man/systemd.unit.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   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 General Public License as published by
  12   the Free Software Foundation; either version 2 of the License, or
  13   (at your option) any later version.
  14
  15   systemd is distributed in the hope that it will be useful, but
  16   WITHOUT ANY WARRANTY; without even the implied warranty of
  17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  18   General Public License for more details.
  19
  20   You should have received a copy of the GNU General Public License
  21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  22 -->
  23
  24 <refentry id="systemd.unit">
  25
  26         <refentryinfo>
  27                 <title>systemd.unit</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.unit</refentrytitle>
  42                 <manvolnum>5</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>systemd.unit</refname>
  47                 <refpurpose>systemd unit configuration files</refpurpose>
  48         </refnamediv>
  49
  50         <refsynopsisdiv>
  51                 <para><filename>systemd.service</filename>,
  52                 <filename>systemd.socket</filename>,
  53                 <filename>systemd.device</filename>,
  54                 <filename>systemd.mount</filename>,
  55                 <filename>systemd.automount</filename>,
  56                 <filename>systemd.swap</filename>,
  57                 <filename>systemd.target</filename>,
  58                 <filename>systemd.path</filename>,
  59                 <filename>systemd.timer</filename>,
  60                 <filename>systemd.snapshot</filename></para>
  61         </refsynopsisdiv>
  62
  63         <refsect1>
  64                 <title>Description</title>
  65
  66                 <para>A unit configuration file encodes information
  67                 about a service, a socket, a device, a mount point, an
  68                 automount point, a swap file or partition, a start-up
  69                 target, a file system path or a timer controlled and
  70                 supervised by
  71                 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>. The
  72                 syntax is inspired by <ulink
  73                 url="http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG
  74                 Desktop Entry Specification</ulink> <filename>.desktop</filename> files, which are in turn
  75                 inspired by Microsoft Windows
  76                 <filename>.ini</filename> files.</para>
  77
  78                 <para>This man pages lists the common configuration
  79                 options of all the unit types. These options need to
  80                 be configured in the [Unit] resp. [Install]
  81                 section of the unit files.</para>
  82
  83                 <para>In addition to the generic [Unit] and [Install]
  84                 sections described here, each unit should have a
  85                 type-specific section, e.g. [Service] for a service
  86                 unit. See the respective man pages for more
  87                 information.</para>
  88
  89                 <para>Unit files may contain additional options on top
  90                 of those listed here. If systemd encounters an unknown
  91                 option it will write a warning log message but
  92                 continue loading the unit. If an option is prefixed
  93                 with <option>X-</option> it is ignored completely by
  94                 systemd. Applications may use this to include
  95                 additional information in the unit files.</para>
  96
  97                 <para>Boolean arguments used in unit files can be
  98                 written in various formats. For positive settings the
  99                 strings <option>1</option>, <option>yes</option>,
 100                 <option>true</option> and <option>on</option> are
 101                 equivalent. For negative settings the strings
 102                 <option>0</option>, <option>no</option>,
 103                 <option>false</option> and <option>off</option> are
 104                 equivalent.</para>
 105
 106                 <para>Time span values encoded in unit files can be
 107                 written in various formats. A stand-alone number
 108                 specifies a time in seconds. If suffixed with a time
 109                 unit, the unit is honored. A concatenation of
 110                 multiple values with units is supported, in which case
 111                 the values are added up. Example: "50" refers to 50
 112                 seconds; "2min 200ms" refers to 2 minutes plus 200
 113                 milliseconds, i.e. 120200ms. The following time units
 114                 are understood: s, min, h, d, w, ms, us.</para>
 115
 116                 <para>Empty lines and lines starting with # or ; are
 117                 ignored. This may be used for commenting. Lines ending
 118                 in a backslash are concatenated with the following
 119                 line while reading and the backslash is replaced by a
 120                 space character. This may be used to wrap long lines.</para>
 121
 122                 <para>If a line starts with <option>.include</option>
 123                 followed by a file name, the specified file will be
 124                 read as if its contents were listed in place of the
 125                 <option>.include</option> directive.</para>
 126
 127                 <para>Along with a unit file
 128                 <filename>foo.service</filename> a directory
 129                 <filename>foo.service.wants/</filename> may exist. All
 130                 units symlinked from such a directory are implicitly
 131                 added as dependencies of type
 132                 <varname>Wanted=</varname> to the unit. This is useful
 133                 to hook units into the start-up of other units,
 134                 without having to modify their unit configuration
 135                 files. For details about the semantics of
 136                 <varname>Wanted=</varname> see below. The preferred
 137                 way to create symlinks in the
 138                 <filename>.wants/</filename> directory of a service is
 139                 with the
 140                 <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 141                 tool which reads information from the [Install]
 142                 section of unit files. (See below.)</para>
 143
 144                 <para>Note that while systemd offers a flexible
 145                 dependency system between units it is recommended to
 146                 use this functionality only sparsely and instead rely
 147                 on techniques such as bus-based or socket-based
