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| <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
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| <!-- SPDX-License-Identifier: LGPL-2.1+ --> |
| |
| <refentry id="systemd-boot" conditional='ENABLE_EFI' |
| xmlns:xi="http://www.w3.org/2001/XInclude"> |
| <refentryinfo> |
| <title>systemd-boot</title> |
| <productname>systemd</productname> |
| </refentryinfo> |
| |
| <refmeta> |
| <refentrytitle>systemd-boot</refentrytitle> |
| <manvolnum>7</manvolnum> |
| </refmeta> |
| |
| <refnamediv> |
| <refname>systemd-boot</refname> |
| <refname>sd-boot</refname> |
| <refpurpose>A simple UEFI boot manager</refpurpose> |
| </refnamediv> |
| |
| <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. <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>/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 |
| systemd-boot 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 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 and the Extended Boot Loader Partition. |
| </para></listitem> |
| |
| <listitem><para>The Microsoft Windows EFI boot manager, if installed</para></listitem> |
| |
| <listitem><para>The Apple MacOS X boot manager, if installed</para></listitem> |
| |
| <listitem><para>The EFI Shell binary, 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 or the Extended Boot Loader Partition 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 and the Extended Boot Loader Partition, list |
| available entries, and install <command>systemd-boot</command> itself.</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> |
| </refsect1> |
| |
| <refsect1> |
| <title>Key bindings</title> |
| <para>The following keys may be used in the boot menu:</para> |
| |
| <variablelist> |
| <varlistentry> |
| <term><keycap>↑</keycap> (Up)</term> |
| <term><keycap>↓</keycap> (Down)</term> |
| <term><keycap>j</keycap></term> |
| <term><keycap>k</keycap></term> |
| <term><keycap>PageUp</keycap></term> |
| <term><keycap>PageDown</keycap></term> |
| <term><keycap>Home</keycap></term> |
| <term><keycap>End</keycap></term> |
| <listitem><para>Navigate up/down in the entry list</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>↵</keycap> (Enter)</term> |
| <listitem><para>Boot selected entry</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>d</keycap></term> |
| <listitem><para>Make selected entry the default</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>e</keycap></term> |
| <listitem><para>Edit the kernel command line for selected entry</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>+</keycap></term> |
| <term><keycap>t</keycap></term> |
| <listitem><para>Increase the timeout before default entry is booted</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>-</keycap></term> |
| <term><keycap>T</keycap></term> |
| <listitem><para>Decrease the timeout</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>v</keycap></term> |
| <listitem><para>Show systemd-boot, UEFI, and firmware versions</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>P</keycap></term> |
| <listitem><para>Print status</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>Q</keycap></term> |
| <listitem><para>Quit</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>h</keycap></term> |
| <term><keycap>?</keycap></term> |
| <listitem><para>Show a help screen</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycombo><keycap>Ctrl</keycap><keycap>l</keycap></keycombo></term> |
| <listitem><para>Reprint the screen</para></listitem> |
| </varlistentry> |
| </variablelist> |
| |
| <para>The following keys may be used during bootup or in the boot menu to |
| directly boot a specific entry:</para> |
| |
| <variablelist> |
| <varlistentry> |
| <term><keycap>l</keycap></term> |
| <listitem><para>Linux</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>w</keycap></term> |
| <listitem><para>Windows</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>a</keycap></term> |
| <listitem><para>OS X</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>s</keycap></term> |
| <listitem><para>EFI shell</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>1</keycap></term> |
| <term><keycap>2</keycap></term> |
| <term><keycap>3</keycap></term> |
| <term><keycap>4</keycap></term> |
| <term><keycap>5</keycap></term> |
| <term><keycap>6</keycap></term> |
| <term><keycap>7</keycap></term> |
| <term><keycap>8</keycap></term> |
| <term><keycap>9</keycap></term> |
| <listitem><para>Boot entry number 1 … 9</para></listitem> |
| </varlistentry> |
| </variablelist> |
| |
| <para>In the editor, most keys simply insert themselves, but the following keys |
| may be used to perform additional actions:</para> |
| |
| <variablelist> |
| <varlistentry> |
| <term><keycap>←</keycap> (Left)</term> |
| <term><keycap>→</keycap> (Right)</term> |
| <term><keycap>Home</keycap></term> |
| <term><keycap>End</keycap></term> |
| <listitem><para>Navigate left/right</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>Esc</keycap></term> |
| <listitem><para>Abort the edit and quit the editor</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycombo><keycap>Ctrl</keycap><keycap>k</keycap></keycombo></term> |
| <listitem><para>Clear the command line</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycombo><keycap>Ctrl</keycap><keycap>w</keycap></keycombo></term> |
| <term><keycombo><keycap>Alt</keycap><keycap>Backspace</keycap></keycombo></term> |
| <listitem><para>Delete word backwards</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycombo><keycap>Alt</keycap><keycap>d</keycap></keycombo></term> |
| <listitem><para>Delete word forwards</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><keycap>↵</keycap> (Enter)</term> |
| <listitem><para>Boot entry with the edited command line</para></listitem> |
| </varlistentry> |
| </variablelist> |
| |
| <para>Note that unless configured otherwise in the UEFI firmware, systemd-boot will |
| use the US keyboard layout, so key labels might not match for keys like +/-. |
| </para> |
| </refsect1> |
| |
| <refsect1> |
| <title>Files</title> |
| |
| <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.</para> |
| </refsect1> |
| |
| <refsect1> |
| <title>EFI Variables</title> |
| |
| <para>The following EFI variables are defined, set and read by <command>systemd-boot</command>, under the vendor |
| UUID <literal>4a67b082-0a4c-41cf-b6c7-440b29bb8c4</literal>, for communication between the OS and the boot |
| loader:</para> |
| |
| <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 |
| encoded. Set by the boot |
| loader. <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| uses this information to mark a boot as successful as determined by the successful activation of the |
