man/systemd-boot.xml

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   2 <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
   3   "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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   5 <!-- SPDX-License-Identifier: LGPL-2.1+ -->
   6
   7 <refentry id="systemd-boot" conditional='ENABLE_EFI'
   8     xmlns:xi="http://www.w3.org/2001/XInclude">
   9   <refentryinfo>
  10     <title>systemd-boot</title>
  11     <productname>systemd</productname>
  12   </refentryinfo>
  13
  14   <refmeta>
  15     <refentrytitle>systemd-boot</refentrytitle>
  16     <manvolnum>7</manvolnum>
  17   </refmeta>
  18
  19   <refnamediv>
  20     <refname>systemd-boot</refname>
  21     <refname>sd-boot</refname>
  22     <refpurpose>A simple UEFI boot manager</refpurpose>
  23   </refnamediv>
  24
  25   <refsect1>
  26     <title>Description</title>
  27
  28     <para><command>systemd-boot</command> (short: <command>sd-boot</command>) is a simple UEFI boot
  29     manager. It provides a graphical menu to select the entry to boot and an editor for the kernel command
  30     line. <command>systemd-boot</command> supports systems with UEFI firmware only.</para>
  31
  32     <para>systemd-boot loads boot entry information from the EFI system partition (ESP), usually mounted at
  33     <filename>/efi/</filename>, <filename>/boot/</filename>, or <filename>/boot/efi/</filename> during OS
  34     runtime, as well as from the Extended Boot Loader partition if it exists (usually mounted to
  35     <filename>/boot/</filename>). Configuration file fragments, kernels, initrds and other EFI images to boot
  36     generally need to reside on the ESP or the Extended Boot Loader partition. Linux kernels must be built
  37     with <option>CONFIG_EFI_STUB</option> to be able to be directly executed as an EFI image. During boot
  38     systemd-boot automatically assembles a list of boot entries from the following sources:</para>
  39
  40     <itemizedlist>
  41       <listitem><para>Boot entries defined with <ulink
  42       url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink> description files
  43       located in <filename>/loader/entries/</filename> on the ESP and the Extended Boot Loader
  44       Partition. These usually describe Linux kernel images with associated initrd images, but alternatively
  45       may also describe arbitrary other EFI executables.</para></listitem>
  46
  47       <listitem><para>Unified kernel images following the <ulink
  48       url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, as executable EFI
  49       binaries in <filename>/EFI/Linux/</filename> on the ESP and the Extended Boot Loader Partition.
  50       </para></listitem>
  51
  52       <listitem><para>The Microsoft Windows EFI boot manager, if installed</para></listitem>
  53
  54       <listitem><para>The Apple MacOS X boot manager, if installed</para></listitem>
  55
  56       <listitem><para>The EFI Shell binary, if installed</para></listitem>
  57
  58       <listitem><para>A reboot into the UEFI firmware setup option, if supported by the firmware</para></listitem>
  59     </itemizedlist>
  60
  61     <para><citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  62     may be used to copy kernel images onto the ESP or the Extended Boot Loader Partition and to generate
  63     description files compliant with the Boot Loader
  64     Specification. <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  65     may be used from a running system to locate the ESP and the Extended Boot Loader Partition, list
  66     available entries, and install <command>systemd-boot</command> itself.</para>
  67
  68     <para>systemd-boot will provide information about the time spent in UEFI firmware using the <ulink
  69     url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>. This information can be displayed
  70     using <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
  71     </para>
  72   </refsect1>
  73
  74   <refsect1>
  75     <title>Key bindings</title>
  76     <para>The following keys may be used in the boot menu:</para>
  77
  78     <variablelist>
  79       <varlistentry>
  80         <term><keycap>↑</keycap> (Up)</term>
  81         <term><keycap>↓</keycap> (Down)</term>
  82         <term><keycap>j</keycap></term>
  83         <term><keycap>k</keycap></term>