 148                 activation which makes dependencies implicit, which
 149                 both results in a simpler and more flexible
 150                 system.</para>
 151
 152                 <para>Some unit names reflect paths existing in the
 153                 file system name space. Example: a device unit
 154                 <filename>dev-sda.device</filename> refers to a device
 155                 with the device node <filename>/dev/sda</filename> in
 156                 the file system namespace. If this applies a special
 157                 way to escape the path name is used, so that the
 158                 result is usable as part of a file name. Basically,
 159                 given a path, "/" is replaced by "-", and all
 160                 unprintable characters and the "-" are replaced by
 161                 C-style "\x20" escapes. The root directory "/" is
 162                 encoded as single dash, while otherwise the initial
 163                 and ending "/" is removed from all paths during
 164                 transformation. This escaping is reversible.</para>
 165
 166                 <para>Optionally, units may be instantiated from a
 167                 template file at runtime. This allows creation of
 168                 multiple units from a single configuration file. If
 169                 systemd looks for a unit configuration file it will
 170                 first search for the literal unit name in the
 171                 filesystem. If that yields no success and the unit
 172                 name contains an @ character, systemd will look for a
 173                 unit template that shares the same name but with the
 174                 instance string (i.e. the part between the @ character
 175                 and the suffix) removed. Example: if a service
 176                 <filename>getty@tty3.service</filename> is requested
 177                 and no file by that name is found, systemd will look
 178                 for <filename>getty@.service</filename> and
 179                 instantiate a service from that configuration file if
 180                 it is found. To refer to the instance string from
 181                 within the configuration file you may use the special
 182                 <literal>%i</literal> specifier in many of the
 183                 configuration options. Other specifiers that may be
 184                 used are <literal>%n</literal>, <literal>%N</literal>,
 185                 <literal>%p</literal>, <literal>%P</literal> and
 186                 <literal>%I</literal>, for the full unit name, the
 187                 unescaped unit name, the prefix name, the unescaped
 188                 prefix name and the unescaped instance name,
 189                 respectively. The prefix name here refers to the
 190                 string before the @, i.e. "getty" in the example
 191                 above, where "tty3" is the instance name.</para>
 192         </refsect1>
 193
 194         <refsect1>
 195                 <title>Options</title>
 196
 197                 <para>Unit file may include a [Unit] section, which
 198                 carries generic information about the unit that is not
 199                 dependent on the type of unit:</para>
 200
 201                 <variablelist>
 202                         <varlistentry>
 203                                 <term><varname>Names=</varname></term>
 204
 205                                 <listitem><para>Additional names for
 206                                 this unit. The names listed here must
 207                                 have the same suffix (i.e. type) as
 208                                 the unit file name. This option may be
 209                                 specified more than once, in which
 210                                 case all listed names are used. Note
 211                                 that this option is different from the
 212                                 <varname>Alias=</varname> option from
 213                                 the [Install] section mentioned
 214                                 below. See below for details.</para>
 215                                 </listitem>
 216                         </varlistentry>
 217
 218                         <varlistentry>
 219                                 <term><varname>Description=</varname></term>
 220                                 <listitem><para>A free-form string
 221                                 describing the unit. This is intended
 222                                 for use in UIs to show descriptive
 223                                 information along with the unit
 224                                 name.</para></listitem>
 225                         </varlistentry>
 226
 227                         <varlistentry>
 228                                 <term><varname>Requires=</varname></term>
 229
 230                                 <listitem><para>Configures requirement
 231                                 dependencies on other units. If this
 232                                 unit gets activated, the units listed
 233                                 here will be activated as well. If one
 234                                 of the other units gets deactivated or
 235                                 its activation fails, this unit will
 236                                 be deactivated. This option may be
 237                                 specified more than once, in which
 238                                 case requirement dependencies for all
 239                                 listed names are created. Note that
 240                                 requirement dependencies do not
 241                                 influence the order in which services
 242                                 are started or stopped. This has to be
 243                                 configured independently with the
 244                                 <varname>After=</varname> or
 245                                 <varname>Before=</varname> options. If
 246                                 a unit
 247                                 <filename>foo.service</filename>
 248                                 requires a unit
 249                                 <filename>bar.service</filename> as
 250                                 configured with
 251                                 <varname>Requires=</varname> and no
 252                                 ordering is configured with
 253                                 <varname>After=</varname> or
 254                                 <varname>Before=</varname>, then both
 255                                 units will be started simultaneously
 256                                 and without any delay between them if
 257                                 <filename>foo.service</filename> is
