
 802                                 <term><varname>$LISTEN_FDS</varname></term>
 803
 804                                 <listitem><para>Set by systemd for
 805                                 supervised processes during
 806                                 socket-based activation. See
 807                                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 808                                 for more information.
 809                                 </para></listitem>
 810                         </varlistentry>
 811
 812                         <varlistentry>
 813                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 814
 815                                 <listitem><para>Set by systemd for
 816                                 supervised processes for status and
 817                                 start-up completion notification. See
 818                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 819                                 for more information.
 820                                 </para></listitem>
 821                         </varlistentry>
 822                 </variablelist>
 823         </refsect1>
 824
 825         <refsect1>
 826                 <title>Kernel Command Line</title>
 827
 828                 <para>When run as system instance systemd parses a few kernel command line arguments:</para>
 829
 830                 <variablelist>
 831                         <varlistentry>
 832                                 <term><varname>systemd.unit=</varname></term>
 833
 834                                 <listitem><para>Overrides the unit to
 835                                 activate on boot. Defaults to
 836                                 <filename>default.target</filename>. This
 837                                 may be used to temporarily boot into a
 838                                 different boot unit, for example
 839                                 <filename>rescue.target</filename> or
 840                                 <filename>emergency.service</filename>. See
 841                                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 842                                 for details about these
 843                                 units.</para></listitem>
 844                         </varlistentry>
 845
 846                         <varlistentry>
 847                                 <term><varname>systemd.dump_core=</varname></term>
 848
 849                                 <listitem><para>Takes a boolean
 850                                 argument. If <option>true</option>
 851                                 systemd dumps core when it
 852                                 crashes. Otherwise no core dump is
 853                                 created. Defaults to
 854                                 <option>true</option>.</para></listitem>
 855                         </varlistentry>
 856
 857                         <varlistentry>
 858                                 <term><varname>systemd.crash_shell=</varname></term>
 859
 860                                 <listitem><para>Takes a boolean
 861                                 argument. If <option>true</option>
 862                                 systemd spawns a shell when it
 863                                 crashes. Otherwise no shell is
 864                                 spawned. Defaults to
 865                                 <option>false</option>, for security
 866                                 reasons, as the shell is not protected
 867                                 by any password
 868                                 authentication.</para></listitem>
 869                         </varlistentry>
 870
 871                         <varlistentry>
 872                                 <term><varname>systemd.crash_chvt=</varname></term>
 873
 874                                 <listitem><para>Takes an integer
 875                                 argument. If positive systemd
 876                                 activates the specified virtual
 877                                 terminal when it crashes. Defaults to
 878                                 <literal>-1</literal>.</para></listitem>
 879                         </varlistentry>
 880
 881                         <varlistentry>
 882                                 <term><varname>systemd.confirm_spawn=</varname></term>
 883
 884                                 <listitem><para>Takes a boolean
 885                                 argument. If <option>true</option>
 886                                 asks for confirmation when spawning
 887                                 processes. Defaults to
 888                                 <option>false</option>.</para></listitem>
 889                         </varlistentry>
 890
 891                         <varlistentry>
 892                                 <term><varname>systemd.show_status=</varname></term>
 893
 894                                 <listitem><para>Takes a boolean
 895                                 argument. If <option>true</option>
 896                                 shows terse service status updates on
 897                                 the console during bootup. Defaults to
 898                                 <option>true</option>.</para></listitem>
 899                         </varlistentry>
 900
 901                         <varlistentry>
 902                                 <term><varname>systemd.sysv_console=</varname></term>
 903
 904                                 <listitem><para>Takes a boolean
 905                                 argument. If <option>true</option>
 906                                 output of SysV init scripts will be
 907                                 directed to the console. Defaults to
 908                                 <option>true</option>, unless
 909                                 <option>quiet</option> is passed as
 910                                 kernel command line option in which
 911                                 case it defaults to
 912                                 <option>false</option>.</para></listitem>
 913                         </varlistentry>
 914
 915                         <varlistentry>
 916                                 <term><varname>systemd.log_target=</varname></term>
 917                                 <term><varname>systemd.log_level=</varname></term>
 918                                 <term><varname>systemd.log_color=</varname></term>
 919                                 <term><varname>systemd.log_location=</varname></term>
 920
 921                                 <listitem><para>Controls log output,
 922                                 with the same effect as the
 923                                 <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
 924                                 environment variables described above.</para></listitem>
 925                         </varlistentry>
 926
 927                 </variablelist>
 928         </refsect1>
 929
 930         <refsect1>
 931                 <title>Sockets and FIFOs</title>
 932
 933                 <variablelist>
 934                         <varlistentry>
 935                                 <term><filename>@/org/freedesktop/systemd1/notify</filename></term>
 936
 937                                 <listitem><para>Daemon status
 938                                 notification socket. This is an AF_UNIX
 939                                 datagram socket in the Linux abstract
 940                                 namespace, and is used to implement
 941                                 the daemon notification logic as
 942                                 implemented by
 943                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 944
 945                         </varlistentry>
 946
 947                         <varlistentry>
 948                                 <term><filename>@/org/freedesktop/systemd1/logger</filename></term>
 949
 950                                 <listitem><para>Used internally by the
 951                                 <filename>systemd-logger.service</filename>
 952                                 unit to connect STDOUT and/or STDERR
 953                                 of spawned processes to
 954                                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 955                                 or the kernel log buffer. This is an
 956                                 AF_UNIX stream socket in the Linux
 957                                 abstract namespace.</para></listitem>
 958                         </varlistentry>
 959
 960                         <varlistentry>
 961                                 <term><filename>@/org/freedesktop/systemd1/shutdown</filename></term>
 962
 963                                 <listitem><para>Used internally by the
 964                                 <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 965                                 tool to implement delayed
 966                                 shutdowns. This is an AF_UNIX datagram
 967                                 socket in the Linux abstract
 968                                 namespace.</para></listitem>
 969                         </varlistentry>
 970
 971                         <varlistentry>
 972                                 <term><filename>@/org/freedesktop/systemd1/private</filename></term>
 973
 974                                 <listitem><para>Used internally as
 975                                 communication channel between
 976                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 977                                 and the systemd process. This is an
 978                                 AF_UNIX stream socket in the Linux
 979                                 abstract namespace. This interface is
 980                                 private to systemd and should not be
 981                                 used in external
 982                                 projects.</para></listitem>
 983                         </varlistentry>
 984
 985                         <varlistentry>
 986                                 <term><filename>/dev/initctl</filename></term>
 987
 988                                 <listitem><para>Limited compatibility
 989                                 support for the SysV client interface,
 990                                 as implemented by the
 991                                 <filename>systemd-initctl.service</filename>
 992                                 unit. This is a named pipe in the file
 993                                 system. This interface is obsolete and
 994                                 should not be used in new
 995                                 applications.</para></listitem>
 996                         </varlistentry>
 997                 </variablelist>
 998         </refsect1>
 999
1000         <refsect1>
1001                 <title>See Also</title>
1002                 <para>
1003                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1004                         <citerefentry><refentrytitle>systemadm</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1005                         <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1006                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1007                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1008                         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1009                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1010                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1011                 </para>
1012         </refsect1>
1013
1014 </refentry>