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/>.
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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 Session Manager</refpurpose>
  49         </refnamediv>
  50
  51         <refsynopsisdiv>
  52                 <cmdsynopsis>
  53                         <command>systemd <arg choice="opt" rep="repeat">OPTIONS</arg></command>
  54                 </cmdsynopsis>
  55                 <cmdsynopsis>
  56                         <command>init <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="req">COMMAND</arg></command>
  57                 </cmdsynopsis>
  58         </refsynopsisdiv>
  59
  60         <refsect1>
  61                 <title>Description</title>
  62
  63                 <para>systemd is a system and session manager for
  64                 Linux operating systems. When run as first process on
  65                 boot (as PID 1), it acts as init system that brings
  66                 up and maintains userspace services.</para>
  67
  68                 <para>For compatibility with SysV, if systemd is called
  69                 as <command>init</command> and a PID that is not
  70                 1, it will execute <command>telinit</command> and pass
  71                 all command line arguments unmodified. That means
  72                 <command>init</command> and <command>telinit</command>
  73                 are mostly equivalent when invoked from normal login sessions. See
  74                 <citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  75                 for more information.</para>
  76
  77                 <para>When run as system instance, systemd interprets
  78                 the configuration file
  79                 <filename>system.conf</filename>, otherwise
  80                 <filename>session.conf</filename>. See
  81                 <citerefentry><refentrytitle>systemd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  82                 for more information.</para>
  83         </refsect1>
  84
  85         <refsect1>
  86                 <title>Options</title>
  87
  88                 <para>The following options are understood:</para>
  89
  90                 <variablelist>
  91                         <varlistentry>
  92                                 <term><option>-h</option></term>
  93                                 <term><option>--help</option></term>
  94
  95                                 <listitem><para>Prints a short help
  96                                 text and exits.</para></listitem>
  97                         </varlistentry>
  98                         <varlistentry>
  99                                 <term><option>--test</option></term>
 100
 101                                 <listitem><para>Determine startup
 102                                 sequence, dump it and exit. This is an
 103                                 option useful for debugging
 104                                 only.</para></listitem>
 105                         </varlistentry>
 106                         <varlistentry>
 107                                 <term><option>--dump-configuration-items</option></term>
 108
 109                                 <listitem><para>Dump understood unit
 110                                 configuration items. This outputs a
 111                                 terse but complete list of
 112                                 configuration items understood in unit
 113                                 definition files.</para></listitem>
 114                         </varlistentry>
 115                         <varlistentry>
 116                                 <term><option>--introspect=</option></term>
 117
 118                                 <listitem><para>Extract D-Bus
 119                                 interface introspection data. This is
 120                                 mostly useful at install time
 121                                 to generate data suitable for the
 122                                 D-Bus interfaces
 123                                 repository. Optionally the interface
 124                                 name for the introspection data may be
 125                                 specified. If omitted, the
 126                                 introspection data for all interfaces
 127                                 is dumped.</para></listitem>
 128                         </varlistentry>
 129                         <varlistentry>
 130                                 <term><option>--unit=</option></term>
 131
 132                                 <listitem><para>Set default unit to
 133                                 activate on startup. If not specified
 134                                 defaults to
 135                                 <filename>default.target</filename>.</para></listitem>
 136                         </varlistentry>
 137                         <varlistentry>
 138                                 <term><option>--system</option></term>
 139                                 <term><option>--session</option></term>
 140
 141                                 <listitem><para>Tell systemd to run a
 142                                 system instance (resp. session
 143                                 instance), even if the process ID is
 144                                 not 1 (resp. is 1), i.e. 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 crash. This switch has no effect when run as session instance.</para></listitem>
 163                         </varlistentry>
 164                         <varlistentry>
 165                                 <term><option>--crash-shell</option></term>
 166
 167                                 <listitem><para>Run shell on crash. This switch has no effect when run as session instance.</para></listitem>
 168                         </varlistentry>
 169                         <varlistentry>
 170                                 <term><option>--confirm-spawn</option></term>
 171
 172                                 <listitem><para>Ask for confirmation when spawning processes. This switch has no effect when run as session instance.</para></listitem>
 173                         </varlistentry>
 174                         <varlistentry>
 175                                 <term><option>--show-status=</option></term>
 176
 177                                 <listitem><para>Show terse service
 178                                 status information while booting. This
 179                                 switch has no effect when run as
 180                                 session instance. Takes a boolean