  84         <term><keycap>PageUp</keycap></term>
  85         <term><keycap>PageDown</keycap></term>
  86         <term><keycap>Home</keycap></term>
  87         <term><keycap>End</keycap></term>
  88         <listitem><para>Navigate up/down in the entry list</para></listitem>
  89       </varlistentry>
  90
  91       <varlistentry>
  92         <term><keycap>↵</keycap> (Enter)</term>
  93         <listitem><para>Boot selected entry</para></listitem>
  94       </varlistentry>
  95
  96       <varlistentry>
  97         <term><keycap>d</keycap></term>
  98         <listitem><para>Make selected entry the default</para></listitem>
  99       </varlistentry>
 100
 101       <varlistentry>
 102         <term><keycap>e</keycap></term>
 103         <listitem><para>Edit the kernel command line for selected entry</para></listitem>
 104       </varlistentry>
 105
 106       <varlistentry>
 107         <term><keycap>+</keycap></term>
 108         <term><keycap>t</keycap></term>
 109         <listitem><para>Increase the timeout before default entry is booted</para></listitem>
 110       </varlistentry>
 111
 112       <varlistentry>
 113         <term><keycap>-</keycap></term>
 114         <term><keycap>T</keycap></term>
 115         <listitem><para>Decrease the timeout</para></listitem>
 116       </varlistentry>
 117
 118       <varlistentry>
 119         <term><keycap>v</keycap></term>
 120         <listitem><para>Show systemd-boot, UEFI, and firmware versions</para></listitem>
 121       </varlistentry>
 122
 123       <varlistentry>
 124         <term><keycap>P</keycap></term>
 125         <listitem><para>Print status</para></listitem>
 126       </varlistentry>
 127
 128       <varlistentry>
 129         <term><keycap>Q</keycap></term>
 130         <listitem><para>Quit</para></listitem>
 131       </varlistentry>
 132
 133       <varlistentry>
 134         <term><keycap>h</keycap></term>
 135         <term><keycap>?</keycap></term>
 136         <listitem><para>Show a help screen</para></listitem>
 137       </varlistentry>
 138
 139       <varlistentry>
 140         <term><keycombo><keycap>Ctrl</keycap><keycap>l</keycap></keycombo></term>
 141         <listitem><para>Reprint the screen</para></listitem>
 142       </varlistentry>
 143     </variablelist>
 144
 145     <para>The following keys may be used during bootup or in the boot menu to
 146     directly boot a specific entry:</para>
 147
 148     <variablelist>
 149       <varlistentry>
 150         <term><keycap>l</keycap></term>
 151         <listitem><para>Linux</para></listitem>
 152       </varlistentry>
 153
 154       <varlistentry>
 155         <term><keycap>w</keycap></term>
 156         <listitem><para>Windows</para></listitem>
 157       </varlistentry>
 158
 159       <varlistentry>
 160         <term><keycap>a</keycap></term>
 161         <listitem><para>OS X</para></listitem>
 162       </varlistentry>
 163
 164       <varlistentry>
 165         <term><keycap>s</keycap></term>
 166         <listitem><para>EFI shell</para></listitem>
 167       </varlistentry>
 168
 169       <varlistentry>
 170         <term><keycap>1</keycap></term>
 171         <term><keycap>2</keycap></term>
 172         <term><keycap>3</keycap></term>
 173         <term><keycap>4</keycap></term>
 174         <term><keycap>5</keycap></term>
 175         <term><keycap>6</keycap></term>
 176         <term><keycap>7</keycap></term>
 177         <term><keycap>8</keycap></term>
 178         <term><keycap>9</keycap></term>
 179         <listitem><para>Boot entry number 1 … 9</para></listitem>
 180       </varlistentry>
 181     </variablelist>
 182
 183     <para>In the editor, most keys simply insert themselves, but the following keys
 184     may be used to perform additional actions:</para>
 185
 186     <variablelist>
 187       <varlistentry>
 188         <term><keycap>←</keycap> (Left)</term>
 189         <term><keycap>→</keycap> (Right)</term>
 190         <term><keycap>Home</keycap></term>
 191         <term><keycap>End</keycap></term>
 192         <listitem><para>Navigate left/right</para></listitem>
 193       </varlistentry>
 194
 195       <varlistentry>
 196         <term><keycap>Esc</keycap></term>
 197         <listitem><para>Abort the edit and quit the editor</para></listitem>
 198       </varlistentry>
 199
 200       <varlistentry>
