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     our 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>Systems which invoke systemd in a container or initrd environment should implement the <ulink
 284     url="https://systemd.io/CONTAINER_INTERFACE">Container Interface</ulink> or <ulink
 285     url="https://www.freedesktop.org/wiki/Software/systemd/InitrdInterface">initrd Interface</ulink>
 286     specifications, respectively.</para>
 287   </refsect1>
 288
 289   <refsect1>
 290     <title>Directories</title>
 291
 292     <variablelist>
 293       <varlistentry>
 294         <term>System unit directories</term>
 295
 296         <listitem><para>The systemd system manager reads unit
 297         configuration from various directories. Packages that want to
 298         install unit files shall place them in the directory returned
 299         by <command>pkg-config systemd
 300         --variable=systemdsystemunitdir</command>. Other directories
 301         checked are <filename>/usr/local/lib/systemd/system</filename>
 302         and <filename>/usr/lib/systemd/system</filename>. User
 303         configuration always takes precedence. <command>pkg-config
 304         systemd --variable=systemdsystemconfdir</command> returns the
 305         path of the system configuration directory. Packages should
 306         alter the content of these directories only with the
 307         <command>enable</command> and <command>disable</command>
 308         commands of the
 309         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 310         tool. Full list of directories is provided in
 311         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 312         </para></listitem>
 313       </varlistentry>
 314     </variablelist>
 315
 316     <variablelist>
 317       <varlistentry>
 318         <term>User unit directories</term>
 319
 320         <listitem><para>Similar rules apply for the user unit
 321         directories. However, here the
 322         <ulink url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 323         Base Directory specification</ulink> is followed to find
 324         units. Applications should place their unit files in the
 325         directory returned by <command>pkg-config systemd
 326         --variable=systemduserunitdir</command>. Global configuration
 327         is done in the directory reported by <command>pkg-config
 328         systemd --variable=systemduserconfdir</command>. The
 329         <command>enable</command> and <command>disable</command>
 330         commands of the
 331         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 332         tool can handle both global (i.e. for all users) and private
 333         (for one user) enabling/disabling of units. Full list of
 334         directories is provided in
 335         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 336         </para></listitem>
 337       </varlistentry>
 338     </variablelist>
 339
 340     <variablelist>
 341       <varlistentry>
 342         <term>SysV init scripts directory</term>
 343
 344         <listitem><para>The location of the SysV init script directory
 345         varies between distributions. If systemd cannot find a native
 346         unit file for a requested service, it will look for a SysV
 347         init script of the same name (with the
 348         <filename>.service</filename> suffix
 349         removed).</para></listitem>
 350       </varlistentry>
 351     </variablelist>
 352
 353     <variablelist>
 354       <varlistentry>
 355         <term>SysV runlevel link farm directory</term>
 356
 357         <listitem><para>The location of the SysV runlevel link farm
 358         directory varies between distributions. systemd will take the
 359         link farm into account when figuring out whether a service
 360         shall be enabled. Note that a service unit with a native unit
 361         configuration file cannot be started by activating it in the
 362         SysV runlevel link farm.</para></listitem>
 363       </varlistentry>
 364     </variablelist>
 365   </refsect1>
 366
 367   <refsect1>
 368     <title>Signals</title>
 369
 370     <variablelist>
 371       <varlistentry>
 372         <term><constant>SIGTERM</constant></term>
 373
 374         <listitem><para>Upon receiving this signal the systemd system
 375         manager serializes its state, reexecutes itself and
 376         deserializes the saved state again. This is mostly equivalent
 377         to <command>systemctl daemon-reexec</command>.</para>
 378
 379         <para>systemd user managers will start the
 380         <filename>exit.target</filename> unit when this signal is
 381         received. This is mostly equivalent to <command>systemctl
 382         --user start exit.target
 383         --job-mode=replace-irreversibly</command>.</para></listitem>
 384       </varlistentry>
 385
 386       <varlistentry>
 387         <term><constant>SIGINT</constant></term>
 388
 389         <listitem><para>Upon receiving this signal the systemd system manager will start the
 390         <filename>ctrl-alt-del.target</filename> unit. This is mostly equivalent to
 391         <command>systemctl start ctrl-alt-del.target --job-mode=replace-irreversibly</command>. If
 392         this signal is received more than 7 times per 2s, an immediate reboot is triggered. Note
 393         that pressing
 394         <keycombo><keycap>Ctrl</keycap><keycap>Alt</keycap><keycap>Del</keycap></keycombo> on the
 395         console will trigger this signal. Hence, if a reboot is hanging, pressing
 396         <keycombo><keycap>Ctrl</keycap><keycap>Alt</keycap><keycap>Del</keycap></keycombo> more than
 397         7 times in 2 seconds is a relatively safe way to trigger an immediate reboot.</para>
 398
 399         <para>systemd user managers treat this signal the same way as
 400         <constant>SIGTERM</constant>.</para></listitem>
 401       </varlistentry>
 402
 403       <varlistentry>
 404         <term><constant>SIGWINCH</constant></term>
 405
 406         <listitem><para>When this signal is received the systemd
 407         system manager will start the
 408         <filename>kbrequest.target</filename> unit. This is mostly
 409         equivalent to <command>systemctl start
 410         kbrequest.target</command>.</para>
 411
 412         <para>This signal is ignored by systemd user
 413         managers.</para></listitem>
 414       </varlistentry>
 415
 416       <varlistentry>
 417         <term><constant>SIGPWR</constant></term>
 418
 419         <listitem><para>When this signal is received the systemd
 420         manager will start the <filename>sigpwr.target</filename>
 421         unit. This is mostly equivalent to <command>systemctl start
 422         sigpwr.target</command>.</para></listitem>
 423       </varlistentry>
 424
 425       <varlistentry>
 426         <term><constant>SIGUSR1</constant></term>
 427
 428         <listitem><para>When this signal is received the systemd
 429         manager will try to reconnect to the D-Bus
 430         bus.</para></listitem>
 431       </varlistentry>
 432
 433       <varlistentry>
 434         <term><constant>SIGUSR2</constant></term>
 435
 436         <listitem><para>When this signal is received the systemd
 437         manager will log its complete state in human-readable form.