 181                                 argument which may be omitted
 182                                 which is interpreted as
 183                                 <option>true</option>.</para></listitem>
 184                         </varlistentry>
 185                         <varlistentry>
 186                                 <term><option>--sysv-console=</option></term>
 187
 188                                 <listitem><para>Controls whether
 189                                 output of SysV init scripts will be
 190                                 directed to the console. This switch
 191                                 has no effect when run as session
 192                                 instance. Takes a boolean argument
 193                                 which may be omitted which is
 194                                 interpreted as
 195                                 <option>true</option>.</para></listitem>
 196                         </varlistentry>
 197                         <varlistentry>
 198                                 <term><option>--log-target=</option></term>
 199
 200                                 <listitem><para>Set log
 201                                 target. Argument must be one of
 202                                 <option>console</option>,
 203                                 <option>syslog</option>,
 204                                 <option>kmsg</option>,
 205                                 <option>syslog-or-kmsg</option>,
 206                                 <option>null</option>.</para></listitem>
 207                         </varlistentry>
 208                         <varlistentry>
 209                                 <term><option>--log-level=</option></term>
 210
 211                                 <listitem><para>Set log level. As
 212                                 argument this accepts a numerical log
 213                                 level or the well-known <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 214                                 symbolic names (lowercase):
 215                                 <option>emerg</option>,
 216                                 <option>alert</option>,
 217                                 <option>crit</option>,
 218                                 <option>err</option>,
 219                                 <option>warning</option>,
 220                                 <option>notice</option>,
 221                                 <option>info</option>,
 222                                 <option>debug</option>.</para></listitem>
 223                         </varlistentry>
 224                         <varlistentry>
 225                                 <term><option>--log-color=</option></term>
 226
 227                                 <listitem><para>Highlight important
 228                                 log messages. Argument is a boolean
 229                                 value. If the argument is omitted it
 230                                 defaults to
 231                                 <option>true</option>.</para></listitem>
 232                         </varlistentry>
 233                         <varlistentry>
 234                                 <term><option>--log-location=</option></term>
 235
 236                                 <listitem><para>Include code location
 237                                 in log messages. This is mostly
 238                                 relevant for debugging
 239                                 purposes. Argument is a boolean
 240                                 value. If the argument is omitted
 241                                 it defaults to
 242                                 <option>true</option>.</para></listitem>
 243                         </varlistentry>
 244                 </variablelist>
 245         </refsect1>
 246
 247         <refsect1>
 248                 <title>Concepts</title>
 249
 250                 <para>systemd provides a dependency system between
 251                 various entities called "units". Units encapsulate
 252                 various objects that are relevant for system boot-up
 253                 and maintenance. The majority of units are configured
 254                 in unit configuration files, whose syntax and basic
 255                 set of options is described in
 256                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 257                 however some are created automatically from other
 258                 configuration or dynamically from system state. Units
 259                 may be 'active' (meaning started, bound, plugged in,
 260                 ...  depending on the unit type, see below), or
 261                 'inactive' (meaning stopped, unbound, unplugged, ...),
 262                 as well as in the process of being activated or
 263                 deactivated, i.e. between the two states (these states
 264                 are called 'activating', 'deactivating'). A special
 265                 'failed' state is available as well which is very
 266                 similar to 'inactive' and is entered when the service
 267                 failed in some way (process returned error code on
 268                 exit, or crashed, or an operation timed out). If this
 269                 state is entered the cause will be logged, for later
 270                 reference. Note that the various unit types may have a
 271                 number of additional substates, which are mapped to
 272                 the five generalized unit states described
 273                 here.</para>
 274
 275                 <para>The following unit types are available:</para>
 276
 277                 <orderedlist>
 278                         <listitem><para>Service units, which control
 279                         daemons and the processes they consist of. For
 280                         details see
 281                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 282
 283                         <listitem><para>Socket units, which
 284                         encapsulate local IPC or network sockets in
 285                         the system, useful for socket-based
 286                         activation. For details about socket units see
 287                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 288                         for details on socket-based activation and
 289                         other forms of activation, see
 290                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 291
 292                         <listitem><para>Target units are useful to
