mirror of
https://github.com/systemd/systemd.git
synced 2024-11-27 20:23:36 +08:00
102 lines
6.1 KiB
XML
102 lines
6.1 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
|
|
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
|
|
|
|
<refentry id="systemd-boot-random-seed.service" conditional='ENABLE_BOOTLOADER'
|
|
xmlns:xi="http://www.w3.org/2001/XInclude">
|
|
|
|
<refentryinfo>
|
|
<title>systemd-boot-random-seed.service</title>
|
|
<productname>systemd</productname>
|
|
</refentryinfo>
|
|
|
|
<refmeta>
|
|
<refentrytitle>systemd-boot-random-seed.service</refentrytitle>
|
|
<manvolnum>8</manvolnum>
|
|
</refmeta>
|
|
|
|
<refnamediv>
|
|
<refname>systemd-boot-random-seed.service</refname>
|
|
<refpurpose>Refresh boot loader random seed at boot</refpurpose>
|
|
</refnamediv>
|
|
|
|
<refsynopsisdiv>
|
|
<para><filename>systemd-boot-random-seed.service</filename></para>
|
|
</refsynopsisdiv>
|
|
|
|
<refsect1>
|
|
<title>Description</title>
|
|
|
|
<para><filename>systemd-boot-random-seed.service</filename> is a system service that automatically
|
|
refreshes the boot loader random seed stored in the EFI System Partition (ESP), from the Linux kernel
|
|
entropy pool. The boot loader random seed is primarily consumed and updated by
|
|
<citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry> from the
|
|
UEFI environment (or
|
|
<citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry> if the
|
|
former is not used, but the latter is), and passed as initial RNG seed to the OS. It is an effective way
|
|
to ensure the OS comes up with a random pool that is fully initialized.</para>
|
|
|
|
<para>The service also automatically generates a 'system token' to store in an EFI variable in the
|
|
system's NVRAM. The boot loader may then combine the on-disk random seed and the system token by
|
|
cryptographic hashing, and pass it to the OS it boots as initialization seed for its entropy pool. Note:
|
|
the random seed stored in the ESP is refreshed on <emphasis>every</emphasis> reboot ensuring that
|
|
multiple subsequent boots will boot with different seeds. On the other hand, the system token is
|
|
generated randomly <emphasis>once</emphasis>, and then persistently stored in the system's EFI variable
|
|
storage, ensuring the same disk image won't result in the same series of boot loader seed values if used
|
|
on multiple systems in parallel.</para>
|
|
|
|
<para>The <filename>systemd-boot-random-seed.service</filename> unit invokes the <command>bootctl
|
|
random-seed</command> command, which updates the random seed in the ESP, and initializes the system
|
|
token if it's not initialized yet. The service is conditionalized so that it is run only when a boot
|
|
loader is used that implements the <ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader
|
|
Interface</ulink>.</para> <para>For further details see
|
|
<citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>, regarding
|
|
the command this service invokes.</para>
|
|
|
|
<para>Note the relationship between <filename>systemd-boot-random-seed.service</filename> and
|
|
<citerefentry><refentrytitle>systemd-random-seed</refentrytitle><manvolnum>8</manvolnum></citerefentry>. The
|
|
former maintains the random seed consumed and updated by the boot environment (i.e. by
|
|
<citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry> or
|
|
<citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry>), the
|
|
latter maintains a random seed consumed and updated by the OS itself. The former ensures that the OS has
|
|
a filled entropy pool already during earliest boot when regular disk access is not available yet
|
|
(i.e. when the OS random seed cannot be loaded yet). The latter is processed much later, once writable
|
|
disk access is available. Thus it cannot be used to seed the initial boot phase, but typically has much
|
|
higher quality of entropy. Both files are consumed and updated at boot, but at different
|
|
times. Specifically:</para>
|
|
|
|
<orderedlist>
|
|
<listitem><para>In UEFI mode, the
|
|
<citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry> or
|
|
<citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry>
|
|
components load the boot loader random seed from the ESP, hash it with available entropy and the system
|
|
token, and then update it on disk. A derived seed is passed to the kernel which writes it to its
|
|
entropy pool.</para></listitem>
|
|
|
|
<listitem><para>In userspace the <filename>systemd-random-seed.service</filename> service loads the OS
|
|
random seed, writes it to the kernel entropy pool, and then updates it on disk with a new value derived
|
|
from the kernel entropy pool.</para></listitem>
|
|
|
|
<listitem><para>In userspace the <filename>systemd-boot-random-seed.service</filename> service updates
|
|
the boot loader random seed with a new value derived from the kernel entropy pool.</para></listitem>
|
|
</orderedlist>
|
|
|
|
<para>This logic should ensure that the kernel's entropy pool is seeded during earliest bool already, if
|
|
possible, but the highest quality entropy is propagated back to both on-disk seeds.</para>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
<title>See Also</title>
|
|
<para><simplelist type="inline">
|
|
<member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>systemd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>systemd-stub</refentrytitle><manvolnum>7</manvolnum></citerefentry></member>
|
|
<member><citerefentry><refentrytitle>systemd-random-seed.service</refentrytitle><manvolnum>8</manvolnum></citerefentry></member>
|
|
</simplelist></para>
|
|
</refsect1>
|
|
|
|
</refentry>
|