 438         The data logged is the same as printed by
 439         <command>systemd-analyze dump</command>.</para></listitem>
 440       </varlistentry>
 441
 442       <varlistentry>
 443         <term><constant>SIGHUP</constant></term>
 444
 445         <listitem><para>Reloads the complete daemon configuration.
 446         This is mostly equivalent to <command>systemctl
 447         daemon-reload</command>.</para></listitem>
 448       </varlistentry>
 449
 450       <varlistentry>
 451         <term><constant>SIGRTMIN+0</constant></term>
 452
 453         <listitem><para>Enters default mode, starts the
 454         <filename>default.target</filename> unit. This is mostly
 455         equivalent to <command>systemctl isolate
 456         default.target</command>.</para></listitem>
 457       </varlistentry>
 458
 459       <varlistentry>
 460         <term><constant>SIGRTMIN+1</constant></term>
 461
 462         <listitem><para>Enters rescue mode, starts the
 463         <filename>rescue.target</filename> unit. This is mostly
 464         equivalent to <command>systemctl isolate
 465         rescue.target</command>.</para></listitem>
 466       </varlistentry>
 467
 468       <varlistentry>
 469         <term><constant>SIGRTMIN+2</constant></term>
 470
 471         <listitem><para>Enters emergency mode, starts the
 472         <filename>emergency.service</filename> unit. This is mostly
 473         equivalent to <command>systemctl isolate
 474         emergency.service</command>.</para></listitem>
 475       </varlistentry>
 476
 477       <varlistentry>
 478         <term><constant>SIGRTMIN+3</constant></term>
 479
 480         <listitem><para>Halts the machine, starts the
 481         <filename>halt.target</filename> unit. This is mostly
 482         equivalent to <command>systemctl start halt.target
 483         --job-mode=replace-irreversibly</command>.</para>
 484         </listitem>
 485       </varlistentry>
 486
 487       <varlistentry>
 488         <term><constant>SIGRTMIN+4</constant></term>
 489
 490         <listitem><para>Powers off the machine, starts the
 491         <filename>poweroff.target</filename> unit. This is mostly
 492         equivalent to <command>systemctl start poweroff.target
 493         --job-mode=replace-irreversibly</command>.</para>
 494         </listitem>
 495       </varlistentry>
 496
 497       <varlistentry>
 498         <term><constant>SIGRTMIN+5</constant></term>
 499
 500         <listitem><para>Reboots the machine, starts the
 501         <filename>reboot.target</filename> unit. This is mostly
 502         equivalent to <command>systemctl start reboot.target
 503         --job-mode=replace-irreversibly</command>.</para>
 504         </listitem>
 505       </varlistentry>
 506
 507       <varlistentry>
 508         <term><constant>SIGRTMIN+6</constant></term>
 509
 510         <listitem><para>Reboots the machine via kexec, starts the
 511         <filename>kexec.target</filename> unit. This is mostly
 512         equivalent to <command>systemctl start kexec.target
 513         --job-mode=replace-irreversibly</command>.</para>
 514         </listitem>
 515       </varlistentry>
 516
 517       <varlistentry>
 518         <term><constant>SIGRTMIN+13</constant></term>
 519
 520         <listitem><para>Immediately halts the machine.</para></listitem>
 521       </varlistentry>
 522
 523       <varlistentry>
 524         <term><constant>SIGRTMIN+14</constant></term>
 525
 526         <listitem><para>Immediately powers off the machine.</para></listitem>
 527       </varlistentry>
 528
 529       <varlistentry>
 530         <term><constant>SIGRTMIN+15</constant></term>
 531
 532         <listitem><para>Immediately reboots the machine.</para></listitem>
 533       </varlistentry>
 534
 535       <varlistentry>
 536         <term><constant>SIGRTMIN+16</constant></term>
 537
 538         <listitem><para>Immediately reboots the machine with kexec.</para></listitem>
 539       </varlistentry>
 540
 541       <varlistentry>
 542         <term><constant>SIGRTMIN+20</constant></term>
 543
 544         <listitem><para>Enables display of status messages on the
 545         console, as controlled via
 546         <varname>systemd.show_status=1</varname> on the kernel command
 547         line.</para></listitem>
 548       </varlistentry>
 549
 550       <varlistentry>
 551         <term><constant>SIGRTMIN+21</constant></term>
 552
 553         <listitem><para>Disables display of
 554         status messages on the console, as
 555         controlled via
 556         <varname>systemd.show_status=0</varname>
 557         on the kernel command
 558         line.</para></listitem>
 559       </varlistentry>
 560
 561       <varlistentry>
 562         <term><constant>SIGRTMIN+22</constant></term>
 563
 564         <listitem><para>Sets the service manager's log level to <literal>debug</literal>, in a fashion equivalent to
 565         <varname>systemd.log_level=debug</varname> on the kernel command line.</para></listitem>
