man/kernel-command-line.xml

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   5
   6 <refentry id="kernel-command-line">
   7
   8   <refentryinfo>
   9     <title>kernel-command-line</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>kernel-command-line</refentrytitle>
  15     <manvolnum>7</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>kernel-command-line</refname>
  20     <refpurpose>Kernel command line parameters</refpurpose>
  21   </refnamediv>
  22
  23   <refsynopsisdiv>
  24     <para><filename>/proc/cmdline</filename></para>
  25   </refsynopsisdiv>
  26
  27   <refsect1>
  28     <title>Description</title>
  29
  30     <para>The kernel, the programs running in the initrd and in the host system may be configured at boot via
  31     kernel command line arguments. In addition, various systemd tools look at the EFI variable
  32     <literal>SystemdOptions</literal> (if available). Both sources are combined, but the kernel command line
  33     has higher priority. Please note that <emphasis>the EFI variable is only used by systemd tools, and is
  34     ignored by the kernel and other user space tools</emphasis>, so it is not a replacement for the kernel
  35     command line.</para>
  36
  37     <para>For command line parameters understood by the kernel, please
  38     see
  39     <ulink url="https://docs.kernel.org/admin-guide/kernel-parameters.html"><filename>kernel-parameters.html</filename></ulink>
  40     and
  41     <citerefentry project='man-pages'><refentrytitle>bootparam</refentrytitle><manvolnum>7</manvolnum></citerefentry>.</para>
  42
  43     <para>For command line parameters understood by the initrd, see
  44     <citerefentry project='man-pages'><refentrytitle>dracut.cmdline</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
  45     or the documentation of the specific initrd implementation of your
  46     installation.</para>
  47   </refsect1>
  48
  49   <refsect1>
  50     <title>Core OS Command Line Arguments</title>
  51
  52     <variablelist class='kernel-commandline-options'>
  53       <varlistentry>
  54         <term><varname>systemd.unit=</varname></term>
  55         <term><varname>rd.systemd.unit=</varname></term>
  56         <term><varname>systemd.dump_core</varname></term>
  57         <term><varname>systemd.early_core_pattern=</varname></term>
  58         <term><varname>systemd.crash_chvt</varname></term>
  59         <term><varname>systemd.crash_shell</varname></term>
  60         <term><varname>systemd.crash_reboot</varname></term>
  61         <term><varname>systemd.confirm_spawn</varname></term>
  62         <term><varname>systemd.service_watchdogs</varname></term>
  63         <term><varname>systemd.show_status</varname></term>
  64         <term><varname>systemd.status_unit_format=</varname></term>
  65         <term><varname>systemd.log_target=</varname></term>
  66         <term><varname>systemd.log_level=</varname></term>
  67         <term><varname>systemd.log_location=</varname></term>
  68         <term><varname>systemd.log_color</varname></term>
  69         <term><varname>systemd.default_standard_output=</varname></term>
  70         <term><varname>systemd.default_standard_error=</varname></term>
  71         <term><varname>systemd.setenv=</varname></term>
  72         <term><varname>systemd.machine_id=</varname></term>
  73         <term><varname>systemd.set_credential=</varname></term>
  74         <term><varname>systemd.import_credentials=</varname></term>
  75         <listitem>
  76           <para>Parameters understood by the system and service
  77           manager to control system behavior. For details, see
  78           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
  79         </listitem>
  80       </varlistentry>
  81
  82       <varlistentry>
  83         <term><varname>systemd.mask=</varname></term>
  84         <term><varname>systemd.wants=</varname></term>
  85         <term><varname>systemd.debug_shell</varname></term>
  86         <listitem>
  87           <para>Additional parameters understood by
  88           <citerefentry><refentrytitle>systemd-debug-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
  89           to mask or start specific units at boot, or invoke a debug
  90           shell on tty9.</para>
  91         </listitem>
  92       </varlistentry>
  93
  94       <varlistentry>
  95         <term><varname>systemd.run=</varname></term>
  96         <term><varname>systemd.run_success_action=</varname></term>
  97         <term><varname>systemd.run_failure_action=</varname></term>
  98         <listitem>
  99           <para>Additional parameters understood by
 100           <citerefentry><refentrytitle>systemd-run-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>, to
