man/systemd.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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   5 <!--
   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 Lesser General Public License as published by
  12   the Free Software Foundation; either version 2.1 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   Lesser General Public License for more details.
  19
  20   You should have received a copy of the GNU Lesser General Public License
  21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  22 -->
  23
  24 <refentry id="systemd">
  25
  26         <refentryinfo>
  27                 <title>systemd</title>
  28                 <productname>systemd</productname>
  29
  30                 <authorgroup>
  31                         <author>
  32                                 <contrib>Developer</contrib>
  33                                 <firstname>Lennart</firstname>
  34                                 <surname>Poettering</surname>
  35                                 <email>lennart@poettering.net</email>
  36                         </author>
  37                 </authorgroup>
  38         </refentryinfo>
  39
  40         <refmeta>
  41                 <refentrytitle>systemd</refentrytitle>
  42                 <manvolnum>1</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>systemd</refname>
  47                 <refname>init</refname>
  48                 <refpurpose>systemd System and Service Manager</refpurpose>
  49         </refnamediv>
  50
  51         <refsynopsisdiv>
  52                 <cmdsynopsis>
  53                         <command>systemd <arg choice="opt" rep="repeat">OPTIONS</arg></command>
  54                 </cmdsynopsis>
  55                 <cmdsynopsis>
  56                         <command>init <arg choice="opt" rep="repeat">OPTIONS</arg> <arg choice="req">COMMAND</arg></command>
  57                 </cmdsynopsis>
  58         </refsynopsisdiv>
  59
  60         <refsect1>
  61                 <title>Description</title>
  62
  63                 <para>systemd is a system and service manager for
  64                 Linux operating systems. When run as first process on
  65                 boot (as PID 1), it acts as init system that brings
  66                 up and maintains userspace services.</para>
  67
  68                 <para>For compatibility with SysV, if systemd is called
  69                 as <command>init</command> and a PID that is not
  70                 1, it will execute <command>telinit</command> and pass
  71                 all command line arguments unmodified. That means
  72                 <command>init</command> and <command>telinit</command>
  73                 are mostly equivalent when invoked from normal login sessions. See
  74                 <citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  75                 for more information.</para>
  76
  77                 <para>When run as system instance, systemd interprets
  78                 the configuration file
  79                 <filename>system.conf</filename>, otherwise
  80                 <filename>user.conf</filename>. See
  81                 <citerefentry><refentrytitle>systemd.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  82                 for more information.</para>
  83         </refsect1>
  84
  85         <refsect1>
  86                 <title>Options</title>
  87
  88                 <para>The following options are understood:</para>
  89
  90                 <variablelist>
  91                         <varlistentry>
  92                                 <term><option>-h</option></term>
  93                                 <term><option>--help</option></term>
  94
  95                                 <listitem><para>Prints a short help
  96                                 text and exits.</para></listitem>
  97                         </varlistentry>
  98                         <varlistentry>
  99                                 <term><option>--test</option></term>
 100
 101                                 <listitem><para>Determine startup
 102                                 sequence, dump it and exit. This is an
 103                                 option useful for debugging
 104                                 only.</para></listitem>
 105                         </varlistentry>
 106                         <varlistentry>
 107                                 <term><option>--dump-configuration-items</option></term>
 108
 109                                 <listitem><para>Dump understood unit
 110                                 configuration items. This outputs a
 111                                 terse but complete list of
 112                                 configuration items understood in unit
 113                                 definition files.</para></listitem>
 114                         </varlistentry>
 115                         <varlistentry>
 116                                 <term><option>--introspect=</option></term>
 117
 118                                 <listitem><para>Extract D-Bus
 119                                 interface introspection data. This is
 120                                 mostly useful at install time
 121                                 to generate data suitable for the
 122                                 D-Bus interfaces
 123                                 repository. Optionally the interface
 124                                 name for the introspection data may be
 125                                 specified. If omitted, the
 126                                 introspection data for all interfaces
 127                                 is dumped.</para></listitem>
 128                         </varlistentry>
 129                         <varlistentry>
 130                                 <term><option>--unit=</option></term>
 131
 132                                 <listitem><para>Set default unit to
 133                                 activate on startup. If not specified
 134                                 defaults to
 135                                 <filename>default.target</filename>.</para></listitem>
 136                         </varlistentry>
 137                         <varlistentry>
 138                                 <term><option>--system</option></term>
 139                                 <term><option>--user</option></term>
 140
 141                                 <listitem><para>Tell systemd to run a
 142                                 system instance (resp. user
 143                                 instance), even if the process ID is
 144                                 not 1 (resp. is 1), i.e. systemd is
 145                                 not (resp. is) run as init process.