 566       </varlistentry>
 567
 568       <varlistentry>
 569         <term><constant>SIGRTMIN+23</constant></term>
 570
 571         <listitem><para>Restores the log level to its configured value. The configured value is derived from – in order
 572         of priority – the value specified with <varname>systemd.log-level=</varname> on the kernel command line, or the
 573         value specified with <option>LogLevel=</option> in the configuration file, or the built-in default of
 574         <literal>info</literal>.</para></listitem>
 575       </varlistentry>
 576
 577       <varlistentry>
 578         <term><constant>SIGRTMIN+24</constant></term>
 579
 580         <listitem><para>Immediately exits the manager (only available
 581         for --user instances).</para></listitem>
 582       </varlistentry>
 583
 584       <varlistentry>
 585         <term><constant>SIGRTMIN+26</constant></term>
 586
 587         <listitem><para>Restores the log target to its configured value. The configured value is derived from – in
 588         order of priority – the value specified with <varname>systemd.log-target=</varname> on the kernel command line,
 589         or the value specified with <option>LogTarget=</option> in the configuration file, or the built-in
 590         default.</para></listitem>
 591       </varlistentry>
 592
 593       <varlistentry>
 594         <term><constant>SIGRTMIN+27</constant></term>
 595         <term><constant>SIGRTMIN+28</constant></term>
 596
 597         <listitem><para>Sets the log target to <literal>console</literal> on <constant>SIGRTMIN+27</constant> (or
 598         <literal>kmsg</literal> on <constant>SIGRTMIN+28</constant>), in a fashion equivalent to
 599         <varname>systemd.log_target=console</varname> (or <varname>systemd.log_target=kmsg</varname> on
 600         <constant>SIGRTMIN+28</constant>) on the kernel command line.</para></listitem>
 601       </varlistentry>
 602     </variablelist>
 603   </refsect1>
 604
 605   <refsect1>
 606     <title>Environment</title>
 607
 608     <variablelist class='environment-variables'>
 609       <varlistentry>
 610         <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 611         <listitem><para>Controls whether systemd highlights important
 612         log messages. This can be overridden with
 613         <option>--log-color</option>.</para></listitem>
 614       </varlistentry>
 615
 616       <varlistentry>
 617         <term><varname>$SYSTEMD_LOG_LEVEL</varname></term>
 618         <listitem><para>systemd reads the log level from this
 619         environment variable. This can be overridden with
 620         <option>--log-level=</option>.</para></listitem>
 621       </varlistentry>
 622
 623       <varlistentry>
 624         <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 625         <listitem><para>Controls whether systemd prints the code
 626         location along with log messages. This can be overridden with
 627         <option>--log-location</option>.</para></listitem>
 628       </varlistentry>
 629
 630       <varlistentry>
 631         <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 632         <listitem><para>systemd reads the log target from this
 633         environment variable. This can be overridden with
 634         <option>--log-target=</option>.</para></listitem>
 635       </varlistentry>
 636
 637       <varlistentry>
 638         <term><varname>$SYSTEMD_LOG_TIME</varname></term>
 639         <listitem><para>Controls whether systemd prefixes log
 640         messages with the current time. This can be overridden with
 641         <option>--log-time=</option>.</para></listitem>
 642       </varlistentry>
 643
 644       <varlistentry>
 645         <term><varname>$XDG_CONFIG_HOME</varname></term>
 646         <term><varname>$XDG_CONFIG_DIRS</varname></term>
 647         <term><varname>$XDG_DATA_HOME</varname></term>
 648         <term><varname>$XDG_DATA_DIRS</varname></term>
 649
 650         <listitem><para>The systemd user manager uses these variables
 651         in accordance to the <ulink
 652         url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 653         Base Directory specification</ulink> to find its
 654         configuration.</para></listitem>
 655       </varlistentry>
 656
 657       <varlistentry>
 658         <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 659         <term><varname>$SYSTEMD_GENERATOR_PATH</varname></term>
 660         <term><varname>$SYSTEMD_ENVIRONMENT_GENERATOR_PATH</varname></term>
 661
 662         <listitem><para>Controls where systemd looks for unit files and
 663         generators.</para>
 664         <para>These variables may contain a list of paths, separated by colons
 665         (<literal>:</literal>). When set, if the list ends with an empty
 666         component (<literal>...:</literal>), this list is prepended to the
 667         usual set of of paths. Otherwise, the specified list replaces the usual
 668         set of paths.