 258                                 activated. Often it is a better choice
 259                                 to use <varname>Wants=</varname>
 260                                 instead of
 261                                 <varname>Requires=</varname> in order
 262                                 to achieve a system that is more
 263                                 robust when dealing with failing
 264                                 services.</para></listitem>
 265                         </varlistentry>
 266
 267
 268                         <varlistentry>
 269                                 <term><varname>RequiresOverridable=</varname></term>
 270
 271                                 <listitem><para>Similar to
 272                                 <varname>Requires=</varname>.
 273                                 Dependencies listed in
 274                                 <varname>RequiresOverridable=</varname>
 275                                 which cannot be fulfilled or fail to
 276                                 start are ignored if the startup was
 277                                 explicitly requested by the user. If
 278                                 the start-up was pulled in indirectly
 279                                 by some dependency or automatic
 280                                 start-up of units that is not
 281                                 requested by the user this dependency
 282                                 must be fulfilled and otherwise the
 283                                 transaction fails. Hence, this option
 284                                 may be used to configure dependencies
 285                                 that are normally honored unless the
 286                                 user explicitly starts up the unit, in
 287                                 which case whether they failed or not
 288                                 is irrelevant.</para></listitem>
 289
 290                         </varlistentry>
 291                         <varlistentry>
 292                                 <term><varname>Requisite=</varname></term>
 293                                 <term><varname>RequisiteOverridable=</varname></term>
 294
 295                                 <listitem><para>Similar to
 296                                 <varname>Requires=</varname>
 297                                 resp. <varname>RequiresOverridable=</varname>. However,
 298                                 if a unit listed here is not started
 299                                 already it will not be started and the
 300                                 transaction fails
 301                                 immediately.</para></listitem>
 302                         </varlistentry>
 303
 304                         <varlistentry>
 305                                 <term><varname>Wants=</varname></term>
 306
 307                                 <listitem><para>A weaker version of
 308                                 <varname>Requires=</varname>. A unit
 309                                 listed in this option will be started
 310                                 if the configuring unit is. However,
 311                                 if the listed unit fails to start up
 312                                 or cannot be added to the transaction
 313                                 this has no impact on the validity of
 314                                 the transaction as a whole. This is
 315                                 the recommended way to hook start-up
 316                                 of one unit to the start-up of another
 317                                 unit. Note that dependencies of this
 318                                 type may also be configured outside of
 319                                 the unit configuration file by
 320                                 adding a symlink to a
 321                                 <filename>.wants/</filename> directory
 322                                 accompanying the unit file. For
 323                                 details see above.</para></listitem>
 324                         </varlistentry>
 325
 326                         <varlistentry>
 327                                 <term><varname>Conflicts=</varname></term>
 328
 329                                 <listitem><para>Configures negative
 330                                 requirement dependencies. If a unit
 331                                 has a
 332                                 <varname>Conflicts=</varname> setting
 333                                 on another unit, starting the former
 334                                 will stop the latter and vice
 335                                 versa. Note that this setting is
 336                                 independent of and orthogonal to the
 337                                 <varname>After=</varname> and
 338                                 <varname>Before=</varname> ordering
 339                                 dependencies.</para></listitem>
 340                         </varlistentry>
 341
 342                         <varlistentry>
 343                                 <term><varname>Before=</varname></term>
 344                                 <term><varname>After=</varname></term>
 345
 346                                 <listitem><para>Configures ordering
 347                                 dependencies between units. If a unit
 348                                 <filename>foo.service</filename>
 349                                 contains a setting
 350                                 <option>Before=bar.service</option>
 351                                 and both units are being started,
 352                                 <filename>bar.service</filename>'s
 353                                 start-up is delayed until
 354                                 <filename>foo.service</filename> is
 355                                 started up. Note that this setting is
 356                                 independent of and orthogonal to the
 357                                 requirement dependencies as configured
 358                                 by <varname>Requires=</varname>. It is
 359                                 a common pattern to include a unit
 360                                 name in both the
 361                                 <varname>After=</varname> and
 362                                 <varname>Requires=</varname> option in
 363                                 which case the unit listed will be
 364                                 started before the unit that is
 365                                 configured with these options. This
 366                                 option may be specified more than
 367                                 once, in which case ordering
