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><command>systemd-boot</command> loads boot entry information from the EFI system partition (ESP),
  32     usually mounted at <filename>/efi/</filename>, <filename>/boot/</filename>, or
  33     <filename>/boot/efi/</filename> during OS runtime, as well as from the Extended Boot Loader partition if
  34     it exists (usually mounted to <filename>/boot/</filename>). Configuration file fragments, kernels,
  35     initrds and other EFI images to boot generally need to reside on the ESP or the Extended Boot Loader
  36     partition. Linux kernels must be built with <option>CONFIG_EFI_STUB</option> to be able to be directly
  37     executed as an EFI image. During boot <command>systemd-boot</command> automatically assembles a list of
  38     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><command>systemd-boot</command> supports the following features:</para>
  62
  63     <itemizedlist>
  64       <listitem><para>Basic boot manager configuration changes (such as timeout
  65       configuration, default boot entry selection, …) may be made directly from the boot loader UI at
  66       boot-time, as well as during system runtime with EFI variables.</para></listitem>
  67
  68       <listitem><para>The boot manager integrates with the <command>systemctl</command> command to implement
  69       features such as <command>systemctl reboot --boot-loader-entry=…</command> (for rebooting into a
  70       specific boot menu entry, i.e. "reboot into Windows") and <command>systemctl reboot
  71       --boot-loader-menu=…</command> (for rebooting into the boot loader menu), by implementing the <ulink
  72       url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>. See
  73       <citerefentry><refentrytitle>systemctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> for
  74       details.</para></listitem>
  75
  76       <listitem><para>An EFI variable set by the boot loader informs the OS about the ESP partition used
  77       during boot. This is then used to automatically mount the correct ESP partition to
  78       <filename>/efi/</filename> or <filename>/boot/</filename> during OS runtime. See
  79       <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
  80       for details.</para></listitem>
  81
  82       <listitem><para>The boot manager provides information about the boot time spent in UEFI firmware using
  83       the <ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>. This
  84       information can be displayed using
  85       <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
  86       </para></listitem>
  87
  88       <listitem><para>The boot manager implements boot counting and automatic fallback to older, working boot
  89       entries on failure. See <ulink url="https://systemd.io/AUTOMATIC_BOOT_ASSESSMENT">Automatic Boot
  90       Assessment</ulink>.</para></listitem>
  91
  92       <listitem><para>The boot manager optionally reads a random seed from the ESP partition, combines it
  93       with a 'system token' stored in a persistent EFI variable and derives a random seed to use by the OS as
  94       entropy pool initialization, providing a full entropy pool during early boot.</para></listitem>
  95     </itemizedlist>
  96
  97     <para><citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>
  98     may be used from a running system to locate the ESP and the Extended Boot Loader Partition, list
  99     available entries, and install <command>systemd-boot</command> itself.</para>
 100
 101     <para><citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 102     may be used to copy kernel images onto the ESP or the Extended Boot Loader Partition and to generate
 103     description files compliant with the Boot Loader
 104     Specification.</para>
 105   </refsect1>
 106
 107   <refsect1>
 108     <title>Key bindings</title>
 109     <para>The following keys may be used in the boot menu:</para>
 110
 111     <variablelist>
 112       <varlistentry>
 113         <term><keycap>↑</keycap> (Up)</term>
 114         <term><keycap>↓</keycap> (Down)</term>
 115         <term><keycap>j</keycap></term>
 116         <term><keycap>k</keycap></term>
 117         <term><keycap>PageUp</keycap></term>
 118         <term><keycap>PageDown</keycap></term>
 119         <term><keycap>Home</keycap></term>
 120         <term><keycap>End</keycap></term>
 121         <listitem><para>Navigate up/down in the entry list</para></listitem>