 669         </para></listitem>
 670       </varlistentry>
 671
 672       <varlistentry>
 673         <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 674
 675         <listitem><para>Controls where systemd looks for SysV init
 676         scripts.</para></listitem>
 677       </varlistentry>
 678
 679       <varlistentry>
 680         <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 681
 682         <listitem><para>Controls where systemd looks for SysV init
 683         script runlevel link farms.</para></listitem>
 684       </varlistentry>
 685
 686       <xi:include href="less-variables.xml" xpointer="pager"/>
 687       <xi:include href="less-variables.xml" xpointer="less"/>
 688       <xi:include href="less-variables.xml" xpointer="lesscharset"/>
 689       <xi:include href="less-variables.xml" xpointer="colors"/>
 690       <xi:include href="less-variables.xml" xpointer="urlify"/>
 691
 692       <varlistentry>
 693         <term><varname>$LISTEN_PID</varname></term>
 694         <term><varname>$LISTEN_FDS</varname></term>
 695         <term><varname>$LISTEN_FDNAMES</varname></term>
 696
 697         <listitem><para>Set by systemd for supervised processes during
 698         socket-based activation. See
 699         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 700         for more information.</para></listitem>
 701       </varlistentry>
 702
 703       <varlistentry>
 704         <term><varname>$NOTIFY_SOCKET</varname></term>
 705
 706         <listitem><para>Set by systemd for supervised processes for
 707         status and start-up completion notification. See
 708         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 709         for more information.</para></listitem>
 710       </varlistentry>
 711     </variablelist>
 712
 713     <para>For further environment variables understood by systemd and its various components, see <ulink
 714     url="https://systemd.io/ENVIRONMENT">Known Environment Variables</ulink>.</para>
 715   </refsect1>
 716
 717   <refsect1>
 718     <title>Kernel Command Line</title>
 719
 720     <para>When run as the system instance systemd parses a number of options listed below. They can be
 721     specified as kernel command line arguments<footnote><para>If run inside a Linux container these arguments
 722     may be passed as command line arguments to systemd itself, next to any of the command line options listed
 723     in the Options section above. If run outside of Linux containers, these arguments are parsed from
 724     <filename>/proc/cmdline</filename> instead.</para></footnote>, or through the
 725     <literal>SystemdOptions</literal> EFI variable (on EFI systems). The kernel command line has higher
 726     priority. Following variables are understood:</para>
 727
 728     <variablelist class='kernel-commandline-options'>
 729       <varlistentry>
 730         <term><varname>systemd.unit=</varname></term>
 731         <term><varname>rd.systemd.unit=</varname></term>
 732
 733         <listitem><para>Overrides the unit to activate on boot.
 734         Defaults to <filename>default.target</filename>. This may be
 735         used to temporarily boot into a different boot unit, for
 736         example <filename>rescue.target</filename> or
 737         <filename>emergency.service</filename>. See
 738         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 739         for details about these units. The option prefixed with
 740         <literal>rd.</literal> is honored only in the initial RAM disk
 741         (initrd), while the one that is not prefixed only in the main
 742         system.</para></listitem>
 743       </varlistentry>
 744
 745       <varlistentry>
 746         <term><varname>systemd.dump_core</varname></term>
 747
 748         <listitem><para>Takes a boolean argument or enables the option if specified
 749         without an argument. If enabled, the systemd manager (PID 1) dumps core when
 750         it crashes. Otherwise, no core dump is created. Defaults to enabled.</para>
 751         </listitem>
 752       </varlistentry>
 753
 754       <varlistentry>
 755         <term><varname>systemd.crash_chvt</varname></term>
 756
 757         <listitem><para>Takes a positive integer, or a boolean argument. Can be also
 758         specified without an argument, with the same effect as a positive boolean. If
 759         a positive integer (in the range 1–63) is specified, the system manager (PID
 760         1) will activate the specified virtual terminal (VT) when it
 761         crashes. Defaults to disabled, meaning that no such switch is attempted. If
 762         set to enabled, the VT the kernel messages are written to is selected.
 763         </para></listitem>
 764       </varlistentry>
 765
 766       <varlistentry>
 767         <term><varname>systemd.crash_shell</varname></term>
 768
 769         <listitem><para>Takes a boolean argument or enables the option if specified
 770         without an argument. If enabled, the system manager (PID 1) spawns a shell
 771         when it crashes, after a 10s delay. Otherwise, no shell is spawned. Defaults
 772         to disabled, for security reasons, as the shell is not protected by password
 773         authentication.</para></listitem>
 774       </varlistentry>
 775
 776       <varlistentry>
 777         <term><varname>systemd.crash_reboot</varname></term>
 778
 779         <listitem><para>Takes a boolean argument or enables the option if specified
 780         without an argument. If enabled, the system manager (PID 1) will reboot the
 781         machine automatically when it crashes, after a 10s delay.  Otherwise, the
 782         system will hang indefinitely. Defaults to disabled, in order to avoid a
 783         reboot loop. If combined with <varname>systemd.crash_shell</varname>, the
 784         system is rebooted after the shell exits.</para></listitem>
 785       </varlistentry>
 786
 787       <varlistentry>
 788         <term><varname>systemd.confirm_spawn</varname></term>
 789
 790         <listitem><para>Takes a boolean argument or a path to the virtual console
 791         where the confirmation messages should be emitted. Can be also specified
 792         without an argument, with the same effect as a positive boolean. If enabled,
 793         the system manager (PID 1) asks for confirmation when spawning processes
 794         using <option>/dev/console</option>. If a path or a console name (such as
 795         <literal>ttyS0</literal>) is provided, the virtual console pointed to by this
 796         path or described by the give name will be used instead. Defaults to disabled.
