man/systemd.xml

   1 <?xml version='1.0'?>
   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
   4 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   5
   6 <refentry id="systemd"
   7     xmlns:xi="http://www.w3.org/2001/XInclude">
   8
   9   <refentryinfo>
  10     <title>systemd</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>systemd</refentrytitle>
  16     <manvolnum>1</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>systemd</refname>
  21     <refname>init</refname>
  22     <refpurpose>systemd system and service manager</refpurpose>
  23   </refnamediv>
  24
  25   <refsynopsisdiv>
  26     <cmdsynopsis>
  27       <command>/usr/lib/systemd/systemd</command>
  28       <arg choice="opt" rep="repeat">OPTIONS</arg>
  29     </cmdsynopsis>
  30     <cmdsynopsis>
  31       <command>init</command>
  32       <arg choice="opt" rep="repeat">OPTIONS</arg>
  33       <arg choice="req">COMMAND</arg>
  34     </cmdsynopsis>
  35   </refsynopsisdiv>
  36
  37   <refsect1>
  38     <title>Description</title>
  39
  40     <para>systemd is a system and service manager for Linux operating systems. When run as first process on
  41     boot (as PID 1), it acts as init system that brings up and maintains userspace services. Separate
  42     instances are started for logged-in users to start their services.</para>
  43
  44     <para><command>systemd</command> is usually not invoked directly by the user, but is installed as the
  45     <filename>/sbin/init</filename> symlink and started during early boot. The user manager instances are
  46     started automatically through the
  47     <citerefentry><refentrytitle>user@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  48     service.</para>
  49
  50     <para>For compatibility with SysV, if the binary is called as <command>init</command> and is not the
  51     first process on the machine (PID is not 1), it will execute <command>telinit</command> and pass all
  52     command line arguments unmodified. That means <command>init</command> and <command>telinit</command> are
  53     mostly equivalent when invoked from normal login sessions. See
  54     <citerefentry><refentrytitle>telinit</refentrytitle><manvolnum>8</manvolnum></citerefentry> for more
  55     information.</para>
  56
  57     <para>When run as a system instance, systemd interprets the
  58     configuration file <filename>system.conf</filename> and the files
  59     in <filename>system.conf.d</filename> directories; when run as a
  60     user instance, systemd interprets the configuration file
  61     <filename>user.conf</filename> and the files in
  62     <filename>user.conf.d</filename> directories. See
  63     <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
  64     for more information.</para>
  65   </refsect1>
  66
  67   <refsect1>
  68     <title>Concepts</title>
  69
  70     <para>systemd provides a dependency system between various
  71     entities called "units" of 11 different types. Units encapsulate
  72     various objects that are relevant for system boot-up and
  73     maintenance. The majority of units are configured in unit
  74     configuration files, whose syntax and basic set of options is
  75     described in
  76     <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
  77     however some are created automatically from other configuration,
  78     dynamically from system state or programmatically at runtime.
  79     Units may be "active" (meaning started, bound, plugged in, …,
  80     depending on the unit type, see below), or "inactive" (meaning
  81     stopped, unbound, unplugged, …), as well as in the process of
  82     being activated or deactivated, i.e. between the two states (these
  83     states are called "activating", "deactivating"). A special
  84     "failed" state is available as well, which is very similar to
  85     "inactive" and is entered when the service failed in some way
  86     (process returned error code on exit, or crashed, an operation
  87     timed out, or after too many restarts). If this state is entered,
  88     the cause will be logged, for later reference. Note that the
  89     various unit types may have a number of additional substates,
  90     which are mapped to the five generalized unit states described
  91     here.</para>
  92
  93     <para>The following unit types are available:</para>
  94
  95     <orderedlist>
  96       <listitem><para>Service units, which start and control daemons
  97       and the processes they consist of. For details, see
  98       <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
  99
 100       <listitem><para>Socket units, which encapsulate local IPC or
 101       network sockets in the system, useful for socket-based
 102       activation. For details about socket units, see
 103       <citerefentry><refentrytitle>systemd.socket</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 104       for details on socket-based activation and other forms of
 105       activation, see
 106       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para></listitem>
 107
 108       <listitem><para>Target units are useful to group units, or
 109       provide well-known synchronization points during boot-up, see
 110       <citerefentry><refentrytitle>systemd.target</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 111
 112       <listitem><para>Device units expose kernel devices in systemd
 113       and may be used to implement device-based activation. For
 114       details, see
 115       <citerefentry><refentrytitle>systemd.device</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 116
 117       <listitem><para>Mount units control mount points in the file
 118       system, for details see
 119       <citerefentry><refentrytitle>systemd.mount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 120
 121       <listitem><para>Automount units provide automount capabilities,
 122       for on-demand mounting of file systems as well as parallelized
 123       boot-up. See
 124       <citerefentry><refentrytitle>systemd.automount</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 125
 126       <listitem><para>Timer units are useful for triggering activation
 127       of other units based on timers. You may find details in
 128       <citerefentry><refentrytitle>systemd.timer</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 129
 130       <listitem><para>Swap units are very similar to mount units and
 131       encapsulate memory swap partitions or files of the operating
 132       system. They are described in
 133       <citerefentry><refentrytitle>systemd.swap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 134
 135       <listitem><para>Path units may be used to activate other
 136       services when file system objects change or are modified. See
 137       <citerefentry><refentrytitle>systemd.path</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 138
 139       <listitem><para>Slice units may be used to group units which
 140       manage system processes (such as service and scope units) in a
 141       hierarchical tree for resource management purposes. See
 142       <citerefentry><refentrytitle>systemd.slice</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 143
 144       <listitem><para>Scope units are similar to service units, but
 145       manage foreign processes instead of starting them as well. See
 146       <citerefentry><refentrytitle>systemd.scope</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para></listitem>
 147
 148     </orderedlist>
 149
 150     <para>Units are named as their configuration files. Some units
 151     have special semantics. A detailed list is available in
 152     <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 153
 154     <para>systemd knows various kinds of dependencies, including
 155     positive and negative requirement dependencies (i.e.
