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 the all 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 value 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.</para>
 118
 119                 <para>If a line starts with <option>.include</option>
 120                 followed by a file name the specified file will be
 121                 read as if its contents where listed in place of the
 122                 <option>.include</option> directive.</para>
 123
 124                 <para>Along with a unit file
 125                 <filename>foo.service</filename> a directory
 126                 <filename>foo.service.wants/</filename> may exist. All
 127                 units symlinked from such a directory are implicitly
 128                 added as dependencies of type
 129                 <varname>Wanted=</varname> to the unit. This is useful
 130                 to hook units into the start-up of other units,
 131                 without having to modify their unit configuration
 132                 files. For details about the semantics of
 133                 <varname>Wanted=</varname> see below. The preferred
 134                 way to create symlinks in the
 135                 <filename>.wants/</filename> directory of a service is
 136                 with the
 137                 <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 138                 tool which reads information from the [Install]
 139                 section of unit files. (See below.)</para>
 140
 141                 <para>Note that while systemd offers a flexible
 142                 dependency system between units it is recommended to
 143                 use this functionality only sparsely and instead rely
 144                 on techniques such as bus-based or socket-based
 145                 activation which makes dependencies implicit, which
 146                 both results in a simpler and more flexible
 147                 system.</para>
 148
 149                 <para>Some unit names reflect paths existing in the
 150                 file system name space. Example: a device unit
 151                 <filename>dev-sda.device</filename> refers to a device
 152                 with the device node <filename>/dev/sda</filename> in
 153                 the file system namespace. If this applies a special
 154                 way to escape the path name is used, so that it is
 155                 usable as part of a file name. Basically, given a
 156                 path, "/" is replaced by "-", and all unprintable
 157                 characters and the "-" are replaced by C-style "\x20"
 158                 escapes. The root directory "/" is encoded as single
 159                 dash, while otherwise the initial and ending "/" is
 160                 removed from all paths during transformation. This
 161                 escaping is reversible.</para>
 162
 163                 <para>Optionally, units may be instantiated from a
 164                 template file at runtime. This allows creation of
 165                 multiple units from a single configuration file. If
 166                 systemd looks for a unit configuration file it will
 167                 first search for the literal unit name in the
 168                 filesystem. If that yields no success and the unit
 169                 name contains an @ character, systemd will look for a
 170                 unit template that shares the same name but with the
 171                 instance string (i.e. the part between the @ character
 172                 and the suffix) removed. Example: if a service
 173                 <filename>getty@tty3.service</filename> is requested
 174                 and no file by that name is found, systemd will look
 175                 for <filename>getty@.service</filename> and
 176                 instantiate a service from that configuration file if
 177                 it is found. To refer to the instance string from
 178                 within the configuration file you may use the special
 179                 <literal>%i</literal> specifier in many of the
 180                 configuration options. Other specifiers that may be
 181                 used are <literal>%n</literal>, <literal>%N</literal>,
 182                 <literal>%p</literal>, <literal>%P</literal> and
 183                 <literal>%I</literal>, for the full unit name, the
 184                 unescaped unit name, the prefix name, the unescaped
 185                 prefix name and the unescaped instance name,
 186                 respectively. The prefix name here refers to the
 187                 string before the @, i.e. "getty" in the example
 188                 above, where "tty3" is the instance name.</para>
 189         </refsect1>
 190
 191         <refsect1>
 192                 <title>Options</title>
 193
 194                 <para>Unit file may include a [Unit] section, which
 195                 carries generic information about the unit that is not
 196                 dependent on the type of unit:</para>
 197
 198                 <variablelist>
 199                         <varlistentry>
 200                                 <term><varname>Names=</varname></term>
 201
 202                                 <listitem><para>Additional names for
 203                                 this unit. The names listed here must
 204                                 have the same suffix (i.e. type) as
 205                                 the unit file name. This option may be
 206                                 specified more than once, in which
 207                                 case all listed names are used. Note
 208                                 that this option is different from the
 209                                 <varname>Alias=</varname> option from
 210                                 the [Install] section mentioned
 211                                 below. See below for details.</para>
 212                                 </listitem>
 213                         </varlistentry>
 214
 215                         <varlistentry>
 216                                 <term><varname>Description=</varname></term>
 217                                 <listitem><para>A free-form string
 218                                 describing the unit. This is intended
 219                                 for use in UIs to show descriptive
 220                                 information along with the unit
 221                                 name.</para></listitem>
 222                         </varlistentry>
 223
 224                         <varlistentry>
 225                                 <term><varname>Requires=</varname></term>
 226
 227                                 <listitem><para>Configures requirement
 228                                 dependencies on other units. If this
 229                                 units get activated the units listed
 230                                 here will be activated as well. If one
 231                                 of the other units gets deactivated or
 232                                 its activation fails, this unit will
 233                                 be deactivated. This option may be
 234                                 specified more than once, in which
