man/systemd-boot-system-token.service.xml

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   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-boot-system-token.service" conditional='ENABLE_EFI'
   7           xmlns:xi="http://www.w3.org/2001/XInclude">
   8
   9   <refentryinfo>
  10     <title>systemd-boot-system-token.service</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>systemd-boot-system-token.service</refentrytitle>
  16     <manvolnum>8</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>systemd-boot-system-token.service</refname>
  21     <refpurpose>Generate an initial boot loader system token and random seed</refpurpose>
  22   </refnamediv>
  23
  24   <refsynopsisdiv>
  25     <para><filename>systemd-boot-system-token.service</filename></para>
  26   </refsynopsisdiv>
  27
  28   <refsect1>
  29     <title>Description</title>
  30
  31     <para><filename>systemd-boot-system-token.service</filename> is a system service that automatically
  32     generates a 'system token' to store in an EFI variable in the system's NVRAM and a random seed to store
  33     on the EFI System Partition ESP on disk. The boot loader may then combine these two randomized data
  34     fields by cryptographic hashing, and pass it to the OS it boots as initialization seed for its entropy
  35     pool. The random seed stored in the ESP is refreshed on each reboot ensuring that multiple subsequent
  36     boots will boot with different seeds. The 'system token' is generated randomly once, and then
  37     persistently stored in the system's EFI variable storage.</para>
  38
  39     <para>The <filename>systemd-boot-system-token.service</filename> unit invokes the <command>bootctl
  40     random-seed</command> command, which updates the random seed in the ESP, and initializes the 'system
  41     token' if it's not initialized yet. The service is conditionalized so that it is run only when all of the
  42     below apply:</para>
  43
  44     <itemizedlist>
  45       <listitem><para>A boot loader is used that implements the <ulink
  46       url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink> (which defines the 'system
  47       token' concept).</para></listitem>
  48
  49       <listitem><para>Either a 'system token' was not set yet, or the boot loader has not passed the OS a
  50       random seed yet (and thus most likely has been missing the random seed file in the
  51       ESP).</para></listitem>
  52
  53       <listitem><para>The system is not running in a VM environment. This case is explicitly excluded since
  54       on VM environments the ESP backing storage and EFI variable storage is typically not physically
  55       separated and hence booting the same OS image in multiple instances would replicate both, thus reusing
  56       the same random seed and 'system token' among all instances, which defeats its purpose. Note that it's
  57       still possible to use boot loader random seed provisioning in this mode, but the automatic logic
  58       implemented by this service has no effect then, and the user instead has to manually invoke the
  59       <command>bootctl random-seed</command> acknowledging these restrictions.</para></listitem>
  60     </itemizedlist>
  61
  62     <para>For further details see
  63     <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, regarding
  64     the command this service invokes.</para>
  65   </refsect1>
  66
  67   <refsect1>
  68     <title>See Also</title>
  69     <para>
  70       <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  71       <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
  72       <citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry>
  73     </para>
  74   </refsect1>
  75
  76 </refentry>