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 not
 145                                 (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
 151                                 debugging.</para></listitem>
 152                         </varlistentry>
 153                         <varlistentry>
 154                                 <term><option>--dump-core</option></term>
 155
 156                                 <listitem><para>Dump core on crash. This switch has no effect when run as session instance.</para></listitem>
 157                         </varlistentry>
 158                         <varlistentry>
 159                                 <term><option>--crash-shell</option></term>
 160
 161                                 <listitem><para>Run shell on crash. This switch has no effect when run as session instance.</para></listitem>
 162                         </varlistentry>
 163                         <varlistentry>
 164                                 <term><option>--confirm-spawn</option></term>
 165
 166                                 <listitem><para>Ask for confirmation when spawning processes. This switch has no effect when run as session instance.</para></listitem>
 167                         </varlistentry>
 168                         <varlistentry>
 169                                 <term><option>--show-status=</option></term>
 170
 171                                 <listitem><para>Show terse service
 172                                 status information while booting. This
 173                                 switch has no effect when run as
 174                                 session instance. Takes a boolean
 175                                 argument which may be omitted
 176                                 which is interpreted as
 177                                 <option>true</option>.</para></listitem>
 178                         </varlistentry>
 179                         <varlistentry>
 180                                 <term><option>--sysv-console=</option></term>
 181
 182                                 <listitem><para>Controls whether
 183                                 output of SysV init scripts will be
 184                                 directed to the console. This switch
 185                                 has no effect when run as session
 186                                 instance. Takes a boolean argument
 187                                 which may be omitted which is
 188                                 interpreted as
 189                                 <option>true</option>.</para></listitem>
 190                         </varlistentry>
 191                         <varlistentry>
 192                                 <term><option>--log-target=</option></term>
 193
 194                                 <listitem><para>Set log
 195                                 target. Argument must be one of
 196                                 <option>console</option>,
 197                                 <option>syslog</option>,
 198                                 <option>kmsg</option>,
 199                                 <option>syslog-or-kmsg</option>,
 200                                 <option>null</option>.</para></listitem>
 201                         </varlistentry>
 202                         <varlistentry>
 203                                 <term><option>--log-level=</option></term>
 204
 205                                 <listitem><para>Set log level. As
 206                                 argument this accepts a numerical log
 207                                 level or the well-known <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 208                                 symbolic names (lowercase):
 209                                 <option>emerg</option>,
 210                                 <option>alert</option>,
 211                                 <option>crit</option>,
 212                                 <option>err</option>,
 213                                 <option>warning</option>,
 214                                 <option>notice</option>,
 215                                 <option>info</option>,
 216                                 <option>debug</option>.</para></listitem>
 217                         </varlistentry>
 218                         <varlistentry>
 219                                 <term><option>--log-color=</option></term>
 220
 221                                 <listitem><para>Highlight important
 222                                 log messages. Argument is a boolean
 223                                 value. If the argument is omitted it
 224                                 defaults to
 225                                 <option>true</option>.</para></listitem>
 226                         </varlistentry>
 227                         <varlistentry>
 228                                 <term><option>--log-location=</option></term>
 229
 230                                 <listitem><para>Include code location
 231                                 in log messages. This is mostly
 232                                 relevant for debugging
 233                                 purposes. Argument is a boolean
 234                                 value. If the argument is omitted
 235                                 it defaults to
 236                                 <option>true</option>.</para></listitem>
 237                         </varlistentry>
 238                 </variablelist>
 239         </refsect1>
 240
 241         <refsect1>
 242                 <title>Concepts</title>
 243
 244                 <para>systemd provides a dependency system between
 245                 various entities called "units". Units encapsulate
 246                 various objects that are relevant for system boot-up
 247                 and maintenance. The majority of units are configured
 248                 in unit configuration files, whose syntax and basic
 249                 set of options is described in
 250                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 251                 however some are created automatically from other
 252                 configuration or dynamically from system state. Units
 253                 may be 'active' (meaning started, bound, plugged in,
 254                 ...  depending on the unit type, see below), or
 255                 'inactive' (meaning stopped, unbound, unplugged, ...),
 256                 as well as in the process of being activated or
 257                 deactivated, i.e. between the two states (these states
 258                 are called 'activating', 'deactivating'). A special
 259                 'failed' state is available as well which is very
 260                 similar to 'inactive' and is entered when the service