| <filename>boot-complete.target</filename> target unit.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>LoaderConfigTimeout</varname></term> |
| <term><varname>LoaderConfigTimeoutOneShot</varname></term> |
| <listitem><para>The menu timeout in seconds. Read by the boot loader. <varname>LoaderConfigTimeout</varname> |
| 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> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>LoaderDevicePartUUID</varname></term> |
| |
| <listitem><para>Contains the partition UUID of the EFI System Partition the boot loader was run from. Set by |
| the boot |
| loader. <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| uses this information to automatically find the disk booted from, in order to discover various other partitions |
| on the same disk automatically.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>LoaderEntries</varname></term> |
| |
| <listitem><para>A list of the identifiers of all discovered boot loader entries. Set by the boot |
| loader.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>LoaderEntryDefault</varname></term> |
| <term><varname>LoaderEntryOneShot</varname></term> |
| |
| <listitem><para>The identifier of the default boot loader entry. Set primarily by the OS and read by the boot |
| loader. <varname>LoaderEntryOneShot</varname> sets the default entry for the next boot only, while |
| <varname>LoaderEntryDefault</varname> sets it persistently for all future |
| 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> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>LoaderEntrySelected</varname></term> |
| |
| <listitem><para>The identifier of the boot loader entry currently being booted. Set by the boot |
| loader.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>LoaderFeatures</varname></term> |
| |
| <listitem><para>A set of flags indicating the features the boot loader supports. Set by the boot loader. Use |
| <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this |
| data.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>LoaderFirmwareInfo</varname></term> |
| <term><varname>LoaderFirmwareType</varname></term> |
| |
| <listitem><para>Brief firmware information. Set by the boot loader. Use |
| <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this |
| data.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>LoaderImageIdentifier</varname></term> |
| |
| <listitem><para>The path of executable of the boot loader used for the current boot, relative to the EFI System |
| Partition's root directory. Set by the boot loader. Use |
| <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this |
| data.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>LoaderInfo</varname></term> |
| |
| <listitem><para>Brief information about the boot loader. Set by the boot loader. Use |
| <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this |
| data.</para></listitem> |
| </varlistentry> |
| |
| <varlistentry> |
| <term><varname>LoaderTimeExecUSec</varname></term> |
| <term><varname>LoaderTimeInitUSec</varname></term> |
| <term><varname>LoaderTimeMenuUsec</varname></term> |
| |
| <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> |
| </varlistentry> |
| </variablelist> |
| </refsect1> |
| |
| <refsect1> |
| <title>Boot Counting</title> |
| |
| <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 |
| 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 |
| decreased by one on every boot attempt, the second of the two numbers ('tries done') is increased by one (if 'tries |
| done' is absent it is considered equivalent to 0). Depending on the current value of these two counters the boot |
| entry is considered to be in one of three states:</para> |
| |
| <orderedlist> |
| <listitem><para>If the 'tries left' counter of an entry is greater than zero the entry is considered to be in |
| 'indeterminate' state. This means the entry has not completed booting successfully yet, but also hasn't been |
| determined not to work.</para></listitem> |
| |
| <listitem><para>If the 'tries left' counter of an entry is zero it is considered to be in 'bad' state. This means |
| no further attempts to boot this item will be made (that is, unless all other boot entries are also in 'bad' |
| state), as all attempts to boot this entry have not completed successfully.</para></listitem> |
| |
| <listitem><para>If the 'tries left' and 'tries done' counters of an entry are absent it is considered to be in |
| 'good' state. This means further boot counting for the entry is turned off, as it successfully booted at least |
| once. The |
| <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry> |
| service moves the currently booted entry from 'indeterminate' into 'good' state when a boot attempt completed |
| successfully.</para></listitem> |
| </orderedlist> |
| |
| <para>Generally, when new entries are added to the boot loader, they first start out in 'indeterminate' state, |
| i.e. with a 'tries left' counter greater than zero. The boot entry remains in this state until either it managed to |
| complete a full boot successfully at least once (in which case it will be in 'good' state) — or the 'tries left' |
| counter reaches zero (in which case it will be in 'bad' state).</para> |
| |
| <para>Example: let's say a boot loader entry file <filename>foo.conf</filename> is set up for 3 boot tries. The |
| installer will hence create it under the name <filename>foo+3.conf</filename>. On first boot, the boot loader will |
| rename it to <filename>foo+2-1.conf</filename>. If that boot does not complete successfully, the boot loader will |
| rename it to <filename>foo+1-2.conf</filename> on the following boot. If that fails too, it will finally be renamed |
| <filename>foo+0-3.conf</filename> by the boot loader on next boot, after which it will be considered 'bad'. If the |
| boot succeeds however the entry file will be renamed to <filename>foo.conf</filename> by the OS, so that it 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 |
| 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 |
| 'indeterminate' entries left.</para> |
| |
| <para>The <citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry> kernel |
| install framework optionally sets the initial 'tries left' counter to the value specified in |
| <filename>/etc/kernel/tries</filename> when a boot loader entry is first created.</para> |
| </refsect1> |
| |
| <refsect1> |
| <title>See Also</title> |
| <para> |
| <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>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> |
| </para> |
| </refsect1> |
| </refentry> |