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 some sort 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>$SYSTEMD_LOG_LEVEL</varname></term>
 611         <listitem><para>systemd reads the log level from this
 612         environment variable. This can be overridden with
 613         <option>--log-level=</option>.</para></listitem>
 614       </varlistentry>
 615
 616       <varlistentry>
 617         <term><varname>$SYSTEMD_LOG_TARGET</varname></term>
 618         <listitem><para>systemd reads the log target from this
 619         environment variable. This can be overridden with
 620         <option>--log-target=</option>.</para></listitem>
 621       </varlistentry>
 622
 623       <varlistentry>
 624         <term><varname>$SYSTEMD_LOG_COLOR</varname></term>
 625         <listitem><para>Controls whether systemd highlights important
 626         log messages. This can be overridden with
 627         <option>--log-color=</option>.</para></listitem>
 628       </varlistentry>
 629
 630       <varlistentry>
 631         <term><varname>$SYSTEMD_LOG_LOCATION</varname></term>
 632         <listitem><para>Controls whether systemd prints the code
 633         location along with log messages. This can be overridden with
 634         <option>--log-location=</option>.</para></listitem>
 635       </varlistentry>
 636
 637       <varlistentry>
 638         <term><varname>$XDG_CONFIG_HOME</varname></term>
 639         <term><varname>$XDG_CONFIG_DIRS</varname></term>
 640         <term><varname>$XDG_DATA_HOME</varname></term>
 641         <term><varname>$XDG_DATA_DIRS</varname></term>
 642
 643         <listitem><para>The systemd user manager uses these variables
 644         in accordance to the <ulink
 645         url="http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html">XDG
 646         Base Directory specification</ulink> to find its
 647         configuration.</para></listitem>
 648       </varlistentry>
 649
 650       <varlistentry>
 651         <term><varname>$SYSTEMD_UNIT_PATH</varname></term>
 652
 653         <listitem><para>Controls where systemd looks for unit
 654         files.</para></listitem>
 655       </varlistentry>
 656
 657       <varlistentry>
 658         <term><varname>$SYSTEMD_SYSVINIT_PATH</varname></term>
 659
 660         <listitem><para>Controls where systemd looks for SysV init
 661         scripts.</para></listitem>
 662       </varlistentry>
 663
 664       <varlistentry>
 665         <term><varname>$SYSTEMD_SYSVRCND_PATH</varname></term>
 666
 667         <listitem><para>Controls where systemd looks for SysV init
 668         script runlevel link farms.</para></listitem>
 669       </varlistentry>
 670
 671       <xi:include href="less-variables.xml" xpointer="pager"/>
 672       <xi:include href="less-variables.xml" xpointer="less"/>
 673       <xi:include href="less-variables.xml" xpointer="lesscharset"/>
 674       <xi:include href="less-variables.xml" xpointer="colors"/>
 675       <xi:include href="less-variables.xml" xpointer="urlify"/>
 676
 677       <varlistentry>
 678         <term><varname>$LISTEN_PID</varname></term>
 679         <term><varname>$LISTEN_FDS</varname></term>
 680         <term><varname>$LISTEN_FDNAMES</varname></term>
 681
 682         <listitem><para>Set by systemd for supervised processes during
 683         socket-based activation. See
 684         <citerefentry><refentrytitle>sd_listen_fds</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 685         for more information.</para></listitem>
 686       </varlistentry>
 687
 688       <varlistentry>
 689         <term><varname>$NOTIFY_SOCKET</varname></term>
 690
 691         <listitem><para>Set by systemd for supervised processes for
 692         status and start-up completion notification. See
 693         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>
 694         for more information.</para></listitem>
 695       </varlistentry>
 696     </variablelist>
 697
 698     <para>For further environment variables understood by systemd and its various components, see <ulink
 699     url="https://systemd.io/ENVIRONMENT">Known Environment Variables</ulink>.</para>
 700   </refsect1>
 701
 702   <refsect1>
 703     <title>Kernel Command Line</title>
 704
 705     <para>When run as the system instance systemd parses a number of options listed below. They can be
 706     specified as kernel command line arguments<footnote><para>If run inside a Linux container these arguments
 707     may be passed as command line arguments to systemd itself, next to any of the command line options listed
 708     in the Options section above. If run outside of Linux containers, these arguments are parsed from
 709     <filename>/proc/cmdline</filename> instead.</para></footnote>, or through the
 710     <literal>SystemdOptions</literal> EFI variable (on EFI systems). The kernel command line has higher
 711     priority. Following variables are understood:</para>
 712
 713     <variablelist class='kernel-commandline-options'>
 714       <varlistentry>
 715         <term><varname>systemd.unit=</varname></term>
 716         <term><varname>rd.systemd.unit=</varname></term>
 717
 718         <listitem><para>Overrides the unit to activate on boot.