 797         </para></listitem>
 798       </varlistentry>
 799
 800       <varlistentry>
 801         <term><varname>systemd.service_watchdogs=</varname></term>
 802
 803         <listitem><para>Takes a boolean argument. If disabled, all service runtime
 804         watchdogs (<option>WatchdogSec=</option>) and emergency actions (e.g.
 805         <option>OnFailure=</option> or <option>StartLimitAction=</option>) are
 806         ignored by the system manager (PID 1); see
 807         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 808         Defaults to enabled, i.e. watchdogs and failure actions are processed
 809         normally. The hardware watchdog is not affected by this
 810         option.</para></listitem>
 811       </varlistentry>
 812
 813       <varlistentry>
 814         <term><varname>systemd.show_status</varname></term>
 815
 816         <listitem><para>Takes a boolean argument or the constants <constant>error</constant> and
 817         <constant>auto</constant>. Can be also specified without an argument, with the same effect as a
 818         positive boolean. If enabled, the systemd manager (PID 1) shows terse service status updates on the
 819         console during bootup. With <constant>error</constant>, only messages about failures are shown, but
 820         boot is otherwise quiet. <constant>auto</constant> behaves like <option>false</option> until there is
 821         a significant delay in boot. Defaults to enabled, unless <option>quiet</option> is passed as kernel
 822         command line option, in which case it defaults to <constant>error</constant>. If specified overrides
 823         the system manager configuration file option <option>ShowStatus=</option>, see
 824         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 825         </para></listitem>
 826       </varlistentry>
 827
 828       <varlistentry>
 829         <term><varname>systemd.status_unit_format=</varname></term>
 830
 831         <listitem><para>Takes either <option>name</option> or <option>description</option> as the value. If
 832         <option>name</option>, the system manager will use unit names in status messages. If specified,
 833         overrides the system manager configuration file option <option>StatusUnitFormat=</option>, see
 834         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 835         </para></listitem>
 836       </varlistentry>
 837
 838       <varlistentry>
 839         <term><varname>systemd.log_color</varname></term>
 840         <term><varname>systemd.log_level=</varname></term>
 841         <term><varname>systemd.log_location</varname></term>
 842         <term><varname>systemd.log_target=</varname></term>
 843         <term><varname>systemd.log_time</varname></term>
 844
 845         <listitem><para>Controls log output, with the same effect as the
 846         <varname>$SYSTEMD_LOG_COLOR</varname>,
 847         <varname>$SYSTEMD_LOG_LEVEL</varname>,
 848         <varname>$SYSTEMD_LOG_LOCATION</varname>,
 849         <varname>$SYSTEMD_LOG_TARGET</varname>,
 850         <varname>$SYSTEMD_LOG_TIME</varname>, environment variables described above.
 851         <varname>systemd.log_color</varname>, <varname>systemd.log_location</varname>, and
 852         <varname>systemd.log_time</varname> can be specified without an argument, with the
 853         same effect as a positive boolean.</para></listitem>
 854       </varlistentry>
 855
 856       <varlistentry>
 857         <term><varname>systemd.default_standard_output=</varname></term>
 858         <term><varname>systemd.default_standard_error=</varname></term>
 859
 860         <listitem><para>Controls default standard output and error output for services and sockets. That is,
 861         controls the default for <option>StandardOutput=</option> and <option>StandardError=</option> (see
 862         <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 863         details). Takes one of <option>inherit</option>, <option>null</option>, <option>tty</option>,
 864         <option>journal</option>, <option>journal+console</option>, <option>kmsg</option>,
 865         <option>kmsg+console</option>. If the argument is omitted
 866         <varname>systemd.default-standard-output=</varname> defaults to <option>journal</option> and
 867         <varname>systemd.default-standard-error=</varname> to <option>inherit</option>.</para></listitem>
 868       </varlistentry>
 869
 870       <varlistentry>
 871         <term><varname>systemd.setenv=</varname></term>
 872
 873         <listitem><para>Takes a string argument in the form
 874         VARIABLE=VALUE. May be used to set default environment
 875         variables to add to forked child processes. May be used more
 876         than once to set multiple variables.</para></listitem>
 877       </varlistentry>
 878
 879       <varlistentry>