 261                 failed in some way (process returned error code on
 262                 exit, or crashed, or an operation timed out). If this
 263                 state is entered the cause will be logged, for later
 264                 reference. Note that the various unit types may have a
 265                 number of additional substates, which are mapped to
 266                 the five generalized unit states described
 267                 here.</para>
 268
 269                 <para>The following unit types are available:</para>
 270
 271                 <orderedlist>
 272                         <listitem><para>Service units, which control
 273                         daemons and the processes they consist of. For
 274                         details see
 275                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 276
 277                         <listitem><para>Socket units, which
 278                         encapsulate local IPC or network sockets in
 279                         the system, useful for socket-based
 280                         activation. For details about socket units see
 281                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 282                         for details on socket-based activation and
 283                         other forms of activation, see
 284                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 285
 286                         <listitem><para>Target units are useful to
 287                         group units, or provide well-known
 288                         synchronization points during boot-up, see
 289                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 290
 291                         <listitem><para>Device units expose kernel
 292                         devices in systemd and may be used to
 293                         implement device-based activation. For details
 294                         see
 295                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 296
 297                         <listitem><para>Mount units control mount
 298                         points in the file system, for details see
 299                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 300
 301                         <listitem><para>Automount units provide
 302                         automount capabilities, for on-demand mounting
 303                         of file systems as well as parallelized
 304                         boot-up. See
 305                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 306
 307                         <listitem><para>Snapshot units can be used to
 308                         temporarily save the state of the set of
 309                         systemd units, which later may be restored by
 310                         activating the saved snapshot unit. For more
 311                         information see
 312                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 313
 314                         <listitem><para>Timer units are useful for
 315                         triggering activation of other units based on
 316                         timers. You may find details in
 317                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 318
 319                         <listitem><para>Swap units are very similar to
 320                         mount units and encapsulated memory swap
 321                         partitions or files of the operating
 322                         systemd. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 323
 324                         <listitem><para>Path units may be used
 325                         to activate other services when file system
 326                         objects change or are modified. See
 327                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 328
 329                 </orderedlist>
 330
 331                 <para>Units are named as their configuration
 332                 files. Some units have special semantics. A detailed
 333                 list you may find in
 334                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 335
 336                 <para>systemd knows various kinds of dependencies,
 337                 including positive and negative requirement
 338                 dependencies (i.e. <varname>Requires=</varname> and
 339                 <varname>Conflicts=</varname>) as well as ordering
 340                 dependencies (<varname>After=</varname> and
 341                 <varname>Before=</varname>). NB: ordering and
 342                 requirement dependencies are orthogonal. If only a
 343                 requirement dependency exists between two units
 344                 (e.g. <filename>foo.service</filename> requires
 345                 <filename>bar.service</filename>), but no ordering
 346                 dependency (e.g. <filename>foo.service</filename>
 347                 after <filename>bar.service</filename>) and both are
 348                 requested to start, they will be started in
 349                 parallel. It is a common pattern that both requirement
 350                 and ordering dependencies are placed between two
 351                 units. Also note that the majority of dependencies are
 352                 implicitly created and maintained by systemd. In most
 353                 cases it should be unnecessary to declare additional
 354                 dependencies manually, however it is possible to do
 355                 this.</para>
 356
 357                 <para>Application programs and units (via
 358                 dependencies) may requests state changes of units. In
 359                 systemd, these requests are encapsulated as 'jobs' and
 360                 maintained in a job queue. Jobs may succeed or can
 361                 fail, their execution is ordered based on the ordering
 362                 dependencies of the units they have been scheduled
 363                 for.</para>
 364
 365                 <para>On boot systemd activates the target unit
 366                 <filename>default.target</filename> whose job is to
 367                 activate on-boot services and other on-boot units by
 368                 pulling them in via dependencies. Usually the unit
 369                 name is just an alias (symlink) for either
 370                 <filename>graphical.target</filename> (for
 371                 fully-featured boots into the UI) or
 372                 <filename>multi-user.target</filename> (for limited
 373                 console-only boots for use in embedded or server
 374                 environments, or similar; a subset of
 375                 graphical.target). However it is at the discretion of
 376                 the administrator to configure it as an alias to any