 293                         group units, or provide well-known
 294                         synchronization points during boot-up, see
 295                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 296
 297                         <listitem><para>Device units expose kernel
 298                         devices in systemd and may be used to
 299                         implement device-based activation. For details
 300                         see
 301                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 302
 303                         <listitem><para>Mount units control mount
 304                         points in the file system, for details see
 305                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 306
 307                         <listitem><para>Automount units provide
 308                         automount capabilities, for on-demand mounting
 309                         of file systems as well as parallelized
 310                         boot-up. See
 311                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 312
 313                         <listitem><para>Snapshot units can be used to
 314                         temporarily save the state of the set of
 315                         systemd units, which later may be restored by
 316                         activating the saved snapshot unit. For more
 317                         information see
 318                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 319
 320                         <listitem><para>Timer units are useful for
 321                         triggering activation of other units based on
 322                         timers. You may find details in
 323                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 324
 325                         <listitem><para>Swap units are very similar to
 326                         mount units and encapsulated memory swap
 327                         partitions or files of the operating
 328                         systemd. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 329
 330                         <listitem><para>Path units may be used
 331                         to activate other services when file system
 332                         objects change or are modified. See
 333                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 334
 335                 </orderedlist>
 336
 337                 <para>Units are named as their configuration
 338                 files. Some units have special semantics. A detailed
 339                 list you may find in
 340                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 341
 342                 <para>systemd knows various kinds of dependencies,
 343                 including positive and negative requirement
 344                 dependencies (i.e. <varname>Requires=</varname> and
 345                 <varname>Conflicts=</varname>) as well as ordering
 346                 dependencies (<varname>After=</varname> and
 347                 <varname>Before=</varname>). NB: ordering and
 348                 requirement dependencies are orthogonal. If only a
 349                 requirement dependency exists between two units
 350                 (e.g. <filename>foo.service</filename> requires
 351                 <filename>bar.service</filename>), but no ordering
 352                 dependency (e.g. <filename>foo.service</filename>
 353                 after <filename>bar.service</filename>) and both are
 354                 requested to start, they will be started in
 355                 parallel. It is a common pattern that both requirement
 356                 and ordering dependencies are placed between two
 357                 units. Also note that the majority of dependencies are
 358                 implicitly created and maintained by systemd. In most
 359                 cases it should be unnecessary to declare additional
 360                 dependencies manually, however it is possible to do
 361                 this.</para>
 362
 363                 <para>Application programs and units (via
 364                 dependencies) may requests state changes of units. In
 365                 systemd, these requests are encapsulated as 'jobs' and
 366                 maintained in a job queue. Jobs may succeed or can
 367                 fail, their execution is ordered based on the ordering
 368                 dependencies of the units they have been scheduled
 369                 for.</para>
 370
 371                 <para>On boot systemd activates the target unit
 372                 <filename>default.target</filename> whose job is to
 373                 activate on-boot services and other on-boot units by
 374                 pulling them in via dependencies. Usually the unit
 375                 name is just an alias (symlink) for either
 376                 <filename>graphical.target</filename> (for
 377                 fully-featured boots into the UI) or
 378                 <filename>multi-user.target</filename> (for limited
 379                 console-only boots for use in embedded or server
 380                 environments, or similar; a subset of
 381                 graphical.target). However it is at the discretion of
 382                 the administrator to configure it as an alias to any
 383                 other target unit. See
 384                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 385                 for details about these target units.</para>
 386
 387                 <para>Processes systemd spawns are placed in
 388                 individual Linux control groups named after the unit
 389                 which they belong to in the private systemd
 390                 hierarchy. (see <ulink
 391                 url="http://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 392                 for more information about control groups, or short
 393                 "cgroups"). systemd uses this to effectively keep
 394                 track of processes. Control group information is
 395                 maintained in the kernel, and is accessible via the
 396                 file system hierarchy (beneath
 397                 <filename>/sys/fs/cgroup/systemd/</filename>), or in tools
 398                 such as
 399                 <citerefentry><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 400                 (<command>ps xawf -eo pid,user,cgroup,args</command>
 401                 is particularly useful to list all processes and the
 402                 systemd units they belong to.).</para>
 403