 122       </varlistentry>
 123
 124       <varlistentry>
 125         <term><keycap>↵</keycap> (Enter)</term>
 126         <term><keycap>→</keycap> (Right)</term>
 127         <listitem><para>Boot selected entry</para></listitem>
 128       </varlistentry>
 129
 130       <varlistentry>
 131         <term><keycap>d</keycap></term>
 132         <listitem><para>Make selected entry the default</para></listitem>
 133       </varlistentry>
 134
 135       <varlistentry>
 136         <term><keycap>e</keycap></term>
 137         <listitem><para>Edit the kernel command line for selected entry</para></listitem>
 138       </varlistentry>
 139
 140       <varlistentry>
 141         <term><keycap>+</keycap></term>
 142         <term><keycap>t</keycap></term>
 143         <listitem><para>Increase the timeout before default entry is booted</para></listitem>
 144       </varlistentry>
 145
 146       <varlistentry>
 147         <term><keycap>-</keycap></term>
 148         <term><keycap>T</keycap></term>
 149         <listitem><para>Decrease the timeout</para></listitem>
 150       </varlistentry>
 151
 152       <varlistentry>
 153         <term><keycap>v</keycap></term>
 154         <listitem><para>Show systemd-boot, UEFI, and firmware versions</para></listitem>
 155       </varlistentry>
 156
 157       <varlistentry>
 158         <term><keycap>P</keycap></term>
 159         <listitem><para>Print status</para></listitem>
 160       </varlistentry>
 161
 162       <varlistentry>
 163         <term><keycap>Q</keycap></term>
 164         <listitem><para>Quit</para></listitem>
 165       </varlistentry>
 166
 167       <varlistentry>
 168         <term><keycap>h</keycap></term>
 169         <term><keycap>?</keycap></term>
 170         <term><keycap>F1</keycap></term>
 171         <listitem><para>Show a help screen</para></listitem>
 172       </varlistentry>
 173
 174       <varlistentry>
 175         <term><keycombo><keycap>Ctrl</keycap><keycap>l</keycap></keycombo></term>
 176         <listitem><para>Reprint the screen</para></listitem>
 177       </varlistentry>
 178     </variablelist>
 179
 180     <para>The following keys may be pressed during bootup or in the boot menu to directly boot a specific
 181     entry:</para>
 182
 183     <variablelist>
 184       <varlistentry>
 185         <term><keycap>l</keycap></term>
 186         <listitem><para>Linux</para></listitem>
 187       </varlistentry>
 188
 189       <varlistentry>
 190         <term><keycap>w</keycap></term>
 191         <listitem><para>Windows</para></listitem>
 192       </varlistentry>
 193
 194       <varlistentry>
 195         <term><keycap>a</keycap></term>
 196         <listitem><para>OS X</para></listitem>
 197       </varlistentry>
 198
 199       <varlistentry>
 200         <term><keycap>s</keycap></term>
 201         <listitem><para>EFI shell</para></listitem>
 202       </varlistentry>
 203
 204       <varlistentry>
 205         <term><keycap>1</keycap></term>
 206         <term><keycap>2</keycap></term>
 207         <term><keycap>3</keycap></term>
 208         <term><keycap>4</keycap></term>
 209         <term><keycap>5</keycap></term>
 210         <term><keycap>6</keycap></term>
 211         <term><keycap>7</keycap></term>
 212         <term><keycap>8</keycap></term>
 213         <term><keycap>9</keycap></term>
 214         <listitem><para>Boot entry number 1 … 9</para></listitem>
 215       </varlistentry>
 216     </variablelist>
 217
 218     <para>The boot menu is shown when a non-zero menu timeout has been configured. If the menu timeout has
 219     been set to zero, it is sufficient to press any key — before the boot loader initializes — to bring up
 220     the boot menu, except for the keys listed immediately above as they directly boot into the selected boot
 221     menu item. Note that depending on the firmware implementation the time window where key presses are
 222     accepted before the boot loader initializes might be short. If the window is missed, reboot and try
 223     again, possibly pressing a suitable key (e.g. the space bar) continuously; on most systems it should be
 224     possible to hit the time window after a few attempts. To avoid this problem, consider setting a non-zero
 225     timeout, thus showing the boot menu unconditionally. Some desktop environments might offer an option to
 226     directly boot into the boot menu, to avoid the problem altogether. Alternatively, use the command line
