<?xml version='1.0'?> <!--*-nxml-*-->
-<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
-
<!-- SPDX-License-Identifier: LGPL-2.1+ -->
<refentry id="systemd-boot" conditional='ENABLE_EFI'
<refsect1>
<title>Description</title>
- <para><command>systemd-boot</command> (short: <command>sd-boot</command>) is a simple UEFI boot manager. It
- provides a graphical menu to select the entry to boot and an editor for the kernel command line. systemd-boot
- supports systems with UEFI firmware only.</para>
+ <para><command>systemd-boot</command> (short: <command>sd-boot</command>) is a simple UEFI boot
+ manager. It provides a graphical menu to select the entry to boot and an editor for the kernel command
+ line. <command>systemd-boot</command> supports systems with UEFI firmware only.</para>
- <para>systemd-boot loads boot entry information from the EFI system partition (ESP), usually mounted at
- <filename>/boot</filename>, <filename>/efi</filename>, or <filename>/boot/efi</filename> during OS
- runtime. Configuration file fragments, kernels, initrds and other EFI images to boot generally need to reside on
- the ESP. Linux kernels must be built with <option>CONFIG_EFI_STUB</option> to be able to be directly executed as an
- EFI image. During boot systemd-boot automatically assembles a list of boot entries from the following
- sources:</para>
+ <para><command>systemd-boot</command> loads boot entry information from the EFI system partition (ESP),
+ usually mounted at <filename>/efi/</filename>, <filename>/boot/</filename>, or
+ <filename>/boot/efi/</filename> during OS runtime, as well as from the Extended Boot Loader partition if
+ it exists (usually mounted to <filename>/boot/</filename>). Configuration file fragments, kernels,
+ initrds and other EFI images to boot generally need to reside on the ESP or the Extended Boot Loader
+ partition. Linux kernels must be built with <option>CONFIG_EFI_STUB</option> to be able to be directly
+ executed as an EFI image. During boot <command>systemd-boot</command> automatically assembles a list of
+ boot entries from the following sources:</para>
<itemizedlist>
<listitem><para>Boot entries defined with <ulink
- url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader
- Specification</ulink> description files located in <filename>/loader/entries/</filename> on the ESP. These
- usually describe Linux kernel images with associated initrd images, but alternatively may also describe
- arbitrary other EFI executables.</para></listitem>
+ url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink> description files
+ located in <filename>/loader/entries/</filename> on the ESP and the Extended Boot Loader
+ Partition. These usually describe Linux kernel images with associated initrd images, but alternatively
+ may also describe arbitrary other EFI executables.</para></listitem>
<listitem><para>Unified kernel images following the <ulink
- url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader
- Specification</ulink>, as executable EFI binaries in <filename>/EFI/Linux/</filename> on the ESP.
+ url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, as executable EFI
+ binaries in <filename>/EFI/Linux/</filename> on the ESP and the Extended Boot Loader Partition.
</para></listitem>
<listitem><para>The Microsoft Windows EFI boot manager, if installed</para></listitem>
<listitem><para>A reboot into the UEFI firmware setup option, if supported by the firmware</para></listitem>
</itemizedlist>
- <para><citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry> may be
- used to copy kernel images onto the ESP and to generate description files compliant with the Boot Loader
- Specification. <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> may be
- used from a running system to locate the ESP, list available entries, and install systemd-boot itself.</para>
+ <para><command>systemd-boot</command> supports the following features:</para>
- <para>systemd-boot will provide information about the time spent in UEFI firmware using the <ulink
- url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>. This information can be displayed
- using <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
- </para>
+ <itemizedlist>
+ <listitem><para>Basic boot manager configuration changes (such as timeout
+ configuration, default boot entry selection, …) may be made directly from the boot loader UI at
+ boot-time, as well as during system runtime with EFI variables.</para></listitem>
+
+ <listitem><para>The boot manager integrates with the <command>systemctl</command> command to implement
+ features such as <command>systemctl reboot --boot-loader-entry=…</command> (for rebooting into a
+ specific boot menu entry, i.e. "reboot into Windows") and <command>systemctl reboot
+ --boot-loader-menu=…</command> (for rebooting into the boot loader menu), by implementing the <ulink
+ url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>. See
+ <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> for
+ details.</para></listitem>
+
+ <listitem><para>An EFI variable set by the boot loader informs the OS about the ESP partition used
+ during boot. This is then used to automatically mount the correct ESP partition to
+ <filename>/efi/</filename> or <filename>/boot/</filename> during OS runtime. See
+ <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ for details.</para></listitem>
+
+ <listitem><para>The boot manager provides information about the boot time spent in UEFI firmware using
