man/systemd.unit.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3         "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4
   5 <!--
   6   This file is part of systemd.
   7
   8   Copyright 2010 Lennart Poettering
   9
  10   systemd is free software; you can redistribute it and/or modify it
  11   under the terms of the GNU General Public License as published by
  12   the Free Software Foundation; either version 2 of the License, or
  13   (at your option) any later version.
  14
  15   systemd is distributed in the hope that it will be useful, but
  16   WITHOUT ANY WARRANTY; without even the implied warranty of
  17   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  18   General Public License for more details.
  19
  20   You should have received a copy of the GNU General Public License
  21   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  22 -->
  23
  24 <refentry id="systemd.unit">
  25
  26         <refentryinfo>
  27                 <title>systemd.unit</title>
  28                 <productname>systemd</productname>
  29
  30                 <authorgroup>
  31                         <author>
  32                                 <contrib>Developer</contrib>
  33                                 <firstname>Lennart</firstname>
  34                                 <surname>Poettering</surname>
  35                                 <email>lennart@poettering.net</email>
  36                         </author>
  37                 </authorgroup>
  38         </refentryinfo>
  39
  40         <refmeta>
  41                 <refentrytitle>systemd.unit</refentrytitle>
  42                 <manvolnum>5</manvolnum>
  43         </refmeta>
  44
  45         <refnamediv>
  46                 <refname>systemd.unit</refname>
  47                 <refpurpose>systemd unit configuration files</refpurpose>
  48         </refnamediv>
  49
  50         <refsynopsisdiv>
  51                 <para><filename>systemd.service</filename>,
  52                 <filename>systemd.socket</filename>,
  53                 <filename>systemd.device</filename>,
  54                 <filename>systemd.mount</filename>,
  55                 <filename>systemd.automount</filename>,
  56                 <filename>systemd.swap</filename>,
  57                 <filename>systemd.target</filename>,
  58                 <filename>systemd.path</filename>,
  59                 <filename>systemd.timer</filename>,
  60                 <filename>systemd.snapshot</filename></para>
  61         </refsynopsisdiv>
  62
  63         <refsect1>
  64                 <title>Description</title>
  65
  66                 <para>A unit configuration file encodes information
  67                 about a service, a socket, a device, a mount point, an
  68                 automount point, a swap file or partition, a start-up
  69                 target, a file system path or a timer controlled and
  70                 supervised by
  71                 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>. The
  72                 syntax is inspired by <ulink
  73                 url="http://standards.freedesktop.org/desktop-entry-spec/latest/">XDG
  74                 Desktop Entry Specification</ulink> <filename>.desktop</filename> files, which are in turn
  75                 inspired by Microsoft Windows
  76                 <filename>.ini</filename> files.</para>
  77
  78                 <para>This man pages lists the common configuration
  79                 options of all the unit types. These options need to
  80                 be configured in the [Unit] resp. [Install]
  81                 section of the unit files.</para>
  82
  83                 <para>In addition to the generic [Unit] and [Install]
  84                 sections described here, each unit should have a
  85                 type-specific section, e.g. [Service] for a service
  86                 unit. See the respective man pages for more
  87                 information.</para>
  88
  89                 <para>Unit files may contain additional options on top
  90                 of those listed here. If systemd encounters an unknown
  91                 option it will write a warning log message but
  92                 continue loading the unit. If an option is prefixed
  93                 with <option>X-</option> it is ignored completely by
  94                 systemd. Applications may use this to include
  95                 additional information in the unit files.</para>
  96
  97                 <para>Boolean arguments used in unit files can be
  98                 written in various formats. For positive settings the
  99                 strings <option>1</option>, <option>yes</option>,
 100                 <option>true</option> and <option>on</option> are
 101                 equivalent. For negative settings the strings
 102                 <option>0</option>, <option>no</option>,
 103                 <option>false</option> and <option>off</option> are
 104                 equivalent.</para>
 105
 106                 <para>Time span values encoded in unit files can be
 107                 written in various formats. A stand-alone number
 108                 specifies a time in seconds. If suffixed with a time