 880         <term><varname>systemd.machine_id=</varname></term>
 881
 882         <listitem><para>Takes a 32 character hex value to be
 883         used for setting the machine-id. Intended mostly for
 884         network booting where the same machine-id is desired
 885         for every boot.</para></listitem>
 886       </varlistentry>
 887
 888       <varlistentry>
 889         <term><varname>systemd.unified_cgroup_hierarchy</varname></term>
 890
 891         <listitem><para>When specified without an argument or with a true argument,
 892         enables the usage of
 893         <ulink url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html">unified cgroup hierarchy</ulink>
 894         (a.k.a. cgroups-v2). When specified with a false argument, fall back to
 895         hybrid or full legacy cgroup hierarchy.</para>
 896
 897         <para>If this option is not specified, the default behaviour is determined
 898         during compilation (the <option>-Ddefault-hierarchy=</option> meson
 899         option). If the kernel does not support unified cgroup hierarchy, the legacy
 900         hierarchy will be used even if this option is specified.</para>
 901         </listitem>
 902       </varlistentry>
 903
 904       <varlistentry>
 905         <term><varname>systemd.legacy_systemd_cgroup_controller</varname></term>
 906
 907         <listitem><para>Takes effect if the full unified cgroup hierarchy is not used
 908         (see previous option). When specified without an argument or with a true
 909         argument, disables the use of "hybrid" cgroup hierarchy (i.e. a cgroups-v2
 910         tree used for systemd, and
 911         <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v1/">legacy
 912         cgroup hierarchy</ulink>, a.k.a. cgroups-v1, for other controllers), and
 913         forces a full "legacy" mode. When specified with a false argument, enables
 914         the use of "hybrid" hierarchy.</para>
 915
 916         <para>If this option is not specified, the default behaviour is determined
 917         during compilation (the <option>-Ddefault-hierarchy=</option> meson
 918         option). If the kernel does not support unified cgroup hierarchy, the legacy
 919         hierarchy will be used  even if this option is specified.</para>
 920         </listitem>
 921       </varlistentry>
 922
 923       <varlistentry>
 924         <term><varname>quiet</varname></term>
 925
 926         <listitem><para>Turn off status output at boot, much like
 927         <varname>systemd.show_status=no</varname> would. Note that
 928         this option is also read by the kernel itself and disables
 929         kernel log output. Passing this option hence turns off the
 930         usual output from both the system manager and the kernel.
 931         </para></listitem>
 932       </varlistentry>
 933
 934       <varlistentry>
 935         <term><varname>debug</varname></term>
 936
 937         <listitem><para>Turn on debugging output. This is equivalent
 938         to <varname>systemd.log_level=debug</varname>. Note that this
 939         option is also read by the kernel itself and enables kernel
 940         debug output. Passing this option hence turns on the debug
 941         output from both the system manager and the
 942         kernel.</para></listitem>
 943       </varlistentry>
 944
 945       <varlistentry>
 946         <term><varname>emergency</varname></term>
 947         <term><varname>rd.emergency</varname></term>
 948         <term><varname>-b</varname></term>
 949
 950         <listitem><para>Boot into emergency mode. This is equivalent
 951         to <varname>systemd.unit=emergency.target</varname> or
 952         <varname>rd.systemd.unit=emergency.target</varname>, respectively, and
 953         provided for compatibility reasons and to be easier to type.</para></listitem>
 954       </varlistentry>
 955
 956       <varlistentry>
 957         <term><varname>rescue</varname></term>
 958         <term><varname>rd.rescue</varname></term>
 959         <term><varname>single</varname></term>
 960         <term><varname>s</varname></term>
 961         <term><varname>S</varname></term>
 962         <term><varname>1</varname></term>
 963
 964         <listitem><para>Boot into rescue mode. This is equivalent to
 965         <varname>systemd.unit=rescue.target</varname> or
 966         <varname>rd.systemd.unit=rescue.target</varname>, respectively, and
 967         provided for compatibility reasons and to be easier to type.</para></listitem>
 968       </varlistentry>
 969
 970       <varlistentry>
 971         <term><varname>2</varname></term>
 972         <term><varname>3</varname></term>
 973         <term><varname>4</varname></term>
 974         <term><varname>5</varname></term>
 975
 976         <listitem><para>Boot into the specified legacy SysV runlevel.