 235                                 case requirement dependencies for all
 236                                 listed names are created. Note that
 237                                 requirement dependencies do not
 238                                 influence the order in which services
 239                                 are started or stopped. This has to be
 240                                 configured independently with the
 241                                 <varname>After=</varname> or
 242                                 <varname>Before=</varname> options. If
 243                                 a unit
 244                                 <filename>foo.service</filename>
 245                                 requires a unit
 246                                 <filename>bar.service</filename> as
 247                                 configured with
 248                                 <varname>Requires=</varname> and no
 249                                 ordering is configured with
 250                                 <varname>After=</varname> or
 251                                 <varname>Before=</varname>, then both
 252                                 units will be started simultaneously
 253                                 and without any delay between them if
 254                                 <filename>foo.service</filename> is
 255                                 activated. Often it is a better choice
 256                                 to use <varname>Wants=</varname>
 257                                 instead of
 258                                 <varname>Requires=</varname> in order
 259                                 to achieve a system that is more
 260                                 robust when dealing with failing
 261                                 services.</para></listitem>
 262                         </varlistentry>
 263
 264
 265                         <varlistentry>
 266                                 <term><varname>RequiresOverridable=</varname></term>
 267
 268                                 <listitem><para>Similar to
 269                                 <varname>Requires=</varname>.
 270                                 Dependencies listed in
 271                                 <varname>RequiresOverridable=</varname>
 272                                 which cannot be fulfilled or fail to
 273                                 start are ignored iff the startup was
 274                                 explicitly requested by the user. If
 275                                 the start-up was pulled in indirectly
 276                                 by some dependency or automatic
 277                                 start-up of units that is not
 278                                 requested by the user this dependency
 279                                 must be fulfilled and otherwise the
 280                                 transaction fails. Hence, this option
 281                                 may be used to configure dependencies
 282                                 that are normally honored unless the
 283                                 user explicitly starts up the unit, in
 284                                 which case whether they failed or not
 285                                 is irrelevant.</para></listitem>
 286
 287                         </varlistentry>
 288                         <varlistentry>
 289                                 <term><varname>Requisite=</varname></term>
 290                                 <term><varname>RequisiteOverridable=</varname></term>
 291
 292                                 <listitem><para>Similar to
 293                                 <varname>Requires=</varname>
 294                                 resp. <varname>RequiresOverridable=</varname>. However,
 295                                 if a unit listed here is not started
 296                                 already it will not be started and the
 297                                 transaction fails
 298                                 immediately.</para></listitem>
 299                         </varlistentry>
 300
 301                         <varlistentry>
 302                                 <term><varname>Wants=</varname></term>
 303
 304                                 <listitem><para>A weaker version of
 305                                 <varname>Requires=</varname>. A unit
 306                                 listed in this option will be started
 307                                 if the configuring unit is. However,
 308                                 it the listed unit fails to start up
 309                                 or cannot be added to the transaction
 310                                 this has no impact on the validity of
 311                                 the transaction as a whole. This is
 312                                 the recommended way to hook start-up
 313                                 of one unit to the start-up of another
 314                                 unit. Note that dependencies of this
 315                                 type may also be configured outside of
 316                                 the unit configuration file by
 317                                 adding a symlink to a
 318                                 <filename>.wants/</filename> directory
 319                                 accompanying the unit file. For
 320                                 details see above.</para></listitem>
 321                         </varlistentry>
 322
 323                         <varlistentry>
 324                                 <term><varname>Conflicts=</varname></term>
 325
 326                                 <listitem><para>Configures negative
 327                                 requirement dependencies. If a unit
 328                                 that has a
 329                                 <varname>Conflicts=</varname> setting
 330                                 on another unit starting the former
 331                                 will stop the latter and vice
 332                                 versa. Note that this setting is
 333                                 independent of and orthogonal to the
 334                                 <varname>After=</varname> and
 335                                 <varname>Before=</varname> ordering
 336                                 dependencies.</para></listitem>
 337                         </varlistentry>
 338
 339                         <varlistentry>
 340                                 <term><varname>Before=</varname></term>
 341                                 <term><varname>After=</varname></term>
 342
 343                                 <listitem><para>Configures ordering
 344                                 dependencies between units. If a unit
 345                                 <filename>foo.service</filename>
 346                                 contains a setting
 347                                 <option>Before=bar.service</option>
 348                                 and both units are being started
 349                                 <filename>bar.service</filename>'s
 350                                 start-up is delayed until
 351                                 <filename>foo.service</filename> is