 227     <command>systemctl reboot --boot-loader-menu=0</command> from the shell.</para>
 228
 229     <para>In the editor, most keys simply insert themselves, but the following keys
 230     may be used to perform additional actions:</para>
 231
 232     <variablelist>
 233       <varlistentry>
 234         <term><keycap>←</keycap> (Left)</term>
 235         <term><keycap>→</keycap> (Right)</term>
 236         <term><keycap>Home</keycap></term>
 237         <term><keycap>End</keycap></term>
 238         <listitem><para>Navigate left/right</para></listitem>
 239       </varlistentry>
 240
 241       <varlistentry>
 242         <term><keycap>Esc</keycap></term>
 243         <listitem><para>Abort the edit and quit the editor</para></listitem>
 244       </varlistentry>
 245
 246       <varlistentry>
 247         <term><keycombo><keycap>Ctrl</keycap><keycap>k</keycap></keycombo></term>
 248         <listitem><para>Clear the command line</para></listitem>
 249       </varlistentry>
 250
 251       <varlistentry>
 252         <term><keycombo><keycap>Ctrl</keycap><keycap>w</keycap></keycombo></term>
 253         <term><keycombo><keycap>Alt</keycap><keycap>Backspace</keycap></keycombo></term>
 254         <listitem><para>Delete word backwards</para></listitem>
 255       </varlistentry>
 256
 257       <varlistentry>
 258         <term><keycombo><keycap>Alt</keycap><keycap>d</keycap></keycombo></term>
 259         <listitem><para>Delete word forwards</para></listitem>
 260       </varlistentry>
 261
 262       <varlistentry>
 263         <term><keycap>↵</keycap> (Enter)</term>
 264         <listitem><para>Boot entry with the edited command line</para></listitem>
 265       </varlistentry>
 266     </variablelist>
 267
 268     <para>Note that unless configured otherwise in the UEFI firmware, systemd-boot will
 269     use the US keyboard layout, so key labels might not match for keys like +/-.
 270     </para>
 271   </refsect1>
 272
 273   <refsect1>
 274     <title>Files</title>
 275
 276     <para>The files <command>systemd-boot</command> processes generally reside on the UEFI ESP which is
 277     usually mounted to <filename>/efi/</filename>, <filename>/boot/</filename> or
 278     <filename>/boot/efi/</filename> during OS runtime. It also processes files on the Extended Boot Loader
 279     partition which is typically mounted to <filename>/boot/</filename>, if it
 280     exists. <command>systemd-boot</command> reads runtime configuration such as the boot timeout and default
 281     entry from <filename>/loader/loader.conf</filename> on the ESP (in combination with data read from EFI
 282     variables). See
 283     <citerefentry><refentrytitle>loader.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>. Boot
 284     entry description files following the <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot
 285     Loader Specification</ulink> are read from <filename>/loader/entries/</filename> on the ESP and the
 286     Extended Boot Loader partition. Unified kernel boot entries following the <ulink
 287     url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink> are read from
 288     <filename>/EFI/Linux/</filename> on the ESP and the Extended Boot Loader partition. Optionally, a random
 289     seed for early boot entropy pool provisioning is stored in <filename>/loader/random-seed</filename> in
 290     the ESP.</para>
 291   </refsect1>
 292
 293   <refsect1>
 294     <title>EFI Variables</title>
 295
 296     <para>The following EFI variables are defined, set and read by <command>systemd-boot</command>, under the vendor
 297     UUID <literal>4a67b082-0a4c-41cf-b6c7-440b29bb8c4</literal>, for communication between the OS and the boot
 298     loader:</para>
 299
 300     <variablelist class='efi-variables'>
 301       <varlistentry>
 302         <term><varname>LoaderBootCountPath</varname></term>
 303         <listitem><para>If boot counting is enabled, contains the path to the file in whose name the boot counters are
 304         encoded. Set by the boot
 305         loader. <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 306         uses this information to mark a boot as successful as determined by the successful activation of the
 307         <filename>boot-complete.target</filename> target unit.</para></listitem>
 308       </varlistentry>
 309
 310       <varlistentry>
 311         <term><varname>LoaderConfigTimeout</varname></term>