 109                 unit, the unit is honored. A concatenation of
 110                 multiple values with units is supported, in which case
 111                 the values are added up. Example: "50" refers to 50
 112                 seconds; "2min 200ms" refers to 2 minutes plus 200
 113                 milliseconds, i.e. 120200ms. The following time units
 114                 are understood: s, min, h, d, w, ms, us.</para>
 115
 116                 <para>Empty lines and lines starting with # or ; are
 117                 ignored. This may be used for commenting. Lines ending
 118                 in a backslash are concatenated with the following
 119                 line while reading and the backslash is replaced by a
 120                 space character. This may be used to wrap long lines.</para>
 121
 122                 <para>If a line starts with <option>.include</option>
 123                 followed by a file name, the specified file will be
 124                 read as if its contents were listed in place of the
 125                 <option>.include</option> directive.</para>
 126
 127                 <para>Along with a unit file
 128                 <filename>foo.service</filename> a directory
 129                 <filename>foo.service.wants/</filename> may exist. All
 130                 units symlinked from such a directory are implicitly
 131                 added as dependencies of type
 132                 <varname>Wanted=</varname> to the unit. This is useful
 133                 to hook units into the start-up of other units,
 134                 without having to modify their unit configuration
 135                 files. For details about the semantics of
 136                 <varname>Wanted=</varname> see below. The preferred
 137                 way to create symlinks in the
 138                 <filename>.wants/</filename> directory of a service is
 139                 with the <command>enable</command> command of the
 140                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 141                 tool which reads information from the [Install]
 142                 section of unit files. (See below.) A similar
 143                 functionality exists for <varname>Requires=</varname>
 144                 type dependencies as well, the directory suffix is
 145                 <filename>.requires/</filename> in this case.</para>
 146
 147                 <para>Note that while systemd offers a flexible
 148                 dependency system between units it is recommended to
 149                 use this functionality only sparsely and instead rely
 150                 on techniques such as bus-based or socket-based
 151                 activation which makes dependencies implicit, which
 152                 both results in a simpler and more flexible
 153                 system.</para>
 154
 155                 <para>Some unit names reflect paths existing in the
 156                 file system name space. Example: a device unit
 157                 <filename>dev-sda.device</filename> refers to a device
 158                 with the device node <filename>/dev/sda</filename> in
 159                 the file system namespace. If this applies a special
 160                 way to escape the path name is used, so that the
 161                 result is usable as part of a file name. Basically,
 162                 given a path, "/" is replaced by "-", and all
 163                 unprintable characters and the "-" are replaced by
 164                 C-style "\x20" escapes. The root directory "/" is
 165                 encoded as single dash, while otherwise the initial
 166                 and ending "/" is removed from all paths during
 167                 transformation. This escaping is reversible.</para>
 168
 169                 <para>Optionally, units may be instantiated from a
 170                 template file at runtime. This allows creation of
 171                 multiple units from a single configuration file. If
 172                 systemd looks for a unit configuration file it will
 173                 first search for the literal unit name in the
 174                 filesystem. If that yields no success and the unit
 175                 name contains an @ character, systemd will look for a
 176                 unit template that shares the same name but with the
 177                 instance string (i.e. the part between the @ character
 178                 and the suffix) removed. Example: if a service
 179                 <filename>getty@tty3.service</filename> is requested
 180                 and no file by that name is found, systemd will look
 181                 for <filename>getty@.service</filename> and
 182                 instantiate a service from that configuration file if
 183                 it is found. To refer to the instance string from
 184                 within the configuration file you may use the special
 185                 <literal>%i</literal> specifier in many of the
 186                 configuration options. Other specifiers that may be
 187                 used are <literal>%n</literal>, <literal>%N</literal>,
