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></para>
  60         </refsynopsisdiv>
  61
  62         <refsect1>
  63                 <title>Description</title>
  64
  65                 <para>A unit configuration file encodes information
  66                 about a service, a socket, a device, a mount point, an
  67                 automount point, a swap file or partition, a start-up
  68                 target, a file system path or a timer controlled and
  69                 supervised by
  70                 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>. The
  71                 syntax is inspired by <ulink
  72                 url="http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG
  73                 Desktop Entry Specification</ulink> <filename>.desktop</filename> files, which are in turn
  74                 inspired by Microsoft Windows
  75                 <filename>.ini</filename> files.</para>
  76
  77                 <para>This man pages lists the common configuration
  78                 options of the all unit types. These options need to
  79                 be configured in the [Unit] resp. [Install]
  80                 section of the unit files.</para>
  81
  82                 <para>In addition to the generic [Unit] and [Install]
  83                 sections described here each unit should have a
  84                 type-specific section, e.g. [Service] for a service
  85                 unit. See the respective man pages for more
  86                 information.</para>
  87
  88                 <para>Unit files may contain additional options on top
  89                 of those listed here. If systemd encounters an unknown
  90                 option it will write a warning log message but
  91                 continue loading the unit. If an option is prefixed
  92                 with <option>X-</option> it is ignored completely by
  93                 systemd. Applications may use this to include
  94                 additional information in the unit files.</para>
  95
  96                 <para>Boolean arguments used in unit files can be
  97                 written in various forms. For positive settings the
  98                 strings <option>1</option>, <option>yes</option>,
  99                 <option>true</option> and <option>on</option> are
 100                 equivalent. For negative settings the strings
 101                 <option>0</option>, <option>no</option>,
 102                 <option>false</option> and <option>off</option> are
 103                 equivalent.</para>
 104
 105                 <para>Time span values encoded in unit files can be
 106                 written in various formats. A stand-alone number
 107                 specifies a time in seconds. If suffixed with a time
 108                 unit, the unit is honored. A concatentation of
 109                 multiple value with units is supported, in which case
 110                 the values are added up. Example: "50" refers to 50
 111                 seconds; "2min 200ms" refers to 2 minutes plus 200
 112                 milliseconds, i.e. 120200ms. The following time units
 113                 are understood: s, min, h, d, w, ms, us.</para>
 114
 115                 <para>Empty lines and lines starting with # or ; are
 116                 ignored. This may be used for commenting.</para>
 117
 118                 <para>If a line starts with <option>.include</option>
 119                 followed by a file name the specified file will be
 120                 read as if its contents where listed in place of the
 121                 <option>.include</option> directive.</para>
 122
 123                 <para>Along with a unit file
 124                 <filename>foo.service</filename> a directory
 125                 <filename>foo.service.wants/</filename> may exist. All
 126                 units symlinked from such a directory are implicitly
 127                 added as dependencies of type
 128                 <varname>Wanted=</varname> to the unit. This is useful
 129                 to hook units into the start-up of other units,
 130                 without having to modify their unit configuration
 131                 files. For details about the semantics of
 132                 <varname>Wanted=</varname> see below. The preferred
 133                 way to create symlinks in the
 134                 <filename>.wants/</filename> directory of a service is
 135                 with the
 136                 <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 137                 tool which reads information from the [Install]
 138                 section of unit files. (See below.)</para>
 139
 140                 <para>Note that while systemd offers a flexible
 141                 dependency system between units it is recommended to
 142                 use this functionality only sparsely and instead rely
 143                 on techniques such as bus-based or socket-based
 144                 activation which makes dependencies implicit, which
 145                 both results in a simpler and more flexible
 146                 system.</para>
 147         </refsect1>
 148
 149         <refsect1>
 150                 <title>Options</title>
 151
 152                 <para>Unit file may include a [Unit] section, which
 153                 carries generic information about the unit that is not
 154                 dependent on the type of unit:</para>
 155
 156                 <variablelist>
 157                         <varlistentry>
 158                                 <term><varname>Names=</varname></term>
 159
 160                                 <listitem><para>Additional names for
 161                                 this unit. The names listed here must
 162                                 have the same suffix (i.e. type) as
 163                                 the unit file name. This option may be
 164                                 specified more than once, in which
 165                                 case all listed names are used. Note
 166                                 that this option is different from the
 167                                 <varname>Alias=</varname> option from
 168                                 the [Install] section mentioned
 169                                 below. See below for details.</para>
 170                                 </listitem>
 171                         </varlistentry>
 172
 173                         <varlistentry>
 174                                 <term><varname>Description=</varname></term>
 175                                 <listitem><para>A free-form string
 176                                 describing the unit. This is intended for use
 177                                 in UIs wanting to show
 178                                 descriptive information along with the
 179                                 unit name.</para></listitem>
