man/systemd-boot.xml

   1 <?xml version='1.0'?> <!--*-nxml-*-->
   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" conditional='ENABLE_EFI'
   7     xmlns:xi="http://www.w3.org/2001/XInclude">
   8   <refentryinfo>
   9     <title>systemd-boot</title>
  10     <productname>systemd</productname>
  11   </refentryinfo>
  12
  13   <refmeta>
  14     <refentrytitle>systemd-boot</refentrytitle>
  15     <manvolnum>7</manvolnum>
  16   </refmeta>
  17
  18   <refnamediv>
  19     <refname>systemd-boot</refname>
  20     <refname>sd-boot</refname>
  21     <refpurpose>A simple UEFI boot manager</refpurpose>
  22   </refnamediv>
  23
  24   <refsect1>
  25     <title>Description</title>
  26
  27     <para><command>systemd-boot</command> (short: <command>sd-boot</command>) is a simple UEFI boot
  28     manager. It provides a graphical menu to select the entry to boot and an editor for the kernel command
  29     line. <command>systemd-boot</command> supports systems with UEFI firmware only.</para>
  30
  31     <para>systemd-boot loads boot entry information from the EFI system partition (ESP), usually mounted at
  32     <filename>/efi/</filename>, <filename>/boot/</filename>, or <filename>/boot/efi/</filename> during OS
  33     runtime, as well as from the Extended Boot Loader partition if it exists (usually mounted to
  34     <filename>/boot/</filename>). Configuration file fragments, kernels, initrds and other EFI images to boot
  35     generally need to reside on the ESP or the Extended Boot Loader partition. Linux kernels must be built
  36     with <option>CONFIG_EFI_STUB</option> to be able to be directly executed as an EFI image. During boot
  37     systemd-boot automatically assembles a list of boot entries from the following sources:</para>
  38
  39     <itemizedlist>
  40       <listitem><para>Boot entries defined with <ulink
  41       url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink> description files
  42       located in <filename>/loader/entries/</filename> on the ESP and the Extended Boot Loader
  43       Partition. These usually describe Linux kernel images with associated initrd images, but alternatively
  44       may also describe arbitrary other EFI executables.</para></listitem>
  45
  46       <listitem><para>Unified kernel images following the <ulink
  47       url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, as executable EFI
  48       binaries in <filename>/EFI/Linux/</filename> on the ESP and the Extended Boot Loader Partition.
  49       </para></listitem>
  50
  51       <listitem><para>The Microsoft Windows EFI boot manager, if installed</para></listitem>
  52
  53       <listitem><para>The Apple MacOS X boot manager, if installed</para></listitem>
  54
  55       <listitem><para>The EFI Shell binary, if installed</para></listitem>
  56
  57       <listitem><para>A reboot into the UEFI firmware setup option, if supported by the firmware</para></listitem>
  58     </itemizedlist>
  59
  60     <para><citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  61     may be used to copy kernel images onto the ESP or the Extended Boot Loader Partition and to generate
  62     description files compliant with the Boot Loader
  63     Specification. <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  64     may be used from a running system to locate the ESP and the Extended Boot Loader Partition, list
  65     available entries, and install <command>systemd-boot</command> itself.</para>
  66
  67     <para>systemd-boot will provide information about the time spent in UEFI firmware using the <ulink
  68     url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>. This information can be displayed
  69     using <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
  70     </para>
  71   </refsect1>
  72
  73   <refsect1>
  74     <title>Key bindings</title>
  75     <para>The following keys may be used in the boot menu:</para>
  76
  77     <variablelist>
  78       <varlistentry>
  79         <term><keycap>↑</keycap> (Up)</term>
  80         <term><keycap>↓</keycap> (Down)</term>
  81         <term><keycap>j</keycap></term>
  82         <term><keycap>k</keycap></term>
  83         <term><keycap>PageUp</keycap></term>
  84         <term><keycap>PageDown</keycap></term>
  85         <term><keycap>Home</keycap></term>