 188                 <literal>%p</literal>, <literal>%P</literal>,
 189                 <literal>%I</literal> and <literal>%f</literal>, for
 190                 the full unit name, the unescaped unit name, the
 191                 prefix name, the unescaped prefix name, the unescaped
 192                 instance name and the unescaped filename,
 193                 respectively. The unescaped filename is either the
 194                 unescaped instance name (if set) with / prepended (if
 195                 necessary), or the prefix name similarly prepended
 196                 with /. The prefix name here refers to the string
 197                 before the @, i.e. "getty" in the example above, where
 198                 "tty3" is the instance name.</para>
 199
 200                 <para>If a unit file is empty (i.e. has the file size
 201                 0) or is symlinked to <filename>/dev/null</filename>
 202                 its configuration will not be loaded and it appears
 203                 with a load state of <literal>masked</literal>, and
 204                 cannot be activated. Use this as an effective way to
 205                 fully disable a unit, making it impossible to start it
 206                 even manually.</para>
 207
 208                 <para>The unit file format is covered by the
 209                 <ulink
 210                 url="http://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 211                 Stability Promise</ulink>.</para>
 212         </refsect1>
 213
 214         <refsect1>
 215                 <title>Options</title>
 216
 217                 <para>Unit file may include a [Unit] section, which
 218                 carries generic information about the unit that is not
 219                 dependent on the type of unit:</para>
 220
 221                 <variablelist>
 222
 223                         <varlistentry>
 224                                 <term><varname>Description=</varname></term>
 225                                 <listitem><para>A free-form string
 226                                 describing the unit. This is intended
 227                                 for use in UIs to show descriptive
 228                                 information along with the unit
 229                                 name.</para></listitem>
 230                         </varlistentry>
 231
 232                         <varlistentry>
 233                                 <term><varname>Requires=</varname></term>
 234
 235                                 <listitem><para>Configures requirement
 236                                 dependencies on other units. If this
 237                                 unit gets activated, the units listed
 238                                 here will be activated as well. If one
 239                                 of the other units gets deactivated or
 240                                 its activation fails, this unit will
 241                                 be deactivated. This option may be
 242                                 specified more than once, in which
 243                                 case requirement dependencies for all
 244                                 listed names are created. Note that
 245                                 requirement dependencies do not
 246                                 influence the order in which services
 247                                 are started or stopped. This has to be
 248                                 configured independently with the
 249                                 <varname>After=</varname> or
 250                                 <varname>Before=</varname> options. If
 251                                 a unit
 252                                 <filename>foo.service</filename>
 253                                 requires a unit
 254                                 <filename>bar.service</filename> as
 255                                 configured with
 256                                 <varname>Requires=</varname> and no
 257                                 ordering is configured with
 258                                 <varname>After=</varname> or
 259                                 <varname>Before=</varname>, then both
 260                                 units will be started simultaneously
 261                                 and without any delay between them if
 262                                 <filename>foo.service</filename> is
 263                                 activated. Often it is a better choice
 264                                 to use <varname>Wants=</varname>
 265                                 instead of
 266                                 <varname>Requires=</varname> in order
 267                                 to achieve a system that is more
 268                                 robust when dealing with failing
 269                                 services.</para></listitem>
 270                         </varlistentry>
 271
 272                         <varlistentry>
 273                                 <term><varname>RequiresOverridable=</varname></term>
 274
 275                                 <listitem><para>Similar to
 276                                 <varname>Requires=</varname>.