 146                                 Normally it should not be necessary to
 147                                 pass these options, as systemd
 148                                 automatically detects the mode it is
 149                                 started in. These options are hence of
 150                                 little use except for debugging. Note
 151                                 that it is not supported booting and
 152                                 maintaining a full system with systemd
 153                                 running in <option>--system</option>
 154                                 mode, but PID not 1. In practice,
 155                                 passing <option>--system</option> explicitly is
 156                                 only useful in conjunction with
 157                                 <option>--test</option>.</para></listitem>
 158                         </varlistentry>
 159                         <varlistentry>
 160                                 <term><option>--dump-core</option></term>
 161
 162                                 <listitem><para>Dump core on
 163                                 crash. This switch has no effect when
 164                                 run as user
 165                                 instance.</para></listitem>
 166                         </varlistentry>
 167                         <varlistentry>
 168                                 <term><option>--crash-shell</option></term>
 169
 170                                 <listitem><para>Run shell on
 171                                 crash. This switch has no effect when
 172                                 run as user
 173                                 instance.</para></listitem>
 174                         </varlistentry>
 175                         <varlistentry>
 176                                 <term><option>--confirm-spawn</option></term>
 177
 178                                 <listitem><para>Ask for confirmation
 179                                 when spawning processes. This switch
 180                                 has no effect when run as user
 181                                 instance.</para></listitem>
 182                         </varlistentry>
 183                         <varlistentry>
 184                                 <term><option>--show-status=</option></term>
 185
 186                                 <listitem><para>Show terse service
 187                                 status information while booting. This
 188                                 switch has no effect when run as user
 189                                 instance. Takes a boolean argument
 190                                 which may be omitted which is
 191                                 interpreted as
 192                                 <option>true</option>.</para></listitem>
 193                         </varlistentry>
 194                         <varlistentry>
 195                                 <term><option>--sysv-console=</option></term>
 196
 197                                 <listitem><para>Controls whether
 198                                 output of SysV init scripts will be
 199                                 directed to the console. This switch
 200                                 has no effect when run as user
 201                                 instance. Takes a boolean argument
 202                                 which may be omitted which is
 203                                 interpreted as
 204                                 <option>true</option>.</para></listitem>
 205                         </varlistentry>
 206                         <varlistentry>
 207                                 <term><option>--log-target=</option></term>
 208
 209                                 <listitem><para>Set log
 210                                 target. Argument must be one of
 211                                 <option>console</option>,
 212                                 <option>journal</option>,
 213                                 <option>syslog</option>,
 214                                 <option>kmsg</option>,
 215                                 <option>journal-or-kmsg</option>,
 216                                 <option>syslog-or-kmsg</option>,
 217                                 <option>null</option>.</para></listitem>
 218                         </varlistentry>
 219                         <varlistentry>
 220                                 <term><option>--log-level=</option></term>
 221
 222                                 <listitem><para>Set log level. As
 223                                 argument this accepts a numerical log
 224                                 level or the well-known <citerefentry><refentrytitle>syslog</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 225                                 symbolic names (lowercase):
 226                                 <option>emerg</option>,
 227                                 <option>alert</option>,
 228                                 <option>crit</option>,
 229                                 <option>err</option>,
 230                                 <option>warning</option>,
 231                                 <option>notice</option>,
 232                                 <option>info</option>,
 233                                 <option>debug</option>.</para></listitem>
 234                         </varlistentry>
 235                         <varlistentry>
 236                                 <term><option>--log-color=</option></term>
 237
 238                                 <listitem><para>Highlight important
 239                                 log messages. Argument is a boolean
 240                                 value. If the argument is omitted it
 241                                 defaults to
 242                                 <option>true</option>.</para></listitem>
 243                         </varlistentry>
 244                         <varlistentry>
 245                                 <term><option>--log-location=</option></term>
 246
 247                                 <listitem><para>Include code location
 248                                 in log messages. This is mostly
 249                                 relevant for debugging
 250                                 purposes. Argument is a boolean
 251                                 value. If the argument is omitted
 252                                 it defaults to
 253                                 <option>true</option>.</para></listitem>
 254                         </varlistentry>
 255                         <varlistentry>
 256                                 <term><option>--default-standard-output=</option></term>
 257                                 <term><option>--default-standard-error=</option></term>
 258
 259                                 <listitem><para>Sets the default
 260                                 output resp. error output for all
 261                                 services and sockets, i.e. controls
 262                                 the default for
 263                                 <option>StandardOutput=</option>
 264                                 resp. <option>StandardError=</option>
 265                                 (see
 266                                 <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 267                                 for details). Takes one of
 268                                 <option>inherit</option>,
 269                                 <option>null</option>,
 270                                 <option>tty</option>,
 271                                 <option>journal</option>,
 272                                 <option>journal+console</option>,
 273                                 <option>syslog</option>,
 274                                 <option>syslog+console</option>,
 275                                 <option>kmsg</option>,
 276                                 <option>kmsg+console</option>.  If the
 277                                 argument is omitted
 278                                 <option>--default-standard-output=</option>
 279                                 defaults to <option>journal</option>
 280                                 and