 377                 other target unit. See
 378                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 379                 for details about these target units.</para>
 380
 381                 <para>Processes systemd spawns are placed in
 382                 individual Linux control groups named after the unit
 383                 which they belong to in the private systemd
 384                 hierarchy. (see <ulink
 385                 url="http://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 386                 for more information about control groups, or short
 387                 "cgroups"). systemd uses this to effectively keep
 388                 track of processes. Control group information is
 389                 maintained in the kernel, and is accessible via the
 390                 file system hierarchy (beneath
 391                 <filename>/sys/fs/cgroup/systemd/</filename>), or in tools
 392                 such as
 393                 <citerefentry><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 394                 (<command>ps xawf -eo pid,user,cgroup,args</command>
 395                 is particularly useful to list all processes and the
 396                 systemd units they belong to.).</para>
 397
 398                 <para>systemd is compatible with the SysV init system
 399                 to a large degree: SysV init scripts are supported and
 400                 simply read as an alternative (though limited)
 401                 configuration file format. The SysV
 402                 <filename>/dev/initctl</filename> interface is
 403                 provided, and compatibility implementations of the
 404                 various SysV client tools are available. In addition to
 405                 that, various established Unix functionality such as
 406                 <filename>/etc/fstab</filename> or the
 407                 <filename>utmp</filename> database are
 408                 supported.</para>
 409
 410                 <para>systemd has a minimal transaction system: if a
 411                 unit is requested to start up or shut down it will add
 412                 it and all its dependencies to a temporary
 413                 transaction. Then, it will verify if the transaction
 414                 is consistent (i.e. whether the ordering of all units
 415                 is cycle-free). If it is not, systemd will try to fix
 416                 it up, and removes non-essential jobs from the
 417                 transaction that might remove the loop. Also, systemd
 418                 tries to suppress non-essential jobs in the
 419                 transaction that would stop a running service. Finally
 420                 it is checked whether the jobs of the transaction
 421                 contradict jobs that have already been queued, and
 422                 optionally the transaction is aborted then. If all
 423                 worked out and the transaction is consistent and
 424                 minimized in its impact it is merged with all already
 425                 outstanding jobs and added to the run
 426                 queue. Effectively this means that before executing a
 427                 requested operation, systemd will verify that it makes
 428                 sense, fixing it if possible, and only failing if it
 429                 really cannot work.</para>
 430
 431                 <para>Systemd contains native implementations of
 432                 various tasks that need to be executed as part of the
 433                 boot process. For example, it sets the host name or
 434                 configures the loopback network device. It also sets
 435                 up and mounts various API file systems, such as
 436                 <filename>/sys</filename> or
 437                 <filename>/proc</filename>.</para>
 438
 439                 <para>For more information about the concepts and
 440                 ideas behind systemd please refer to the <ulink
 441                 url="http://0pointer.de/blog/projects/systemd.html">Original
 442                 Design Document</ulink>.</para>
 443         </refsect1>
 444
 445         <refsect1>
 446                 <title>Directories</title>
 447
 448                 <variablelist>
 449                         <varlistentry>
 450                                 <term>System unit directories</term>
 451
 452                                 <listitem><para>The systemd system
 453                                 manager reads unit configuration from
 454                                 various directories. Packages that
 455                                 want to install unit files shall place
 456                                 them in the directory returned by
 457                                 <command>pkg-config systemd
 458                                 --variable=systemdsystemunitdir</command>. Other
 459                                 directories checked are
 460                                 <filename>/usr/local/share/systemd/system</filename>
 461                                 and
 462                                 <filename>/usr/share/systemd/system</filename>. User
 463                                 configuration always takes
 464                                 precedence. <command>pkg-config
 465                                 systemd
 466                                 --variable=systemdsystemconfdir</command>
 467                                 returns the path of the system
 468                                 configuration directory. Packages
 469                                 should alter the content of these
 470                                 directories only with the
 471                                 <command>enable</command> and
 472                                 <command>disable</command> commands of
 473                                 the
 474                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 475                                 tool.</para></listitem>
 476                         </varlistentry>
 477                 </variablelist>
 478
 479                 <variablelist>
 480                         <varlistentry>
 481                                 <term>Session unit directories</term>
 482
 483                                 <listitem><para>Similar rules apply
 484                                 for the session unit
 485                                 directories. However, here the <ulink
 486                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 487                                 Base Directory specification</ulink>
 488                                 is followed to find
 489                                 units. Applications should place their
 490                                 unit files in the directory returned