 277                                 Dependencies listed in
 278                                 <varname>RequiresOverridable=</varname>
 279                                 which cannot be fulfilled or fail to
 280                                 start are ignored if the startup was
 281                                 explicitly requested by the user. If
 282                                 the start-up was pulled in indirectly
 283                                 by some dependency or automatic
 284                                 start-up of units that is not
 285                                 requested by the user this dependency
 286                                 must be fulfilled and otherwise the
 287                                 transaction fails. Hence, this option
 288                                 may be used to configure dependencies
 289                                 that are normally honored unless the
 290                                 user explicitly starts up the unit, in
 291                                 which case whether they failed or not
 292                                 is irrelevant.</para></listitem>
 293
 294                         </varlistentry>
 295                         <varlistentry>
 296                                 <term><varname>Requisite=</varname></term>
 297                                 <term><varname>RequisiteOverridable=</varname></term>
 298
 299                                 <listitem><para>Similar to
 300                                 <varname>Requires=</varname>
 301                                 resp. <varname>RequiresOverridable=</varname>. However,
 302                                 if a unit listed here is not started
 303                                 already it will not be started and the
 304                                 transaction fails
 305                                 immediately.</para></listitem>
 306                         </varlistentry>
 307
 308                         <varlistentry>
 309                                 <term><varname>Wants=</varname></term>
 310
 311                                 <listitem><para>A weaker version of
 312                                 <varname>Requires=</varname>. A unit
 313                                 listed in this option will be started
 314                                 if the configuring unit is. However,
 315                                 if the listed unit fails to start up
 316                                 or cannot be added to the transaction
 317                                 this has no impact on the validity of
 318                                 the transaction as a whole. This is
 319                                 the recommended way to hook start-up
 320                                 of one unit to the start-up of another
 321                                 unit. Note that dependencies of this
 322                                 type may also be configured outside of
 323                                 the unit configuration file by
 324                                 adding a symlink to a
 325                                 <filename>.wants/</filename> directory
 326                                 accompanying the unit file. For
 327                                 details see above.</para></listitem>
 328                         </varlistentry>
 329
 330                         <varlistentry>
 331                                 <term><varname>BindTo=</varname></term>
 332
 333                                 <listitem><para>Configures requirement
 334                                 dependencies, very similar in style to
 335                                 <varname>Requires=</varname>, however
 336                                 in addition to this behaviour it also
 337                                 declares that this unit is stopped
 338                                 when any of the units listed suddenly
 339                                 disappears. Units can suddenly,
 340                                 unexpectedly disappear if a service
 341                                 terminates on its own choice, a device
 342                                 is unplugged or a mount point
 343                                 unmounted without involvement of
 344                                 systemd.</para></listitem>
 345                         </varlistentry>
 346
 347                         <varlistentry>
 348                                 <term><varname>Conflicts=</varname></term>
 349
 350                                 <listitem><para>Configures negative
 351                                 requirement dependencies. If a unit
 352                                 has a
 353                                 <varname>Conflicts=</varname> setting
 354                                 on another unit, starting the former
 355                                 will stop the latter and vice
 356                                 versa. Note that this setting is
 357                                 independent of and orthogonal to the
 358                                 <varname>After=</varname> and
 359                                 <varname>Before=</varname> ordering
 360                                 dependencies.</para>
 361
 362                                 <para>If a unit A that conflicts with
 363                                 a unit B is scheduled to be started at
 364                                 the same time as B, the transaction
 365                                 will either fail (in case both are
 366                                 required part of the transaction) or
 367                                 be modified to be fixed (in case one
 368                                 or both jobs are not a required part
 369                                 of the transaction). In the latter
 370                                 case the job that is not the required
 371                                 will be removed, or in case both are
 372                                 not required the unit that conflicts
 373                                 will be started and the unit that is
 374                                 conflicted is
 375                                 stopped.</para></listitem>
 376                         </varlistentry>
 377
 378                         <varlistentry>
 379                                 <term><varname>Before=</varname></term>
 380                                 <term><varname>After=</varname></term>
 381
 382                                 <listitem><para>Configures ordering
 383                                 dependencies between units. If a unit
 384                                 <filename>foo.service</filename>
 385                                 contains a setting
 386                                 <option>Before=bar.service</option>
 387                                 and both units are being started,
 388                                 <filename>bar.service</filename>'s
 389                                 start-up is delayed until
 390                                 <filename>foo.service</filename> is
 391                                 started up. Note that this setting is
 392                                 independent of and orthogonal to the
 393                                 requirement dependencies as configured
 394                                 by <varname>Requires=</varname>. It is
 395                                 a common pattern to include a unit
 396                                 name in both the
 397                                 <varname>After=</varname> and
 398                                 <varname>Requires=</varname> option in