 156     <varname>Requires=</varname> and <varname>Conflicts=</varname>) as
 157     well as ordering dependencies (<varname>After=</varname> and
 158     <varname>Before=</varname>). NB: ordering and requirement
 159     dependencies are orthogonal. If only a requirement dependency
 160     exists between two units (e.g. <filename>foo.service</filename>
 161     requires <filename>bar.service</filename>), but no ordering
 162     dependency (e.g. <filename>foo.service</filename> after
 163     <filename>bar.service</filename>) and both are requested to start,
 164     they will be started in parallel. It is a common pattern that both
 165     requirement and ordering dependencies are placed between two
 166     units. Also note that the majority of dependencies are implicitly
 167     created and maintained by systemd. In most cases, it should be
 168     unnecessary to declare additional dependencies manually, however
 169     it is possible to do this.</para>
 170
 171     <para>Application programs and units (via dependencies) may
 172     request state changes of units. In systemd, these requests are
 173     encapsulated as 'jobs' and maintained in a job queue. Jobs may
 174     succeed or can fail, their execution is ordered based on the
 175     ordering dependencies of the units they have been scheduled
 176     for.</para>
 177
 178     <para>On boot systemd activates the target unit
 179     <filename>default.target</filename> whose job is to activate
 180     on-boot services and other on-boot units by pulling them in via
 181     dependencies. Usually, the unit name is just an alias (symlink) for
 182     either <filename>graphical.target</filename> (for fully-featured
 183     boots into the UI) or <filename>multi-user.target</filename> (for
 184     limited console-only boots for use in embedded or server
 185     environments, or similar; a subset of graphical.target). However,
 186     it is at the discretion of the administrator to configure it as an
 187     alias to any other target unit. See
 188     <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 189     for details about these target units.</para>
 190
 191     <para>systemd only keeps a minimal set of units loaded into memory. Specifically, the only units that are kept
 192     loaded into memory are those for which at least one of the following conditions is true:</para>
 193
 194     <orderedlist>
 195       <listitem><para>It is in an active, activating, deactivating or failed state (i.e. in any unit state except for <literal>inactive</literal>)</para></listitem>
 196       <listitem><para>It has a job queued for it</para></listitem>
 197       <listitem><para>It is a dependency of at least one other unit that is loaded into memory</para></listitem>
 198       <listitem><para>It has some form of resource still allocated (e.g. a service unit that is inactive but for which
 199       a process is still lingering that ignored the request to be terminated)</para></listitem>
 200       <listitem><para>It has been pinned into memory programmatically by a D-Bus call</para></listitem>
 201     </orderedlist>
 202
 203     <para>systemd will automatically and implicitly load units from disk — if they are not loaded yet — as soon as
 204     operations are requested for them. Thus, in many respects, the fact whether a unit is loaded or not is invisible to
 205     clients. Use <command>systemctl list-units --all</command> to comprehensively list all units currently loaded. Any
 206     unit for which none of the conditions above applies is promptly unloaded. Note that when a unit is unloaded from
 207     memory its accounting data is flushed out too. However, this data is generally not lost, as a journal log record
 208     is generated declaring the consumed resources whenever a unit shuts down.</para>
 209
 210     <para>Processes systemd spawns are placed in individual Linux
 211     control groups named after the unit which they belong to in the
 212     private systemd hierarchy. (see <ulink
 213     url="https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt">cgroups.txt</ulink>
 214     for more information about control groups, or short "cgroups").
 215     systemd uses this to effectively keep track of processes. Control
 216     group information is maintained in the kernel, and is accessible
 217     via the file system hierarchy (beneath
 218     <filename>/sys/fs/cgroup/systemd/</filename>), or in tools such as
 219     <citerefentry project='man-pages'><refentrytitle>systemd-cgls</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 220     or
 221     <citerefentry project='man-pages'><refentrytitle>ps</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 222     (<command>ps xawf -eo pid,user,cgroup,args</command> is
 223     particularly useful to list all processes and the systemd units
 224     they belong to.).</para>
 225
 226     <para>systemd is compatible with the SysV init system to a large
 227     degree: SysV init scripts are supported and simply read as an
 228     alternative (though limited) configuration file format. The SysV
 229     <filename>/dev/initctl</filename> interface is provided, and
 230     compatibility implementations of the various SysV client tools are
 231     available. In addition to that, various established Unix
 232     functionality such as <filename>/etc/fstab</filename> or the
 233     <filename>utmp</filename> database are supported.</para>
 234
 235     <para>systemd has a minimal transaction system: if a unit is
 236     requested to start up or shut down it will add it and all its
 237     dependencies to a temporary transaction. Then, it will verify if
 238     the transaction is consistent (i.e. whether the ordering of all
 239     units is cycle-free). If it is not, systemd will try to fix it up,
 240     and removes non-essential jobs from the transaction that might
 241     remove the loop. Also, systemd tries to suppress non-essential
 242     jobs in the transaction that would stop a running service. Finally
 243     it is checked whether the jobs of the transaction contradict jobs
 244     that have already been queued, and optionally the transaction is
 245     aborted then. If all worked out and the transaction is consistent
 246     and minimized in its impact it is merged with all already
 247     outstanding jobs and added to the run queue. Effectively this
 248     means that before executing a requested operation, systemd will
 249     verify that it makes sense, fixing it if possible, and only
 250     failing if it really cannot work.</para>
 251
 252     <para>Note that transactions are generated independently of a unit's
 253     state at runtime, hence, for example, if a start job is requested on an
 254     already started unit, it will still generate a transaction and wake up any
 255     inactive dependencies (and cause propagation of other jobs as per the
 256     defined relationships). This is because the enqueued job is at the time of
 257     execution compared to the target unit's state and is marked successful and
 258     complete when both satisfy. However, this job also pulls in other
 259     dependencies due to the defined relationships and thus leads to, in our
 260     example, start jobs for any of those inactive units getting queued as
 261     well.</para>
 262
 263     <para>systemd contains native implementations of various tasks
 264     that need to be executed as part of the boot process. For example,
 265     it sets the hostname or configures the loopback network device. It
 266     also sets up and mounts various API file systems, such as
 267     <filename>/sys</filename> or <filename>/proc</filename>.</para>
 268
 269     <para>For more information about the concepts and
 270     ideas behind systemd, please refer to the
 271     <ulink url="http://0pointer.de/blog/projects/systemd.html">Original Design Document</ulink>.</para>
 272
 273     <para>Note that some but not all interfaces provided
 274     by systemd are covered by the
 275     <ulink url="https://www.freedesktop.org/wiki/Software/systemd/InterfaceStabilityPromise">Interface
 276     Stability Promise</ulink>.</para>
 277