 491                                 by <command>pkg-config systemd
 492                                 --variable=systemdsessionunitdir</command>. Global
 493                                 configuration is done in the directory
 494                                 reported by <command>pkg-config
 495                                 systemd
 496                                 --variable=systemdsessionconfdir</command>. The
 497                                 <command>enable</command> and
 498                                 <command>disable</command> commands of
 499                                 the
 500                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 501                                 tool can handle both global (i.e. for
 502                                 all users) and private (for one user)
 503                                 enabling/disabling of
 504                                 units.</para></listitem>
 505                         </varlistentry>
 506                 </variablelist>
 507
 508                 <variablelist>
 509                         <varlistentry>
 510                                 <term>SysV init scripts directory</term>
 511
 512                                 <listitem><para>The location of the
 513                                 SysV init script directory varies
 514                                 between distributions. If systemd
 515                                 cannot find a native unit file for a
 516                                 requested service, it will look for a
 517                                 SysV init script of the same name
 518                                 (with the
 519                                 <filename>.service</filename> suffix
 520                                 removed).</para></listitem>
 521                         </varlistentry>
 522                 </variablelist>
 523
 524                 <variablelist>
 525                         <varlistentry>
 526                                 <term>SysV runlevel link farm directory</term>
 527
 528                                 <listitem><para>The location of the
 529                                 SysV runlevel link farm directory
 530                                 varies between distributions. systemd
 531                                 will take the link farm into account
 532                                 when figuring out whether a service
 533                                 shall be enabled. Note that a service
 534                                 unit with a native unit configuration
 535                                 file cannot be started by activating it
 536                                 in the SysV runlevel link
 537                                 farm.</para></listitem>
 538                         </varlistentry>
 539                 </variablelist>
 540         </refsect1>
 541
 542         <refsect1>
 543                 <title>Signals</title>
 544
 545                 <variablelist>
 546                         <varlistentry>
 547                                 <term>SIGTERM</term>
 548
 549                                 <listitem><para>Upon receiving this
 550                                 signal the systemd system manager
 551                                 serializes its state, reexecutes
 552                                 itself and deserializes the saved
 553                                 state again. This is mostly equivalent
 554                                 to <command>systemctl
 555                                 daemon-reexec</command>.</para>
 556
 557                                 <para>systemd session managers will
 558                                 start the
 559                                 <filename>exit.target</filename> unit
 560                                 when this signal is received. This is
 561                                 mostly equivalent to
 562                                 <command>systemctl --session start
 563                                 exit.target</command>.</para></listitem>
 564                         </varlistentry>
 565
 566                         <varlistentry>
 567                                 <term>SIGINT</term>
 568
 569                                 <listitem><para>Upon receiving this
 570                                 signal the systemd system manager will
 571                                 start the
 572                                 <filename>ctrl-alt-del.target</filename> unit. This
 573                                 is mostly equivalent to
 574                                 <command>systemctl start
 575                                 ctl-alt-del.target</command>.</para>
 576
 577                                 <para>systemd session managers
 578                                 treat this signal the same way as
 579                                 SIGTERM.</para></listitem>
 580                         </varlistentry>
 581
 582                         <varlistentry>
 583                                 <term>SIGWINCH</term>
 584
 585                                 <listitem><para>When this signal is
 586                                 received the systemd system manager
 587                                 will start the
 588                                 <filename>kbrequest.target</filename>
 589                                 unit. This is mostly equivalent to
 590                                 <command>systemctl start
 591                                 kbrequest.target</command>.</para>
 592
 593                                 <para>This signal is ignored by
 594                                 systemd session
 595                                 managers.</para></listitem>
 596                         </varlistentry>
 597
 598                         <varlistentry>
 599                                 <term>SIGPWR</term>
 600
 601                                 <listitem><para>When this signal is
 602                                 received the systemd manager
 603                                 will start the
 604                                 <filename>sigpwr.target</filename>
 605                                 unit. This is mostly equivalent to
 606                                 <command>systemctl start
 607                                 sigpwr.target</command>.</para></listitem>
 608                         </varlistentry>
 609
 610                         <varlistentry>
 611                                 <term>SIGUSR1</term>
 612
 613                                 <listitem><para>When this signal is
 614                                 received the systemd manager will try
 615                                 to reconnect to the D-Bus
 616                                 bus.</para></listitem>