 404                 <para>systemd is compatible with the SysV init system
 405                 to a large degree: SysV init scripts are supported and
 406                 simply read as an alternative (though limited)
 407                 configuration file format. The SysV
 408                 <filename>/dev/initctl</filename> interface is
 409                 provided, and compatibility implementations of the
 410                 various SysV client tools are available. In addition to
 411                 that, various established Unix functionality such as
 412                 <filename>/etc/fstab</filename> or the
 413                 <filename>utmp</filename> database are
 414                 supported.</para>
 415
 416                 <para>systemd has a minimal transaction system: if a
 417                 unit is requested to start up or shut down it will add
 418                 it and all its dependencies to a temporary
 419                 transaction. Then, it will verify if the transaction
 420                 is consistent (i.e. whether the ordering of all units
 421                 is cycle-free). If it is not, systemd will try to fix
 422                 it up, and removes non-essential jobs from the
 423                 transaction that might remove the loop. Also, systemd
 424                 tries to suppress non-essential jobs in the
 425                 transaction that would stop a running service. Finally
 426                 it is checked whether the jobs of the transaction
 427                 contradict jobs that have already been queued, and
 428                 optionally the transaction is aborted then. If all
 429                 worked out and the transaction is consistent and
 430                 minimized in its impact it is merged with all already
 431                 outstanding jobs and added to the run
 432                 queue. Effectively this means that before executing a
 433                 requested operation, systemd will verify that it makes
 434                 sense, fixing it if possible, and only failing if it
 435                 really cannot work.</para>
 436
 437                 <para>Systemd contains native implementations of
 438                 various tasks that need to be executed as part of the
 439                 boot process. For example, it sets the host name or
 440                 configures the loopback network device. It also sets
 441                 up and mounts various API file systems, such as
 442                 <filename>/sys</filename> or
 443                 <filename>/proc</filename>.</para>
 444
 445                 <para>For more information about the concepts and
 446                 ideas behind systemd please refer to the <ulink
 447                 url="http://0pointer.de/blog/projects/systemd.html">Original
 448                 Design Document</ulink>.</para>
 449
 450                 <para>Note that some but not all interfaces provided
 451                 by systemd are covered by the <ulink
 452                 url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 453                 Stability Promise</ulink>.</para>
 454         </refsect1>
 455
 456         <refsect1>
 457                 <title>Directories</title>
 458
 459                 <variablelist>
 460                         <varlistentry>
 461                                 <term>System unit directories</term>
 462
 463                                 <listitem><para>The systemd system
 464                                 manager reads unit configuration from
 465                                 various directories. Packages that
 466                                 want to install unit files shall place
 467                                 them in the directory returned by
 468                                 <command>pkg-config systemd
 469                                 --variable=systemdsystemunitdir</command>. Other
 470                                 directories checked are
 471                                 <filename>/usr/local/share/systemd/system</filename>
 472                                 and
 473                                 <filename>/usr/share/systemd/system</filename>. User
 474                                 configuration always takes
 475                                 precedence. <command>pkg-config
 476                                 systemd
 477                                 --variable=systemdsystemconfdir</command>
 478                                 returns the path of the system
 479                                 configuration directory. Packages
 480                                 should alter the content of these
 481                                 directories only with the
 482                                 <command>enable</command> and
 483                                 <command>disable</command> commands of
 484                                 the
 485                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 486                                 tool.</para></listitem>
 487                         </varlistentry>
 488                 </variablelist>
 489
 490                 <variablelist>
 491                         <varlistentry>
 492                                 <term>Session unit directories</term>
 493
 494                                 <listitem><para>Similar rules apply
 495                                 for the session unit
 496                                 directories. However, here the <ulink
 497                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 498                                 Base Directory specification</ulink>
 499                                 is followed to find
 500                                 units. Applications should place their
 501                                 unit files in the directory returned
 502                                 by <command>pkg-config systemd
 503                                 --variable=systemdsessionunitdir</command>. Global
 504                                 configuration is done in the directory
 505                                 reported by <command>pkg-config
 506                                 systemd
 507                                 --variable=systemdsessionconfdir</command>. The
 508                                 <command>enable</command> and
 509                                 <command>disable</command> commands of
 510                                 the
 511                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 512                                 tool can handle both global (i.e. for