 368                                 dependencies for all listed names are
 369                                 created. <varname>After=</varname> is
 370                                 the inverse of
 371                                 <varname>Before=</varname>, i.e. while
 372                                 <varname>After=</varname> ensures that
 373                                 the configured unit is started after
 374                                 the listed unit finished starting up,
 375                                 <varname>Before=</varname> ensures the
 376                                 opposite, i.e.  that the configured
 377                                 unit is fully started up before the
 378                                 listed unit is started. Note that when
 379                                 two units with an ordering dependency
 380                                 between them are shut down, the
 381                                 inverse of the start-up order is
 382                                 applied. i.e. if a unit is configured
 383                                 with <varname>After=</varname> on
 384                                 another unit, the former is stopped
 385                                 before the latter if both are shut
 386                                 down. If one unit with an ordering
 387                                 dependency on another unit is shut
 388                                 down while the latter is started up,
 389                                 the shut down is ordered before the
 390                                 start-up regardless whether the
 391                                 ordering dependency is actually of
 392                                 type <varname>After=</varname> or
 393                                 <varname>Before=</varname>. If two
 394                                 units have no ordering dependencies
 395                                 between them they are shut down
 396                                 resp. started up simultaneously, and
 397                                 no ordering takes
 398                                 place. </para></listitem>
 399                         </varlistentry>
 400
 401                         <varlistentry>
 402                                 <term><varname>RecursiveStop=</varname></term>
 403
 404                                 <listitem><para>Takes a boolean
 405                                 argument. If <option>true</option> and
 406                                 the unit stops without being requested
 407                                 by the user, all units
 408                                 depending on it will be stopped as
 409                                 well. (e.g. if a service exits or
 410                                 crashes on its own behalf, units using
 411                                 it will be stopped) Note that normally
 412                                 if a unit stops without a user request,
 413                                 units depending on it will not be
 414                                 terminated. Only if the user requested
 415                                 shutdown of a unit, all units depending
 416                                 on that unit will be shut down as well
 417                                 and at the same time. Defaults to
 418                                 <option>false</option>.</para></listitem>
 419                         </varlistentry>
 420
 421                         <varlistentry>
 422                                 <term><varname>StopWhenUnneeded=</varname></term>
 423
 424                                 <listitem><para>Takes a boolean
 425                                 argument. If <option>true</option>
 426                                 this unit will be stopped when it is
 427                                 no longer used. Note that in order to
 428                                 minimize the work to be executed,
 429                                 systemd will not stop units by default
 430                                 unless they are conflicting with other
 431                                 units, or the user explicitly
 432                                 requested their shut down. If this
 433                                 option is set, a unit will be
 434                                 automatically cleaned up if no other
 435                                 active unit requires it. Defaults to
 436                                 <option>false</option>.</para></listitem>
 437                         </varlistentry>
 438
 439                         <varlistentry>
 440                                 <term><varname>OnlyByDependency=</varname></term>
 441
 442                                 <listitem><para>Takes a boolean
 443                                 argument. If <option>true</option>
 444                                 this unit can only be activated
 445                                 indirectly. In this case explicit
 446                                 start-up requested by the user is
 447                                 denied, however if it is started as a
 448                                 dependency of another unit, start-up
 449                                 will succeed. This is mostly a safety
 450                                 feature to ensure that the user does
 451                                 not accidentally activate units that are
 452                                 not intended to be activated
 453                                 explicitly. This option defaults to
 454                                 <option>false</option>.</para></listitem>
 455                         </varlistentry>
 456
 457                         <varlistentry>
 458                                 <term><varname>DefaultDependencies=</varname></term>
 459
 460                                 <listitem><para>Takes a boolean
 461                                 argument. If <option>true</option>
 462                                 (the default), a few default
 463                                 dependencies will implicitly be
 464                                 created for the unit. The actual
 465                                 dependencies created depend on the
 466                                 unit type. For example, for service
 467                                 units, these dependencies ensure that
 468                                 the service is started only after
 469                                 basic system initialization is
 470                                 completed and is properly terminated on
 471                                 system shutdown. See the respective
 472                                 man pages for details. Generally, only