 278     <para>Units may be generated dynamically at boot and system
 279     manager reload time, for example based on other configuration
 280     files or parameters passed on the kernel command line. For details, see
 281     <citerefentry><refentrytitle>systemd.generator</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 282
 283     <para>The D-Bus API of <command>systemd</command> is described in
 284     <citerefentry><refentrytitle>org.freedesktop.systemd1</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 285     and
 286     <citerefentry><refentrytitle>org.freedesktop.LogControl1</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 287     </para>
 288
 289     <para>Systems which invoke systemd in a container or initrd environment should implement the <ulink
 290     url="https://systemd.io/CONTAINER_INTERFACE">Container Interface</ulink> or <ulink
 291     url="https://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd Interface</ulink>
 292     specifications, respectively.</para>
 293   </refsect1>
 294
 295   <refsect1>
 296     <title>Directories</title>
 297
 298     <variablelist>
 299       <varlistentry>
 300         <term>System unit directories</term>
 301
 302         <listitem><para>The systemd system manager reads unit
 303         configuration from various directories. Packages that want to
 304         install unit files shall place them in the directory returned
 305         by <command>pkg-config systemd
 306         --variable=systemdsystemunitdir</command>. Other directories
 307         checked are <filename>/usr/local/lib/systemd/system</filename>
 308         and <filename>/usr/lib/systemd/system</filename>. User
 309         configuration always takes precedence. <command>pkg-config
 310         systemd --variable=systemdsystemconfdir</command> returns the
 311         path of the system configuration directory. Packages should
 312         alter the content of these directories only with the
 313         <command>enable</command> and <command>disable</command>
 314         commands of the
 315         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 316         tool. Full list of directories is provided in
 317         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 318         </para></listitem>
 319       </varlistentry>
 320     </variablelist>
 321
 322     <variablelist>
 323       <varlistentry>
 324         <term>User unit directories</term>
 325
 326         <listitem><para>Similar rules apply for the user unit
 327         directories. However, here the
 328         <ulink url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 329         Base Directory specification</ulink> is followed to find
 330         units. Applications should place their unit files in the
 331         directory returned by <command>pkg-config systemd
 332         --variable=systemduserunitdir</command>. Global configuration
 333         is done in the directory reported by <command>pkg-config
 334         systemd --variable=systemduserconfdir</command>. The
 335         <command>enable</command> and <command>disable</command>
 336         commands of the
 337         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 338         tool can handle both global (i.e. for all users) and private
 339         (for one user) enabling/disabling of units. Full list of
 340         directories is provided in
 341         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 342         </para></listitem>
 343       </varlistentry>
 344     </variablelist>
 345
 346     <variablelist>
 347       <varlistentry>
 348         <term>SysV init scripts directory</term>
 349
 350         <listitem><para>The location of the SysV init script directory
 351         varies between distributions. If systemd cannot find a native
 352         unit file for a requested service, it will look for a SysV
 353         init script of the same name (with the
 354         <filename>.service</filename> suffix
 355         removed).</para></listitem>
 356       </varlistentry>
 357     </variablelist>
 358
 359     <variablelist>
 360       <varlistentry>
 361         <term>SysV runlevel link farm directory</term>
 362
 363         <listitem><para>The location of the SysV runlevel link farm
 364         directory varies between distributions. systemd will take the
 365         link farm into account when figuring out whether a service
 366         shall be enabled. Note that a service unit with a native unit
 367         configuration file cannot be started by activating it in the
 368         SysV runlevel link farm.</para></listitem>
 369       </varlistentry>
 370     </variablelist>
 371   </refsect1>
 372
 373   <refsect1>
 374     <title>Signals</title>
 375
 376     <variablelist>
 377       <varlistentry>
 378         <term><constant>SIGTERM</constant></term>
 379
 380         <listitem><para>Upon receiving this signal the systemd system
 381         manager serializes its state, reexecutes itself and
 382         deserializes the saved state again. This is mostly equivalent
 383         to <command>systemctl daemon-reexec</command>.</para>
 384
 385         <para>systemd user managers will start the
 386         <filename>exit.target</filename> unit when this signal is
 387         received. This is mostly equivalent to <command>systemctl
 388         --user start exit.target
 389         --job-mode=replace-irreversibly</command>.</para></listitem>
 390       </varlistentry>
 391
 392       <varlistentry>
 393         <term><constant>SIGINT</constant></term>
 394
 395         <listitem><para>Upon receiving this signal the systemd system manager will start the
 396         <filename>ctrl-alt-del.target</filename> unit. This is mostly equivalent to
 397         <command>systemctl start ctrl-alt-del.target --job-mode=replace-irreversibly</command>. If
 398         this signal is received more than 7 times per 2s, an immediate reboot is triggered. Note
 399         that pressing
 400         <keycombo><keycap>Ctrl</keycap><keycap>Alt</keycap><keycap>Del</keycap></keycombo> on the
 401         console will trigger this signal. Hence, if a reboot is hanging, pressing
 402         <keycombo><keycap>Ctrl</keycap><keycap>Alt</keycap><keycap>Del</keycap></keycombo> more than
 403         7 times in 2 seconds is a relatively safe way to trigger an immediate reboot.</para>
 404
 405         <para>systemd user managers treat this signal the same way as
 406         <constant>SIGTERM</constant>.</para></listitem>
 407       </varlistentry>
 408
 409       <varlistentry>
 410         <term><constant>SIGWINCH</constant></term>
 411
 412         <listitem><para>When this signal is received the systemd
 413         system manager will start the
 414         <filename>kbrequest.target</filename> unit. This is mostly
 415         equivalent to <command>systemctl start
 416         kbrequest.target</command>.</para>
 417
 418         <para>This signal is ignored by systemd user
 419         managers.</para></listitem>
 420       </varlistentry>
 421
 422       <varlistentry>
 423         <term><constant>SIGPWR</constant></term>
 424
 425         <listitem><para>When this signal is received the systemd
 426         manager will start the <filename>sigpwr.target</filename>
 427         unit. This is mostly equivalent to <command>systemctl start
 428         sigpwr.target</command>.</para></listitem>
 429       </varlistentry>
 430
 431       <varlistentry>
 432         <term><constant>SIGUSR1</constant></term>
 433
 434         <listitem><para>When this signal is received the systemd
 435         manager will try to reconnect to the D-Bus
 436         bus.</para></listitem>
 437       </varlistentry>
 438
 439       <varlistentry>
 440         <term><constant>SIGUSR2</constant></term>
 441
 442         <listitem><para>When this signal is received the systemd
 443         manager will log its complete state in human-readable form.
 444         The data logged is the same as printed by
 445         <command>systemd-analyze dump</command>.</para></listitem>
 446       </varlistentry>
 447
 448       <varlistentry>
 449         <term><constant>SIGHUP</constant></term>
 450
 451         <listitem><para>Reloads the complete daemon configuration.