 201         <term><keycombo><keycap>Ctrl</keycap><keycap>k</keycap></keycombo></term>
 202         <listitem><para>Clear the command line</para></listitem>
 203       </varlistentry>
 204
 205       <varlistentry>
 206         <term><keycombo><keycap>Ctrl</keycap><keycap>w</keycap></keycombo></term>
 207         <term><keycombo><keycap>Alt</keycap><keycap>Backspace</keycap></keycombo></term>
 208         <listitem><para>Delete word backwards</para></listitem>
 209       </varlistentry>
 210
 211       <varlistentry>
 212         <term><keycombo><keycap>Alt</keycap><keycap>d</keycap></keycombo></term>
 213         <listitem><para>Delete word forwards</para></listitem>
 214       </varlistentry>
 215
 216       <varlistentry>
 217         <term><keycap>↵</keycap> (Enter)</term>
 218         <listitem><para>Boot entry with the edited command line</para></listitem>
 219       </varlistentry>
 220     </variablelist>
 221
 222     <para>Note that unless configured otherwise in the UEFI firmware, systemd-boot will
 223     use the US keyboard layout, so key labels might not match for keys like +/-.
 224     </para>
 225   </refsect1>
 226
 227   <refsect1>
 228     <title>Files</title>
 229
 230     <para>The files <command>systemd-boot</command> processes generally reside on the UEFI ESP which is
 231     usually mounted to <filename>/efi/</filename>, <filename>/boot/</filename> or
 232     <filename>/boot/efi/</filename> during OS runtime. It also processes files on the Extended Boot Loader
 233     partition which is typically mounted to <filename>/boot/</filename>, if it
 234     exists. <command>systemd-boot</command> reads runtime configuration such as the boot timeout and default
 235     entry from <filename>/loader/loader.conf</filename> on the ESP (in combination with data read from EFI
 236     variables). See
 237     <citerefentry><refentrytitle>loader.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Boot
 238     entry description files following the <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot
 239     Loader Specification</ulink> are read from <filename>/loader/entries/</filename> on the ESP and the
 240     Extended Boot Loader partition. Unified kernel boot entries following the <ulink
 241     url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink> are read from
 242     <filename>/EFI/Linux/</filename> on the ESP and the Extended Boot Loader partition.</para>
 243   </refsect1>
 244
 245   <refsect1>
 246     <title>EFI Variables</title>
 247
 248     <para>The following EFI variables are defined, set and read by <command>systemd-boot</command>, under the vendor
 249     UUID <literal>4a67b082-0a4c-41cf-b6c7-440b29bb8c4</literal>, for communication between the OS and the boot
 250     loader:</para>
 251
 252     <variablelist class='efi-variables'>
 253       <varlistentry>
 254         <term><varname>LoaderBootCountPath</varname></term>
 255         <listitem><para>If boot counting is enabled, contains the path to the file in whose name the boot counters are
 256         encoded. Set by the boot
 257         loader. <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 258         uses this information to mark a boot as successful as determined by the successful activation of the
 259         <filename>boot-complete.target</filename> target unit.</para></listitem>
 260       </varlistentry>
 261
 262       <varlistentry>
 263         <term><varname>LoaderConfigTimeout</varname></term>
 264         <term><varname>LoaderConfigTimeoutOneShot</varname></term>
 265         <listitem><para>The menu timeout in seconds. Read by the boot loader. <varname>LoaderConfigTimeout</varname>
 266         is maintained persistently, while <varname>LoaderConfigTimeoutOneShot</varname> is a one-time override which is
 267         read once (in which case it takes precedence over <varname>LoaderConfigTimeout</varname>) and then
 268         removed. <varname>LoaderConfigTimeout</varname> may be manipulated with the
 269         <keycap>t</keycap>/<keycap>T</keycap> keys, see above.)</para></listitem>
 270       </varlistentry>
 271
 272       <varlistentry>
 273         <term><varname>LoaderDevicePartUUID</varname></term>
 274
 275         <listitem><para>Contains the partition UUID of the EFI System Partition the boot loader was run from. Set by
 276         the boot