 281                                 <option>--default-standard-error=</option>
 282                                 to
 283                                 <option>inherit</option>.</para></listitem>
 284                         </varlistentry>
 285                 </variablelist>
 286         </refsect1>
 287
 288         <refsect1>
 289                 <title>Concepts</title>
 290
 291                 <para>systemd provides a dependency system between
 292                 various entities called "units". Units encapsulate
 293                 various objects that are relevant for system boot-up
 294                 and maintenance. The majority of units are configured
 295                 in unit configuration files, whose syntax and basic
 296                 set of options is described in
 297                 <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 298                 however some are created automatically from other
 299                 configuration or dynamically from system state. Units
 300                 may be 'active' (meaning started, bound, plugged in,
 301                 ...  depending on the unit type, see below), or
 302                 'inactive' (meaning stopped, unbound, unplugged, ...),
 303                 as well as in the process of being activated or
 304                 deactivated, i.e. between the two states (these states
 305                 are called 'activating', 'deactivating'). A special
 306                 'failed' state is available as well which is very
 307                 similar to 'inactive' and is entered when the service
 308                 failed in some way (process returned error code on
 309                 exit, or crashed, or an operation timed out). If this
 310                 state is entered the cause will be logged, for later
 311                 reference. Note that the various unit types may have a
 312                 number of additional substates, which are mapped to
 313                 the five generalized unit states described
 314                 here.</para>
 315
 316                 <para>The following unit types are available:</para>
 317
 318                 <orderedlist>
 319                         <listitem><para>Service units, which control
 320                         daemons and the processes they consist of. For
 321                         details see
 322                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 323
 324                         <listitem><para>Socket units, which
 325                         encapsulate local IPC or network sockets in
 326                         the system, useful for socket-based
 327                         activation. For details about socket units see
 328                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 329                         for details on socket-based activation and
 330                         other forms of activation, see
 331                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 332
 333                         <listitem><para>Target units are useful to
 334                         group units, or provide well-known
 335                         synchronization points during boot-up, see
 336                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 337
 338                         <listitem><para>Device units expose kernel
 339                         devices in systemd and may be used to
 340                         implement device-based activation. For details
 341                         see
 342                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 343
 344                         <listitem><para>Mount units control mount
 345                         points in the file system, for details see
 346                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 347
 348                         <listitem><para>Automount units provide
 349                         automount capabilities, for on-demand mounting
 350                         of file systems as well as parallelized
 351                         boot-up. See
 352                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 353
 354                         <listitem><para>Snapshot units can be used to
 355                         temporarily save the state of the set of
 356                         systemd units, which later may be restored by
 357                         activating the saved snapshot unit. For more
 358                         information see
 359                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 360
 361                         <listitem><para>Timer units are useful for
 362                         triggering activation of other units based on
 363                         timers. You may find details in
 364                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 365
 366                         <listitem><para>Swap units are very similar to
 367                         mount units and encapsulate memory swap
 368                         partitions or files of the operating
 369                         system. They are described in <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 370
 371                         <listitem><para>Path units may be used
 372                         to activate other services when file system
 373                         objects change or are modified. See
 374                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 375
 376                 </orderedlist>
 377
 378                 <para>Units are named as their configuration
 379                 files. Some units have special semantics. A detailed
 380                 list is available in
 381                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 382
 383                 <para>systemd knows various kinds of dependencies,
 384                 including positive and negative requirement
 385                 dependencies (i.e. <varname>Requires=</varname> and
 386                 <varname>Conflicts=</varname>) as well as ordering
 387                 dependencies (<varname>After=</varname> and
 388                 <varname>Before=</varname>). NB: ordering and
 389                 requirement dependencies are orthogonal. If only a
 390                 requirement dependency exists between two units
 391                 (e.g. <filename>foo.service</filename> requires
 392                 <filename>bar.service</filename>), but no ordering
 393                 dependency (e.g. <filename>foo.service</filename>
 394                 after <filename>bar.service</filename>) and both are
 395                 requested to start, they will be started in
 396                 parallel. It is a common pattern that both requirement
 397                 and ordering dependencies are placed between two
 398                 units. Also note that the majority of dependencies are
 399                 implicitly created and maintained by systemd. In most
 400                 cases it should be unnecessary to declare additional
 401                 dependencies manually, however it is possible to do
 402                 this.</para>
 403
 404                 <para>Application programs and units (via
 405                 dependencies) may request state changes of units. In
 406                 systemd, these requests are encapsulated as 'jobs' and
 407                 maintained in a job queue. Jobs may succeed or can
 408                 fail, their execution is ordered based on the ordering
 409                 dependencies of the units they have been scheduled
 410                 for.</para>
 411
 412                 <para>On boot systemd activates the target unit
 413                 <filename>default.target</filename> whose job is to
 414                 activate on-boot services and other on-boot units by
 415                 pulling them in via dependencies. Usually the unit
 416                 name is just an alias (symlink) for either
 417                 <filename>graphical.target</filename> (for
 418                 fully-featured boots into the UI) or
 419                 <filename>multi-user.target</filename> (for limited
 420                 console-only boots for use in embedded or server