 452         This is mostly equivalent to <command>systemctl
 453         daemon-reload</command>.</para></listitem>
 454       </varlistentry>
 455
 456       <varlistentry>
 457         <term><constant>SIGRTMIN+0</constant></term>
 458
 459         <listitem><para>Enters default mode, starts the
 460         <filename>default.target</filename> unit. This is mostly
 461         equivalent to <command>systemctl isolate
 462         default.target</command>.</para></listitem>
 463       </varlistentry>
 464
 465       <varlistentry>
 466         <term><constant>SIGRTMIN+1</constant></term>
 467
 468         <listitem><para>Enters rescue mode, starts the
 469         <filename>rescue.target</filename> unit. This is mostly
 470         equivalent to <command>systemctl isolate
 471         rescue.target</command>.</para></listitem>
 472       </varlistentry>
 473
 474       <varlistentry>
 475         <term><constant>SIGRTMIN+2</constant></term>
 476
 477         <listitem><para>Enters emergency mode, starts the
 478         <filename>emergency.service</filename> unit. This is mostly
 479         equivalent to <command>systemctl isolate
 480         emergency.service</command>.</para></listitem>
 481       </varlistentry>
 482
 483       <varlistentry>
 484         <term><constant>SIGRTMIN+3</constant></term>
 485
 486         <listitem><para>Halts the machine, starts the
 487         <filename>halt.target</filename> unit. This is mostly
 488         equivalent to <command>systemctl start halt.target
 489         --job-mode=replace-irreversibly</command>.</para>
 490         </listitem>
 491       </varlistentry>
 492
 493       <varlistentry>
 494         <term><constant>SIGRTMIN+4</constant></term>
 495
 496         <listitem><para>Powers off the machine, starts the
 497         <filename>poweroff.target</filename> unit. This is mostly
 498         equivalent to <command>systemctl start poweroff.target
 499         --job-mode=replace-irreversibly</command>.</para>
 500         </listitem>
 501       </varlistentry>
 502
 503       <varlistentry>
 504         <term><constant>SIGRTMIN+5</constant></term>
 505
 506         <listitem><para>Reboots the machine, starts the
 507         <filename>reboot.target</filename> unit. This is mostly
 508         equivalent to <command>systemctl start reboot.target
 509         --job-mode=replace-irreversibly</command>.</para>
 510         </listitem>
 511       </varlistentry>
 512
 513       <varlistentry>
 514         <term><constant>SIGRTMIN+6</constant></term>
 515
 516         <listitem><para>Reboots the machine via kexec, starts the
 517         <filename>kexec.target</filename> unit. This is mostly
 518         equivalent to <command>systemctl start kexec.target
 519         --job-mode=replace-irreversibly</command>.</para>
 520         </listitem>
 521       </varlistentry>
 522
 523       <varlistentry>
 524         <term><constant>SIGRTMIN+13</constant></term>
 525
 526         <listitem><para>Immediately halts the machine.</para></listitem>
 527       </varlistentry>
 528
 529       <varlistentry>
 530         <term><constant>SIGRTMIN+14</constant></term>
 531
 532         <listitem><para>Immediately powers off the machine.</para></listitem>
 533       </varlistentry>
 534
 535       <varlistentry>
 536         <term><constant>SIGRTMIN+15</constant></term>
 537
 538         <listitem><para>Immediately reboots the machine.</para></listitem>
 539       </varlistentry>
 540
 541       <varlistentry>
 542         <term><constant>SIGRTMIN+16</constant></term>
 543
 544         <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
 545       </varlistentry>
 546
 547       <varlistentry>
 548         <term><constant>SIGRTMIN+20</constant></term>
 549
 550         <listitem><para>Enables display of status messages on the
 551         console, as controlled via
 552         <varname>systemd.show_status=1</varname> on the kernel command
 553         line.</para></listitem>
 554       </varlistentry>
 555
 556       <varlistentry>
 557         <term><constant>SIGRTMIN+21</constant></term>
 558
 559         <listitem><para>Disables display of
 560         status messages on the console, as
 561         controlled via
 562         <varname>systemd.show_status=0</varname>
 563         on the kernel command
 564         line.</para></listitem>
 565       </varlistentry>
 566
 567       <varlistentry>
 568         <term><constant>SIGRTMIN+22</constant></term>
 569
 570         <listitem><para>Sets the service manager's log level to <literal>debug</literal>, in a fashion equivalent to
 571         <varname>systemd.log_level=debug</varname> on the kernel command line.</para></listitem>
 572       </varlistentry>
 573
 574       <varlistentry>
 575         <term><constant>SIGRTMIN+23</constant></term>
 576
 577         <listitem><para>Restores the log level to its configured value. The configured value is derived from – in order
 578         of priority – the value specified with <varname>systemd.log-level=</varname> on the kernel command line, or the
 579         value specified with <option>LogLevel=</option> in the configuration file, or the built-in default of
 580         <literal>info</literal>.</para></listitem>
 581       </varlistentry>
 582
 583       <varlistentry>
 584         <term><constant>SIGRTMIN+24</constant></term>
 585
 586         <listitem><para>Immediately exits the manager (only available
 587         for --user instances).</para></listitem>
 588       </varlistentry>
 589
 590       <varlistentry>
 591         <term><constant>SIGRTMIN+26</constant></term>
 592
 593         <listitem><para>Restores the log target to its configured value. The configured value is derived from – in
 594         order of priority – the value specified with <varname>systemd.log-target=</varname> on the kernel command line,
 595         or the value specified with <option>LogTarget=</option> in the configuration file, or the built-in
 596         default.</para></listitem>
 597       </varlistentry>
 598
 599       <varlistentry>
 600         <term><constant>SIGRTMIN+27</constant></term>
 601         <term><constant>SIGRTMIN+28</constant></term>
 602
 603         <listitem><para>Sets the log target to <literal>console</literal> on <constant>SIGRTMIN+27</constant> (or
 604         <literal>kmsg</literal> on <constant>SIGRTMIN+28</constant>), in a fashion equivalent to
 605         <varname>systemd.log_target=console</varname> (or <varname>systemd.log_target=kmsg</varname> on
 606         <constant>SIGRTMIN+28</constant>) on the kernel command line.</para></listitem>
 607       </varlistentry>
 608     </variablelist>
 609   </refsect1>
 610
 611   <refsect1>
 612     <title>Environment</title>
 613
 614     <variablelist class='environment-variables'>
 615       <varlistentry>
 616         <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 617         <listitem><para>Controls whether systemd highlights important
 618         log messages. This can be overridden with
 619         <option>--log-color</option>.</para></listitem>
 620       </varlistentry>
 621
 622       <varlistentry>
 623         <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 624         <listitem><para>systemd reads the log level from this
 625         environment variable. This can be overridden with
 626         <option>--log-level=</option>.</para></listitem>
 627       </varlistentry>
 628
 629       <varlistentry>
 630         <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 631         <listitem><para>Controls whether systemd prints the code
 632         location along with log messages. This can be overridden with
 633         <option>--log-location</option>.</para></listitem>
 634       </varlistentry>
 635
 636       <varlistentry>
 637         <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 638         <listitem><para>systemd reads the log target from this
 639         environment variable. This can be overridden with
 640         <option>--log-target=</option>.</para></listitem>
 641       </varlistentry>
 642
 643       <varlistentry>
 644         <term><varname>$SYSTEMD_LOG_TIME</varname></term>
 645         <listitem><para>Controls whether systemd prefixes log
 646         messages with the current time. This can be overridden with
 647         <option>--log-time=</option>.</para></listitem>
 648       </varlistentry>
 649
 650       <varlistentry>
 651         <term><varname>$XDG_CONFIG_HOME</varname></term>
 652         <term><varname>$XDG_CONFIG_DIRS</varname></term>
 653         <term><varname>$XDG_DATA_HOME</varname></term>
 654         <term><varname>$XDG_DATA_DIRS</varname></term>
 655
 656         <listitem><para>The systemd user manager uses these variables
 657         in accordance to the <ulink
 658         url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 659         Base Directory specification</ulink> to find its
 660         configuration.</para></listitem>
 661       </varlistentry>
 662
 663       <varlistentry>
 664         <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 665         <term><varname>$SYSTEMD_GENERATOR_PATH</varname></term>
 666         <term><varname>$SYSTEMD_ENVIRONMENT_GENERATOR_PATH</varname></term>
 667
 668         <listitem><para>Controls where systemd looks for unit files and
 669         generators.</para>
 670         <para>These variables may contain a list of paths, separated by colons
 671         (<literal>:</literal>). When set, if the list ends with an empty
 672         component (<literal>...:</literal>), this list is prepended to the
 673         usual set of of paths. Otherwise, the specified list replaces the usual
 674         set of paths.