 312         <term><varname>LoaderConfigTimeoutOneShot</varname></term>
 313         <listitem><para>The menu timeout in seconds. Read by the boot loader. <varname>LoaderConfigTimeout</varname>
 314         is maintained persistently, while <varname>LoaderConfigTimeoutOneShot</varname> is a one-time override which is
 315         read once (in which case it takes precedence over <varname>LoaderConfigTimeout</varname>) and then
 316         removed. <varname>LoaderConfigTimeout</varname> may be manipulated with the
 317         <keycap>t</keycap>/<keycap>T</keycap> keys, see above.</para></listitem>
 318       </varlistentry>
 319
 320       <varlistentry>
 321         <term><varname>LoaderDevicePartUUID</varname></term>
 322
 323         <listitem><para>Contains the partition UUID of the EFI System Partition the boot loader was run from. Set by
 324         the boot
 325         loader. <citerefentry><refentrytitle>systemd-gpt-auto-generator</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 326         uses this information to automatically find the disk booted from, in order to discover various other partitions
 327         on the same disk automatically.</para></listitem>
 328       </varlistentry>
 329
 330       <varlistentry>
 331         <term><varname>LoaderEntries</varname></term>
 332
 333         <listitem><para>A list of the identifiers of all discovered boot loader entries. Set by the boot
 334         loader.</para></listitem>
 335       </varlistentry>
 336
 337       <varlistentry>
 338         <term><varname>LoaderEntryDefault</varname></term>
 339         <term><varname>LoaderEntryOneShot</varname></term>
 340
 341         <listitem><para>The identifier of the default boot loader entry. Set primarily by the OS and read by the boot
 342         loader. <varname>LoaderEntryOneShot</varname> sets the default entry for the next boot only, while
 343         <varname>LoaderEntryDefault</varname> sets it persistently for all future
 344         boots. <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
 345         <option>set-default</option> and <option>set-oneshot</option> commands make use of these variables. The boot
 346         loader modifies <varname>LoaderEntryDefault</varname> on request, when the <keycap>d</keycap> key is used, see
 347         above.</para></listitem>
 348       </varlistentry>
 349
 350       <varlistentry>
 351         <term><varname>LoaderEntrySelected</varname></term>
 352
 353         <listitem><para>The identifier of the boot loader entry currently being booted. Set by the boot
 354         loader.</para></listitem>
 355       </varlistentry>
 356
 357       <varlistentry>
 358         <term><varname>LoaderFeatures</varname></term>
 359
 360         <listitem><para>A set of flags indicating the features the boot loader supports. Set by the boot loader. Use
 361         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this
 362         data.</para></listitem>
 363       </varlistentry>
 364
 365       <varlistentry>
 366         <term><varname>LoaderFirmwareInfo</varname></term>
 367         <term><varname>LoaderFirmwareType</varname></term>
 368
 369         <listitem><para>Brief firmware information. Set by the boot loader. Use
 370         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this
 371         data.</para></listitem>
 372       </varlistentry>
 373
 374       <varlistentry>
 375         <term><varname>LoaderImageIdentifier</varname></term>
 376
 377         <listitem><para>The path of executable of the boot loader used for the current boot, relative to the EFI System
 378         Partition's root directory. Set by the boot loader. Use
 379         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this
 380         data.</para></listitem>
 381       </varlistentry>
 382
 383       <varlistentry>
 384         <term><varname>LoaderInfo</varname></term>
 385
 386         <listitem><para>Brief information about the boot loader. Set by the boot loader. Use
 387         <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry> to view this
 388         data.</para></listitem>
 389       </varlistentry>
 390
 391       <varlistentry>
 392         <term><varname>LoaderTimeExecUSec</varname></term>
 393         <term><varname>LoaderTimeInitUSec</varname></term>
 394         <term><varname>LoaderTimeMenuUsec</varname></term>
 395
 396         <listitem><para>Information about the time spent in various parts of the boot loader. Set by the boot