+ the <ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>. This
+ information can be displayed using
+ <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
+ </para></listitem>
+
+ <listitem><para>The boot manager implements boot counting and automatic fallback to older, working boot
+ entries on failure. See <ulink url="https://systemd.io/AUTOMATIC_BOOT_ASSESSMENT">Automatic Boot
+ Assessment</ulink>.</para></listitem>
+
+ <listitem><para>The boot manager optionally reads a random seed from the ESP partition, combines it
+ with a 'system token' stored in a persistent EFI variable and derives a random seed to use by the OS as
+ entropy pool initialization, providing a full entropy pool during early boot.</para></listitem>
+ </itemizedlist>
+
+ <para><citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ may be used from a running system to locate the ESP and the Extended Boot Loader Partition, list
+ available entries, and install <command>systemd-boot</command> itself.</para>
+
+ <para><citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ may be used to copy kernel images onto the ESP or the Extended Boot Loader Partition and to generate
+ description files compliant with the Boot Loader
+ Specification.</para>
</refsect1>
<refsect1>
<varlistentry>
<term><keycap>↵</keycap> (Enter)</term>
+ <term><keycap>→</keycap> (Right)</term>
<listitem><para>Boot selected entry</para></listitem>
</varlistentry>
<varlistentry>
<term><keycap>h</keycap></term>
<term><keycap>?</keycap></term>
+ <term><keycap>F1</keycap></term>
<listitem><para>Show a help screen</para></listitem>
</varlistentry>
</varlistentry>
</variablelist>
- <para>The following keys may be used during bootup or in the boot menu to
- directly boot a specific entry:</para>
+ <para>The following keys may be pressed during bootup or in the boot menu to directly boot a specific
+ entry:</para>
<variablelist>
<varlistentry>
</varlistentry>
</variablelist>
+ <para>The boot menu is shown when a non-zero menu timeout has been configured. If the menu timeout has
+ been set to zero, it is sufficient to press any key — before the boot loader initializes — to bring up
+ the boot menu, except for the keys listed immediately above as they directly boot into the selected boot
+ menu item. Note that depending on the firmware implementation the time window where key presses are
+ accepted before the boot loader initializes might be short. If the window is missed, reboot and try
+ again, possibly pressing a suitable key (e.g. the space bar) continuously; on most systems it should be
+ possible to hit the time window after a few attempts. To avoid this problem, consider setting a non-zero
+ timeout, thus showing the boot menu unconditionally. Some desktop environments might offer an option to
+ directly boot into the boot menu, to avoid the problem altogether. Alternatively, use the command line
+ <command>systemctl reboot --boot-loader-menu=0</command> from the shell.</para>
+
<para>In the editor, most keys simply insert themselves, but the following keys
may be used to perform additional actions:</para>
<refsect1>
<title>Files</title>
- <para>The files systemd-boot reads generally reside on the UEFI ESP which is usually mounted to
- <filename>/boot/</filename>, <filename>/efi/</filename> or <filename>/boot/efi</filename> during OS
- runtime. systemd-boot reads runtime configuration such as the boot timeout and default entry from
- <filename>/loader/loader.conf</filename> on the ESP (in combination with data read from EFI variables). See
- <citerefentry><refentrytitle>loader.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Boot entry
- description files following the <ulink
- url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader
- Specification</ulink> are read from <filename>/loader/entries/</filename> on the ESP. Unified kernel boot entries
- following the <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot
- Loader Specification</ulink> are read from <filename>/EFI/Linux/</filename> on the ESP.</para>
+ <para>The files <command>systemd-boot</command> processes generally reside on the UEFI ESP which is
+ usually mounted to <filename>/efi/</filename>, <filename>/boot/</filename> or
+ <filename>/boot/efi/</filename> during OS runtime. It also processes files on the Extended Boot Loader
+ partition which is typically mounted to <filename>/boot/</filename>, if it
+ exists. <command>systemd-boot</command> reads runtime configuration such as the boot timeout and default
+ entry from <filename>/loader/loader.conf</filename> on the ESP (in combination with data read from EFI
+ variables). See
+ <citerefentry><refentrytitle>loader.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Boot
+ entry description files following the <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot
+ Loader Specification</ulink> are read from <filename>/loader/entries/</filename> on the ESP and the
+ Extended Boot Loader partition. Unified kernel boot entries following the <ulink
+ url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink> are read from
+ <filename>/EFI/Linux/</filename> on the ESP and the Extended Boot Loader partition. Optionally, a random
+ seed for early boot entropy pool provisioning is stored in <filename>/loader/random-seed</filename> in
+ the ESP.</para>
</refsect1>
<refsect1>
UUID <literal>4a67b082-0a4c-41cf-b6c7-440b29bb8c4</literal>, for communication between the OS and the boot
loader:</para>
- <variablelist>
+ <variablelist class='efi-variables'>
<varlistentry>