 675         </para></listitem>
 676       </varlistentry>
 677
 678       <varlistentry>
 679         <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 680
 681         <listitem><para>Controls where systemd looks for SysV init
 682         scripts.</para></listitem>
 683       </varlistentry>
 684
 685       <varlistentry>
 686         <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 687
 688         <listitem><para>Controls where systemd looks for SysV init
 689         script runlevel link farms.</para></listitem>
 690       </varlistentry>
 691
 692       <xi:include href="less-variables.xml" xpointer="pager"/>
 693       <xi:include href="less-variables.xml" xpointer="less"/>
 694       <xi:include href="less-variables.xml" xpointer="lesscharset"/>
 695       <xi:include href="less-variables.xml" xpointer="colors"/>
 696       <xi:include href="less-variables.xml" xpointer="urlify"/>
 697
 698       <varlistentry>
 699         <term><varname>$LISTEN_PID</varname></term>
 700         <term><varname>$LISTEN_FDS</varname></term>
 701         <term><varname>$LISTEN_FDNAMES</varname></term>
 702
 703         <listitem><para>Set by systemd for supervised processes during
 704         socket-based activation. See
 705         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 706         for more information.</para></listitem>
 707       </varlistentry>
 708
 709       <varlistentry>
 710         <term><varname>$NOTIFY_SOCKET</varname></term>
 711
 712         <listitem><para>Set by systemd for supervised processes for
 713         status and start-up completion notification. See
 714         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 715         for more information.</para></listitem>
 716       </varlistentry>
 717     </variablelist>
 718
 719     <para>For further environment variables understood by systemd and its various components, see <ulink
 720     url="https://systemd.io/ENVIRONMENT">Known Environment Variables</ulink>.</para>
 721   </refsect1>
 722
 723   <refsect1>
 724     <title>Kernel Command Line</title>
 725
 726     <para>When run as the system instance systemd parses a number of options listed below. They can be
 727     specified as kernel command line arguments<footnote><para>If run inside a Linux container these arguments
 728     may be passed as command line arguments to systemd itself, next to any of the command line options listed
 729     in the Options section above. If run outside of Linux containers, these arguments are parsed from
 730     <filename>/proc/cmdline</filename> instead.</para></footnote>, or through the
 731     <literal>SystemdOptions</literal> EFI variable (on EFI systems). The kernel command line has higher
 732     priority. Following variables are understood:</para>
 733
 734     <variablelist class='kernel-commandline-options'>
 735       <varlistentry>
 736         <term><varname>systemd.unit=</varname></term>
 737         <term><varname>rd.systemd.unit=</varname></term>
 738
 739         <listitem><para>Overrides the unit to activate on boot.
 740         Defaults to <filename>default.target</filename>. This may be
 741         used to temporarily boot into a different boot unit, for
 742         example <filename>rescue.target</filename> or
 743         <filename>emergency.service</filename>. See
 744         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 745         for details about these units. The option prefixed with
 746         <literal>rd.</literal> is honored only in the initial RAM disk
 747         (initrd), while the one that is not prefixed only in the main
 748         system.</para></listitem>
 749       </varlistentry>
 750
 751       <varlistentry>
 752         <term><varname>systemd.dump_core</varname></term>
 753
 754         <listitem><para>Takes a boolean argument or enables the option if specified
 755         without an argument. If enabled, the systemd manager (PID 1) dumps core when
 756         it crashes. Otherwise, no core dump is created. Defaults to enabled.</para>
 757         </listitem>
 758       </varlistentry>
 759
 760       <varlistentry>
 761         <term><varname>systemd.crash_chvt</varname></term>
 762
 763         <listitem><para>Takes a positive integer, or a boolean argument. Can be also specified without an
 764         argument, with the same effect as a positive boolean. If a positive integer (in the range 1–63) is
 765         specified, the system manager (PID 1) will activate the specified virtual terminal when it crashes.
 766         Defaults to disabled, meaning that no such switch is attempted. If set to enabled, the virtual
 767         terminal the kernel messages are written to is used instead.</para></listitem>
 768       </varlistentry>
 769
 770       <varlistentry>
 771         <term><varname>systemd.crash_shell</varname></term>
 772
 773         <listitem><para>Takes a boolean argument or enables the option if specified
 774         without an argument. If enabled, the system manager (PID 1) spawns a shell
 775         when it crashes, after a 10s delay. Otherwise, no shell is spawned. Defaults
 776         to disabled, for security reasons, as the shell is not protected by password
 777         authentication.</para></listitem>
 778       </varlistentry>
 779
 780       <varlistentry>
 781         <term><varname>systemd.crash_reboot</varname></term>
 782
 783         <listitem><para>Takes a boolean argument or enables the option if specified
 784         without an argument. If enabled, the system manager (PID 1) will reboot the
 785         machine automatically when it crashes, after a 10s delay.  Otherwise, the
 786         system will hang indefinitely. Defaults to disabled, in order to avoid a
 787         reboot loop. If combined with <varname>systemd.crash_shell</varname>, the
 788         system is rebooted after the shell exits.</para></listitem>
 789       </varlistentry>
 790
 791       <varlistentry>
 792         <term><varname>systemd.confirm_spawn</varname></term>
 793
 794         <listitem><para>Takes a boolean argument or a path to the virtual console
 795         where the confirmation messages should be emitted. Can be also specified
 796         without an argument, with the same effect as a positive boolean. If enabled,
 797         the system manager (PID 1) asks for confirmation when spawning processes
 798         using <option>/dev/console</option>. If a path or a console name (such as
 799         <literal>ttyS0</literal>) is provided, the virtual console pointed to by this
 800         path or described by the give name will be used instead. Defaults to disabled.