 101           run a command line specified on the kernel command line as system service after booting up.</para>
 102         </listitem>
 103       </varlistentry>
 104
 105       <varlistentry>
 106         <term><varname>systemd.early_core_pattern=</varname></term>
 107         <listitem>
 108           <para>During early boot, the generation of core dump files is disabled until a core dump handler (if any)
 109           takes over. This parameter allows specifying an absolute path where core dump files should be stored until
 110           a handler is installed. The path should be absolute and may contain specifiers, see
 111           <citerefentry project='man-pages'><refentrytitle>core</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details.</para>
 112         </listitem>
 113       </varlistentry>
 114
 115       <varlistentry>
 116         <term><varname>systemd.restore_state=</varname></term>
 117         <listitem>
 118           <para>This parameter is understood by several system tools
 119           to control whether or not they should restore system state
 120           from the previous boot. For details, see
 121           <citerefentry><refentrytitle>systemd-backlight@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 122           and
 123           <citerefentry><refentrytitle>systemd-rfkill.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
 124           </para>
 125         </listitem>
 126       </varlistentry>
 127
 128       <varlistentry>
 129         <term><varname>systemd.volatile=</varname></term>
 130         <listitem>
 131           <para>This parameter controls whether the system shall boot up in volatile mode. Takes a boolean argument, or
 132           the special value <literal>state</literal>. If false (the default), normal boot mode is selected, the root
 133           directory and <filename>/var/</filename> are mounted as specified on the kernel command line or
 134           <filename>/etc/fstab</filename>, or otherwise configured. If true, full state-less boot mode is selected. In
 135           this case the root directory is mounted as volatile memory file system (<literal>tmpfs</literal>), and only
 136           <filename>/usr/</filename> is mounted from the file system configured as root device, in read-only mode. This
 137           enables fully state-less boots were the vendor-supplied OS is used as shipped, with only default
 138           configuration and no stored state in effect, as <filename>/etc/</filename> and <filename>/var/</filename> (as
 139           well as all other resources shipped in the root file system) are reset at boot and lost on shutdown. If this
 140           setting is set to <literal>state</literal> the root file system is mounted read-only, however
 141           <filename>/var/</filename> is mounted as a volatile memory file system (<literal>tmpfs</literal>), so that the
 142           system boots up with the normal configuration applied, but all state reset at boot and lost at shutdown. If
 143           this setting is set to <literal>overlay</literal> the root file system is set up as
 144           <literal>overlayfs</literal> mount combining the read-only root directory with a writable
 145           <literal>tmpfs</literal>, so that no modifications are made to disk, but the file system may be modified
 146           nonetheless with all changes being lost at reboot. For details, see
 147           <citerefentry><refentrytitle>systemd-volatile-root.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 148           and
 149           <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 150         </listitem>
 151       </varlistentry>
 152
 153       <varlistentry>
 154         <term><varname>quiet</varname></term>
 155         <listitem>
 156           <para>Parameter understood by both the kernel and the system
 157           and service manager to control console log verbosity. For
 158           details, see
 159           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
 160         </listitem>
 161       </varlistentry>
 162
 163       <varlistentry>
 164         <term><varname>debug</varname></term>
 165         <listitem>
 166           <para>Parameter understood by both the kernel and the system
 167           and service manager to control console log verbosity. For
 168           details, see
 169           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
 170         </listitem>
 171       </varlistentry>
 172
 173       <varlistentry>
 174         <term><varname>-b</varname></term>
 175         <term><varname>rd.emergency</varname></term>
 176         <term><varname>emergency</varname></term>
 177         <term><varname>rd.rescue</varname></term>
 178         <term><varname>rescue</varname></term>