<term><varname>LoaderBootCountPath</varname></term>
<listitem><para>If boot counting is enabled, contains the path to the file in whose name the boot counters are
is maintained persistently, while <varname>LoaderConfigTimeoutOneShot</varname> is a one-time override which is
read once (in which case it takes precedence over <varname>LoaderConfigTimeout</varname>) and then
removed. <varname>LoaderConfigTimeout</varname> may be manipulated with the
- <keycap>t</keycap>/<keycap>T</keycap> keys, see above.)</para></listitem>
+ <keycap>t</keycap>/<keycap>T</keycap> keys, see above.</para></listitem>
</varlistentry>
<varlistentry>
boots. <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
<option>set-default</option> and <option>set-oneshot</option> commands make use of these variables. The boot
loader modifies <varname>LoaderEntryDefault</varname> on request, when the <keycap>d</keycap> key is used, see
- above.)</para></listitem>
+ above.</para></listitem>
</varlistentry>
<varlistentry>
<listitem><para>Information about the time spent in various parts of the boot loader. Set by the boot
loader. Use <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- to view this data. These variables are defined by the <ulink
- url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>.</para></listitem>
+ to view this data. </para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>LoaderRandomSeed</varname></term>
+
+ <listitem><para>A binary random seed <command>systemd-boot</command> may optionally pass to the
+ OS. This is a volatile EFI variable that is hashed at boot from the combination of a random seed
+ stored in the ESP (in <filename>/loader/random-seed</filename>) and a "system token" persistently
+ stored in the EFI variable <varname>LoaderSystemToken</varname> (see below). During early OS boot the
+ system manager reads this variable and passes it to the OS kernel's random pool, crediting the full
+ entropy it contains. This is an efficient way to ensure the system starts up with a fully initialized
+ kernel random pool — as early as the initial RAM disk phase. <command>systemd-boot</command> reads
+ the random seed from the ESP, combines it with the "system token", and both derives a new random seed
+ to update in-place the seed stored in the ESP, and the random seed to pass to the OS from it via
+ SHA256 hashing in counter mode. This ensures that different physical systems that boot the same
+ "golden" OS image — i.e. containing the same random seed file in the ESP — will still pass a
+ different random seed to the OS. It is made sure the random seed stored in the ESP is fully
+ overwritten before the OS is booted, to ensure different random seed data is used between subsequent
+ boots.</para>
+
+ <para>See <ulink url="https://systemd.io/RANDOM_SEEDS">Random Seeds</ulink> for
+ further information.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>LoaderSystemToken</varname></term>
+
+ <listitem><para>A binary random data field, that is used for generating the random seed to pass to
+ the OS (see above). Note that this random data is generally only generated once, during OS
+ installation, and is then never updated again.</para></listitem>
</varlistentry>
</variablelist>
+
+ <para>Many of these variables are defined by the <ulink
+ url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>.</para>
</refsect1>
<refsect1>
<para><command>systemd-boot</command> implements a simple boot counting mechanism on top of the <ulink
url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, for automatic and unattended
- fallback to older kernel versions/boot loader entries when a specific entry continously fails. Any boot loader
+ fallback to older kernel versions/boot loader entries when a specific entry continuously fails. Any boot loader
entry file and unified kernel image file that contains a <literal>+</literal> followed by one or two numbers (if
two they need to be separated by a <literal>-</literal>), before the <filename>.conf</filename> or
<filename>.efi</filename> suffix is subject to boot counting: the first of the two numbers ('tries left') is
considered 'good' from then on.</para>
<para>The boot menu takes the 'tries left' counter into account when sorting the menu entries: entries in 'bad'
- state are ordered at the end of the list, and entries in 'good' or 'indeterminate' at the beginning. The user can
+ state are ordered at the beginning of the list, and entries in 'good' or 'indeterminate' at the end. The user can
freely choose to boot any entry of the menu, including those already marked 'bad'. If the menu entry to boot is
- automatically determined, this means that 'good' or 'indeterminate' entries are generally preferred (as the top item of
- the menu is the one booted by default), and 'bad' entries will only be considered if there are no 'good' or
+ automatically determined, this means that 'good' or 'indeterminate' entries are generally preferred (as the bottom
+ item of the menu is the one booted by default), and 'bad' entries will only be considered if there are no 'good' or
'indeterminate' entries left.</para>
<para>The <citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry> kernel
<citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>loader.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
<citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-boot-system-token.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>,
<ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>
projects / thirdparty / systemd.git / blobdiff