 977         These are equivalent to
 978         <varname>systemd.unit=runlevel2.target</varname>,
 979         <varname>systemd.unit=runlevel3.target</varname>,
 980         <varname>systemd.unit=runlevel4.target</varname>, and
 981         <varname>systemd.unit=runlevel5.target</varname>,
 982         respectively, and provided for compatibility reasons and to be
 983         easier to type.</para></listitem>
 984       </varlistentry>
 985
 986       <varlistentry>
 987         <term><varname>locale.LANG=</varname></term>
 988         <term><varname>locale.LANGUAGE=</varname></term>
 989         <term><varname>locale.LC_CTYPE=</varname></term>
 990         <term><varname>locale.LC_NUMERIC=</varname></term>
 991         <term><varname>locale.LC_TIME=</varname></term>
 992         <term><varname>locale.LC_COLLATE=</varname></term>
 993         <term><varname>locale.LC_MONETARY=</varname></term>
 994         <term><varname>locale.LC_MESSAGES=</varname></term>
 995         <term><varname>locale.LC_PAPER=</varname></term>
 996         <term><varname>locale.LC_NAME=</varname></term>
 997         <term><varname>locale.LC_ADDRESS=</varname></term>
 998         <term><varname>locale.LC_TELEPHONE=</varname></term>
 999         <term><varname>locale.LC_MEASUREMENT=</varname></term>
1000         <term><varname>locale.LC_IDENTIFICATION=</varname></term>
1001
1002         <listitem><para>Set the system locale to use. This overrides
1003         the settings in <filename>/etc/locale.conf</filename>. For
1004         more information, see
1005         <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1006         and
1007         <citerefentry project='man-pages'><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
1008         </para></listitem>
1009       </varlistentry>
1010     </variablelist>
1011
1012     <para>For other kernel command line parameters understood by
1013     components of the core OS, please refer to
1014     <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
1015   </refsect1>
1016
1017   <refsect1>
1018     <title>Options</title>
1019
1020     <para><command>systemd</command> is only very rarely invoked directly, since it is started early and is
1021     already running by the time users may interact with it. Normally, tools like
1022     <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> are used to
1023     give commands to the manager. Since <command>systemd</command> is usually not invoked directly, the
1024     options listed below are mostly useful for debugging and special purposes.</para>
1025
1026     <refsect2>
1027       <title>Introspection and debugging options</title>
1028
1029       <para>Those options are used for testing and introspection, and <command>systemd</command> may
1030       be invoked with them at any time:</para>
1031
1032       <variablelist>
1033         <varlistentry>
1034           <term><option>--dump-configuration-items</option></term>
1035
1036           <listitem><para>Dump understood unit configuration items. This outputs a terse but complete list of
1037           configuration items understood in unit definition files.</para></listitem>
1038         </varlistentry>
1039
1040         <varlistentry>
1041           <term><option>--dump-bus-properties</option></term>
1042
1043           <listitem><para>Dump exposed bus properties. This outputs a terse but complete list of properties
1044           exposed on D-Bus.</para></listitem>
1045         </varlistentry>
1046
1047         <varlistentry>
1048           <term><option>--test</option></term>
1049
1050           <listitem><para>Determine the initial start-up transaction (i.e. the list of jobs enqueued at
1051           start-up), dump it and exit — without actually executing any of the determined jobs. This option is
1052           useful for debugging only. Note that during regular service manager start-up additional units not
1053           shown by this operation may be started, because hardware, socket, bus or other kinds of activation
1054           might add additional jobs as the transaction is executed. Use <option>--system</option> to request
1055           the initial transaction of the system service manager (this is also the implied default), combine
1056           with <option>--user</option> to request the initial transaction of the per-user service manager
1057           instead.</para></listitem>
1058         </varlistentry>
1059
1060         <varlistentry>
1061           <term><option>--system</option></term>
1062           <term><option>--user</option></term>
1063
1064           <listitem><para>When used in conjunction with <option>--test</option>, selects whether to calculate
1065           the initial transaction for the system instance or for a per-user instance. These options have no
1066           effect when invoked without <option>--test</option>, as during regular
1067           (i.e. non-<option>--test</option>) invocations the service manager will automatically detect
1068           whether it shall operate in system or per-user mode, by checking whether the PID it is run as is 1
1069           or not. Note that it is not supported booting and maintaining a system with the service manager
1070           running in <option>--system</option> mode but with a PID other than 1.</para></listitem>
1071         </varlistentry>
1072
1073         <xi:include href="standard-options.xml" xpointer="help" />
1074         <xi:include href="standard-options.xml" xpointer="version" />
1075       </variablelist>
1076     </refsect2>
1077
1078     <refsect2>
1079       <title>Options that duplicate kernel command line settings</title>
1080
1081       <para>Those options correspond directly to options listed above in "Kernel Command Line". Both forms
1082       may be used equivalently for the system manager, but it is recommended to use the forms listed above in
1083       this context, because they are properly namespaced. When an option is specified both on the kernel
1084       command line, and as a normal command line argument, the latter has higher precedence.</para>
1085
1086       <para>When <command>systemd</command> is used a user manager, the kernel command line is ignored and
1087       the options described are understood. Nevertheless, <command>systemd</command> is usually started in
1088       this mode through the
1089       <citerefentry><refentrytitle>user@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1090       service, which is shared between all users, and it may be more convenient to use configuration files to
1091       modify settings, see
1092       <citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1093       or a drop-in that specifies one of the environment variables listed above in "Environment, see
1094       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1095
1096       <variablelist>
1097         <varlistentry>
1098           <term><option>--unit=</option></term>
1099
1100           <listitem><para>Set default unit to activate on startup. If not specified, defaults to
1101           <filename>default.target</filename>. See <varname>systemd.unit=</varname> above.</para></listitem>
1102         </varlistentry>
1103
1104         <varlistentry>
1105           <term><option>--dump-core</option></term>
1106
1107           <listitem><para>Enable core dumping on crash. This switch has no effect when running as user
1108           instance. Same as <varname>systemd.dump_core=</varname> above.</para></listitem>
1109         </varlistentry>
1110
1111         <varlistentry>
1112           <term><option>--crash-vt=</option><replaceable>VT</replaceable></term>
1113
1114           <listitem><para>Switch to a specific virtual console (VT) on crash. This switch has no effect when
1115           running as user instance. Same as <varname>systemd.crash_chvt=</varname> above (but not the
1116           different spelling!).</para></listitem>
1117         </varlistentry>
1118
1119         <varlistentry>
1120           <term><option>--crash-shell</option></term>
1121
1122           <listitem><para>Run a shell on crash. This switch has no effect when running as user instance. See
1123           <varname>systemd.crash_shell=</varname> above.</para></listitem>
1124         </varlistentry>
1125
1126         <varlistentry>
1127           <term><option>--crash-reboot</option></term>
1128
1129           <listitem><para>Automatically reboot the system on crash. This switch has no effect when running as
1130           user instance. See <varname>systemd.crash_reboot</varname> above.</para></listitem>
1131         </varlistentry>
1132
1133         <varlistentry>
1134           <term><option>--confirm-spawn</option></term>
1135
1136           <listitem><para>Ask for confirmation when spawning processes. This switch has no effect when run as
1137           user instance. See <varname>systemd.confirm_spawn</varname> above.</para></listitem>
1138         </varlistentry>
1139
1140         <varlistentry>
1141           <term><option>--show-status</option></term>
1142
1143           <listitem><para>Show terse unit status information is shown on the console during boot-up and
1144           shutdown. See <varname>systemd.show_status</varname> above.</para></listitem>
1145         </varlistentry>
1146
1147         <varlistentry>
1148           <term><option>--log-color</option></term>
1149
1150           <listitem><para>Highlight important log messages. See <varname>systemd.log_color</varname> above.