 399                                 which case the unit listed will be
 400                                 started before the unit that is
 401                                 configured with these options. This
 402                                 option may be specified more than
 403                                 once, in which case ordering
 404                                 dependencies for all listed names are
 405                                 created. <varname>After=</varname> is
 406                                 the inverse of
 407                                 <varname>Before=</varname>, i.e. while
 408                                 <varname>After=</varname> ensures that
 409                                 the configured unit is started after
 410                                 the listed unit finished starting up,
 411                                 <varname>Before=</varname> ensures the
 412                                 opposite, i.e.  that the configured
 413                                 unit is fully started up before the
 414                                 listed unit is started. Note that when
 415                                 two units with an ordering dependency
 416                                 between them are shut down, the
 417                                 inverse of the start-up order is
 418                                 applied. i.e. if a unit is configured
 419                                 with <varname>After=</varname> on
 420                                 another unit, the former is stopped
 421                                 before the latter if both are shut
 422                                 down. If one unit with an ordering
 423                                 dependency on another unit is shut
 424                                 down while the latter is started up,
 425                                 the shut down is ordered before the
 426                                 start-up regardless whether the
 427                                 ordering dependency is actually of
 428                                 type <varname>After=</varname> or
 429                                 <varname>Before=</varname>. If two
 430                                 units have no ordering dependencies
 431                                 between them they are shut down
 432                                 resp. started up simultaneously, and
 433                                 no ordering takes
 434                                 place. </para></listitem>
 435                         </varlistentry>
 436
 437                         <varlistentry>
 438                                 <term><varname>OnFailure=</varname></term>
 439
 440                                 <listitem><para>Lists one or more
 441                                 units that are activated when this
 442                                 unit enters the
 443                                 '<literal>failed</literal>'
 444                                 state.</para></listitem>
 445                         </varlistentry>
 446
 447                         <varlistentry>
 448                                 <term><varname>OnFailureIsolate=</varname></term>
 449
 450                                 <listitem><para>Takes a boolean
 451                                 argument. If <option>true</option> the
 452                                 unit listed in
 453                                 <varname>OnFailure=</varname> will be
 454                                 enqueued in isolation mode, i.e. all
 455                                 units that are not its dependency will
 456                                 be stopped. If this is set only a
 457                                 single unit may be listed in
 458                                 <varname>OnFailure=</varname>. Defaults
 459                                 to
 460                                 <option>false</option>.</para></listitem>
 461                         </varlistentry>
 462
 463                         <varlistentry>
 464                                 <term><varname>IgnoreOnIsolate=</varname></term>
 465
 466                                 <listitem><para>Takes a boolean
 467                                 argument. If <option>true</option>
 468                                 this unit will not be stopped when
 469                                 isolating another unit. Defaults to
 470                                 <option>false</option>.</para></listitem>
 471                         </varlistentry>
 472
 473                         <varlistentry>
 474                                 <term><varname>IgnoreOnSnapshot=</varname></term>
 475
 476                                 <listitem><para>Takes a boolean
 477                                 argument. If <option>true</option>
 478                                 this unit will not be included in
 479                                 snapshots. Defaults to
 480                                 <option>false</option> for device and
 481                                 snapshot units, <option>true</option>
 482                                 for the others.</para></listitem>
 483                         </varlistentry>
 484
 485                         <varlistentry>
 486                                 <term><varname>StopWhenUnneeded=</varname></term>
 487
 488                                 <listitem><para>Takes a boolean
 489                                 argument. If <option>true</option>
 490                                 this unit will be stopped when it is
 491                                 no longer used. Note that in order to
 492                                 minimize the work to be executed,
 493                                 systemd will not stop units by default
 494                                 unless they are conflicting with other
 495                                 units, or the user explicitly
 496                                 requested their shut down. If this
 497                                 option is set, a unit will be
 498                                 automatically cleaned up if no other
 499                                 active unit requires it. Defaults to
 500                                 <option>false</option>.</para></listitem>
 501                         </varlistentry>
 502
 503                         <varlistentry>
 504                                 <term><varname>RefuseManualStart=</varname></term>
 505                                 <term><varname>RefuseManualStop=</varname></term>
 506
 507                                 <listitem><para>Takes a boolean
 508                                 argument. If <option>true</option>
 509                                 this unit can only be activated
 510                                 (resp. deactivated) indirectly. In
 511                                 this case explicit start-up
 512                                 (resp. termination) requested by the
 513                                 user is denied, however if it is
 514                                 started (resp. stopped) as a
 515                                 dependency of another unit, start-up
 516                                 (resp. termination) will succeed. This
 517                                 is mostly a safety feature to ensure
 518                                 that the user does not accidentally
 519                                 activate units that are not intended
 520                                 to be activated explicitly, and not
 521                                 accidentally deactivate units that are
 522                                 not intended to be deactivated.