 421                 environments, or similar; a subset of
 422                 graphical.target). However it is at the discretion of
 423                 the administrator to configure it as an alias to any
 424                 other target unit. See
 425                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 426                 for details about these target units.</para>
 427
 428                 <para>Processes systemd spawns are placed in
 429                 individual Linux control groups named after the unit
 430                 which they belong to in the private systemd
 431                 hierarchy. (see <ulink
 432                 url="http://www.kernel.org/doc/Documentation/cgroups/cgroups.txt">cgroups.txt</ulink>
 433                 for more information about control groups, or short
 434                 "cgroups"). systemd uses this to effectively keep
 435                 track of processes. Control group information is
 436                 maintained in the kernel, and is accessible via the
 437                 file system hierarchy (beneath
 438                 <filename>/sys/fs/cgroup/systemd/</filename>), or in tools
 439                 such as
 440                 <citerefentry><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 441                 (<command>ps xawf -eo pid,user,cgroup,args</command>
 442                 is particularly useful to list all processes and the
 443                 systemd units they belong to.).</para>
 444
 445                 <para>systemd is compatible with the SysV init system
 446                 to a large degree: SysV init scripts are supported and
 447                 simply read as an alternative (though limited)
 448                 configuration file format. The SysV
 449                 <filename>/dev/initctl</filename> interface is
 450                 provided, and compatibility implementations of the
 451                 various SysV client tools are available. In addition to
 452                 that, various established Unix functionality such as
 453                 <filename>/etc/fstab</filename> or the
 454                 <filename>utmp</filename> database are
 455                 supported.</para>
 456
 457                 <para>systemd has a minimal transaction system: if a
 458                 unit is requested to start up or shut down it will add
 459                 it and all its dependencies to a temporary
 460                 transaction. Then, it will verify if the transaction
 461                 is consistent (i.e. whether the ordering of all units
 462                 is cycle-free). If it is not, systemd will try to fix
 463                 it up, and removes non-essential jobs from the
 464                 transaction that might remove the loop. Also, systemd
 465                 tries to suppress non-essential jobs in the
 466                 transaction that would stop a running service. Finally
 467                 it is checked whether the jobs of the transaction
 468                 contradict jobs that have already been queued, and
 469                 optionally the transaction is aborted then. If all
 470                 worked out and the transaction is consistent and
 471                 minimized in its impact it is merged with all already
 472                 outstanding jobs and added to the run
 473                 queue. Effectively this means that before executing a
 474                 requested operation, systemd will verify that it makes
 475                 sense, fixing it if possible, and only failing if it
 476                 really cannot work.</para>
 477
 478                 <para>Systemd contains native implementations of
 479                 various tasks that need to be executed as part of the
 480                 boot process. For example, it sets the host name or
 481                 configures the loopback network device. It also sets
 482                 up and mounts various API file systems, such as
 483                 <filename>/sys</filename> or
 484                 <filename>/proc</filename>.</para>
 485
 486                 <para>For more information about the concepts and
 487                 ideas behind systemd please refer to the <ulink
 488                 url="http://0pointer.de/blog/projects/systemd.html">Original
 489                 Design Document</ulink>.</para>
 490
 491                 <para>Note that some but not all interfaces provided
 492                 by systemd are covered by the <ulink
 493                 url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 494                 Stability Promise</ulink>.</para>
 495         </refsect1>
 496
 497         <refsect1>
 498                 <title>Directories</title>
 499
 500                 <variablelist>
 501                         <varlistentry>
 502                                 <term>System unit directories</term>
 503
 504                                 <listitem><para>The systemd system
 505                                 manager reads unit configuration from
 506                                 various directories. Packages that
 507                                 want to install unit files shall place
 508                                 them in the directory returned by
 509                                 <command>pkg-config systemd
 510                                 --variable=systemdsystemunitdir</command>. Other
 511                                 directories checked are
 512                                 <filename>/usr/local/lib/systemd/system</filename>
 513                                 and
 514                                 <filename>/usr/lib/systemd/system</filename>. User
 515                                 configuration always takes
 516                                 precedence. <command>pkg-config
 517                                 systemd
 518                                 --variable=systemdsystemconfdir</command>
 519                                 returns the path of the system
 520                                 configuration directory. Packages
 521                                 should alter the content of these
 522                                 directories only with the
 523                                 <command>enable</command> and
 524                                 <command>disable</command> commands of
 525                                 the
 526                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 527                                 tool.</para></listitem>
 528                         </varlistentry>
 529                 </variablelist>
 530
 531                 <variablelist>
 532                         <varlistentry>
 533                                 <term>User unit directories</term>
 534
 535                                 <listitem><para>Similar rules apply
 536                                 for the user unit
 537                                 directories. However, here the <ulink
 538                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 539                                 Base Directory specification</ulink>
 540                                 is followed to find
 541                                 units. Applications should place their
 542                                 unit files in the directory returned
 543                                 by <command>pkg-config systemd
 544                                 --variable=systemduserunitdir</command>. Global
 545                                 configuration is done in the directory
 546                                 reported by <command>pkg-config
 547                                 systemd
 548                                 --variable=systemduserconfdir</command>. The
 549                                 <command>enable</command> and
 550                                 <command>disable</command> commands of
 551                                 the
 552                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 553                                 tool can handle both global (i.e. for
 554                                 all users) and private (for one user)
 555                                 enabling/disabling of
 556                                 units.</para></listitem>