  86         <term><keycap>End</keycap></term>
  87         <listitem><para>Navigate up/down in the entry list</para></listitem>
  88       </varlistentry>
  89
  90       <varlistentry>
  91         <term><keycap>↵</keycap> (Enter)</term>
  92         <listitem><para>Boot selected entry</para></listitem>
  93       </varlistentry>
  94
  95       <varlistentry>
  96         <term><keycap>d</keycap></term>
  97         <listitem><para>Make selected entry the default</para></listitem>
  98       </varlistentry>
  99
 100       <varlistentry>
 101         <term><keycap>e</keycap></term>
 102         <listitem><para>Edit the kernel command line for selected entry</para></listitem>
 103       </varlistentry>
 104
 105       <varlistentry>
 106         <term><keycap>+</keycap></term>
 107         <term><keycap>t</keycap></term>
 108         <listitem><para>Increase the timeout before default entry is booted</para></listitem>
 109       </varlistentry>
 110
 111       <varlistentry>
 112         <term><keycap>-</keycap></term>
 113         <term><keycap>T</keycap></term>
 114         <listitem><para>Decrease the timeout</para></listitem>
 115       </varlistentry>
 116
 117       <varlistentry>
 118         <term><keycap>v</keycap></term>
 119         <listitem><para>Show systemd-boot, UEFI, and firmware versions</para></listitem>
 120       </varlistentry>
 121
 122       <varlistentry>
 123         <term><keycap>P</keycap></term>
 124         <listitem><para>Print status</para></listitem>
 125       </varlistentry>
 126
 127       <varlistentry>
 128         <term><keycap>Q</keycap></term>
 129         <listitem><para>Quit</para></listitem>
 130       </varlistentry>
 131
 132       <varlistentry>
 133         <term><keycap>h</keycap></term>
 134         <term><keycap>?</keycap></term>
 135         <listitem><para>Show a help screen</para></listitem>
 136       </varlistentry>
 137
 138       <varlistentry>
 139         <term><keycombo><keycap>Ctrl</keycap><keycap>l</keycap></keycombo></term>
 140         <listitem><para>Reprint the screen</para></listitem>
 141       </varlistentry>
 142     </variablelist>
 143
 144     <para>The following keys may be used during bootup or in the boot menu to
 145     directly boot a specific entry:</para>
 146
 147     <variablelist>
 148       <varlistentry>
 149         <term><keycap>l</keycap></term>
 150         <listitem><para>Linux</para></listitem>
 151       </varlistentry>
 152
 153       <varlistentry>
 154         <term><keycap>w</keycap></term>
 155         <listitem><para>Windows</para></listitem>
 156       </varlistentry>
 157
 158       <varlistentry>
 159         <term><keycap>a</keycap></term>
 160         <listitem><para>OS X</para></listitem>
 161       </varlistentry>
 162
 163       <varlistentry>
 164         <term><keycap>s</keycap></term>
 165         <listitem><para>EFI shell</para></listitem>
 166       </varlistentry>
 167
 168       <varlistentry>
 169         <term><keycap>1</keycap></term>
 170         <term><keycap>2</keycap></term>
 171         <term><keycap>3</keycap></term>
 172         <term><keycap>4</keycap></term>
 173         <term><keycap>5</keycap></term>
 174         <term><keycap>6</keycap></term>
 175         <term><keycap>7</keycap></term>
 176         <term><keycap>8</keycap></term>
 177         <term><keycap>9</keycap></term>
 178         <listitem><para>Boot entry number 1 … 9</para></listitem>
 179       </varlistentry>
 180     </variablelist>
 181
 182     <para>In the editor, most keys simply insert themselves, but the following keys
 183     may be used to perform additional actions:</para>
 184
 185     <variablelist>
 186       <varlistentry>
 187         <term><keycap>←</keycap> (Left)</term>
 188         <term><keycap>→</keycap> (Right)</term>
 189         <term><keycap>Home</keycap></term>
 190         <term><keycap>End</keycap></term>
 191         <listitem><para>Navigate left/right</para></listitem>
 192       </varlistentry>
 193
 194       <varlistentry>
 195         <term><keycap>Esc</keycap></term>
 196         <listitem><para>Abort the edit and quit the editor</para></listitem>
 197       </varlistentry>
 198
 199       <varlistentry>
 200         <term><keycombo><keycap>Ctrl</keycap><keycap>k</keycap></keycombo></term>
 201         <listitem><para>Clear the command line</para></listitem>