 352                                 started up. Note that this setting is
 353                                 independent of and orthogonal to the
 354                                 requirement dependencies as configured
 355                                 by <varname>Requires=</varname>. It is
 356                                 a common pattern to include a unit
 357                                 name in both the
 358                                 <varname>After=</varname> and
 359                                 <varname>Requires=</varname> option in
 360                                 which case the unit listed will be
 361                                 started before the unit that is
 362                                 configured with these options. This
 363                                 option may be specified more than
 364                                 once, in which case ordering
 365                                 dependencies for all listed names are
 366                                 created. <varname>After=</varname> is
 367                                 the inverse of
 368                                 <varname>Before=</varname>, i.e. while
 369                                 <varname>After=</varname> ensures that
 370                                 the configured unit is started after
 371                                 the listed unit finished starting up,
 372                                 <varname>Before=</varname> ensures the
 373                                 opposite, i.e.  that the configured
 374                                 unit is fully started up before the
 375                                 listed unit is started. Note that when
 376                                 two units with an ordering dependency
 377                                 between them are shut down, the
 378                                 inverse of of the start-up order is
 379                                 applied. i.e. if a unit is configured
 380                                 with <varname>After=</varname> on
 381                                 another unit, the former is stopped
 382                                 before the latter if both are shut
 383                                 down. If one unit with an ordering
 384                                 dependency on another unit is shut
 385                                 down while the latter is started up,
 386                                 the shut down is ordered before the
 387                                 start-up regardless whether the
 388                                 ordering dependency is actually of
 389                                 type <varname>After=</varname> or
 390                                 <varname>Before=</varname>. If two
 391                                 units have no ordering dependencies
 392                                 between them they are shut down
 393                                 resp. started up simultaneously, and
 394                                 no ordering takes
 395                                 place. </para></listitem>
 396                         </varlistentry>
 397
 398                         <varlistentry>
 399                                 <term><varname>RecursiveStop=</varname></term>
 400
 401                                 <listitem><para>Takes a boolean
 402                                 argument. If <option>true</option> and
 403                                 the unit stops without this being
 404                                 requested by the user all units
 405                                 depending on it will be stopped as
 406                                 well. (e.g. if a service exits or
 407                                 crashes on its own behalf, units using
 408                                 it will be stopped) Note that normally
 409                                 if a unit stops without user request
 410                                 units depending on it will not be
 411                                 terminated. Only if the user requested
 412                                 shutdown of a unit all units depending
 413                                 on the unit will be shut down as well
 414                                 and at the same time. Defaults to
 415                                 <option>false</option>.</para></listitem>
 416                         </varlistentry>
 417
 418                         <varlistentry>
 419                                 <term><varname>StopWhenUnneeded=</varname></term>
 420
 421                                 <listitem><para>Takes a boolean
 422                                 argument. If <option>true</option>
 423                                 this unit will be stopped when it is
 424                                 no longer used. Note that in order to
 425                                 minimize the work to be executed
 426                                 systemd will by default not stop units
 427                                 unless they are conflicting with other
 428                                 units, or the user explicitly
 429                                 requested their shut down. If this
 430                                 option is set a unit will be
 431                                 automatically cleaned up if no other
 432                                 active unit requires it. Defaults to
 433                                 <option>false</option>.</para></listitem>
 434                         </varlistentry>
 435
 436                         <varlistentry>
 437                                 <term><varname>OnlyByDependency=</varname></term>
 438
 439                                 <listitem><para>Takes a boolean
 440                                 argument. If <option>true</option>
 441                                 this unit may only be activated
 442                                 indirectly. In this case explicit
 443                                 start-up requested by the user is
 444                                 denied, however if it is started as
 445                                 dependency of another unit start-up
 446                                 will succeed. This is mostly a safety
 447                                 feature to ensure that the user does
 448                                 not accidentally activate units that are
 449                                 not intended to be activated
 450                                 explicitly. This option defaults to
 451                                 <option>false</option>.</para></listitem>
 452                         </varlistentry>
 453
 454                         <varlistentry>
 455                                 <term><varname>DefaultDependencies=</varname></term>
 456
 457                                 <listitem><para>Takes a boolean
 458                                 argument. If <option>true</option>
 459                                 (the default), a few default
 460                                 dependencies will implicitly be
 461                                 created for the unit. The actual
 462                                 dependencies created depend on the
 463                                 unit type. For example, for service