 557                         </varlistentry>
 558                 </variablelist>
 559
 560                 <variablelist>
 561                         <varlistentry>
 562                                 <term>SysV init scripts directory</term>
 563
 564                                 <listitem><para>The location of the
 565                                 SysV init script directory varies
 566                                 between distributions. If systemd
 567                                 cannot find a native unit file for a
 568                                 requested service, it will look for a
 569                                 SysV init script of the same name
 570                                 (with the
 571                                 <filename>.service</filename> suffix
 572                                 removed).</para></listitem>
 573                         </varlistentry>
 574                 </variablelist>
 575
 576                 <variablelist>
 577                         <varlistentry>
 578                                 <term>SysV runlevel link farm directory</term>
 579
 580                                 <listitem><para>The location of the
 581                                 SysV runlevel link farm directory
 582                                 varies between distributions. systemd
 583                                 will take the link farm into account
 584                                 when figuring out whether a service
 585                                 shall be enabled. Note that a service
 586                                 unit with a native unit configuration
 587                                 file cannot be started by activating it
 588                                 in the SysV runlevel link
 589                                 farm.</para></listitem>
 590                         </varlistentry>
 591                 </variablelist>
 592         </refsect1>
 593
 594         <refsect1>
 595                 <title>Signals</title>
 596
 597                 <variablelist>
 598                         <varlistentry>
 599                                 <term>SIGTERM</term>
 600
 601                                 <listitem><para>Upon receiving this
 602                                 signal the systemd system manager
 603                                 serializes its state, reexecutes
 604                                 itself and deserializes the saved
 605                                 state again. This is mostly equivalent
 606                                 to <command>systemctl
 607                                 daemon-reexec</command>.</para>
 608
 609                                 <para>systemd user managers will
 610                                 start the
 611                                 <filename>exit.target</filename> unit
 612                                 when this signal is received. This is
 613                                 mostly equivalent to
 614                                 <command>systemctl --user start
 615                                 exit.target</command>.</para></listitem>
 616                         </varlistentry>
 617
 618                         <varlistentry>
 619                                 <term>SIGINT</term>
 620
 621                                 <listitem><para>Upon receiving this
 622                                 signal the systemd system manager will
 623                                 start the
 624                                 <filename>ctrl-alt-del.target</filename> unit. This
 625                                 is mostly equivalent to
 626                                 <command>systemctl start
 627                                 ctl-alt-del.target</command>.</para>
 628
 629                                 <para>systemd user managers
 630                                 treat this signal the same way as
 631                                 SIGTERM.</para></listitem>
 632                         </varlistentry>
 633
 634                         <varlistentry>
 635                                 <term>SIGWINCH</term>
 636
 637                                 <listitem><para>When this signal is
 638                                 received the systemd system manager
 639                                 will start the
 640                                 <filename>kbrequest.target</filename>
 641                                 unit. This is mostly equivalent to
 642                                 <command>systemctl start
 643                                 kbrequest.target</command>.</para>
 644
 645                                 <para>This signal is ignored by
 646                                 systemd user
 647                                 managers.</para></listitem>
 648                         </varlistentry>
 649
 650                         <varlistentry>
 651                                 <term>SIGPWR</term>
 652
 653                                 <listitem><para>When this signal is
 654                                 received the systemd manager
 655                                 will start the
 656                                 <filename>sigpwr.target</filename>
 657                                 unit. This is mostly equivalent to
 658                                 <command>systemctl start
 659                                 sigpwr.target</command>.</para></listitem>
 660                         </varlistentry>
 661
 662                         <varlistentry>
 663                                 <term>SIGUSR1</term>
 664
 665                                 <listitem><para>When this signal is
 666                                 received the systemd manager will try
 667                                 to reconnect to the D-Bus
 668                                 bus.</para></listitem>
 669                         </varlistentry>
 670
 671                         <varlistentry>
 672                                 <term>SIGUSR2</term>
 673
 674                                 <listitem><para>When this signal is
 675                                 received the systemd manager will log
 676                                 its complete state in human readable
 677                                 form. The data logged is the same as
 678                                 printed by <command>systemctl
 679                                 dump</command>.</para></listitem>
 680                         </varlistentry>
 681
 682                         <varlistentry>
 683                                 <term>SIGHUP</term>
 684
 685                                 <listitem><para>Reloads the complete
 686                                 daemon configuration. This is mostly
 687                                 equivalent to <command>systemctl
 688                                 daemon-reload</command>.</para></listitem>
 689                         </varlistentry>
 690
 691                         <varlistentry>
 692                                 <term>SIGRTMIN+0</term>
 693
 694                                 <listitem><para>Enters default mode, starts the
 695                                 <filename>default.target</filename>
 696                                 unit. This is mostly equivalent to
 697                                 <command>systemctl start
 698                                 default.target</command>.</para></listitem>
 699                         </varlistentry>
 700
 701                         <varlistentry>
 702                                 <term>SIGRTMIN+1</term>
 703
 704                                 <listitem><para>Enters rescue mode,
 705                                 starts the
 706                                 <filename>rescue.target</filename>
 707                                 unit. This is mostly equivalent to
 708                                 <command>systemctl isolate
 709                                 rescue.target</command>.</para></listitem>
 710                         </varlistentry>
 711
 712                         <varlistentry>
 713                                 <term>SIGRTMIN+2</term>
 714
 715                                 <listitem><para>Enters emergency mode,
 716                                 starts the
 717                                 <filename>emergency.service</filename>