 801         </para></listitem>
 802       </varlistentry>
 803
 804       <varlistentry>
 805         <term><varname>systemd.service_watchdogs=</varname></term>
 806
 807         <listitem><para>Takes a boolean argument. If disabled, all service runtime
 808         watchdogs (<option>WatchdogSec=</option>) and emergency actions (e.g.
 809         <option>OnFailure=</option> or <option>StartLimitAction=</option>) are
 810         ignored by the system manager (PID 1); see
 811         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 812         Defaults to enabled, i.e. watchdogs and failure actions are processed
 813         normally. The hardware watchdog is not affected by this
 814         option.</para></listitem>
 815       </varlistentry>
 816
 817       <varlistentry>
 818         <term><varname>systemd.show_status</varname></term>
 819
 820         <listitem><para>Takes a boolean argument or the constants <constant>error</constant> and
 821         <constant>auto</constant>. Can be also specified without an argument, with the same effect as a
 822         positive boolean. If enabled, the systemd manager (PID 1) shows terse service status updates on the
 823         console during bootup. With <constant>error</constant>, only messages about failures are shown, but
 824         boot is otherwise quiet. <constant>auto</constant> behaves like <option>false</option> until there is
 825         a significant delay in boot. Defaults to enabled, unless <option>quiet</option> is passed as kernel
 826         command line option, in which case it defaults to <constant>error</constant>. If specified overrides
 827         the system manager configuration file option <option>ShowStatus=</option>, see
 828         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 829         </para></listitem>
 830       </varlistentry>
 831
 832       <varlistentry>
 833         <term><varname>systemd.status_unit_format=</varname></term>
 834
 835         <listitem><para>Takes either <option>name</option> or <option>description</option> as the value. If
 836         <option>name</option>, the system manager will use unit names in status messages. If specified,
 837         overrides the system manager configuration file option <option>StatusUnitFormat=</option>, see
 838         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 839         </para></listitem>
 840       </varlistentry>
 841
 842       <varlistentry>
 843         <term><varname>systemd.log_color</varname></term>
 844         <term><varname>systemd.log_level=</varname></term>
 845         <term><varname>systemd.log_location</varname></term>
 846         <term><varname>systemd.log_target=</varname></term>
 847         <term><varname>systemd.log_time</varname></term>
 848
 849         <listitem><para>Controls log output, with the same effect as the
 850         <varname>$SYSTEMD_LOG_COLOR</varname>,
 851         <varname>$SYSTEMD_LOG_LEVEL</varname>,
 852         <varname>$SYSTEMD_LOG_LOCATION</varname>,
 853         <varname>$SYSTEMD_LOG_TARGET</varname>,
 854         <varname>$SYSTEMD_LOG_TIME</varname>, environment variables described above.
 855         <varname>systemd.log_color</varname>, <varname>systemd.log_location</varname>, and
 856         <varname>systemd.log_time</varname> can be specified without an argument, with the
 857         same effect as a positive boolean.</para></listitem>
 858       </varlistentry>
 859
 860       <varlistentry>
 861         <term><varname>systemd.default_standard_output=</varname></term>
 862         <term><varname>systemd.default_standard_error=</varname></term>
 863
 864         <listitem><para>Controls default standard output and error output for services and sockets. That is,
 865         controls the default for <option>StandardOutput=</option> and <option>StandardError=</option> (see
 866         <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 867         details). Takes one of <option>inherit</option>, <option>null</option>, <option>tty</option>,
 868         <option>journal</option>, <option>journal+console</option>, <option>kmsg</option>,
 869         <option>kmsg+console</option>. If the argument is omitted
 870         <varname>systemd.default-standard-output=</varname> defaults to <option>journal</option> and
 871         <varname>systemd.default-standard-error=</varname> to <option>inherit</option>.</para></listitem>
 872       </varlistentry>
 873
 874       <varlistentry>
 875         <term><varname>systemd.setenv=</varname></term>
 876
 877         <listitem><para>Takes a string argument in the form
 878         VARIABLE=VALUE. May be used to set default environment
 879         variables to add to forked child processes. May be used more
 880         than once to set multiple variables.</para></listitem>
 881       </varlistentry>
 882
 883       <varlistentry>
 884         <term><varname>systemd.machine_id=</varname></term>
 885
 886         <listitem><para>Takes a 32 character hex value to be
 887         used for setting the machine-id. Intended mostly for
 888         network booting where the same machine-id is desired
 889         for every boot.</para></listitem>
 890       </varlistentry>
 891
 892       <varlistentry>
 893         <term><varname>systemd.unified_cgroup_hierarchy</varname></term>
 894
 895         <listitem><para>When specified without an argument or with a true argument,
 896         enables the usage of
 897         <ulink url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html">unified cgroup hierarchy</ulink>
 898         (a.k.a. cgroups-v2). When specified with a false argument, fall back to
 899         hybrid or full legacy cgroup hierarchy.</para>
 900
 901         <para>If this option is not specified, the default behaviour is determined
 902         during compilation (the <option>-Ddefault-hierarchy=</option> meson
 903         option). If the kernel does not support unified cgroup hierarchy, the legacy
 904         hierarchy will be used even if this option is specified.</para>
 905         </listitem>
 906       </varlistentry>
 907
 908       <varlistentry>
 909         <term><varname>systemd.legacy_systemd_cgroup_controller</varname></term>
 910
 911         <listitem><para>Takes effect if the full unified cgroup hierarchy is not used
 912         (see previous option). When specified without an argument or with a true
 913         argument, disables the use of "hybrid" cgroup hierarchy (i.e. a cgroups-v2
 914         tree used for systemd, and
 915         <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v1/">legacy
 916         cgroup hierarchy</ulink>, a.k.a. cgroups-v1, for other controllers), and
 917         forces a full "legacy" mode. When specified with a false argument, enables
 918         the use of "hybrid" hierarchy.</para>
 919
 920         <para>If this option is not specified, the default behaviour is determined
 921         during compilation (the <option>-Ddefault-hierarchy=</option> meson
 922         option). If the kernel does not support unified cgroup hierarchy, the legacy
 923         hierarchy will be used  even if this option is specified.</para>
 924         </listitem>
 925       </varlistentry>
 926
 927       <varlistentry>
 928         <term><varname>quiet</varname></term>
 929
 930         <listitem><para>Turn off status output at boot, much like
 931         <varname>systemd.show_status=no</varname> would. Note that
 932         this option is also read by the kernel itself and disables
 933         kernel log output. Passing this option hence turns off the
 934         usual output from both the system manager and the kernel.