1151           </para></listitem>
1152         </varlistentry>
1153
1154         <varlistentry>
1155           <term><option>--log-level=</option></term>
1156
1157           <listitem><para>Set log level. See <varname>systemd.log_level</varname> above.</para></listitem>
1158         </varlistentry>
1159
1160         <varlistentry>
1161           <term><option>--log-location</option></term>
1162
1163           <listitem><para>Include code location in log messages. See <varname>systemd.log_location</varname>
1164           above.</para></listitem>
1165         </varlistentry>
1166
1167         <varlistentry>
1168           <term><option>--log-target=</option></term>
1169
1170           <listitem><para>Set log target. See <varname>systemd.log_target</varname> above.</para></listitem>
1171         </varlistentry>
1172
1173         <varlistentry>
1174           <term><option>--log-time=</option></term>
1175
1176           <listitem><para>Prefix messages with timestamp. See <varname>systemd.log_time</varname> above.
1177           </para></listitem>
1178         </varlistentry>
1179
1180         <varlistentry>
1181           <term><option>--machine-id=</option></term>
1182
1183           <listitem><para>Override the machine-id set on the hard drive. See
1184           <varname>systemd.machine_id=</varname> above.</para></listitem>
1185         </varlistentry>
1186
1187         <varlistentry>
1188           <term><option>--service-watchdogs</option></term>
1189
1190           <listitem><para>Globally enable/disable all service watchdog timeouts and emergency actions. See
1191           <varname>systemd.service_watchdogs</varname> above.</para></listitem>
1192         </varlistentry>
1193
1194         <varlistentry>
1195           <term><option>--default-standard-output=</option></term>
1196           <term><option>--default-standard-error=</option></term>
1197
1198           <listitem><para>Sets the default output or error output for all services and sockets,
1199           respectively. See <varname>systemd.default_standard_output=</varname> and
1200           <varname>systemd.default_standard_error=</varname> above.</para></listitem>
1201         </varlistentry>
1202       </variablelist>
1203     </refsect2>
1204   </refsect1>
1205
1206   <refsect1>
1207     <title>Sockets and FIFOs</title>
1208
1209     <variablelist>
1210       <varlistentry>
1211         <term><filename>/run/systemd/notify</filename></term>
1212
1213         <listitem><para>Daemon status notification socket. This is an
1214         <constant>AF_UNIX</constant> datagram socket and is used to
1215         implement the daemon notification logic as implemented by
1216         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1217
1218       </varlistentry>
1219
1220       <varlistentry>
1221         <term><filename>/run/systemd/private</filename></term>
1222
1223         <listitem><para>Used internally as communication channel
1224         between
1225         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1226         and the systemd process. This is an
1227         <constant>AF_UNIX</constant> stream socket. This interface is
1228         private to systemd and should not be used in external
1229         projects.</para></listitem>
1230       </varlistentry>
1231
1232       <varlistentry>
1233         <term><filename>/dev/initctl</filename></term>
1234
1235         <listitem><para>Limited compatibility support for the SysV
1236         client interface, as implemented by the
1237         <filename>systemd-initctl.service</filename> unit. This is a
1238         named pipe in the file system. This interface is obsolete and
1239         should not be used in new applications.</para></listitem>
1240       </varlistentry>
1241     </variablelist>
1242   </refsect1>
1243
1244   <refsect1>
1245     <title>See Also</title>
1246     <para>
1247       The <ulink url="https://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
1248       <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1249       <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1250       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1251       <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1252       <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1253       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1254       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1255       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1256       <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1257       <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1258       <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1259       <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1260       <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1261     </para>
1262   </refsect1>
1263
1264 </refentry>