 718                                 unit. This is mostly equivalent to
 719                                 <command>systemctl isolate
 720                                 emergency.service</command>.</para></listitem>
 721                         </varlistentry>
 722
 723                         <varlistentry>
 724                                 <term>SIGRTMIN+3</term>
 725
 726                                 <listitem><para>Halts the machine,
 727                                 starts the
 728                                 <filename>halt.target</filename>
 729                                 unit. This is mostly equivalent to
 730                                 <command>systemctl start
 731                                 halt.target</command>.</para></listitem>
 732                         </varlistentry>
 733
 734                         <varlistentry>
 735                                 <term>SIGRTMIN+4</term>
 736
 737                                 <listitem><para>Powers off the machine,
 738                                 starts the
 739                                 <filename>poweroff.target</filename>
 740                                 unit. This is mostly equivalent to
 741                                 <command>systemctl start
 742                                 poweroff.target</command>.</para></listitem>
 743                         </varlistentry>
 744
 745                         <varlistentry>
 746                                 <term>SIGRTMIN+5</term>
 747
 748                                 <listitem><para>Reboots the machine,
 749                                 starts the
 750                                 <filename>reboot.target</filename>
 751                                 unit. This is mostly equivalent to
 752                                 <command>systemctl start
 753                                 reboot.target</command>.</para></listitem>
 754                         </varlistentry>
 755
 756                         <varlistentry>
 757                                 <term>SIGRTMIN+6</term>
 758
 759                                 <listitem><para>Reboots the machine via kexec,
 760                                 starts the
 761                                 <filename>kexec.target</filename>
 762                                 unit. This is mostly equivalent to
 763                                 <command>systemctl start
 764                                 kexec.target</command>.</para></listitem>
 765                         </varlistentry>
 766
 767                         <varlistentry>
 768                                 <term>SIGRTMIN+13</term>
 769
 770                                 <listitem><para>Immediately halts the machine.</para></listitem>
 771                         </varlistentry>
 772
 773                         <varlistentry>
 774                                 <term>SIGRTMIN+14</term>
 775
 776                                 <listitem><para>Immediately powers off the machine.</para></listitem>
 777                         </varlistentry>
 778
 779                         <varlistentry>
 780                                 <term>SIGRTMIN+15</term>
 781
 782                                 <listitem><para>Immediately reboots the machine.</para></listitem>
 783                         </varlistentry>
 784
 785                         <varlistentry>
 786                                 <term>SIGRTMIN+16</term>
 787
 788                                 <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
 789                         </varlistentry>
 790
 791                         <varlistentry>
 792                                 <term>SIGRTMIN+20</term>
 793
 794                                 <listitem><para>Enables display of
 795                                 status messages on the console, as
 796                                 controlled via
 797                                 <varname>systemd.show_status=1</varname>
 798                                 on the kernel command
 799                                 line.</para></listitem>
 800                         </varlistentry>
 801
 802                         <varlistentry>
 803                                 <term>SIGRTMIN+21</term>
 804
 805                                 <listitem><para>Disables display of
 806                                 status messages on the console, as
 807                                 controlled via
 808                                 <varname>systemd.show_status=0</varname>
 809                                 on the kernel command
 810                                 line.</para></listitem>
 811                         </varlistentry>
 812
 813                         <varlistentry>
 814                                 <term>SIGRTMIN+22</term>
 815                                 <term>SIGRTMIN+23</term>
 816
 817                                 <listitem><para>Sets the log level to
 818                                 <literal>debug</literal>
 819                                 (resp. <literal>info</literal> on
 820                                 <literal>SIGRTMIN+23</literal>), as
 821                                 controlled via
 822                                 <varname>systemd.log_level=debug</varname>
 823                                 (resp. <varname>systemd.log_level=info</varname>
 824                                 on <literal>SIGRTMIN+23</literal>) on
 825                                 the kernel command
 826                                 line.</para></listitem>
 827                         </varlistentry>
 828
 829                         <varlistentry>
 830                                 <term>SIGRTMIN+26</term>
 831                                 <term>SIGRTMIN+27</term>
 832                                 <term>SIGRTMIN+28</term>
 833                                 <term>SIGRTMIN+29</term>
 834
 835                                 <listitem><para>Sets the log level to
 836                                 <literal>journal-or-kmsg</literal>
 837                                 (resp. <literal>console</literal> on
 838                                 <literal>SIGRTMIN+27</literal>;
 839                                 resp. <literal>kmsg</literal> on
 840                                 <literal>SIGRTMIN+28</literal>;
 841                                 resp. <literal>syslog-or-kmsg</literal>
 842                                 on <literal>SIGRTMIN+29</literal>), as
 843                                 controlled via
 844                                 <varname>systemd.log_target=journal-or-kmsg</varname>
 845                                 (resp. <varname>systemd.log_target=console</varname>
 846                                 on <literal>SIGRTMIN+27</literal>;
 847                                 resp. <varname>systemd.log_target=kmsg</varname>
 848                                 on <literal>SIGRTMIN+28</literal>;
 849                                 resp
 850                                 <varname>systemd.log_target=syslog-or-kmsg</varname>
 851                                 on <literal>SIGRTMIN+29</literal>) on
 852                                 the kernel command
 853                                 line.</para></listitem>
 854                         </varlistentry>
 855                 </variablelist>
 856         </refsect1>
 857
 858         <refsect1>
 859                 <title>Environment</title>
 860
 861                 <variablelist>
 862                         <varlistentry>
 863                                 <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 864                                 <listitem><para>systemd reads the
 865                                 log level from this environment
 866                                 variable. This can be overridden with
 867                                 <option>--log-level=</option>.</para></listitem>
 868                         </varlistentry>
 869
 870                         <varlistentry>
 871                                 <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 872                                 <listitem><para>systemd reads the
 873                                 log target from this environment