 473                                 services involved with early boot or
 474                                 late shutdown should set this option
 475                                 to <option>false</option>. It is
 476                                 highly recommended to leave this
 477                                 option enabled for the majority of
 478                                 common units. If set to
 479                                 <option>false</option> this option
 480                                 does not disable all implicit
 481                                 dependencies, just non-essential
 482                                 ones.</para></listitem>
 483                         </varlistentry>
 484
 485                 </variablelist>
 486
 487                 <para>Unit file may include a [Install] section, which
 488                 carries installation information for the unit. This
 489                 section is not interpreted by
 490                 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 491                 during runtime. It is used exclusively by the
 492                 <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 493                 tool during installation of a unit:</para>
 494
 495                 <variablelist>
 496                         <varlistentry>
 497                                 <term><varname>Alias=</varname></term>
 498
 499                                 <listitem><para>Additional names this
 500                                 unit shall be installed under. The
 501                                 names listed here must have the same
 502                                 suffix (i.e. type) as the unit file
 503                                 name. This option may be specified
 504                                 more than once, in which case all
 505                                 listed names are used. At installation
 506                                 time,
 507                                 <command>systemd-install</command>
 508                                 will create symlinks from these names
 509                                 to the unit file name. Note that this
 510                                 is different from the
 511                                 <varname>Names=</varname> option from
 512                                 the [Unit] section mentioned above:
 513                                 The names from
 514                                 <varname>Names=</varname> apply
 515                                 unconditionally if the unit is
 516                                 loaded. The names from
 517                                 <varname>Alias=</varname> apply only
 518                                 if the unit has actually been
 519                                 installed with the
 520                                 <command>systemd-install</command>
 521                                 tool.  Also, if systemd searches for a
 522                                 unit, it will discover symlinked alias
 523                                 names as configured with
 524                                 <varname>Alias=</varname>, but not
 525                                 names configured with
 526                                 <varname>Names=</varname> only. It is
 527                                 a common pattern to list a name in
 528                                 both options. In this case, a unit
 529                                 will be active under all names if
 530                                 installed, but also if not installed
 531                                 but requested explicitly under its
 532                                 main name.</para></listitem>
 533                         </varlistentry>
 534
 535                         <varlistentry>
 536                                 <term><varname>WantedBy=</varname></term>
 537
 538                                 <listitem><para>Installs a symlink in
 539                                 the <filename>.wants/</filename>
 540                                 subdirectory for a unit. This has the
 541                                 effect that when the listed unit name
 542                                 is activated the unit listing it is
 543                                 activated
 544                                 too. <command>WantedBy=foo.service</command>
 545                                 in a service
 546                                 <filename>bar.service</filename> is
 547                                 mostly equivalent to
 548                                 <command>Alias=foo.service.wants/bar.service</command>
 549                                 in the same file.</para></listitem>
 550                         </varlistentry>
 551
 552                         <varlistentry>
 553                                 <term><varname>Also=</varname></term>
 554
 555                                 <listitem><para>Additional units to
 556                                 install when this unit is
 557                                 installed. If the user requests
 558                                 installation of a unit with this
 559                                 option configured,
 560                                 <command>systemd-install</command>
 561                                 will automatically install units
 562                                 listed in this option as
 563                                 well.</para></listitem>
 564                         </varlistentry>
 565                 </variablelist>
 566
 567         </refsect1>
 568
 569         <refsect1>
 570                 <title>See Also</title>
 571                 <para>
 572                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 573                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 574                         <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 575                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 576                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 577                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 578                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 579                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 580                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 581                         <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 582                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 583                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 584                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 585                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 586                 </para>
 587         </refsect1>
 588
 589 </refentry>