 180                         </varlistentry>
 181
 182                         <varlistentry>
 183                                 <term><varname>Requires=</varname></term>
 184
 185                                 <listitem><para>Configures requirement
 186                                 dependencies on other units. If this
 187                                 units get activated the units listed
 188                                 here will be activated as well. If one
 189                                 of the other units gets deactivated or
 190                                 its activation fails, this unit will
 191                                 be deactivated. This option may be
 192                                 specified more than once, in which
 193                                 case requirement dependencies for all
 194                                 listed names are created. Note that
 195                                 requirement dependencies do not
 196                                 influence the order in which services
 197                                 are started or stopped. This has to be
 198                                 configured independently with the
 199                                 <varname>After=</varname> or
 200                                 <varname>Before=</varname> options. If
 201                                 a unit
 202                                 <filename>foo.service</filename>
 203                                 requires a unit
 204                                 <filename>bar.service</filename> as
 205                                 configured with
 206                                 <varname>Requires=</varname> and no
 207                                 ordering is configured with
 208                                 <varname>After=</varname> or
 209                                 <varname>Before=</varname>, then both
 210                                 units will be started simultaneously
 211                                 and without any delay between them if
 212                                 <filename>foo.service</filename> is
 213                                 activated. Often it is a better choice
 214                                 to use <varname>Wants=</varname>
 215                                 instead of
 216                                 <varname>Requires=</varname> in order
 217                                 to achieve a system that is more
 218                                 robust when dealing with failing
 219                                 services.</para></listitem>
 220                         </varlistentry>
 221
 222
 223                         <varlistentry>
 224                                 <term><varname>RequiresOverridable=</varname></term>
 225
 226                                 <listitem><para>Similar to
 227                                 <varname>Requires=</varname>.
 228                                 Dependencies listed in
 229                                 <varname>RequiresOverridable=</varname>
 230                                 which cannot be fulfilled or fail to
 231                                 start are ignored iff the startup was
 232                                 explicitly requested by the user. If
 233                                 the start-up was pulled in indirectly
 234                                 by some dependency or automatic
 235                                 start-up of units that is not
 236                                 requested by the user this dependency
 237                                 must be fulfilled and otherwise the
 238                                 transaction fails. Hence, this option
 239                                 may be used to configure dependencies
 240                                 that are normally honored unless the
 241                                 user explicitly starts up the unit, in
 242                                 which case whether they failed or not
 243                                 is irrelevant.</para></listitem>
 244
 245                         </varlistentry>
 246                         <varlistentry>
 247                                 <term><varname>Requisite=</varname></term>
 248                                 <term><varname>RequisiteOverridable=</varname></term>
 249
 250                                 <listitem><para>Similar to
 251                                 <varname>Requires=</varname>
 252                                 resp. <varname>RequiresOverridable=</varname>. However,
 253                                 if a unit listed here is not started
 254                                 already it will not be started and the
 255                                 transaction fails
 256                                 immediately.</para></listitem>
 257                         </varlistentry>
 258
 259                         <varlistentry>
 260                                 <term><varname>Wants=</varname></term>
 261
 262                                 <listitem><para>A weaker version of
 263                                 <varname>Requires=</varname>. A unit
 264                                 listed in this option will be started
 265                                 if the configuring unit is. However,
 266                                 it the listed unit fails to start up
 267                                 or cannot be added to the transaction
 268                                 this has no impact on the validity of
 269                                 the transaction as a whole. This is
 270                                 the recommended way to hook start-up
 271                                 of one unit to the start-up of another
 272                                 unit. Note that dependencies of this
 273                                 type may also be configured outside of
 274                                 the unit configuration file by
 275                                 adding a symlink to a
 276                                 <filename>.wants/</filename> directory
 277                                 accompanying the unit file. For
 278                                 details see above.</para></listitem>
 279                         </varlistentry>
 280
 281                         <varlistentry>
 282                                 <term><varname>Conflicts=</varname></term>
 283
 284                                 <listitem><para>Configures negative
 285                                 requirement dependencies. If a unit
 286                                 that has a
 287                                 <varname>Conflicts=</varname> setting
 288                                 on another unit starting the former
 289                                 will stop the latter and vice
 290                                 versa. Note that this setting is
 291                                 independent of and orthogonal to the