 874                                 variable. This can be overridden with
 875                                 <option>--log-target=</option>.</para></listitem>
 876                         </varlistentry>
 877
 878                         <varlistentry>
 879                                 <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 880                                 <listitem><para>Controls whether
 881                                 systemd highlights important log
 882                                 messages. This can be overridden with
 883                                 <option>--log-color=</option>.</para></listitem>
 884                         </varlistentry>
 885
 886                         <varlistentry>
 887                                 <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 888                                 <listitem><para>Controls whether
 889                                 systemd prints the code location along
 890                                 with log messages. This can be
 891                                 overridden with
 892                                 <option>--log-location=</option>.</para></listitem>
 893                         </varlistentry>
 894
 895                         <varlistentry>
 896                                 <term><varname>$XDG_CONFIG_HOME</varname></term>
 897                                 <term><varname>$XDG_CONFIG_DIRS</varname></term>
 898                                 <term><varname>$XDG_DATA_HOME</varname></term>
 899                                 <term><varname>$XDG_DATA_DIRS</varname></term>
 900
 901                                 <listitem><para>The systemd user
 902                                 manager uses these variables in
 903                                 accordance to the <ulink
 904                                 url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 905                                 Base Directory specification</ulink>
 906                                 to find its configuration.</para></listitem>
 907                         </varlistentry>
 908
 909                         <varlistentry>
 910                                 <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 911
 912                                 <listitem><para>Controls where systemd
 913                                 looks for unit
 914                                 files.</para></listitem>
 915                         </varlistentry>
 916
 917                         <varlistentry>
 918                                 <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 919
 920                                 <listitem><para>Controls where systemd
 921                                 looks for SysV init scripts.</para></listitem>
 922                         </varlistentry>
 923
 924                         <varlistentry>
 925                                 <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 926
 927                                 <listitem><para>Controls where systemd
 928                                 looks for SysV init script runlevel link
 929                                 farms.</para></listitem>
 930                         </varlistentry>
 931
 932                         <varlistentry>
 933                                 <term><varname>$LISTEN_PID</varname></term>
 934                                 <term><varname>$LISTEN_FDS</varname></term>
 935
 936                                 <listitem><para>Set by systemd for
 937                                 supervised processes during
 938                                 socket-based activation. See
 939                                 <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 940                                 for more information.
 941                                 </para></listitem>
 942                         </varlistentry>
 943
 944                         <varlistentry>
 945                                 <term><varname>$NOTIFY_SOCKET</varname></term>
 946
 947                                 <listitem><para>Set by systemd for
 948                                 supervised processes for status and
 949                                 start-up completion notification. See
 950                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 951                                 for more information.
 952                                 </para></listitem>
 953                         </varlistentry>
 954                 </variablelist>
 955         </refsect1>
 956
 957         <refsect1>
 958                 <title>Kernel Command Line</title>
 959
 960                 <para>When run as system instance systemd parses a
 961                 number of kernel command line
 962                 arguments<footnote><para>If run inside a Linux
 963                 container these arguments may be passed as command
 964                 line arguments to systemd itself, next to any of the
 965                 command line options listed in the Options section
 966                 above. If run outside of Linux containers, these
 967                 arguments are parsed from
 968                 <filename>/proc/cmdline</filename>
 969                 instead.</para></footnote>:</para>
 970
 971                 <variablelist>
 972                         <varlistentry>
 973                                 <term><varname>systemd.unit=</varname></term>
 974
 975                                 <listitem><para>Overrides the unit to
 976                                 activate on boot. Defaults to
 977                                 <filename>default.target</filename>. This
 978                                 may be used to temporarily boot into a
 979                                 different boot unit, for example
 980                                 <filename>rescue.target</filename> or
 981                                 <filename>emergency.service</filename>. See
 982                                 <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 983                                 for details about these
 984                                 units.</para></listitem>
 985                         </varlistentry>
 986
 987                         <varlistentry>
 988                                 <term><varname>systemd.dump_core=</varname></term>
 989
 990                                 <listitem><para>Takes a boolean
 991                                 argument. If <option>true</option>
 992                                 systemd dumps core when it
 993                                 crashes. Otherwise no core dump is
 994                                 created. Defaults to
 995                                 <option>true</option>.</para></listitem>
 996                         </varlistentry>
 997
 998                         <varlistentry>
 999                                 <term><varname>systemd.crash_shell=</varname></term>
1000
1001                                 <listitem><para>Takes a boolean
1002                                 argument. If <option>true</option>
1003                                 systemd spawns a shell when it
1004                                 crashes. Otherwise no shell is
1005                                 spawned. Defaults to
1006                                 <option>false</option>, for security
1007                                 reasons, as the shell is not protected
1008                                 by any password
1009                                 authentication.</para></listitem>
1010                         </varlistentry>
1011
1012                         <varlistentry>
1013                                 <term><varname>systemd.crash_chvt=</varname></term>
1014
1015                                 <listitem><para>Takes an integer
1016                                 argument. If positive systemd
1017                                 activates the specified virtual
1018                                 terminal when it crashes. Defaults to
1019                                 <literal>-1</literal>.</para></listitem>
1020                         </varlistentry>
1021
1022                         <varlistentry>
1023                                 <term><varname>systemd.confirm_spawn=</varname></term>