 719         Defaults to <filename>default.target</filename>. This may be
 720         used to temporarily boot into a different boot unit, for
 721         example <filename>rescue.target</filename> or
 722         <filename>emergency.service</filename>. See
 723         <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>7</manvolnum></citerefentry>
 724         for details about these units. The option prefixed with
 725         <literal>rd.</literal> is honored only in the initial RAM disk
 726         (initrd), while the one that is not prefixed only in the main
 727         system.</para></listitem>
 728       </varlistentry>
 729
 730       <varlistentry>
 731         <term><varname>systemd.dump_core</varname></term>
 732
 733         <listitem><para>Takes a boolean argument or enables the option if specified
 734         without an argument. If enabled, the systemd manager (PID 1) dumps core when
 735         it crashes. Otherwise, no core dump is created. Defaults to enabled.</para>
 736         </listitem>
 737       </varlistentry>
 738
 739       <varlistentry>
 740         <term><varname>systemd.crash_chvt</varname></term>
 741
 742         <listitem><para>Takes a positive integer, or a boolean argument. Can be also
 743         specified without an argument, with the same effect as a positive boolean. If
 744         a positive integer (in the range 1–63) is specified, the system manager (PID
 745         1) will activate the specified virtual terminal (VT) when it
 746         crashes. Defaults to disabled, meaning that no such switch is attempted. If
 747         set to enabled, the VT the kernel messages are written to is selected.
 748         </para></listitem>
 749       </varlistentry>
 750
 751       <varlistentry>
 752         <term><varname>systemd.crash_shell</varname></term>
 753
 754         <listitem><para>Takes a boolean argument or enables the option if specified
 755         without an argument. If enabled, the system manager (PID 1) spawns a shell
 756         when it crashes, after a 10s delay. Otherwise, no shell is spawned. Defaults
 757         to disabled, for security reasons, as the shell is not protected by password
 758         authentication.</para></listitem>
 759       </varlistentry>
 760
 761       <varlistentry>
 762         <term><varname>systemd.crash_reboot</varname></term>
 763
 764         <listitem><para>Takes a boolean argument or enables the option if specified
 765         without an argument. If enabled, the system manager (PID 1) will reboot the
 766         machine automatically when it crashes, after a 10s delay.  Otherwise, the
 767         system will hang indefinitely. Defaults to disabled, in order to avoid a
 768         reboot loop. If combined with <varname>systemd.crash_shell</varname>, the
 769         system is rebooted after the shell exits.</para></listitem>
 770       </varlistentry>
 771
 772       <varlistentry>
 773         <term><varname>systemd.confirm_spawn</varname></term>
 774
 775         <listitem><para>Takes a boolean argument or a path to the virtual console
 776         where the confirmation messages should be emitted. Can be also specified
 777         without an argument, with the same effect as a positive boolean. If enabled,
 778         the system manager (PID 1) asks for confirmation when spawning processes
 779         using <option>/dev/console</option>. If a path or a console name (such as
 780         <literal>ttyS0</literal>) is provided, the virtual console pointed to by this
 781         path or described by the give name will be used instead. Defaults to disabled.
 782         </para></listitem>
 783       </varlistentry>
 784
 785       <varlistentry>
 786         <term><varname>systemd.service_watchdogs=</varname></term>
 787
 788         <listitem><para>Takes a boolean argument. If disabled, all service runtime
 789         watchdogs (<option>WatchdogSec=</option>) and emergency actions (e.g.