 202       </varlistentry>
 203
 204       <varlistentry>
 205         <term><keycombo><keycap>Ctrl</keycap><keycap>w</keycap></keycombo></term>
 206         <term><keycombo><keycap>Alt</keycap><keycap>Backspace</keycap></keycombo></term>
 207         <listitem><para>Delete word backwards</para></listitem>
 208       </varlistentry>
 209
 210       <varlistentry>
 211         <term><keycombo><keycap>Alt</keycap><keycap>d</keycap></keycombo></term>
 212         <listitem><para>Delete word forwards</para></listitem>
 213       </varlistentry>
 214
 215       <varlistentry>
 216         <term><keycap>↵</keycap> (Enter)</term>
 217         <listitem><para>Boot entry with the edited command line</para></listitem>
 218       </varlistentry>
 219     </variablelist>
 220
 221     <para>Note that unless configured otherwise in the UEFI firmware, systemd-boot will
 222     use the US keyboard layout, so key labels might not match for keys like +/-.
 223     </para>
 224   </refsect1>
 225
 226   <refsect1>
 227     <title>Files</title>
 228
 229     <para>The files <command>systemd-boot</command> processes generally reside on the UEFI ESP which is
 230     usually mounted to <filename>/efi/</filename>, <filename>/boot/</filename> or
 231     <filename>/boot/efi/</filename> during OS runtime. It also processes files on the Extended Boot Loader
 232     partition which is typically mounted to <filename>/boot/</filename>, if it
 233     exists. <command>systemd-boot</command> reads runtime configuration such as the boot timeout and default
 234     entry from <filename>/loader/loader.conf</filename> on the ESP (in combination with data read from EFI
 235     variables). See
 236     <citerefentry><refentrytitle>loader.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Boot
 237     entry description files following the <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot
 238     Loader Specification</ulink> are read from <filename>/loader/entries/</filename> on the ESP and the
 239     Extended Boot Loader partition. Unified kernel boot entries following the <ulink
 240     url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink> are read from
 241     <filename>/EFI/Linux/</filename> on the ESP and the Extended Boot Loader partition.</para>
 242   </refsect1>
 243
 244   <refsect1>
 245     <title>EFI Variables</title>
 246
 247     <para>The following EFI variables are defined, set and read by <command>systemd-boot</command>, under the vendor
 248     UUID <literal>4a67b082-0a4c-41cf-b6c7-440b29bb8c4</literal>, for communication between the OS and the boot
 249     loader:</para>
 250
 251     <variablelist class='efi-variables'>
 252       <varlistentry>
 253         <term><varname>LoaderBootCountPath</varname></term>
 254         <listitem><para>If boot counting is enabled, contains the path to the file in whose name the boot counters are
 255         encoded. Set by the boot
 256         loader. <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 257         uses this information to mark a boot as successful as determined by the successful activation of the
 258         <filename>boot-complete.target</filename> target unit.</para></listitem>
 259       </varlistentry>
 260
 261       <varlistentry>
 262         <term><varname>LoaderConfigTimeout</varname></term>
 263         <term><varname>LoaderConfigTimeoutOneShot</varname></term>
 264         <listitem><para>The menu timeout in seconds. Read by the boot loader. <varname>LoaderConfigTimeout</varname>
 265         is maintained persistently, while <varname>LoaderConfigTimeoutOneShot</varname> is a one-time override which is
 266         read once (in which case it takes precedence over <varname>LoaderConfigTimeout</varname>) and then
 267         removed. <varname>LoaderConfigTimeout</varname> may be manipulated with the
 268         <keycap>t</keycap>/<keycap>T</keycap> keys, see above.)</para></listitem>
 269       </varlistentry>
 270
 271       <varlistentry>
 272         <term><varname>LoaderDevicePartUUID</varname></term>
 273
 274         <listitem><para>Contains the partition UUID of the EFI System Partition the boot loader was run from. Set by
 275         the boot
 276         loader. <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 277         uses this information to automatically find the disk booted from, in order to discover various other partitions