 292                                 <varname>After=</varname> and
 293                                 <varname>Before=</varname> ordering
 294                                 dependencies.</para></listitem>
 295                         </varlistentry>
 296
 297                         <varlistentry>
 298                                 <term><varname>Before=</varname></term>
 299                                 <term><varname>After=</varname></term>
 300
 301                                 <listitem><para>Configures ordering
 302                                 dependencies between units. If a unit
 303                                 <filename>foo.service</filename>
 304                                 contains a setting
 305                                 <option>Before=bar.service</option>
 306                                 and both units are being started
 307                                 <filename>bar.service</filename>'s
 308                                 start-up is delayed until
 309                                 <filename>foo.service</filename> is
 310                                 started up. Note that this setting is
 311                                 independent of and orthogonal to the
 312                                 requirement dependencies as configured
 313                                 by <varname>Requires=</varname>. It is
 314                                 a common pattern to include a unit
 315                                 name in both the
 316                                 <varname>After=</varname> and
 317                                 <varname>Requires=</varname> option in
 318                                 which case the unit listed will be
 319                                 started before the unit that is
 320                                 configured with these options. This
 321                                 option may be specified more than
 322                                 once, in which case ordering
 323                                 dependencies for all listed names are
 324                                 created. <varname>After=</varname> is
 325                                 the inverse of
 326                                 <varname>Before=</varname>, i.e. while
 327                                 <varname>After=</varname> ensures that
 328                                 the configured unit is started after
 329                                 the listed unit finished starting up,
 330                                 <varname>Before=</varname> ensures the
 331                                 opposite, i.e.  that the configured
 332                                 unit is fully started up before the
 333                                 listed unit is started. Note that when
 334                                 two units with an ordering dependency
 335                                 between them are shut down, the
 336                                 inverse of of the start-up order is
 337                                 applied. i.e. if a unit is configured
 338                                 with <varname>After=</varname> on
 339                                 another unit, the former is stopped
 340                                 before the latter if both are shut
 341                                 down. If one unit with an ordering
 342                                 dependency on another unit is shut
 343                                 down while the latter is started up,
 344                                 the shut down is ordered before the
 345                                 start-up regardless whether the
 346                                 ordering dependency is actually of
 347                                 type <varname>After=</varname> or
 348                                 <varname>Before=</varname>. If two
 349                                 units have no ordering dependencies
 350                                 between them they are shut down
 351                                 resp. started up simultaneously, and
 352                                 no ordering takes
 353                                 place. </para></listitem>
 354                         </varlistentry>
 355
 356                         <varlistentry>
 357                                 <term><varname>RecursiveStop=</varname></term>
 358
 359                                 <listitem><para>Takes a boolean
 360                                 argument. If <option>true</option> and
 361                                 the unit stops without this being
 362                                 requested by the user all units
 363                                 depending on it will be stopped as
 364                                 well. (e.g. if a service exits or
 365                                 crashes on its own behalf, units using
 366                                 it will be stopped) Note that normally
 367                                 if a unit stops without user request
 368                                 units depending on it will not be
 369                                 terminated. Only if the user requested
 370                                 shutdown of a unit all units depending
 371                                 on the unit will be shut down as well
 372                                 and at the same time. Defaults to
 373                                 <option>false</option>.</para></listitem>
 374                         </varlistentry>
 375
 376                         <varlistentry>
 377                                 <term><varname>StopWhenUnneeded=</varname></term>
 378
 379                                 <listitem><para>Takes a boolean
 380                                 argument. If <option>true</option>
 381                                 this unit will be stopped when it is
 382                                 no longer used. Note that in order to
 383                                 minimize the work to be executed
 384                                 systemd will by default not stop units
 385                                 unless they are conflicting with other
 386                                 units, or the user explicitly
 387                                 requested their shut down. If this
 388                                 option is set a unit will be
 389                                 automatically cleaned up if no other
 390                                 active unit requires it. Defaults to
 391                                 <option>false</option>.</para></listitem>
 392                         </varlistentry>
 393
 394                         <varlistentry>
 395                                 <term><varname>OnlyByDependency=</varname></term>
 396
 397                                 <listitem><para>Takes a boolean
 398                                 argument. If <option>true</option>