 790         <option>OnFailure=</option> or <option>StartLimitAction=</option>) are
 791         ignored by the system manager (PID 1); see
 792         <citerefentry><refentrytitle>systemd.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 793         Defaults to enabled, i.e. watchdogs and failure actions are processed
 794         normally. The hardware watchdog is not affected by this
 795         option.</para></listitem>
 796       </varlistentry>
 797
 798       <varlistentry>
 799         <term><varname>systemd.show_status</varname></term>
 800
 801         <listitem><para>Takes a boolean argument or the constants <constant>error</constant> and
 802         <constant>auto</constant>. Can be also specified without an argument, with the same effect as a
 803         positive boolean. If enabled, the systemd manager (PID 1) shows terse service status updates on the
 804         console during bootup. With <constant>error</constant>, only messages about failures are shown, but
 805         boot is otherwise quiet. <constant>auto</constant> behaves like <option>false</option> until there is
 806         a significant delay in boot. Defaults to enabled, unless <option>quiet</option> is passed as kernel
 807         command line option, in which case it defaults to <constant>error</constant>. If specified overrides
 808         the system manager configuration file option <option>ShowStatus=</option>, see
 809         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 810         </para></listitem>
 811       </varlistentry>
 812
 813       <varlistentry>
 814         <term><varname>systemd.status_unit_format=</varname></term>
 815
 816         <listitem><para>Takes either <option>name</option> or <option>description</option> as the value. If
 817         <option>name</option>, the system manager will use unit names in status messages. If specified,
 818         overrides the system manager configuration file option <option>StatusUnitFormat=</option>, see
 819         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
 820         </para></listitem>
 821       </varlistentry>
 822
 823       <varlistentry>
 824         <term><varname>systemd.log_target=</varname></term>
 825         <term><varname>systemd.log_level=</varname></term>
 826         <term><varname>systemd.log_location=</varname></term>
 827         <term><varname>systemd.log_color</varname></term>
 828
 829         <listitem><para>Controls log output, with the same effect as the
 830         <varname>$SYSTEMD_LOG_TARGET</varname>,
 831         <varname>$SYSTEMD_LOG_LEVEL</varname>,
 832         <varname>$SYSTEMD_LOG_LOCATION</varname>,
 833         <varname>$SYSTEMD_LOG_COLOR</varname> environment variables described above.
 834         <varname>systemd.log_color</varname> can be specified without an argument,
 835         with the same effect as a positive boolean.</para></listitem>
 836       </varlistentry>
 837
 838       <varlistentry>
 839         <term><varname>systemd.default_standard_output=</varname></term>
 840         <term><varname>systemd.default_standard_error=</varname></term>
 841
 842         <listitem><para>Controls default standard output and error output for services and sockets. That is,
 843         controls the default for <option>StandardOutput=</option> and <option>StandardError=</option> (see
 844         <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 845         details). Takes one of <option>inherit</option>, <option>null</option>, <option>tty</option>,
 846         <option>journal</option>, <option>journal+console</option>, <option>kmsg</option>,
 847         <option>kmsg+console</option>. If the argument is omitted
 848         <varname>systemd.default-standard-output=</varname> defaults to <option>journal</option> and
 849         <varname>systemd.default-standard-error=</varname> to <option>inherit</option>.</para></listitem>
 850       </varlistentry>
 851
 852       <varlistentry>
 853         <term><varname>systemd.setenv=</varname></term>
 854
 855         <listitem><para>Takes a string argument in the form
 856         VARIABLE=VALUE. May be used to set default environment
 857         variables to add to forked child processes. May be used more
 858         than once to set multiple variables.</para></listitem>
 859       </varlistentry>
 860
 861       <varlistentry>
 862         <term><varname>systemd.machine_id=</varname></term>
 863
 864         <listitem><para>Takes a 32 character hex value to be
 865         used for setting the machine-id. Intended mostly for
 866         network booting where the same machine-id is desired