 464                                 units, these dependencies ensure that
 465                                 the service is started only after
 466                                 basic system initialization is
 467                                 complete and is properly terminated on
 468                                 system shutdown. See the respective
 469                                 man pages for details. Generally, only
 470                                 services involved with early boot or
 471                                 late shutdown should set this option
 472                                 to <option>false</option>. It is
 473                                 highly recommended to leave this
 474                                 option enabled for the majority of
 475                                 common units. If set to
 476                                 <option>false</option> this option
 477                                 does not disable all implicit
 478                                 dependencies, just non-essential
 479                                 ones.</para></listitem>
 480                         </varlistentry>
 481
 482                 </variablelist>
 483
 484                 <para>Unit file may include a [Install] section, which
 485                 carries installation information for the unit. This
 486                 section is not interpreted by
 487                 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 488                 during runtime. It is used exclusively by the
 489                 <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 490                 tool during installation of a unit:</para>
 491
 492                 <variablelist>
 493                         <varlistentry>
 494                                 <term><varname>Alias=</varname></term>
 495
 496                                 <listitem><para>Additional names this
 497                                 unit shall be installed under. The
 498                                 names listed here must have the same
 499                                 suffix (i.e. type) as the unit file
 500                                 name. This option may be specified
 501                                 more than once, in which case all
 502                                 listed names are used. At installation
 503                                 time,
 504                                 <command>systemd-install</command>
 505                                 will create symlinks from these names
 506                                 to the unit file name. Note that this
 507                                 is different from the
 508                                 <varname>Names=</varname> option from
 509                                 the [Unit] section mentioned above:
 510                                 The names from
 511                                 <varname>Names=</varname> apply
 512                                 unconditionally if the unit is
 513                                 loaded. The names from
 514                                 <varname>Alias=</varname> apply only
 515                                 if the unit has actually been
 516                                 installed with the
 517                                 <command>systemd-install</command>
 518                                 tool.  Also, if systemd searches for a
 519                                 unit, it will discover symlinked alias
 520                                 names as configured with
 521                                 <varname>Alias=</varname>, but not
 522                                 names configured with
 523                                 <varname>Names=</varname> only. It is
 524                                 a common pattern to list a name in
 525                                 both options. In this case, a unit
 526                                 will be active under all names if
 527                                 installed, but also if not installed
 528                                 but requested explicitly under its
 529                                 main name.</para></listitem>
 530                         </varlistentry>
 531
 532                         <varlistentry>
 533                                 <term><varname>WantedBy=</varname></term>
 534
 535                                 <listitem><para>Installs a symlink in
 536                                 the <filename>.wants/</filename>
 537                                 subdirectory for a unit. This has the
 538                                 effect that when the listed unit name
 539                                 is activated the unit listing it is
 540                                 activated
 541                                 too. <command>WantedBy=foo.service</command>
 542                                 in a service
 543                                 <filename>bar.service</filename> is
 544                                 mostly equivalent to
 545                                 <command>Alias=foo.service.wants/bar.service</command>
 546                                 in the same file.</para></listitem>
 547                         </varlistentry>
 548
 549                         <varlistentry>
 550                                 <term><varname>Also=</varname></term>
 551
 552                                 <listitem><para>Additional units to
 553                                 install when this unit is
 554                                 installed. If the user requests
 555                                 installation of a unit with this
 556                                 option configured
 557                                 <command>systemd-install</command>
 558                                 will automatically install units
 559                                 listed in this option as
 560                                 well.</para></listitem>
 561                         </varlistentry>
 562                 </variablelist>
 563
 564         </refsect1>
 565
 566         <refsect1>
 567                 <title>See Also</title>
 568                 <para>
 569                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 570                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 571                         <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 572                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 573                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 574                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 575                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 576                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 577                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 578                         <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 579                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 580                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 581                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 582                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 583                 </para>
 584         </refsect1>
 585
 586 </refentry>