 523                                 These options default to
 524                                 <option>false</option>.</para></listitem>
 525                         </varlistentry>
 526
 527                         <varlistentry>
 528                                 <term><varname>AllowIsolate=</varname></term>
 529
 530                                 <listitem><para>Takes a boolean
 531                                 argument. If <option>true</option>
 532                                 this unit may be used with the
 533                                 <command>systemctl isolate</command>
 534                                 command. Otherwise this will be
 535                                 refused. It probably is a good idea to
 536                                 leave this disabled except for target
 537                                 units that shall be used similar to
 538                                 runlevels in SysV init systems, just
 539                                 as a precaution to avoid unusable
 540                                 system states. This option defaults to
 541                                 <option>false</option>.</para></listitem>
 542                         </varlistentry>
 543
 544                         <varlistentry>
 545                                 <term><varname>DefaultDependencies=</varname></term>
 546
 547                                 <listitem><para>Takes a boolean
 548                                 argument. If <option>true</option>
 549                                 (the default), a few default
 550                                 dependencies will implicitly be
 551                                 created for the unit. The actual
 552                                 dependencies created depend on the
 553                                 unit type. For example, for service
 554                                 units, these dependencies ensure that
 555                                 the service is started only after
 556                                 basic system initialization is
 557                                 completed and is properly terminated on
 558                                 system shutdown. See the respective
 559                                 man pages for details. Generally, only
 560                                 services involved with early boot or
 561                                 late shutdown should set this option
 562                                 to <option>false</option>. It is
 563                                 highly recommended to leave this
 564                                 option enabled for the majority of
 565                                 common units. If set to
 566                                 <option>false</option> this option
 567                                 does not disable all implicit
 568                                 dependencies, just non-essential
 569                                 ones.</para></listitem>
 570                         </varlistentry>
 571
 572                         <varlistentry>
 573                                 <term><varname>JobTimeoutSec=</varname></term>
 574
 575                                 <listitem><para>When clients are
 576                                 waiting for a job of this unit to
 577                                 complete, time out after the specified
 578                                 time. If this time limit is reached
 579                                 the job will be cancelled, the unit
 580                                 however will not change state or even
 581                                 enter the '<literal>failed</literal>'
 582                                 mode. This value defaults to 0 (job
 583                                 timeouts disabled), except for device
 584                                 units. NB: this timeout is independent
 585                                 from any unit-specific timeout (for
 586                                 example, the timeout set with
 587                                 <varname>Timeout=</varname> in service
 588                                 units) as the job timeout has no
 589                                 effect on the unit itself, only on the
 590                                 job that might be pending for it. Or
 591                                 in other words: unit-specific timeouts
 592                                 are useful to abort unit state
 593                                 changes, and revert them. The job
 594                                 timeout set with this option however
 595                                 is useful to abort only the job
 596                                 waiting for the unit state to
 597                                 change.</para></listitem>
 598                         </varlistentry>
 599
 600                         <varlistentry>
 601                                 <term><varname>ConditionPathExists=</varname></term>
 602                                 <term><varname>ConditionPathIsDirectory=</varname></term>
 603                                 <term><varname>ConditionDirectoryNotEmpty=</varname></term>
 604                                 <term><varname>ConditionKernelCommandLine=</varname></term>
 605                                 <term><varname>ConditionVirtualization=</varname></term>
 606                                 <term><varname>ConditionSecurity=</varname></term>
 607                                 <term><varname>ConditionNull=</varname></term>
 608
 609                                 <listitem><para>Before starting a unit
 610                                 verify that the specified condition is
 611                                 true. With
 612                                 <varname>ConditionPathExists=</varname>
 613                                 a file existence condition can be
 614                                 checked before a unit is started. If
 615                                 the specified absolute path name does
 616                                 not exist startup of a unit will not
 617                                 actually happen, however the unit is
 618                                 still useful for ordering purposes in
 619                                 this case. The condition is checked at
 620                                 the time the queued start job is to be
 621                                 executed. If the absolute path name
 622                                 passed to
 623                                 <varname>ConditionPathExists=</varname>
 624                                 is prefixed with an exclamation mark
 625                                 (!), the test is negated, and the unit
 626                                 only started if the path does not
 627                                 exist. <varname>ConditionPathIsDirectory=</varname>
 628                                 is similar to
 629                                 <varname>ConditionPathExists=</varname>
 630                                 but verifies whether a certain path
 631                                 exists and is a directory.