1024
1025                                 <listitem><para>Takes a boolean
1026                                 argument. If <option>true</option>
1027                                 asks for confirmation when spawning
1028                                 processes. Defaults to
1029                                 <option>false</option>.</para></listitem>
1030                         </varlistentry>
1031
1032                         <varlistentry>
1033                                 <term><varname>systemd.show_status=</varname></term>
1034
1035                                 <listitem><para>Takes a boolean
1036                                 argument. If <option>true</option>
1037                                 shows terse service status updates on
1038                                 the console during bootup. Defaults to
1039                                 <option>true</option>.</para></listitem>
1040                         </varlistentry>
1041
1042                         <varlistentry>
1043                                 <term><varname>systemd.sysv_console=</varname></term>
1044
1045                                 <listitem><para>Takes a boolean
1046                                 argument. If <option>true</option>
1047                                 output of SysV init scripts will be
1048                                 directed to the console. Defaults to
1049                                 <option>true</option>, unless
1050                                 <option>quiet</option> is passed as
1051                                 kernel command line option in which
1052                                 case it defaults to
1053                                 <option>false</option>.</para></listitem>
1054                         </varlistentry>
1055
1056                         <varlistentry>
1057                                 <term><varname>systemd.log_target=</varname></term>
1058                                 <term><varname>systemd.log_level=</varname></term>
1059                                 <term><varname>systemd.log_color=</varname></term>
1060                                 <term><varname>systemd.log_location=</varname></term>
1061
1062                                 <listitem><para>Controls log output,
1063                                 with the same effect as the
1064                                 <varname>$SYSTEMD_LOG_TARGET</varname>, <varname>$SYSTEMD_LOG_LEVEL</varname>, <varname>$SYSTEMD_LOG_COLOR</varname>, <varname>$SYSTEMD_LOG_LOCATION</varname>
1065                                 environment variables described above.</para></listitem>
1066                         </varlistentry>
1067
1068                         <varlistentry>
1069                                 <term><varname>systemd.default_standard_output=</varname></term>
1070                                 <term><varname>systemd.default_standard_error=</varname></term>
1071                                 <listitem><para>Controls default
1072                                 standard output/error output for
1073                                 services, with the same effect as the
1074                                 <option>--default-standard-output=</option>
1075                                 resp. <option>--default-standard-error=</option>
1076                                 command line arguments described
1077                                 above.</para></listitem>
1078                         </varlistentry>
1079
1080                         <varlistentry>
1081                                 <term><varname>systemd.setenv=</varname></term>
1082
1083                                 <listitem><para>Takes a string
1084                                 argument in the form
1085                                 VARIABLE=VALUE. May be used to set
1086                                 environment variables for the init
1087                                 process and all its children at boot
1088                                 time. May be used more than once to
1089                                 set multiple variables. If the equal
1090                                 sign and variable are missing unsets
1091                                 an environment variable which might be
1092                                 passed in from the initial ram
1093                                 disk.</para></listitem>
1094                         </varlistentry>
1095
1096                 </variablelist>
1097         </refsect1>
1098
1099         <refsect1>
1100                 <title>Sockets and FIFOs</title>
1101
1102                 <variablelist>
1103                         <varlistentry>
1104                                 <term><filename>/run/systemd/notify</filename></term>
1105
1106                                 <listitem><para>Daemon status
1107                                 notification socket. This is an
1108                                 AF_UNIX datagram socket and is used to
1109                                 implement the daemon notification
1110                                 logic as implemented by
1111                                 <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1112
1113                         </varlistentry>
1114
1115                         <varlistentry>
1116                                 <term><filename>/run/systemd/shutdownd</filename></term>
1117
1118                                 <listitem><para>Used internally by the
1119                                 <citerefentry><refentrytitle>shutdown</refentrytitle><manvolnum>8</manvolnum></citerefentry>
1120                                 tool to implement delayed
1121                                 shutdowns. This is an AF_UNIX datagram
1122                                 socket.</para></listitem>
1123                         </varlistentry>
1124
1125                         <varlistentry>
1126                                 <term><filename>/run/systemd/private</filename></term>
1127
1128                                 <listitem><para>Used internally as
1129                                 communication channel between
1130                                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1131                                 and the systemd process. This is an
1132                                 AF_UNIX stream socket. This interface
1133                                 is private to systemd and should not
1134                                 be used in external
1135                                 projects.</para></listitem>
1136                         </varlistentry>
1137
1138                         <varlistentry>
1139                                 <term><filename>/dev/initctl</filename></term>
1140
1141                                 <listitem><para>Limited compatibility
1142                                 support for the SysV client interface,
1143                                 as implemented by the
1144                                 <filename>systemd-initctl.service</filename>
1145                                 unit. This is a named pipe in the file
1146                                 system. This interface is obsolete and
1147                                 should not be used in new
1148                                 applications.</para></listitem>
1149                         </varlistentry>
1150                 </variablelist>
1151         </refsect1>
1152
1153         <refsect1>
1154                 <title>See Also</title>
1155                 <para>
1156                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1157                         <citerefentry><refentrytitle>systemadm</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1158                         <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1159                         <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1160                         <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1161                         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1162                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1163                         <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1164                 </para>
1165         </refsect1>
1166
1167 </refentry>