 278         on the same disk automatically.</para></listitem>
 279       </varlistentry>
 280
 281       <varlistentry>
 282         <term><varname>LoaderEntries</varname></term>
 283
 284         <listitem><para>A list of the identifiers of all discovered boot loader entries. Set by the boot
 285         loader.</para></listitem>
 286       </varlistentry>
 287
 288       <varlistentry>
 289         <term><varname>LoaderEntryDefault</varname></term>
 290         <term><varname>LoaderEntryOneShot</varname></term>
 291
 292         <listitem><para>The identifier of the default boot loader entry. Set primarily by the OS and read by the boot
 293         loader. <varname>LoaderEntryOneShot</varname> sets the default entry for the next boot only, while
 294         <varname>LoaderEntryDefault</varname> sets it persistently for all future
 295         boots. <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
 296         <option>set-default</option> and <option>set-oneshot</option> commands make use of these variables. The boot
 297         loader modifies <varname>LoaderEntryDefault</varname> on request, when the <keycap>d</keycap> key is used, see
 298         above.)</para></listitem>
 299       </varlistentry>
 300
 301       <varlistentry>
 302         <term><varname>LoaderEntrySelected</varname></term>
 303
 304         <listitem><para>The identifier of the boot loader entry currently being booted. Set by the boot
 305         loader.</para></listitem>
 306       </varlistentry>
 307
 308       <varlistentry>
 309         <term><varname>LoaderFeatures</varname></term>
 310
 311         <listitem><para>A set of flags indicating the features the boot loader supports. Set by the boot loader. Use
 312         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this
 313         data.</para></listitem>
 314       </varlistentry>
 315
 316       <varlistentry>
 317         <term><varname>LoaderFirmwareInfo</varname></term>
 318         <term><varname>LoaderFirmwareType</varname></term>
 319
 320         <listitem><para>Brief firmware information. Set by the boot loader. Use
 321         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this
 322         data.</para></listitem>
 323       </varlistentry>
 324
 325       <varlistentry>
 326         <term><varname>LoaderImageIdentifier</varname></term>
 327
 328         <listitem><para>The path of executable of the boot loader used for the current boot, relative to the EFI System
 329         Partition's root directory. Set by the boot loader. Use
 330         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this
 331         data.</para></listitem>
 332       </varlistentry>
 333
 334       <varlistentry>
 335         <term><varname>LoaderInfo</varname></term>
 336
 337         <listitem><para>Brief information about the boot loader. Set by the boot loader. Use
 338         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this
 339         data.</para></listitem>
 340       </varlistentry>
 341
 342       <varlistentry>
 343         <term><varname>LoaderTimeExecUSec</varname></term>
 344         <term><varname>LoaderTimeInitUSec</varname></term>
 345         <term><varname>LoaderTimeMenuUsec</varname></term>
 346
 347         <listitem><para>Information about the time spent in various parts of the boot loader. Set by the boot
 348         loader. Use <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 349         to view this data. These variables are defined by the <ulink
 350         url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>.</para></listitem>
 351       </varlistentry>
 352     </variablelist>
 353   </refsect1>
 354
 355   <refsect1>
 356     <title>Boot Counting</title>
 357
 358     <para><command>systemd-boot</command> implements a simple boot counting mechanism on top of the <ulink
 359     url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, for automatic and unattended
 360     fallback to older kernel versions/boot loader entries when a specific entry continuously fails. Any boot loader
 361     entry file and unified kernel image file that contains a <literal>+</literal> followed by one or two numbers (if
 362     two they need to be separated by a <literal>-</literal>), before the <filename>.conf</filename> or