 867         for every boot.</para></listitem>
 868       </varlistentry>
 869
 870       <varlistentry>
 871         <term><varname>systemd.unified_cgroup_hierarchy</varname></term>
 872
 873         <listitem><para>When specified without an argument or with a true argument,
 874         enables the usage of
 875         <ulink url="https://www.kernel.org/doc/html/latest/admin-guide/cgroup-v2.html">unified cgroup hierarchy</ulink>
 876         (a.k.a. cgroups-v2). When specified with a false argument, fall back to
 877         hybrid or full legacy cgroup hierarchy.</para>
 878
 879         <para>If this option is not specified, the default behaviour is determined
 880         during compilation (the <option>-Ddefault-hierarchy=</option> meson
 881         option). If the kernel does not support unified cgroup hierarchy, the legacy
 882         hierarchy will be used even if this option is specified.</para>
 883         </listitem>
 884       </varlistentry>
 885
 886       <varlistentry>
 887         <term><varname>systemd.legacy_systemd_cgroup_controller</varname></term>
 888
 889         <listitem><para>Takes effect if the full unified cgroup hierarchy is not used
 890         (see previous option). When specified without an argument or with a true
 891         argument, disables the use of "hybrid" cgroup hierarchy (i.e. a cgroups-v2
 892         tree used for systemd, and
 893         <ulink url="https://www.kernel.org/doc/Documentation/cgroup-v1/">legacy
 894         cgroup hierarchy</ulink>, a.k.a. cgroups-v1, for other controllers), and
 895         forces a full "legacy" mode. When specified with a false argument, enables
 896         the use of "hybrid" hierarchy.</para>
 897
 898         <para>If this option is not specified, the default behaviour is determined
 899         during compilation (the <option>-Ddefault-hierarchy=</option> meson
 900         option). If the kernel does not support unified cgroup hierarchy, the legacy
 901         hierarchy will be used  even if this option is specified.</para>
 902         </listitem>
 903       </varlistentry>
 904
 905       <varlistentry>
 906         <term><varname>quiet</varname></term>
 907
 908         <listitem><para>Turn off status output at boot, much like
 909         <varname>systemd.show_status=no</varname> would. Note that
 910         this option is also read by the kernel itself and disables
 911         kernel log output. Passing this option hence turns off the
 912         usual output from both the system manager and the kernel.
 913         </para></listitem>
 914       </varlistentry>
 915
 916       <varlistentry>
 917         <term><varname>debug</varname></term>
 918
 919         <listitem><para>Turn on debugging output. This is equivalent
 920         to <varname>systemd.log_level=debug</varname>. Note that this
 921         option is also read by the kernel itself and enables kernel
 922         debug output. Passing this option hence turns on the debug
 923         output from both the system manager and the
 924         kernel.</para></listitem>
 925       </varlistentry>
 926
 927       <varlistentry>
 928         <term><varname>emergency</varname></term>
 929         <term><varname>rd.emergency</varname></term>
 930         <term><varname>-b</varname></term>
 931
 932         <listitem><para>Boot into emergency mode. This is equivalent
 933         to <varname>systemd.unit=emergency.target</varname> or
 934         <varname>rd.systemd.unit=emergency.target</varname>, respectively, and
 935         provided for compatibility reasons and to be easier to type.</para></listitem>
 936       </varlistentry>
 937
 938       <varlistentry>
 939         <term><varname>rescue</varname></term>
 940         <term><varname>rd.rescue</varname></term>
 941         <term><varname>single</varname></term>
 942         <term><varname>s</varname></term>
 943         <term><varname>S</varname></term>
 944         <term><varname>1</varname></term>
 945
 946         <listitem><para>Boot into rescue mode. This is equivalent to
 947         <varname>systemd.unit=rescue.target</varname> or
 948         <varname>rd.systemd.unit=rescue.target</varname>, respectively, and
 949         provided for compatibility reasons and to be easier to type.</para></listitem>
 950       </varlistentry>
 951
 952       <varlistentry>
 953         <term><varname>2</varname></term>
 954         <term><varname>3</varname></term>
 955         <term><varname>4</varname></term>
 956         <term><varname>5</varname></term>
 957
 958         <listitem><para>Boot into the specified legacy SysV runlevel.