 632                                 <varname>ConditionDirectoryNotEmpty=</varname>
 633                                 is similar to
 634                                 <varname>ConditionPathExists=</varname>
 635                                 but verifies whether a certain path
 636                                 exists and is a non-empty
 637                                 directory. Similarly
 638                                 <varname>ConditionKernelCommandLine=</varname>
 639                                 may be used to check whether a
 640                                 specific kernel command line option is
 641                                 set (or if prefixed with the
 642                                 exclamation mark unset). The argument
 643                                 must either be a single word, or an
 644                                 assignment (i.e. two words, separated
 645                                 by the equality sign). In the former
 646                                 case the kernel command line is
 647                                 searched for the word appearing as is,
 648                                 or as left hand side of an
 649                                 assignment. In the latter case the
 650                                 exact assignment is looked for with
 651                                 right and left hand side
 652                                 matching. <varname>ConditionVirtualization=</varname>
 653                                 may be used to check whether the
 654                                 system is executed in a virtualized
 655                                 environment and optionally test
 656                                 whether it is a specific
 657                                 implementation. Takes either boolean
 658                                 value to check if being executed in
 659                                 any virtual environment or one of the
 660                                 <varname>qemu</varname>,
 661                                 <varname>kvm</varname>,
 662                                 <varname>vmware</varname>,
 663                                 <varname>microsoft</varname>,
 664                                 <varname>oracle</varname>,
 665                                 <varname>xen</varname>,
 666                                 <varname>pidns</varname>,
 667                                 <varname>openvz</varname> to test
 668                                 against a specific implementation. The
 669                                 test may be negated by prepending an
 670                                 exclamation mark.
 671                                 <varname>ConditionSecurity=</varname>
 672                                 may be used to check whether the given security
 673                                 module is enabled on the system.
 674                                 Currently the only recognized value is
 675                                 <varname>selinux</varname>.
 676                                 The test may be negated by prepending an
 677                                 exclamation mark. Finally,
 678                                 <varname>ConditionNull=</varname> may
 679                                 be used to add a constant condition
 680                                 check value to the unit. It takes a
 681                                 boolean argument. If set to
 682                                 <varname>false</varname> the condition
 683                                 will always fail, otherwise
 684                                 succeed. If multiple conditions are
 685                                 specified the unit will be executed if
 686                                 all of them apply (i.e. a logical AND
 687                                 is applied). Condition checks can be
 688                                 prefixed with a pipe symbol (|) in
 689                                 which case a condition becomes a
 690                                 triggering condition. If at least one
 691                                 triggering condition is defined for a
 692                                 unit then the unit will be executed if
 693                                 at least one of the triggering
 694                                 conditions apply and all of the
 695                                 non-triggering conditions. If you
 696                                 prefix an argument with the pipe
 697                                 symbol and an exclamation mark the
 698                                 pipe symbol must be passed first, the
 699                                 exclamation second.</para></listitem>
 700                         </varlistentry>
 701
 702                         <varlistentry>
 703                                 <term><varname>Names=</varname></term>
 704
 705                                 <listitem><para>Additional names for
 706                                 this unit. The names listed here must
 707                                 have the same suffix (i.e. type) as
 708                                 the unit file name. This option may be
 709                                 specified more than once, in which
 710                                 case all listed names are used. Note
 711                                 that this option is different from the
 712                                 <varname>Alias=</varname> option from
 713                                 the [Install] section mentioned
 714                                 below. See below for details. Note
 715                                 that in almost all cases this option
 716                                 is not what you want. A symlink alias
 717                                 in the file system is generally
 718                                 preferable since it can be used as
 719                                 lookup key. If a unit with a symlinked
 720                                 alias name is not loaded and needs to
 721                                 be it is easily found via the
 722                                 symlink. However, if a unit with an
 723                                 alias name configured with this
 724                                 setting is not loaded it will not be
 725                                 discovered. This settings' only use is