 179         <term><varname>single</varname></term>
 180         <term><varname>s</varname></term>
 181         <term><varname>S</varname></term>
 182         <term><varname>1</varname></term>
 183         <term><varname>2</varname></term>
 184         <term><varname>3</varname></term>
 185         <term><varname>4</varname></term>
 186         <term><varname>5</varname></term>
 187         <listitem>
 188           <para>Parameters understood by the system and service
 189           manager, as compatibility and convenience options. For details, see
 190           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
 191         </listitem>
 192       </varlistentry>
 193
 194       <varlistentry>
 195         <term><varname>locale.LANG=</varname></term>
 196         <term><varname>locale.LANGUAGE=</varname></term>
 197         <term><varname>locale.LC_CTYPE=</varname></term>
 198         <term><varname>locale.LC_NUMERIC=</varname></term>
 199         <term><varname>locale.LC_TIME=</varname></term>
 200         <term><varname>locale.LC_COLLATE=</varname></term>
 201         <term><varname>locale.LC_MONETARY=</varname></term>
 202         <term><varname>locale.LC_MESSAGES=</varname></term>
 203         <term><varname>locale.LC_PAPER=</varname></term>
 204         <term><varname>locale.LC_NAME=</varname></term>
 205         <term><varname>locale.LC_ADDRESS=</varname></term>
 206         <term><varname>locale.LC_TELEPHONE=</varname></term>
 207         <term><varname>locale.LC_MEASUREMENT=</varname></term>
 208         <term><varname>locale.LC_IDENTIFICATION=</varname></term>
 209         <listitem>
 210           <para>Parameters understood by the system and service
 211           manager to control locale and language settings. For
 212           details, see
 213           <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>.</para>
 214         </listitem>
 215       </varlistentry>
 216
 217       <varlistentry>
 218         <term><varname>fsck.mode=</varname></term>
 219         <term><varname>fsck.repair=</varname></term>
 220
 221         <listitem>
 222           <para>Parameters understood by the file system checker
 223           services. For details, see
 224           <citerefentry><refentrytitle>systemd-fsck@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 225         </listitem>
 226       </varlistentry>
 227
 228       <varlistentry>
 229         <term><varname>quotacheck.mode=</varname></term>
 230
 231         <listitem>
 232           <para>Parameter understood by the file quota checker
 233           service. For details, see
 234           <citerefentry><refentrytitle>systemd-quotacheck.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 235         </listitem>
 236       </varlistentry>
 237
 238       <varlistentry>
 239         <term><varname>systemd.journald.forward_to_syslog=</varname></term>
 240         <term><varname>systemd.journald.forward_to_kmsg=</varname></term>
 241         <term><varname>systemd.journald.forward_to_console=</varname></term>
 242         <term><varname>systemd.journald.forward_to_wall=</varname></term>
 243
 244         <listitem>
 245           <para>Parameters understood by the journal service. For
 246           details, see
 247           <citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 248         </listitem>
 249       </varlistentry>
 250
 251       <varlistentry>
 252         <term><varname>vconsole.keymap=</varname></term>
 253         <term><varname>vconsole.keymap_toggle=</varname></term>
 254         <term><varname>vconsole.font=</varname></term>
 255         <term><varname>vconsole.font_map=</varname></term>
 256         <term><varname>vconsole.font_unimap=</varname></term>
 257
 258         <listitem>
 259           <para>Parameters understood by the virtual console setup logic. For details, see
 260           <citerefentry><refentrytitle>vconsole.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 261         </listitem>
 262       </varlistentry>
 263
 264       <varlistentry>
 265         <term><varname>udev.log_level=</varname></term>
 266         <term><varname>rd.udev.log_level=</varname></term>
 267         <term><varname>udev.children_max=</varname></term>
 268         <term><varname>rd.udev.children_max=</varname></term>
 269         <term><varname>udev.exec_delay=</varname></term>
 270         <term><varname>rd.udev.exec_delay=</varname></term>
 271         <term><varname>udev.event_timeout=</varname></term>
 272         <term><varname>rd.udev.event_timeout=</varname></term>
 273         <term><varname>udev.timeout_signal=</varname></term>
 274         <term><varname>rd.udev.timeout_signal=</varname></term>
 275         <term><varname>udev.blockdev_read_only</varname></term>
 276         <term><varname>rd.udev.blockdev_read_only</varname></term>