 513                                 all users) and private (for one user)
 514                                 enabling/disabling of
 515                                 units.</para></listitem>
 516                         </varlistentry>
 517                 </variablelist>
 518
 519                 <variablelist>
 520                         <varlistentry>
 521                                 <term>SysV init scripts directory</term>
 522
 523                                 <listitem><para>The location of the
 524                                 SysV init script directory varies
 525                                 between distributions. If systemd
 526                                 cannot find a native unit file for a
 527                                 requested service, it will look for a
 528                                 SysV init script of the same name
 529                                 (with the
 530                                 <filename>.service</filename> suffix
 531                                 removed).</para></listitem>
 532                         </varlistentry>
 533                 </variablelist>
 534
 535                 <variablelist>
 536                         <varlistentry>
 537                                 <term>SysV runlevel link farm directory</term>
 538
 539                                 <listitem><para>The location of the
 540                                 SysV runlevel link farm directory
 541                                 varies between distributions. systemd
 542                                 will take the link farm into account
 543                                 when figuring out whether a service
 544                                 shall be enabled. Note that a service
 545                                 unit with a native unit configuration
 546                                 file cannot be started by activating it
 547                                 in the SysV runlevel link
 548                                 farm.</para></listitem>
 549                         </varlistentry>
 550                 </variablelist>
 551         </refsect1>
 552
 553         <refsect1>
 554                 <title>Signals</title>
 555
 556                 <variablelist>
 557                         <varlistentry>
 558                                 <term>SIGTERM</term>
 559
 560                                 <listitem><para>Upon receiving this
 561                                 signal the systemd system manager
 562                                 serializes its state, reexecutes
 563                                 itself and deserializes the saved
 564                                 state again. This is mostly equivalent
 565                                 to <command>systemctl
 566                                 daemon-reexec</command>.</para>
 567
 568                                 <para>systemd session managers will
 569                                 start the
 570                                 <filename>exit.target</filename> unit
 571                                 when this signal is received. This is
 572                                 mostly equivalent to
 573                                 <command>systemctl --session start
 574                                 exit.target</command>.</para></listitem>
 575                         </varlistentry>
 576
 577                         <varlistentry>
 578                                 <term>SIGINT</term>
 579
 580                                 <listitem><para>Upon receiving this
 581                                 signal the systemd system manager will
 582                                 start the
 583                                 <filename>ctrl-alt-del.target</filename> unit. This
 584                                 is mostly equivalent to
 585                                 <command>systemctl start
 586                                 ctl-alt-del.target</command>.</para>
 587
 588                                 <para>systemd session managers
 589                                 treat this signal the same way as
 590                                 SIGTERM.</para></listitem>
 591                         </varlistentry>
 592
 593                         <varlistentry>
 594                                 <term>SIGWINCH</term>
 595
 596                                 <listitem><para>When this signal is
 597                                 received the systemd system manager
 598                                 will start the
 599                                 <filename>kbrequest.target</filename>
 600                                 unit. This is mostly equivalent to
 601                                 <command>systemctl start
 602                                 kbrequest.target</command>.</para>
 603
 604                                 <para>This signal is ignored by
 605                                 systemd session
 606                                 managers.</para></listitem>
 607                         </varlistentry>
 608
 609                         <varlistentry>
 610                                 <term>SIGPWR</term>
 611
 612                                 <listitem><para>When this signal is
 613                                 received the systemd manager
 614                                 will start the
 615                                 <filename>sigpwr.target</filename>
 616                                 unit. This is mostly equivalent to
 617                                 <command>systemctl start
 618                                 sigpwr.target</command>.</para></listitem>
 619                         </varlistentry>
 620
 621                         <varlistentry>
 622                                 <term>SIGUSR1</term>
 623
 624                                 <listitem><para>When this signal is
 625                                 received the systemd manager will try
 626                                 to reconnect to the D-Bus
 627                                 bus.</para></listitem>
 628                         </varlistentry>
 629
 630                         <varlistentry>
 631                                 <term>SIGUSR2</term>
 632
 633                                 <listitem><para>When this signal is
 634                                 received the systemd manager will log
 635                                 its complete state in human readable
 636                                 form. The data logged is the same as
 637                                 printed by <command>systemctl
 638                                 dump</command>.</para></listitem>