 617                         </varlistentry>
 618
 619                         <varlistentry>
 620                                 <term>SIGUSR2</term>
 621
 622                                 <listitem><para>When this signal is
 623                                 received the systemd manager will log
 624                                 its complete state in human readable
 625                                 form. The data logged is the same as
 626                                 printed by <command>systemctl
 627                                 dump</command>.</para></listitem>
 628                         </varlistentry>
 629
 630                         <varlistentry>
 631                                 <term>SIGHUP</term>
 632
 633                                 <listitem><para>Reloads the complete
 634                                 daemon configuration. This is mostly
 635                                 equivalent to <command>systemctl
 636                                 daemon-reload</command>.</para></listitem>
 637                         </varlistentry>
 638
 639                         <varlistentry>
 640                                 <term>SIGRTMIN+0</term>
 641
 642                                 <listitem><para>Enters default mode, starts the
 643                                 <filename>default.target</filename>
 644                                 unit. This is mostly equivalent to
 645                                 <command>systemctl start
 646                                 default.target</command>.</para></listitem>
 647                         </varlistentry>
 648
 649                         <varlistentry>
 650                                 <term>SIGRTMIN+1</term>
 651
 652                                 <listitem><para>Enters rescue mode,
 653                                 starts the
 654                                 <filename>rescue.target</filename>
 655                                 unit. This is mostly equivalent to
 656                                 <command>systemctl isolate
 657                                 rescue.target</command>.</para></listitem>
 658                         </varlistentry>
 659
 660                         <varlistentry>
 661                                 <term>SIGRTMIN+2</term>
 662
 663                                 <listitem><para>Enters emergency mode,
 664                                 starts the
 665                                 <filename>emergency.service</filename>
 666                                 unit. This is mostly equivalent to
 667                                 <command>systemctl isolate
 668                                 emergency.service</command>.</para></listitem>
 669                         </varlistentry>
 670
 671                         <varlistentry>
 672                                 <term>SIGRTMIN+3</term>
 673
 674                                 <listitem><para>Halts the machine,
 675                                 starts the
 676                                 <filename>halt.target</filename>
 677                                 unit. This is mostly equivalent to
 678                                 <command>systemctl start
 679                                 halt.target</command>.</para></listitem>
 680                         </varlistentry>
 681
 682                         <varlistentry>
 683                                 <term>SIGRTMIN+4</term>
 684
 685                                 <listitem><para>Powers off the machine,
 686                                 starts the
 687                                 <filename>poweroff.target</filename>
 688                                 unit. This is mostly equivalent to
 689                                 <command>systemctl start
 690                                 poweroff.target</command>.</para></listitem>
 691                         </varlistentry>
 692
 693                         <varlistentry>
 694                                 <term>SIGRTMIN+5</term>
 695
 696                                 <listitem><para>Reboots the machine,
 697                                 starts the
 698                                 <filename>reboot.target</filename>
 699                                 unit. This is mostly equivalent to
 700                                 <command>systemctl start
 701                                 reboot.target</command>.</para></listitem>
 702                         </varlistentry>
 703                 </variablelist>
 704         </refsect1>
 705
 706         <refsect1>
 707                 <title>Environment</title>
 708
 709                 <variablelist>
 710                         <varlistentry>
 711                                 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 712                                 <listitem><para>systemd reads the
 713                                 log level from this environment
 714                                 variable. This can be overridden with
 715                                 <option>--log-level=</option>.</para></listitem>
 716                         </varlistentry>
 717
 718                         <varlistentry>
 719                                 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 720                                 <listitem><para>systemd reads the
 721                                 log target from this environment
 722                                 variable. This can be overridden with
 723                                 <option>--log-target=</option>.</para></listitem>
 724                         </varlistentry>
 725
 726                         <varlistentry>
 727                                 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 728                                 <listitem><para>Controls whether
 729                                 systemd highlights important log
 730                                 messages. This can be overridden with
 731                                 <option>--log-color=</option>.</para></listitem>
 732                         </varlistentry>
 733
 734                         <varlistentry>
 735                                 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 736                                 <listitem><para>Controls whether
 737                                 systemd prints the code location along
 738                                 with log messages. This can be
 739                                 overridden with
 740                                 <option>--log-location=</option>.</para></listitem>
 741                         </varlistentry>
 742
 743                         <varlistentry>
 744                                 <term><varname>$XDG_CONFIG_HOME</varname></term>
 745                                 <term><varname>$XDG_CONFIG_DIRS</varname></term>