 726                                 in conjunction with service
 727                                 instances.</para>
 728                                 </listitem>
 729                         </varlistentry>
 730                 </variablelist>
 731
 732                 <para>Unit file may include a [Install] section, which
 733                 carries installation information for the unit. This
 734                 section is not interpreted by
 735                 <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 736                 during runtime. It is used exclusively by the
 737                 <command>enable</command> and
 738                 <command>disable</command> commands of the
 739                 <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 740                 tool during installation of a unit:</para>
 741
 742                 <variablelist>
 743                         <varlistentry>
 744                                 <term><varname>Alias=</varname></term>
 745
 746                                 <listitem><para>Additional names this
 747                                 unit shall be installed under. The
 748                                 names listed here must have the same
 749                                 suffix (i.e. type) as the unit file
 750                                 name. This option may be specified
 751                                 more than once, in which case all
 752                                 listed names are used. At installation
 753                                 time,
 754                                 <command>systemctl enable</command>
 755                                 will create symlinks from these names
 756                                 to the unit file name. Note that this
 757                                 is different from the
 758                                 <varname>Names=</varname> option from
 759                                 the [Unit] section mentioned above:
 760                                 The names from
 761                                 <varname>Names=</varname> apply
 762                                 unconditionally if the unit is
 763                                 loaded. The names from
 764                                 <varname>Alias=</varname> apply only
 765                                 if the unit has actually been
 766                                 installed with the
 767                                 <command>systemctl enable</command>
 768                                 command.  Also, if systemd searches for a
 769                                 unit, it will discover symlinked alias
 770                                 names as configured with
 771                                 <varname>Alias=</varname>, but not
 772                                 names configured with
 773                                 <varname>Names=</varname> only. It is
 774                                 a common pattern to list a name in
 775                                 both options. In this case, a unit
 776                                 will be active under all names if
 777                                 installed, but also if not installed
 778                                 but requested explicitly under its
 779                                 main name.</para></listitem>
 780                         </varlistentry>
 781
 782                         <varlistentry>
 783                                 <term><varname>WantedBy=</varname></term>
 784
 785                                 <listitem><para>Installs a symlink in
 786                                 the <filename>.wants/</filename>
 787                                 subdirectory for a unit. This has the
 788                                 effect that when the listed unit name
 789                                 is activated the unit listing it is
 790                                 activated
 791                                 too. <command>WantedBy=foo.service</command>
 792                                 in a service
 793                                 <filename>bar.service</filename> is
 794                                 mostly equivalent to
 795                                 <command>Alias=foo.service.wants/bar.service</command>
 796                                 in the same file.</para></listitem>
 797                         </varlistentry>
 798
 799                         <varlistentry>
 800                                 <term><varname>Also=</varname></term>
 801
 802                                 <listitem><para>Additional units to
 803                                 install when this unit is
 804                                 installed. If the user requests
 805                                 installation of a unit with this
 806                                 option configured,
 807                                 <command>systemctl enable</command>
 808                                 will automatically install units
 809                                 listed in this option as
 810                                 well.</para></listitem>
 811                         </varlistentry>
 812                 </variablelist>
 813
 814         </refsect1>
 815
 816         <refsect1>
 817                 <title>See Also</title>
 818                 <para>
 819                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 820                         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 821                         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 822                         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 823                         <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 824                         <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 825                         <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 826                         <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 827                         <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 828                         <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 829                         <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 830                         <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 831                         <citerefentry><refentrytitle>systemd.snapshot</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 832                 </para>
 833         </refsect1>
 834
 835 </refentry>