 935         </para></listitem>
 936       </varlistentry>
 937
 938       <varlistentry>
 939         <term><varname>debug</varname></term>
 940
 941         <listitem><para>Turn on debugging output. This is equivalent
 942         to <varname>systemd.log_level=debug</varname>. Note that this
 943         option is also read by the kernel itself and enables kernel
 944         debug output. Passing this option hence turns on the debug
 945         output from both the system manager and the
 946         kernel.</para></listitem>
 947       </varlistentry>
 948
 949       <varlistentry>
 950         <term><varname>emergency</varname></term>
 951         <term><varname>rd.emergency</varname></term>
 952         <term><varname>-b</varname></term>
 953
 954         <listitem><para>Boot into emergency mode. This is equivalent
 955         to <varname>systemd.unit=emergency.target</varname> or
 956         <varname>rd.systemd.unit=emergency.target</varname>, respectively, and
 957         provided for compatibility reasons and to be easier to type.</para></listitem>
 958       </varlistentry>
 959
 960       <varlistentry>
 961         <term><varname>rescue</varname></term>
 962         <term><varname>rd.rescue</varname></term>
 963         <term><varname>single</varname></term>
 964         <term><varname>s</varname></term>
 965         <term><varname>S</varname></term>
 966         <term><varname>1</varname></term>
 967
 968         <listitem><para>Boot into rescue mode. This is equivalent to
 969         <varname>systemd.unit=rescue.target</varname> or
 970         <varname>rd.systemd.unit=rescue.target</varname>, respectively, and
 971         provided for compatibility reasons and to be easier to type.</para></listitem>
 972       </varlistentry>
 973
 974       <varlistentry>
 975         <term><varname>2</varname></term>
 976         <term><varname>3</varname></term>
 977         <term><varname>4</varname></term>
 978         <term><varname>5</varname></term>
 979
 980         <listitem><para>Boot into the specified legacy SysV runlevel.
 981         These are equivalent to
 982         <varname>systemd.unit=runlevel2.target</varname>,
 983         <varname>systemd.unit=runlevel3.target</varname>,
 984         <varname>systemd.unit=runlevel4.target</varname>, and
 985         <varname>systemd.unit=runlevel5.target</varname>,
 986         respectively, and provided for compatibility reasons and to be
 987         easier to type.</para></listitem>
 988       </varlistentry>
 989
 990       <varlistentry>
 991         <term><varname>locale.LANG=</varname></term>
 992         <term><varname>locale.LANGUAGE=</varname></term>
 993         <term><varname>locale.LC_CTYPE=</varname></term>
 994         <term><varname>locale.LC_NUMERIC=</varname></term>
 995         <term><varname>locale.LC_TIME=</varname></term>
 996         <term><varname>locale.LC_COLLATE=</varname></term>
 997         <term><varname>locale.LC_MONETARY=</varname></term>
 998         <term><varname>locale.LC_MESSAGES=</varname></term>
 999         <term><varname>locale.LC_PAPER=</varname></term>
1000         <term><varname>locale.LC_NAME=</varname></term>
1001         <term><varname>locale.LC_ADDRESS=</varname></term>
1002         <term><varname>locale.LC_TELEPHONE=</varname></term>
1003         <term><varname>locale.LC_MEASUREMENT=</varname></term>
1004         <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1005
1006         <listitem><para>Set the system locale to use. This overrides
1007         the settings in <filename>/etc/locale.conf</filename>. For
1008         more information, see
1009         <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1010         and
1011         <citerefentry project='man-pages'><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1012         </para></listitem>
1013       </varlistentry>
1014     </variablelist>
1015
1016     <para>For other kernel command line parameters understood by
1017     components of the core OS, please refer to
1018     <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1019   </refsect1>
1020
1021   <refsect1>
1022     <title>Options</title>
1023
1024     <para><command>systemd</command> is only very rarely invoked directly, since it is started early and is
1025     already running by the time users may interact with it. Normally, tools like
1026     <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> are used to
1027     give commands to the manager. Since <command>systemd</command> is usually not invoked directly, the
1028     options listed below are mostly useful for debugging and special purposes.</para>
1029
1030     <refsect2>
1031       <title>Introspection and debugging options</title>
1032
1033       <para>Those options are used for testing and introspection, and <command>systemd</command> may
1034       be invoked with them at any time:</para>
1035
1036       <variablelist>
1037         <varlistentry>
1038           <term><option>--dump-configuration-items</option></term>
1039
1040           <listitem><para>Dump understood unit configuration items. This outputs a terse but complete list of
1041           configuration items understood in unit definition files.</para></listitem>
1042         </varlistentry>
1043
1044         <varlistentry>
1045           <term><option>--dump-bus-properties</option></term>
1046
1047           <listitem><para>Dump exposed bus properties. This outputs a terse but complete list of properties
1048           exposed on D-Bus.</para></listitem>
1049         </varlistentry>
1050
1051         <varlistentry>
1052           <term><option>--test</option></term>
1053
1054           <listitem><para>Determine the initial start-up transaction (i.e. the list of jobs enqueued at
1055           start-up), dump it and exit — without actually executing any of the determined jobs. This option is
1056           useful for debugging only. Note that during regular service manager start-up additional units not
1057           shown by this operation may be started, because hardware, socket, bus or other kinds of activation
1058           might add additional jobs as the transaction is executed. Use <option>--system</option> to request
1059           the initial transaction of the system service manager (this is also the implied default), combine
1060           with <option>--user</option> to request the initial transaction of the per-user service manager
1061           instead.</para></listitem>
1062         </varlistentry>
1063
1064         <varlistentry>
1065           <term><option>--system</option></term>
1066           <term><option>--user</option></term>
1067
1068           <listitem><para>When used in conjunction with <option>--test</option>, selects whether to calculate
1069           the initial transaction for the system instance or for a per-user instance. These options have no
1070           effect when invoked without <option>--test</option>, as during regular
1071           (i.e. non-<option>--test</option>) invocations the service manager will automatically detect
1072           whether it shall operate in system or per-user mode, by checking whether the PID it is run as is 1
1073           or not. Note that it is not supported booting and maintaining a system with the service manager
1074           running in <option>--system</option> mode but with a PID other than 1.</para></listitem>
1075         </varlistentry>
1076
1077         <xi:include href="standard-options.xml" xpointer="help" />
1078         <xi:include href="standard-options.xml" xpointer="version" />
1079       </variablelist>
1080     </refsect2>
1081
1082     <refsect2>
1083       <title>Options that duplicate kernel command line settings</title>
1084
1085       <para>Those options correspond directly to options listed above in "Kernel Command Line". Both forms
1086       may be used equivalently for the system manager, but it is recommended to use the forms listed above in
1087       this context, because they are properly namespaced. When an option is specified both on the kernel
1088       command line, and as a normal command line argument, the latter has higher precedence.</para>
1089
1090       <para>When <command>systemd</command> is used as a user manager, the kernel command line is ignored and