 959         These are equivalent to
 960         <varname>systemd.unit=runlevel2.target</varname>,
 961         <varname>systemd.unit=runlevel3.target</varname>,
 962         <varname>systemd.unit=runlevel4.target</varname>, and
 963         <varname>systemd.unit=runlevel5.target</varname>,
 964         respectively, and provided for compatibility reasons and to be
 965         easier to type.</para></listitem>
 966       </varlistentry>
 967
 968       <varlistentry>
 969         <term><varname>locale.LANG=</varname></term>
 970         <term><varname>locale.LANGUAGE=</varname></term>
 971         <term><varname>locale.LC_CTYPE=</varname></term>
 972         <term><varname>locale.LC_NUMERIC=</varname></term>
 973         <term><varname>locale.LC_TIME=</varname></term>
 974         <term><varname>locale.LC_COLLATE=</varname></term>
 975         <term><varname>locale.LC_MONETARY=</varname></term>
 976         <term><varname>locale.LC_MESSAGES=</varname></term>
 977         <term><varname>locale.LC_PAPER=</varname></term>
 978         <term><varname>locale.LC_NAME=</varname></term>
 979         <term><varname>locale.LC_ADDRESS=</varname></term>
 980         <term><varname>locale.LC_TELEPHONE=</varname></term>
 981         <term><varname>locale.LC_MEASUREMENT=</varname></term>
 982         <term><varname>locale.LC_IDENTIFICATION=</varname></term>
 983
 984         <listitem><para>Set the system locale to use. This overrides
 985         the settings in <filename>/etc/locale.conf</filename>. For
 986         more information, see
 987         <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 988         and
 989         <citerefentry project='man-pages'><refentrytitle>locale</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
 990         </para></listitem>
 991       </varlistentry>
 992     </variablelist>
 993
 994     <para>For other kernel command line parameters understood by
 995     components of the core OS, please refer to
 996     <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
 997   </refsect1>
 998
 999   <refsect1>
1000     <title>Options</title>
1001
1002     <para><command>systemd</command> is only very rarely invoked directly, since it is started early and is
1003     already running by the time users may interact with it. Normally, tools like
1004     <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> are used to
1005     give commands to the manager. Since <command>systemd</command> is usually not invoked directly, the
1006     options listed below are mostly useful for debugging and special purposes.</para>
1007
1008     <refsect2>
1009       <title>Introspection and debugging options</title>
1010
1011       <para>Those options are used for testing and introspection, and <command>systemd</command> may
1012       be invoked with them at any time:</para>
1013
1014       <variablelist>
1015         <varlistentry>
1016           <term><option>--dump-configuration-items</option></term>
1017
1018           <listitem><para>Dump understood unit configuration items. This outputs a terse but complete list of
1019           configuration items understood in unit definition files.</para></listitem>
1020         </varlistentry>
1021
1022         <varlistentry>
1023           <term><option>--dump-bus-properties</option></term>
1024
1025           <listitem><para>Dump exposed bus properties. This outputs a terse but complete list of properties
1026           exposed on D-Bus.</para></listitem>
1027         </varlistentry>
1028
1029         <varlistentry>
1030           <term><option>--test</option></term>
1031
1032           <listitem><para>Determine the initial start-up transaction (i.e. the list of jobs enqueued at
1033           start-up), dump it and exit — without actually executing any of the determined jobs. This option is
1034           useful for debugging only. Note that during regular service manager start-up additional units not
1035           shown by this operation may be started, because hardware, socket, bus or other kinds of activation
1036           might add additional jobs as the transaction is executed. Use <option>--system</option> to request
1037           the initial transaction of the system service manager (this is also the implied default), combine
1038           with <option>--user</option> to request the initial transaction of the per-user service manager
1039           instead.</para></listitem>
1040         </varlistentry>
1041
1042         <varlistentry>
1043           <term><option>--system</option></term>
1044           <term><option>--user</option></term>
1045
1046           <listitem><para>When used in conjunction with <option>--test</option>, selects whether to calculate
1047           the initial transaction for the system instance or for a per-user instance. These options have no
1048           effect when invoked without <option>--test</option>, as during regular
1049           (i.e. non-<option>--test</option>) invocations the service manager will automatically detect