 277         loader. <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 278         uses this information to automatically find the disk booted from, in order to discover various other partitions
 279         on the same disk automatically.</para></listitem>
 280       </varlistentry>
 281
 282       <varlistentry>
 283         <term><varname>LoaderEntries</varname></term>
 284
 285         <listitem><para>A list of the identifiers of all discovered boot loader entries. Set by the boot
 286         loader.</para></listitem>
 287       </varlistentry>
 288
 289       <varlistentry>
 290         <term><varname>LoaderEntryDefault</varname></term>
 291         <term><varname>LoaderEntryOneShot</varname></term>
 292
 293         <listitem><para>The identifier of the default boot loader entry. Set primarily by the OS and read by the boot
 294         loader. <varname>LoaderEntryOneShot</varname> sets the default entry for the next boot only, while
 295         <varname>LoaderEntryDefault</varname> sets it persistently for all future
 296         boots. <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
 297         <option>set-default</option> and <option>set-oneshot</option> commands make use of these variables. The boot
 298         loader modifies <varname>LoaderEntryDefault</varname> on request, when the <keycap>d</keycap> key is used, see
 299         above.)</para></listitem>
 300       </varlistentry>
 301
 302       <varlistentry>
 303         <term><varname>LoaderEntrySelected</varname></term>
 304
 305         <listitem><para>The identifier of the boot loader entry currently being booted. Set by the boot
 306         loader.</para></listitem>
 307       </varlistentry>
 308
 309       <varlistentry>
 310         <term><varname>LoaderFeatures</varname></term>
 311
 312         <listitem><para>A set of flags indicating the features the boot loader supports. Set by the boot loader. Use
 313         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this
 314         data.</para></listitem>
 315       </varlistentry>
 316
 317       <varlistentry>
 318         <term><varname>LoaderFirmwareInfo</varname></term>
 319         <term><varname>LoaderFirmwareType</varname></term>
 320
 321         <listitem><para>Brief firmware information. Set by the boot loader. Use
 322         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this
 323         data.</para></listitem>
 324       </varlistentry>
 325
 326       <varlistentry>
 327         <term><varname>LoaderImageIdentifier</varname></term>
 328
 329         <listitem><para>The path of executable of the boot loader used for the current boot, relative to the EFI System
 330         Partition's root directory. Set by the boot loader. Use
 331         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this
 332         data.</para></listitem>
 333       </varlistentry>
 334
 335       <varlistentry>
 336         <term><varname>LoaderInfo</varname></term>
 337
 338         <listitem><para>Brief information about the boot loader. Set by the boot loader. Use
 339         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this
 340         data.</para></listitem>
 341       </varlistentry>
 342
 343       <varlistentry>
 344         <term><varname>LoaderTimeExecUSec</varname></term>
 345         <term><varname>LoaderTimeInitUSec</varname></term>
 346         <term><varname>LoaderTimeMenuUsec</varname></term>
 347
 348         <listitem><para>Information about the time spent in various parts of the boot loader. Set by the boot
 349         loader. Use <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 350         to view this data. These variables are defined by the <ulink
 351         url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>.</para></listitem>
 352       </varlistentry>
 353     </variablelist>
 354   </refsect1>
 355
 356   <refsect1>
 357     <title>Boot Counting</title>
 358
 359     <para><command>systemd-boot</command> implements a simple boot counting mechanism on top of the <ulink
 360     url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, for automatic and unattended
 361     fallback to older kernel versions/boot loader entries when a specific entry continously fails. Any boot loader
 362     entry file and unified kernel image file that contains a <literal>+</literal> followed by one or two numbers (if
 363     two they need to be separated by a <literal>-</literal>), before the <filename>.conf</filename> or
