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