1091       the options described are understood. Nevertheless, <command>systemd</command> is usually started in
1092       this mode through the
1093       <citerefentry><refentrytitle>user@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1094       service, which is shared between all users, and it may be more convenient to use configuration files to
1095       modify settings, see
1096       <citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1097       or a drop-in that specifies one of the environment variables listed above in the Environment section,
1098       see
1099       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1100
1101       <variablelist>
1102         <varlistentry>
1103           <term><option>--unit=</option></term>
1104
1105           <listitem><para>Set default unit to activate on startup. If not specified, defaults to
1106           <filename>default.target</filename>. See <varname>systemd.unit=</varname> above.</para></listitem>
1107         </varlistentry>
1108
1109         <varlistentry>
1110           <term><option>--dump-core</option></term>
1111
1112           <listitem><para>Enable core dumping on crash. This switch has no effect when running as user
1113           instance. Same as <varname>systemd.dump_core=</varname> above.</para></listitem>
1114         </varlistentry>
1115
1116         <varlistentry>
1117           <term><option>--crash-vt=</option><replaceable>VT</replaceable></term>
1118
1119           <listitem><para>Switch to a specific virtual console (VT) on crash. This switch has no effect when
1120           running as user instance. Same as <varname>systemd.crash_chvt=</varname> above (but not the
1121           different spelling!).</para></listitem>
1122         </varlistentry>
1123
1124         <varlistentry>
1125           <term><option>--crash-shell</option></term>
1126
1127           <listitem><para>Run a shell on crash. This switch has no effect when running as user instance. See
1128           <varname>systemd.crash_shell=</varname> above.</para></listitem>
1129         </varlistentry>
1130
1131         <varlistentry>
1132           <term><option>--crash-reboot</option></term>
1133
1134           <listitem><para>Automatically reboot the system on crash. This switch has no effect when running as
1135           user instance. See <varname>systemd.crash_reboot</varname> above.</para></listitem>
1136         </varlistentry>
1137
1138         <varlistentry>
1139           <term><option>--confirm-spawn</option></term>
1140
1141           <listitem><para>Ask for confirmation when spawning processes. This switch has no effect when run as
1142           user instance. See <varname>systemd.confirm_spawn</varname> above.</para></listitem>
1143         </varlistentry>
1144
1145         <varlistentry>
1146           <term><option>--show-status</option></term>
1147
1148           <listitem><para>Show terse unit status information on the console during boot-up and shutdown. See
1149           <varname>systemd.show_status</varname> above.</para></listitem>
1150         </varlistentry>
1151
1152         <varlistentry>
1153           <term><option>--log-color</option></term>
1154
1155           <listitem><para>Highlight important log messages. See <varname>systemd.log_color</varname> above.
1156           </para></listitem>
1157         </varlistentry>
1158
1159         <varlistentry>
1160           <term><option>--log-level=</option></term>
1161
1162           <listitem><para>Set log level. See <varname>systemd.log_level</varname> above.</para></listitem>
1163         </varlistentry>
1164
1165         <varlistentry>
1166           <term><option>--log-location</option></term>
1167
1168           <listitem><para>Include code location in log messages. See <varname>systemd.log_location</varname>
1169           above.</para></listitem>
1170         </varlistentry>
1171
1172         <varlistentry>
1173           <term><option>--log-target=</option></term>
1174
1175           <listitem><para>Set log target. See <varname>systemd.log_target</varname> above.</para></listitem>
1176         </varlistentry>
1177
1178         <varlistentry>
1179           <term><option>--log-time=</option></term>
1180
1181           <listitem><para>Prefix messages with timestamp. See <varname>systemd.log_time</varname> above.
1182           </para></listitem>
1183         </varlistentry>
1184
1185         <varlistentry>
1186           <term><option>--machine-id=</option></term>
1187
1188           <listitem><para>Override the machine-id set on the hard drive. See
1189           <varname>systemd.machine_id=</varname> above.</para></listitem>
1190         </varlistentry>
1191
1192         <varlistentry>
1193           <term><option>--service-watchdogs</option></term>
1194
1195           <listitem><para>Globally enable/disable all service watchdog timeouts and emergency actions. See
1196           <varname>systemd.service_watchdogs</varname> above.</para></listitem>
1197         </varlistentry>
1198
1199         <varlistentry>
1200           <term><option>--default-standard-output=</option></term>
1201           <term><option>--default-standard-error=</option></term>
1202
1203           <listitem><para>Sets the default output or error output for all services and sockets,
1204           respectively. See <varname>systemd.default_standard_output=</varname> and
1205           <varname>systemd.default_standard_error=</varname> above.</para></listitem>
1206         </varlistentry>
1207       </variablelist>
1208     </refsect2>
1209   </refsect1>
1210
1211   <refsect1>
1212     <title>Sockets and FIFOs</title>
1213
1214     <variablelist>
1215       <varlistentry>
1216         <term><filename>/run/systemd/notify</filename></term>
1217
1218         <listitem><para>Daemon status notification socket. This is an
1219         <constant>AF_UNIX</constant> datagram socket and is used to
1220         implement the daemon notification logic as implemented by
1221         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1222
1223       </varlistentry>
1224
1225       <varlistentry>
1226         <term><filename>/run/systemd/private</filename></term>
1227
1228         <listitem><para>Used internally as communication channel
1229         between
1230         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1231         and the systemd process. This is an
1232         <constant>AF_UNIX</constant> stream socket. This interface is
1233         private to systemd and should not be used in external
1234         projects.</para></listitem>
1235       </varlistentry>
1236
1237       <varlistentry>
1238         <term><filename>/dev/initctl</filename></term>
1239
1240         <listitem><para>Limited compatibility support for the SysV
1241         client interface, as implemented by the
1242         <filename>systemd-initctl.service</filename> unit. This is a
1243         named pipe in the file system. This interface is obsolete and
1244         should not be used in new applications.</para></listitem>
1245       </varlistentry>
1246     </variablelist>
1247   </refsect1>
1248
1249   <refsect1>
1250     <title>See Also</title>
1251     <para>
1252       The <ulink url="https://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
1253       <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1254       <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1255       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1256       <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1257       <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1258       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1259       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1260       <citerefentry><refentrytitle>org.freedesktop.systemd1</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1261       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1262       <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1263       <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1264       <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1265       <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1266       <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1267     </para>
1268   </refsect1>
1269
1270 </refentry>