 277         <term><varname>net.ifnames=</varname></term>
 278         <term><varname>net.naming-scheme=</varname></term>
 279
 280         <listitem>
 281           <para>Parameters understood by the device event managing
 282           daemon. For details, see
 283           <citerefentry><refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 284         </listitem>
 285       </varlistentry>
 286
 287       <varlistentry>
 288         <term><varname>plymouth.enable=</varname></term>
 289
 290         <listitem>
 291           <para>May be used to disable the Plymouth boot splash. For
 292           details, see
 293           <citerefentry project='die-net'><refentrytitle>plymouth</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 294         </listitem>
 295       </varlistentry>
 296
 297       <varlistentry>
 298         <term><varname>luks=</varname></term>
 299         <term><varname>rd.luks=</varname></term>
 300         <term><varname>luks.crypttab=</varname></term>
 301         <term><varname>rd.luks.crypttab=</varname></term>
 302         <term><varname>luks.name=</varname></term>
 303         <term><varname>rd.luks.name=</varname></term>
 304         <term><varname>luks.uuid=</varname></term>
 305         <term><varname>rd.luks.uuid=</varname></term>
 306         <term><varname>luks.options=</varname></term>
 307         <term><varname>rd.luks.options=</varname></term>
 308         <term><varname>luks.key=</varname></term>
 309         <term><varname>rd.luks.key=</varname></term>
 310
 311         <listitem>
 312           <para>Configures the LUKS full-disk encryption logic at
 313           boot. For details, see
 314           <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 315         </listitem>
 316       </varlistentry>
 317
 318       <varlistentry>
 319         <term><varname>fstab=</varname></term>
 320         <term><varname>rd.fstab=</varname></term>
 321
 322         <listitem>
 323           <para>Configures the <filename>/etc/fstab</filename> logic
 324           at boot. For details, see
 325           <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 326         </listitem>
 327       </varlistentry>
 328
 329       <varlistentry>
 330         <term><varname>root=</varname></term>
 331         <term><varname>rootfstype=</varname></term>
 332         <term><varname>rootflags=</varname></term>
 333         <term><varname>ro</varname></term>
 334         <term><varname>rw</varname></term>
 335
 336         <listitem>
 337           <para>Configures the root file system and its file system
 338           type and mount options, as well as whether it shall be
 339           mounted read-only or read-write initially. For details,
 340           see
 341           <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 342         </listitem>
 343       </varlistentry>
 344
 345       <varlistentry>
 346         <term><varname>mount.usr=</varname></term>
 347         <term><varname>mount.usrfstype=</varname></term>
 348         <term><varname>mount.usrflags=</varname></term>
 349
 350         <listitem>
 351           <para>Configures the /usr file system (if required) and
 352           its file system type and mount options. For details, see
 353           <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 354         </listitem>
 355       </varlistentry>
 356
 357       <varlistentry>
 358         <term><varname>veritytab=</varname></term>
 359         <term><varname>rd.veritytab=</varname></term>
 360         <term><varname>roothash=</varname></term>
 361         <term><varname>systemd.verity=</varname></term>
 362         <term><varname>rd.systemd.verity=</varname></term>
 363         <term><varname>systemd.verity_root_data=</varname></term>
 364         <term><varname>systemd.verity_root_hash=</varname></term>
 365         <term><varname>systemd.verity.root_options=</varname></term>
 366         <term><varname>usrhash=</varname></term>
 367         <term><varname>systemd.verity_usr_data=</varname></term>
 368         <term><varname>systemd.verity_usr_hash=</varname></term>
 369         <term><varname>systemd.verity_usr_options=</varname></term>
 370         <listitem>
 371           <para>Configures the integrity protection root hash for the root and <filename>/usr</filename> file systems, and other related
 372           parameters. For details, see
 373           <citerefentry><refentrytitle>systemd-veritysetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 374         </listitem>
 375       </varlistentry>
 376
 377       <varlistentry>
 378         <term><varname>systemd.getty_auto=</varname></term>
 379
 380         <listitem>
 381           <para>Configures whether the <filename>serial-getty@.service</filename> will run.