 639                         </varlistentry>
 640
 641                         <varlistentry>
 642                                 <term>SIGHUP</term>
 643
 644                                 <listitem><para>Reloads the complete
 645                                 daemon configuration. This is mostly
 646                                 equivalent to <command>systemctl
 647                                 daemon-reload</command>.</para></listitem>
 648                         </varlistentry>
 649
 650                         <varlistentry>
 651                                 <term>SIGRTMIN+0</term>
 652
 653                                 <listitem><para>Enters default mode, starts the
 654                                 <filename>default.target</filename>
 655                                 unit. This is mostly equivalent to
 656                                 <command>systemctl start
 657                                 default.target</command>.</para></listitem>
 658                         </varlistentry>
 659
 660                         <varlistentry>
 661                                 <term>SIGRTMIN+1</term>
 662
 663                                 <listitem><para>Enters rescue mode,
 664                                 starts the
 665                                 <filename>rescue.target</filename>
 666                                 unit. This is mostly equivalent to
 667                                 <command>systemctl isolate
 668                                 rescue.target</command>.</para></listitem>
 669                         </varlistentry>
 670
 671                         <varlistentry>
 672                                 <term>SIGRTMIN+2</term>
 673
 674                                 <listitem><para>Enters emergency mode,
 675                                 starts the
 676                                 <filename>emergency.service</filename>
 677                                 unit. This is mostly equivalent to
 678                                 <command>systemctl isolate
 679                                 emergency.service</command>.</para></listitem>
 680                         </varlistentry>
 681
 682                         <varlistentry>
 683                                 <term>SIGRTMIN+3</term>
 684
 685                                 <listitem><para>Halts the machine,
 686                                 starts the
 687                                 <filename>halt.target</filename>
 688                                 unit. This is mostly equivalent to
 689                                 <command>systemctl start
 690                                 halt.target</command>.</para></listitem>
 691                         </varlistentry>
 692
 693                         <varlistentry>
 694                                 <term>SIGRTMIN+4</term>
 695
 696                                 <listitem><para>Powers off the machine,
 697                                 starts the
 698                                 <filename>poweroff.target</filename>
 699                                 unit. This is mostly equivalent to
 700                                 <command>systemctl start
 701                                 poweroff.target</command>.</para></listitem>
 702                         </varlistentry>
 703
 704                         <varlistentry>
 705                                 <term>SIGRTMIN+5</term>
 706
 707                                 <listitem><para>Reboots the machine,
 708                                 starts the
 709                                 <filename>reboot.target</filename>
 710                                 unit. This is mostly equivalent to
 711                                 <command>systemctl start
 712                                 reboot.target</command>.</para></listitem>
 713                         </varlistentry>
 714                 </variablelist>
 715         </refsect1>
 716
 717         <refsect1>
 718                 <title>Environment</title>
 719
 720                 <variablelist>
 721                         <varlistentry>
 722                                 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 723                                 <listitem><para>systemd reads the
 724                                 log level from this environment
 725                                 variable. This can be overridden with
 726                                 <option>--log-level=</option>.</para></listitem>
 727                         </varlistentry>
 728
 729                         <varlistentry>
 730                                 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 731                                 <listitem><para>systemd reads the
 732                                 log target from this environment
 733                                 variable. This can be overridden with
 734                                 <option>--log-target=</option>.</para></listitem>
 735                         </varlistentry>
 736
 737                         <varlistentry>
 738                                 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 739                                 <listitem><para>Controls whether
 740                                 systemd highlights important log
 741                                 messages. This can be overridden with
 742                                 <option>--log-color=</option>.</para></listitem>
 743                         </varlistentry>
 744
 745                         <varlistentry>
 746                                 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 747                                 <listitem><para>Controls whether
 748                                 systemd prints the code location along
 749                                 with log messages. This can be
 750                                 overridden with
 751                                 <option>--log-location=</option>.</para></listitem>
 752                         </varlistentry>
 753
 754                         <varlistentry>
 755                                 <term><varname>$XDG_CONFIG_HOME</varname></term>
 756                                 <term><varname>$XDG_CONFIG_DIRS</varname></term>
 757                                 <term><varname>$XDG_DATA_HOME</varname></term>
 758                                 <term><varname>$XDG_DATA_DIRS</varname></term>
 759
 760                                 <listitem><para>The systemd session
 761                                 manager uses these variables in
 762                                 accordance to the <ulink