1050           whether it shall operate in system or per-user mode, by checking whether the PID it is run as is 1
1051           or not. Note that it is not supported booting and maintaining a system with the service manager
1052           running in <option>--system</option> mode but with a PID other than 1.</para></listitem>
1053         </varlistentry>
1054
1055         <xi:include href="standard-options.xml" xpointer="help" />
1056         <xi:include href="standard-options.xml" xpointer="version" />
1057       </variablelist>
1058     </refsect2>
1059
1060     <refsect2>
1061       <title>Options that duplicate kernel command line settings</title>
1062
1063       <para>Those options correspond directly to options listed above in "Kernel Command Line". Both forms
1064       may be used equivalently for the system manager, but it is recommended to use the forms listed above in
1065       this context, because they are properly namespaced. When an option is specified both on the kernel
1066       command line, and as a normal command line argument, the latter has higher precedence.</para>
1067
1068       <para>When <command>systemd</command> is used a user manager, the kernel command line is ignored and
1069       the options described are understood. Nevertheless, <command>systemd</command> is usually started in
1070       this mode through the
1071       <citerefentry><refentrytitle>user@.service</refentrytitle><manvolnum>5</manvolnum></citerefentry>
1072       service, which is shared between all users, and it may be more convenient to use configuration files to
1073       modify settings, see
1074       <citerefentry><refentrytitle>systemd-user.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1075       or a drop-in that specifies one of the environment variables listed above in "Environment, see
1076       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
1077
1078       <variablelist>
1079         <varlistentry>
1080           <term><option>--unit=</option></term>
1081
1082           <listitem><para>Set default unit to activate on startup. If not specified, defaults to
1083           <filename>default.target</filename>. See <varname>systemd.unit=</varname> above.</para></listitem>
1084         </varlistentry>
1085
1086         <varlistentry>
1087           <term><option>--dump-core</option></term>
1088
1089           <listitem><para>Enable core dumping on crash. This switch has no effect when running as user
1090           instance. Same as <varname>systemd.dump_core=</varname> above.</para></listitem>
1091         </varlistentry>
1092
1093         <varlistentry>
1094           <term><option>--crash-vt=</option><replaceable>VT</replaceable></term>
1095
1096           <listitem><para>Switch to a specific virtual console (VT) on crash. This switch has no effect when
1097           running as user instance. Same as <varname>systemd.crash_chvt=</varname> above (but not the
1098           different spelling!).</para></listitem>
1099         </varlistentry>
1100
1101         <varlistentry>
1102           <term><option>--crash-shell</option></term>
1103
1104           <listitem><para>Run a shell on crash. This switch has no effect when running as user instance. See
1105           <varname>systemd.crash_shell=</varname> above.</para></listitem>
1106         </varlistentry>
1107
1108         <varlistentry>
1109           <term><option>--crash-reboot</option></term>
1110
1111           <listitem><para>Automatically reboot the system on crash. This switch has no effect when running as
1112           user instance. See <varname>systemd.crash_reboot</varname> above.</para></listitem>
1113         </varlistentry>
1114
1115         <varlistentry>
1116           <term><option>--confirm-spawn</option></term>
1117
1118           <listitem><para>Ask for confirmation when spawning processes. This switch has no effect when run as
1119           user instance. See <varname>systemd.confirm_spawn</varname> above.</para></listitem>
1120         </varlistentry>
1121
1122         <varlistentry>
1123           <term><option>--show-status</option></term>
1124
1125           <listitem><para>Show terse unit status information is shown on the console during boot-up and
1126           shutdown. See <varname>systemd.show_status</varname> above.</para></listitem>
1127         </varlistentry>
1128
1129         <varlistentry>
1130           <term><option>--log-target=</option></term>
1131
1132           <listitem><para>Set log target. See <varname>systemd.log_target</varname> above.</para></listitem>
1133         </varlistentry>
1134
1135         <varlistentry>
1136           <term><option>--log-level=</option></term>
1137
1138           <listitem><para>Set log level. See <varname>systemd.log_level</varname> above.</para></listitem>
1139         </varlistentry>
1140
1141         <varlistentry>
1142           <term><option>--log-color</option></term>
1143
1144           <listitem><para>Highlight important log messages. See <varname>systemd.log_color</varname> above.