 382           For details, see
 383           <citerefentry><refentrytitle>systemd-getty-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 384         </listitem>
 385       </varlistentry>
 386
 387       <varlistentry>
 388         <term><varname>systemd.gpt_auto=</varname></term>
 389         <term><varname>rd.systemd.gpt_auto=</varname></term>
 390
 391         <listitem>
 392           <para>Configures whether GPT based partition auto-discovery
 393           shall be attempted. For details, see
 394           <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 395         </listitem>
 396       </varlistentry>
 397
 398       <varlistentry>
 399         <term><varname>systemd.default_timeout_start_sec=</varname></term>
 400
 401         <listitem>
 402           <para>Overrides the default start job timeout <varname>DefaultTimeoutStartSec=</varname> at
 403           boot. For details, see
 404           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 405         </listitem>
 406       </varlistentry>
 407
 408       <varlistentry>
 409         <term><varname>systemd.watchdog_device=</varname></term>
 410
 411         <listitem>
 412           <para>Overrides the watchdog device path <varname>WatchdogDevice=</varname>. For details, see
 413           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 414         </listitem>
 415       </varlistentry>
 416
 417       <varlistentry>
 418         <term><varname>systemd.watchdog_sec=</varname></term>
 419
 420         <listitem>
 421           <para>Overrides the watchdog timeout settings otherwise configured with
 422           <varname>RuntimeWatchdog=</varname>, <varname>RebootWatchdog=</varname> and
 423           <varname>KExecWatchdogSec=</varname>. Takes a time value (if no unit is specified, seconds is the
 424           implicitly assumed time unit) or the special strings <literal>off</literal> or
 425           <literal>default</literal>. For details, see
 426           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 427         </listitem>
 428       </varlistentry>
 429
 430       <varlistentry>
 431         <term><varname>systemd.watchdog_pre_sec=</varname></term>
 432
 433         <listitem>
 434           <para>Overrides the watchdog pre-timeout settings otherwise configured with
 435           <varname>RuntimeWatchdogPreSec=</varname>. Takes a time value (if no unit is specified, seconds is the
 436           implicitly assumed time unit) or the special strings <literal>off</literal> or
 437           <literal>default</literal>. For details, see
 438           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 439         </listitem>
 440       </varlistentry>
 441
 442       <varlistentry>
 443         <term><varname>systemd.watchdog_pretimeout_governor=</varname></term>
 444
 445         <listitem>
 446           <para>Overrides the watchdog pre-timeout settings otherwise configured with
 447           <varname>RuntimeWatchdogPreGovernor=</varname>. Takes a string value. For details, see
 448           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para>
 449         </listitem>
 450       </varlistentry>
 451
 452       <varlistentry>
 453         <term><varname>systemd.cpu_affinity=</varname></term>
 454
 455         <listitem>
 456           <para>Overrides the CPU affinity mask for the service manager and the default for all child
 457           processes it forks. This takes precedence over <varname>CPUAffinity=</varname>, see
 458           <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
 459           for details.</para>
 460         </listitem>
 461       </varlistentry>
 462
 463       <varlistentry>
 464         <term><varname>modules_load=</varname></term>
 465         <term><varname>rd.modules_load=</varname></term>
 466
 467         <listitem>
 468           <para>Load a specific kernel module early at boot. For
 469           details, see
 470           <citerefentry><refentrytitle>systemd-modules-load.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 471         </listitem>
 472       </varlistentry>
 473
 474       <varlistentry>
 475         <term><varname>resume=</varname></term>
 476         <term><varname>resumeflags=</varname></term>
 477
 478         <listitem>
 479           <para>Enables resume from hibernation using the specified
 480           device and mount options. All
 481           <citerefentry project='man-pages'><refentrytitle>fstab</refentrytitle><manvolnum>5</manvolnum></citerefentry>-like
 482           paths are supported. For details, see
 483           <citerefentry><refentrytitle>systemd-hibernate-resume-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
 484         </listitem>
 485       </varlistentry>
 486
 487       <varlistentry>
 488         <term><varname>systemd.firstboot=</varname></term>
 489
 490         <listitem><para>Takes a boolean argument, defaults to on. If off,
 491         <citerefentry><refentrytitle>systemd-firstboot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 492         will not query the user for basic system settings, even if the system boots up for the first time and
 493         the relevant settings are not initialized yet. Not to be confused with
 494         <varname>systemd.condition-first-boot=</varname> (see below), which overrides the result of the
 495         <varname>ConditionFirstBoot=</varname> unit file condition, and thus controls more than just
 496         <filename>systemd-firstboot.service</filename> behaviour.</para></listitem>
 497       </varlistentry>
 498
 499       <varlistentry>
 500         <term><varname>systemd.condition-needs-update=</varname></term>
 501
 502         <listitem><para>Takes a boolean argument. If specified, overrides the result of
 503         <varname>ConditionNeedsUpdate=</varname> unit condition checks. See
 504         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 505         details.</para></listitem>
 506       </varlistentry>
 507
 508       <varlistentry>
 509         <term><varname>systemd.condition-first-boot=</varname></term>
 510