 763                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 764                                 Base Directory specification</ulink>
 765                                 to find its configuration.</para></listitem>
 766                         </varlistentry>
 767
 768                         <varlistentry>
 769                                 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 770
 771                                 <listitem><para>Controls where systemd
 772                                 looks for unit
 773                                 files.</para></listitem>
 774                         </varlistentry>
 775
 776                         <varlistentry>
 777                                 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 778
 779                                 <listitem><para>Controls where systemd
 780                                 looks for SysV init scripts.</para></listitem>
 781                         </varlistentry>
 782
 783                         <varlistentry>
 784                                 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 785
 786                                 <listitem><para>Controls where systemd
 787                                 looks for SysV init script runlevel link
 788                                 farms.</para></listitem>
 789                         </varlistentry>
 790
 791                         <varlistentry>
 792                                 <term><varname>$LISTEN_PID</varname></term>
 793                                 <term><varname>$LISTEN_FDS</varname></term>
 794
 795                                 <listitem><para>Set by systemd for
 796                                 supervised processes during
 797                                 socket-based activation. See
 798                                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 799                                 for more information.
 800                                 </para></listitem>
 801                         </varlistentry>
 802
 803                         <varlistentry>
 804                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 805
 806                                 <listitem><para>Set by systemd for
 807                                 supervised processes for status and
 808                                 start-up completion notification. See
 809                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 810                                 for more information.
 811                                 </para></listitem>
 812                         </varlistentry>
 813                 </variablelist>
 814         </refsect1>
 815
 816         <refsect1>
 817                 <title>Kernel Command Line</title>
 818
 819                 <para>When run as system instance systemd parses a few kernel command line arguments:</para>
 820
 821                 <variablelist>
 822                         <varlistentry>
 823                                 <term><varname>systemd.unit=</varname></term>
 824
 825                                 <listitem><para>Overrides the unit to
 826                                 activate on boot. Defaults to
 827                                 <filename>default.target</filename>. This
 828                                 may be used to temporarily boot into a
 829                                 different boot unit, for example
 830                                 <filename>rescue.target</filename> or
 831                                 <filename>emergency.service</filename>. See
 832                                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 833                                 for details about these
 834                                 units.</para></listitem>
 835                         </varlistentry>
 836
 837                         <varlistentry>
 838                                 <term><varname>systemd.dump_core=</varname></term>
 839
 840                                 <listitem><para>Takes a boolean
 841                                 argument. If <option>true</option>
 842                                 systemd dumps core when it
 843                                 crashes. Otherwise no core dump is
 844                                 created. Defaults to
 845                                 <option>true</option>.</para></listitem>
 846                         </varlistentry>
 847
 848                         <varlistentry>
 849                                 <term><varname>systemd.crash_shell=</varname></term>
 850
 851                                 <listitem><para>Takes a boolean
 852                                 argument. If <option>true</option>
 853                                 systemd spawns a shell when it
 854                                 crashes. Otherwise no core dump is
 855                                 created. Defaults to
 856                                 <option>false</option>, for security
 857                                 reasons, as the shell is not protected
 858                                 by any password
 859                                 authentication.</para></listitem>
 860                         </varlistentry>
 861
 862                         <varlistentry>
 863                                 <term><varname>systemd.crash_chvt=</varname></term>
 864
 865                                 <listitem><para>Takes an integer
 866                                 argument. If positive systemd
 867                                 activates the specified virtual
 868                                 terminal when it crashes. Defaults to
 869                                 <literal>-1</literal>.</para></listitem>
 870                         </varlistentry>
 871
 872                         <varlistentry>
 873                                 <term><varname>systemd.confirm_spawn=</varname></term>
 874
 875                                 <listitem><para>Takes a boolean
 876                                 argument. If <option>true</option>
 877                                 asks for confirmation when spawning
 878                                 processes. Defaults to
 879                                 <option>false</option>.</para></listitem>
 880                         </varlistentry>
 881
 882                         <varlistentry>
 883                                 <term><varname>systemd.show_status=</varname></term>
 884
 885                                 <listitem><para>Takes a boolean
 886                                 argument. If <option>true</option>