 746                                 <term><varname>$XDG_DATA_HOME</varname></term>
 747                                 <term><varname>$XDG_DATA_DIRS</varname></term>
 748
 749                                 <listitem><para>The systemd session
 750                                 manager uses these variables in
 751                                 accordance to the <ulink
 752                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 753                                 Base Directory specification</ulink>
 754                                 to find its configuration.</para></listitem>
 755                         </varlistentry>
 756
 757                         <varlistentry>
 758                                 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 759
 760                                 <listitem><para>Controls where systemd
 761                                 looks for unit
 762                                 files.</para></listitem>
 763                         </varlistentry>
 764
 765                         <varlistentry>
 766                                 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 767
 768                                 <listitem><para>Controls where systemd
 769                                 looks for SysV init scripts.</para></listitem>
 770                         </varlistentry>
 771
 772                         <varlistentry>
 773                                 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 774
 775                                 <listitem><para>Controls where systemd
 776                                 looks for SysV init script runlevel link
 777                                 farms.</para></listitem>
 778                         </varlistentry>
 779
 780                         <varlistentry>
 781                                 <term><varname>$LISTEN_PID</varname></term>
 782                                 <term><varname>$LISTEN_FDS</varname></term>
 783
 784                                 <listitem><para>Set by systemd for
 785                                 supervised processes during
 786                                 socket-based activation. See
 787                                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 788                                 for more information.
 789                                 </para></listitem>
 790                         </varlistentry>
 791
 792                         <varlistentry>
 793                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 794
 795                                 <listitem><para>Set by systemd for
 796                                 supervised processes for status and
 797                                 start-up completion notification. See
 798                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 799                                 for more information.
 800                                 </para></listitem>
 801                         </varlistentry>
 802                 </variablelist>
 803         </refsect1>
 804
 805         <refsect1>
 806                 <title>Kernel Command Line</title>
 807
 808                 <para>When run as system instance systemd parses a few kernel command line arguments:</para>
 809
 810                 <variablelist>
 811                         <varlistentry>
 812                                 <term><varname>systemd.unit=</varname></term>
 813
 814                                 <listitem><para>Overrides the unit to
 815                                 activate on boot. Defaults to
 816                                 <filename>default.target</filename>. This
 817                                 may be used to temporarily boot into a
 818                                 different boot unit, for example
 819                                 <filename>rescue.target</filename> or
 820                                 <filename>emergency.service</filename>. See
 821                                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 822                                 for details about these
 823                                 units.</para></listitem>
 824                         </varlistentry>
 825
 826                         <varlistentry>
 827                                 <term><varname>systemd.dump_core=</varname></term>
 828
 829                                 <listitem><para>Takes a boolean
 830                                 argument. If <option>true</option>
 831                                 systemd dumps core when it
 832                                 crashes. Otherwise no core dump is
 833                                 created. Defaults to
 834                                 <option>true</option>.</para></listitem>
 835                         </varlistentry>
 836
 837                         <varlistentry>
 838                                 <term><varname>systemd.crash_shell=</varname></term>
 839
 840                                 <listitem><para>Takes a boolean
 841                                 argument. If <option>true</option>
 842                                 systemd spawns a shell when it
 843                                 crashes. Otherwise no core dump is
 844                                 created. Defaults to
 845                                 <option>false</option>, for security
 846                                 reasons, as the shell is not protected
 847                                 by any password
 848                                 authentication.</para></listitem>
 849                         </varlistentry>
 850
 851                         <varlistentry>
 852                                 <term><varname>systemd.crash_chvt=</varname></term>
 853
 854                                 <listitem><para>Takes an integer
 855                                 argument. If positive systemd
 856                                 activates the specified virtual
 857                                 terminal when it crashes. Defaults to
 858                                 <literal>-1</literal>.</para></listitem>
 859                         </varlistentry>
 860
 861                         <varlistentry>
 862                                 <term><varname>systemd.confirm_spawn=</varname></term>
 863
 864                                 <listitem><para>Takes a boolean
 865                                 argument. If <option>true</option>
 866                                 asks for confirmation when spawning
 867                                 processes. Defaults to
 868                                 <option>false</option>.</para></listitem>
 869                         </varlistentry>
 870
 871                         <varlistentry>
 872                                 <term><varname>systemd.show_status=</varname></term>