 363     <filename>.efi</filename> suffix is subject to boot counting: the first of the two numbers ('tries left') is
 364     decreased by one on every boot attempt, the second of the two numbers ('tries done') is increased by one (if 'tries
 365     done' is absent it is considered equivalent to 0). Depending on the current value of these two counters the boot
 366     entry is considered to be in one of three states:</para>
 367
 368     <orderedlist>
 369       <listitem><para>If the 'tries left' counter of an entry is greater than zero the entry is considered to be in
 370       'indeterminate' state. This means the entry has not completed booting successfully yet, but also hasn't been
 371       determined not to work.</para></listitem>
 372
 373       <listitem><para>If the 'tries left' counter of an entry is zero it is considered to be in 'bad' state. This means
 374       no further attempts to boot this item will be made (that is, unless all other boot entries are also in 'bad'
 375       state), as all attempts to boot this entry have not completed successfully.</para></listitem>
 376
 377       <listitem><para>If the 'tries left' and 'tries done' counters of an entry are absent it is considered to be in
 378       'good' state. This means further boot counting for the entry is turned off, as it successfully booted at least
 379       once. The
 380       <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 381       service moves the currently booted entry from 'indeterminate' into 'good' state when a boot attempt completed
 382       successfully.</para></listitem>
 383     </orderedlist>
 384
 385     <para>Generally, when new entries are added to the boot loader, they first start out in 'indeterminate' state,
 386     i.e. with a 'tries left' counter greater than zero. The boot entry remains in this state until either it managed to
 387     complete a full boot successfully at least once (in which case it will be in 'good' state) — or the 'tries left'
 388     counter reaches zero (in which case it will be in 'bad' state).</para>
 389
 390     <para>Example: let's say a boot loader entry file <filename>foo.conf</filename> is set up for 3 boot tries. The
 391     installer will hence create it under the name <filename>foo+3.conf</filename>. On first boot, the boot loader will
 392     rename it to <filename>foo+2-1.conf</filename>. If that boot does not complete successfully, the boot loader will
 393     rename it to <filename>foo+1-2.conf</filename> on the following boot. If that fails too, it will finally be renamed
 394     <filename>foo+0-3.conf</filename> by the boot loader on next boot, after which it will be considered 'bad'. If the
 395     boot succeeds however the entry file will be renamed to <filename>foo.conf</filename> by the OS, so that it is
 396     considered 'good' from then on.</para>
 397
 398     <para>The boot menu takes the 'tries left' counter into account when sorting the menu entries: entries in 'bad'
 399     state are ordered at the end of the list, and entries in 'good' or 'indeterminate' at the beginning. The user can
 400     freely choose to boot any entry of the menu, including those already marked 'bad'. If the menu entry to boot is
 401     automatically determined, this means that 'good' or 'indeterminate' entries are generally preferred (as the top item of
 402     the menu is the one booted by default), and 'bad' entries will only be considered if there are no 'good' or
 403     'indeterminate' entries left.</para>
 404
 405     <para>The <citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry> kernel
 406     install framework optionally sets the initial 'tries left' counter to the value specified in
 407     <filename>/etc/kernel/tries</filename> when a boot loader entry is first created.</para>
 408   </refsect1>
 409
 410   <refsect1>
 411     <title>See Also</title>
 412     <para>
 413       <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 414       <citerefentry><refentrytitle>loader.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 415       <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 416       <citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 417       <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>,
 418       <ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>
 419     </para>
 420   </refsect1>
 421 </refentry>