 399                                 this unit may only be activated
 400                                 indirectly. In this case explicit
 401                                 start-up requested by the user is
 402                                 denied, however if it is started as
 403                                 dependency of another unit start-up
 404                                 will succeed. This is mostly a safety
 405                                 feature to ensure that the user does
 406                                 not accidentally activate units that are
 407                                 not intended to be activated
 408                                 explicitly. This option defaults to
 409                                 <option>false</option>.</para></listitem>
 410                         </varlistentry>
 411
 412                 </variablelist>
 413
 414                 <para>Unit file may include a [Install] section, which
 415                 carries installation information for the unit. This
 416                 section is not interpreted by
 417                 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 418                 during runtime. It is used exclusively by the
 419                 <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 420                 tool during installation of a unit:</para>
 421
 422                 <variablelist>
 423                         <varlistentry>
 424                                 <term><varname>Alias=</varname></term>
 425
 426                                 <listitem><para>Additional names, this
 427                                 unit shall be installed under. The
 428                                 names listed here must have the same
 429                                 suffix (i.e. type) as the unit file
 430                                 name. This option may be specified
 431                                 more than once, in which case all
 432                                 listed names are used. At installation
 433                                 time,
 434                                 <command>systemd-install</command>
 435                                 will create symlinks from these names
 436                                 to the unit file name. Note that this
 437                                 is different from the
 438                                 <varname>Names=</varname> option from
 439                                 the [Unit] section mentioned above:
 440                                 The names from
 441                                 <varname>Names=</varname> apply
 442                                 unconditionally if the unit is
 443                                 loaded. The names from
 444                                 <varname>Alias=</varname> apply only
 445                                 if the unit has actually been
 446                                 installed with the
 447                                 <command>systemd-install</command>
 448                                 tool.  Also, if systemd searches for a
 449                                 unit, it will discover symlinked alias
 450                                 names as configured with
 451                                 <varname>Alias=</varname>, but not
 452                                 names configured with
 453                                 <varname>Names=</varname> only. It is
 454                                 a common pattern to list a name in
 455                                 both options. In this case, a unit
 456                                 will be active under all names if
 457                                 installed, but also if not installed
 458                                 but requested explicitly under its
 459                                 main name.</para></listitem>
 460                         </varlistentry>
 461
 462                         <varlistentry>
 463                                 <term><varname>WantedBy=</varname></term>
 464
 465                                 <listitem><para>Installs a symlink in
 466                                 the <filename>.wants/</filename>
 467                                 subdirectory for a unit. This has the
 468                                 effect that when the listed unit name
 469                                 is activated the unit listing it is
 470                                 activated
 471                                 to. <command>WantedBy=foo.service</command>
 472                                 in a service
 473                                 <filename>bar.service</filename> is
 474                                 mostly equivalent to
 475                                 <command>Alias=foo.service.wants/bar.service</command>
 476                                 in the same file.</para></listitem>
 477                         </varlistentry>
 478
 479                         <varlistentry>
 480                                 <term><varname>Also=</varname></term>
 481
 482                                 <listitem><para>Additional units to
 483                                 install when this unit is
 484                                 installed. If the user requests
 485                                 installation of a unit with this
 486                                 option configured
 487                                 <command>systemd-install</command>
 488                                 will automatically install units
 489                                 listed in this option as
 490                                 well.</para></listitem>
 491                         </varlistentry>
 492                 </variablelist>
 493
 494         </refsect1>
 495
 496         <refsect1>
 497                 <title>See Also</title>
 498                 <para>
 499                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 500                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 501                         <citerefentry><refentrytitle>systemd-install</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 502                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 503                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 504                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 505                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 506                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 507                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 508                         <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 509                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 510                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 511                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 512                 </para>
 513         </refsect1>
 514
 515 </refentry>