 511         <listitem><para>Takes a boolean argument. If specified, overrides the result of
 512         <varname>ConditionFirstBoot=</varname> unit condition checks. See
 513         <citerefentry><refentrytitle>systemd.unit</refentrytitle><manvolnum>5</manvolnum></citerefentry> for
 514         details. Not to be confused with <varname>systemd.firstboot=</varname> which only controls behaviour
 515         of the <filename>systemd-firstboot.service</filename> system service but has no effect on the
 516         condition check (see above).</para></listitem>
 517       </varlistentry>
 518
 519       <varlistentry>
 520         <term><varname>systemd.clock-usec=</varname></term>
 521
 522         <listitem><para>Takes a decimal, numeric timestamp in µs since January 1st 1970, 00:00am, to set the
 523         system clock to. The system time is set to the specified timestamp early during boot. It is not
 524         propagated to the hardware clock (RTC).</para></listitem>
 525       </varlistentry>
 526
 527       <varlistentry>
 528         <term><varname>systemd.random-seed=</varname></term>
 529
 530         <listitem><para>Takes a base64 encoded random seed value to credit with full entropy to the kernel's
 531         random pool during early service manager initialization. This option is useful in testing
 532         environments where delays due to random pool initialization in entropy starved virtual machines shall
 533         be avoided.</para>
 534
 535         <para>Note that if this option is used the seed is accessible to unprivileged programs from
 536         <filename>/proc/cmdline</filename>. This option is hence a security risk when used outside of test
 537         systems, since the (possibly) only seed used for initialization of the kernel's entropy pool might be
 538         easily acquired by unprivileged programs.</para>
 539
 540         <para>It is recommended to pass 512 bytes of randomized data (as that matches the Linux kernel pool
 541         size), which may be generated with a command like the following:</para>
 542
 543         <programlisting>dd if=/dev/urandom bs=512 count=1 status=none | base64 -w 0</programlisting>
 544
 545         <para>Again: do not use this option outside of testing environments, it's a security risk elsewhere,
 546         as secret key material derived from the entropy pool can possibly be reconstructed by unprivileged
 547         programs.</para>
 548         </listitem>
 549       </varlistentry>
 550
 551       <varlistentry>
 552         <term><varname>systemd.hostname=</varname></term>
 553
 554         <listitem><para>Accepts a hostname to set during early boot. If specified takes precedence over what
 555         is set in <filename>/etc/hostname</filename>. Note that this does not bar later runtime changes to
 556         the hostname, it simply controls the initial hostname set during early boot.</para></listitem>
 557       </varlistentry>
 558     </variablelist>
 559   </refsect1>
 560
 561   <refsect1>
 562       <title>History</title>
 563
 564       <variablelist>
 565         <varlistentry>
 566           <term>systemd 252</term>
 567           <listitem><para>Kernel command-line arguments <varname>systemd.unified_cgroup_hierarchy</varname>
 568           and <varname>systemd.legacy_systemd_cgroup_controller</varname> were deprecated. Please switch to
 569           the unified cgroup hierarchy.</para></listitem>
 570         </varlistentry>
 571       </variablelist>
 572   </refsect1>
 573
 574   <refsect1>
 575       <title>See Also</title>
 576       <para>
 577         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 578         <citerefentry><refentrytitle>systemd-system.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 579         <citerefentry project='man-pages'><refentrytitle>bootparam</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 580         <citerefentry project='man-pages'><refentrytitle>dracut.cmdline</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
 581         <citerefentry><refentrytitle>systemd-debug-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 582         <citerefentry><refentrytitle>systemd-fsck@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 583         <citerefentry><refentrytitle>systemd-quotacheck.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 584         <citerefentry><refentrytitle>systemd-journald.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 585         <citerefentry><refentrytitle>systemd-vconsole-setup.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 586         <citerefentry><refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 587         <citerefentry project='die-net'><refentrytitle>plymouth</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 588         <citerefentry><refentrytitle>systemd-cryptsetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 589         <citerefentry><refentrytitle>systemd-veritysetup-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 590         <citerefentry><refentrytitle>systemd-fstab-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 591         <citerefentry><refentrytitle>systemd-getty-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 592         <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 593         <citerefentry><refentrytitle>systemd-volatile-root.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 594         <citerefentry><refentrytitle>systemd-modules-load.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 595         <citerefentry><refentrytitle>systemd-backlight@.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 596         <citerefentry><refentrytitle>systemd-rfkill.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 597         <citerefentry><refentrytitle>systemd-hibernate-resume-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 598         <citerefentry><refentrytitle>systemd-firstboot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 599         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 600       </para>
 601   </refsect1>
 602
 603 </refentry>