 873
 874                                 <listitem><para>Takes a boolean
 875                                 argument. If <option>true</option>
 876                                 shows terse service status updates on
 877                                 the console during bootup. Defaults to
 878                                 <option>true</option>.</para></listitem>
 879                         </varlistentry>
 880
 881                         <varlistentry>
 882                                 <term><varname>systemd.sysv_console=</varname></term>
 883
 884                                 <listitem><para>Takes a boolean
 885                                 argument. If <option>true</option>
 886                                 output of SysV init scripts will be
 887                                 directed to the console. Defaults to
 888                                 <option>true</option>, unless
 889                                 <option>quiet</option> is passed as
 890                                 kernel command line option in which
 891                                 case it defaults to
 892                                 <option>false</option>.</para></listitem>
 893                         </varlistentry>
 894
 895                         <varlistentry>
 896                                 <term><varname>systemd.log_target=</varname></term>
 897                                 <term><varname>systemd.log_level=</varname></term>
 898                                 <term><varname>systemd.log_color=</varname></term>
 899                                 <term><varname>systemd.log_location=</varname></term>
 900
 901                                 <listitem><para>Controls log output,
 902                                 with the same effect as the
 903                                 <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
 904                                 environment variables described above.</para></listitem>
 905                         </varlistentry>
 906
 907                 </variablelist>
 908         </refsect1>
 909
 910         <refsect1>
 911                 <title>Sockets and FIFOs</title>
 912
 913                 <variablelist>
 914                         <varlistentry>
 915                                 <term><filename>@/org/freedesktop/systemd1/notify</filename></term>
 916
 917                                 <listitem><para>Daemon status
 918                                 notification socket. This is an AF_UNIX
 919                                 datagram socket in the Linux abstract
 920                                 namespace, and is used to implement
 921                                 the daemon notification logic as
 922                                 implemented by
 923                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
 924
 925                         </varlistentry>
 926
 927                         <varlistentry>
 928                                 <term><filename>@/org/freedesktop/systemd1/logger</filename></term>
 929
 930                                 <listitem><para>Used internally by the
 931                                 <filename>systemd-logger.service</filename>
 932                                 unit to connect STDOUT and/or STDERR
 933                                 of spawned processes to
 934                                 <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 935                                 or the kernel log buffer. This is an
 936                                 AF_UNIX stream socket in the Linux
 937                                 abstract namespace.</para></listitem>
 938                         </varlistentry>
 939
 940                         <varlistentry>
 941                                 <term><filename>@/org/freedesktop/systemd1/shutdown</filename></term>
 942
 943                                 <listitem><para>Used internally by the
 944                                 <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 945                                 tool to implement delayed
 946                                 shutdowns. This is an AF_UNIX datagram
 947                                 socket in the Linux abstract
 948                                 namespace.</para></listitem>
 949                         </varlistentry>
 950
 951                         <varlistentry>
 952                                 <term><filename>@/org/freedesktop/systemd1/private</filename></term>
 953
 954                                 <listitem><para>Used internally as
 955                                 communication channel between
 956                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 957                                 and the systemd process. This is an
 958                                 AF_UNIX stream socket in the Linux
 959                                 abstract namespace. This interface is
 960                                 private to systemd and should not be
 961                                 used in external
 962                                 projects.</para></listitem>
 963                         </varlistentry>
 964
 965                         <varlistentry>
 966                                 <term><filename>/dev/initctl</filename></term>
 967
 968                                 <listitem><para>Limited compatibility
 969                                 support for the SysV client interface,
 970                                 as implemented by the
 971                                 <filename>systemd-initctl.service</filename>
 972                                 unit. This is a named pipe in the file
 973                                 system. This interface is obsolete and
 974                                 should not be used in new
 975                                 applications.</para></listitem>
 976                         </varlistentry>
 977                 </variablelist>
 978         </refsect1>
 979
 980         <refsect1>
 981                 <title>See Also</title>
 982                 <para>
 983                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 984                         <citerefentry><refentrytitle>systemadm</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 985                         <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 986                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 987                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 988                         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 989                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 990                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 991                 </para>
 992         </refsect1>
 993
 994 </refentry>