 364     <filename>.efi</filename> suffix is subject to boot counting: the first of the two numbers ('tries left') is
 365     decreased by one on every boot attempt, the second of the two numbers ('tries done') is increased by one (if 'tries
 366     done' is absent it is considered equivalent to 0). Depending on the current value of these two counters the boot
 367     entry is considered to be in one of three states:</para>
 368
 369     <orderedlist>
 370       <listitem><para>If the 'tries left' counter of an entry is greater than zero the entry is considered to be in
 371       'indeterminate' state. This means the entry has not completed booting successfully yet, but also hasn't been
 372       determined not to work.</para></listitem>
 373
 374       <listitem><para>If the 'tries left' counter of an entry is zero it is considered to be in 'bad' state. This means
 375       no further attempts to boot this item will be made (that is, unless all other boot entries are also in 'bad'
 376       state), as all attempts to boot this entry have not completed successfully.</para></listitem>
 377
 378       <listitem><para>If the 'tries left' and 'tries done' counters of an entry are absent it is considered to be in
 379       'good' state. This means further boot counting for the entry is turned off, as it successfully booted at least
 380       once. The
 381       <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 382       service moves the currently booted entry from 'indeterminate' into 'good' state when a boot attempt completed
 383       successfully.</para></listitem>
 384     </orderedlist>
 385
 386     <para>Generally, when new entries are added to the boot loader, they first start out in 'indeterminate' state,
 387     i.e. with a 'tries left' counter greater than zero. The boot entry remains in this state until either it managed to
 388     complete a full boot successfully at least once (in which case it will be in 'good' state) — or the 'tries left'
 389     counter reaches zero (in which case it will be in 'bad' state).</para>
 390
 391     <para>Example: let's say a boot loader entry file <filename>foo.conf</filename> is set up for 3 boot tries. The
 392     installer will hence create it under the name <filename>foo+3.conf</filename>. On first boot, the boot loader will
 393     rename it to <filename>foo+2-1.conf</filename>. If that boot does not complete successfully, the boot loader will
 394     rename it to <filename>foo+1-2.conf</filename> on the following boot. If that fails too, it will finally be renamed
 395     <filename>foo+0-3.conf</filename> by the boot loader on next boot, after which it will be considered 'bad'. If the
 396     boot succeeds however the entry file will be renamed to <filename>foo.conf</filename> by the OS, so that it is
 397     considered 'good' from then on.</para>
 398
 399     <para>The boot menu takes the 'tries left' counter into account when sorting the menu entries: entries in 'bad'
 400     state are ordered at the end of the list, and entries in 'good' or 'indeterminate' at the beginning. The user can
 401     freely choose to boot any entry of the menu, including those already marked 'bad'. If the menu entry to boot is
 402     automatically determined, this means that 'good' or 'indeterminate' entries are generally preferred (as the top item of
 403     the menu is the one booted by default), and 'bad' entries will only be considered if there are no 'good' or
 404     'indeterminate' entries left.</para>
 405
 406     <para>The <citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry> kernel
 407     install framework optionally sets the initial 'tries left' counter to the value specified in
 408     <filename>/etc/kernel/tries</filename> when a boot loader entry is first created.</para>
 409   </refsect1>
 410
 411   <refsect1>
 412     <title>See Also</title>
 413     <para>
 414       <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 415       <citerefentry><refentrytitle>loader.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 416       <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 417       <citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 418       <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>,
 419       <ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>
 420     </para>
 421   </refsect1>
 422 </refentry>