1145           </para></listitem>
1146         </varlistentry>
1147
1148         <varlistentry>
1149           <term><option>--log-location</option></term>
1150
1151           <listitem><para>Include code location in log messages. See <varname>systemd.log_location</varname>
1152           above.</para></listitem>
1153         </varlistentry>
1154
1155         <varlistentry>
1156           <term><option>--machine-id=</option></term>
1157
1158           <listitem><para>Override the machine-id set on the hard drive. See
1159           <varname>systemd.machine_id=</varname> above.</para></listitem>
1160         </varlistentry>
1161
1162         <varlistentry>
1163           <term><option>--service-watchdogs</option></term>
1164
1165           <listitem><para>Globally enable/disable all service watchdog timeouts and emergency actions. See
1166           <varname>systemd.service_watchdogs</varname> above.</para></listitem>
1167         </varlistentry>
1168
1169         <varlistentry>
1170           <term><option>--default-standard-output=</option></term>
1171           <term><option>--default-standard-error=</option></term>
1172
1173           <listitem><para>Sets the default output or error output for all services and sockets,
1174           respectively. See <varname>systemd.default_standard_output=</varname> and
1175           <varname>systemd.default_standard_error=</varname> above.</para></listitem>
1176         </varlistentry>
1177       </variablelist>
1178     </refsect2>
1179   </refsect1>
1180
1181   <refsect1>
1182     <title>Sockets and FIFOs</title>
1183
1184     <variablelist>
1185       <varlistentry>
1186         <term><filename>/run/systemd/notify</filename></term>
1187
1188         <listitem><para>Daemon status notification socket. This is an
1189         <constant>AF_UNIX</constant> datagram socket and is used to
1190         implement the daemon notification logic as implemented by
1191         <citerefentry><refentrytitle>sd_notify</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para></listitem>
1192
1193       </varlistentry>
1194
1195       <varlistentry>
1196         <term><filename>/run/systemd/private</filename></term>
1197
1198         <listitem><para>Used internally as communication channel
1199         between
1200         <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
1201         and the systemd process. This is an
1202         <constant>AF_UNIX</constant> stream socket. This interface is
1203         private to systemd and should not be used in external
1204         projects.</para></listitem>
1205       </varlistentry>
1206
1207       <varlistentry>
1208         <term><filename>/dev/initctl</filename></term>
1209
1210         <listitem><para>Limited compatibility support for the SysV
1211         client interface, as implemented by the
1212         <filename>systemd-initctl.service</filename> unit. This is a
1213         named pipe in the file system. This interface is obsolete and
1214         should not be used in new applications.</para></listitem>
1215       </varlistentry>
1216     </variablelist>
1217   </refsect1>
1218
1219   <refsect1>
1220     <title>See Also</title>
1221     <para>
1222       The <ulink url="https://www.freedesktop.org/wiki/Software/systemd/">systemd Homepage</ulink>,
1223       <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1224       <citerefentry project='man-pages'><refentrytitle>locale.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1225       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1226       <citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1227       <citerefentry><refentrytitle>systemd-notify</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1228       <citerefentry><refentrytitle>daemon</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1229       <citerefentry><refentrytitle>sd-daemon</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
1230       <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1231       <citerefentry><refentrytitle>systemd.special</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
1232       <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
1233       <citerefentry><refentrytitle>kernel-command-line</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1234       <citerefentry project='man-pages'><refentrytitle>bootup</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
1235       <citerefentry><refentrytitle>systemd.directives</refentrytitle><manvolnum>7</manvolnum></citerefentry>
1236     </para>
1237   </refsect1>
1238
1239 </refentry>