 887                                 shows terse service status updates on
 888                                 the console during bootup. Defaults to
 889                                 <option>true</option>.</para></listitem>
 890                         </varlistentry>
 891
 892                         <varlistentry>
 893                                 <term><varname>systemd.sysv_console=</varname></term>
 894
 895                                 <listitem><para>Takes a boolean
 896                                 argument. If <option>true</option>
 897                                 output of SysV init scripts will be
 898                                 directed to the console. Defaults to
 899                                 <option>true</option>, unless
 900                                 <option>quiet</option> is passed as
 901                                 kernel command line option in which
 902                                 case it defaults to
 903                                 <option>false</option>.</para></listitem>
 904                         </varlistentry>
 905
 906                         <varlistentry>
 907                                 <term><varname>systemd.log_target=</varname></term>
 908                                 <term><varname>systemd.log_level=</varname></term>
 909                                 <term><varname>systemd.log_color=</varname></term>
 910                                 <term><varname>systemd.log_location=</varname></term>
 911
 912                                 <listitem><para>Controls log output,
 913                                 with the same effect as the
 914                                 <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
 915                                 environment variables described above.</para></listitem>
 916                         </varlistentry>
 917
 918                 </variablelist>
 919         </refsect1>
 920
 921         <refsect1>
 922                 <title>Sockets and FIFOs</title>
 923
 924                 <variablelist>
 925                         <varlistentry>
 926                                 <term><filename>@/org/freedesktop/systemd1/notify</filename></term>
 927
 928                                 <listitem><para>Daemon status
 929                                 notification socket. This is an AF_UNIX
 930                                 datagram socket in the Linux abstract
 931                                 namespace, and is used to implement
 932                                 the daemon notification logic as
 933                                 implemented by
 934                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 935
 936                         </varlistentry>
 937
 938                         <varlistentry>
 939                                 <term><filename>@/org/freedesktop/systemd1/logger</filename></term>
 940
 941                                 <listitem><para>Used internally by the
 942                                 <filename>systemd-logger.service</filename>
 943                                 unit to connect STDOUT and/or STDERR
 944                                 of spawned processes to
 945                                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 946                                 or the kernel log buffer. This is an
 947                                 AF_UNIX stream socket in the Linux
 948                                 abstract namespace.</para></listitem>
 949                         </varlistentry>
 950
 951                         <varlistentry>
 952                                 <term><filename>@/org/freedesktop/systemd1/shutdown</filename></term>
 953
 954                                 <listitem><para>Used internally by the
 955                                 <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 956                                 tool to implement delayed
 957                                 shutdowns. This is an AF_UNIX datagram
 958                                 socket in the Linux abstract
 959                                 namespace.</para></listitem>
 960                         </varlistentry>
 961
 962                         <varlistentry>
 963                                 <term><filename>@/org/freedesktop/systemd1/private</filename></term>
 964
 965                                 <listitem><para>Used internally as
 966                                 communication channel between
 967                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 968                                 and the systemd process. This is an
 969                                 AF_UNIX stream socket in the Linux
 970                                 abstract namespace. This interface is
 971                                 private to systemd and should not be
 972                                 used in external
 973                                 projects.</para></listitem>
 974                         </varlistentry>
 975
 976                         <varlistentry>
 977                                 <term><filename>/dev/initctl</filename></term>
 978
 979                                 <listitem><para>Limited compatibility
 980                                 support for the SysV client interface,
 981                                 as implemented by the
 982                                 <filename>systemd-initctl.service</filename>
 983                                 unit. This is a named pipe in the file
 984                                 system. This interface is obsolete and
 985                                 should not be used in new
 986                                 applications.</para></listitem>
 987                         </varlistentry>
 988                 </variablelist>
 989         </refsect1>
 990
 991         <refsect1>
 992                 <title>See Also</title>
 993                 <para>
 994                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 995                         <citerefentry><refentrytitle>systemadm</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 996                         <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 997                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 998                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 999                         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1000                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1001                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1002                 </para>
1003         </refsect1>
1004
1005 </refentry>