 397         loader. Use <citerefentry><refentrytitle>systemd-analyze</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 398         to view this data. </para></listitem>
 399       </varlistentry>
 400
 401       <varlistentry>
 402         <term><varname>LoaderRandomSeed</varname></term>
 403
 404         <listitem><para>A binary random seed <command>systemd-boot</command> may optionally pass to the
 405         OS. This is a volatile EFI variable that is hashed at boot from the combination of a random seed
 406         stored in the ESP (in <filename>/loader/random-seed</filename>) and a "system token" persistently
 407         stored in the EFI variable <varname>LoaderSystemToken</varname> (see below). During early OS boot the
 408         system manager reads this variable and passes it to the OS kernel's random pool, crediting the full
 409         entropy it contains. This is an efficient way to ensure the system starts up with a fully initialized
 410         kernel random pool — as early as the initial RAM disk phase. <command>systemd-boot</command> reads
 411         the random seed from the ESP, combines it with the "system token", and both derives a new random seed
 412         to update in-place the seed stored in the ESP, and the random seed to pass to the OS from it via
 413         SHA256 hashing in counter mode. This ensures that different physical systems that boot the same
 414         "golden" OS image — i.e. containing the same random seed file in the ESP — will still pass a
 415         different random seed to the OS. It is made sure the random seed stored in the ESP is fully
 416         overwritten before the OS is booted, to ensure different random seed data is used between subsequent
 417         boots.</para>
 418
 419         <para>See <ulink url="https://systemd.io/RANDOM_SEEDS">Random Seeds</ulink> for
 420         further information.</para></listitem>
 421       </varlistentry>
 422
 423       <varlistentry>
 424         <term><varname>LoaderSystemToken</varname></term>
 425
 426         <listitem><para>A binary random data field, that is used for generating the random seed to pass to
 427         the OS (see above). Note that this random data is generally only generated once, during OS
 428         installation, and is then never updated again.</para></listitem>
 429       </varlistentry>
 430     </variablelist>
 431
 432     <para>Many of these variables are defined by the <ulink
 433     url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>.</para>
 434   </refsect1>
 435
 436   <refsect1>
 437     <title>Boot Counting</title>
 438
 439     <para><command>systemd-boot</command> implements a simple boot counting mechanism on top of the <ulink
 440     url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>, for automatic and unattended
 441     fallback to older kernel versions/boot loader entries when a specific entry continuously fails. Any boot loader
 442     entry file and unified kernel image file that contains a <literal>+</literal> followed by one or two numbers (if
 443     two they need to be separated by a <literal>-</literal>), before the <filename>.conf</filename> or
 444     <filename>.efi</filename> suffix is subject to boot counting: the first of the two numbers ('tries left') is
 445     decreased by one on every boot attempt, the second of the two numbers ('tries done') is increased by one (if 'tries
 446     done' is absent it is considered equivalent to 0). Depending on the current value of these two counters the boot
 447     entry is considered to be in one of three states:</para>
 448
 449     <orderedlist>
 450       <listitem><para>If the 'tries left' counter of an entry is greater than zero the entry is considered to be in
 451       'indeterminate' state. This means the entry has not completed booting successfully yet, but also hasn't been
 452       determined not to work.</para></listitem>
 453
 454       <listitem><para>If the 'tries left' counter of an entry is zero it is considered to be in 'bad' state. This means
 455       no further attempts to boot this item will be made (that is, unless all other boot entries are also in 'bad'
 456       state), as all attempts to boot this entry have not completed successfully.</para></listitem>
 457
 458       <listitem><para>If the 'tries left' and 'tries done' counters of an entry are absent it is considered to be in
 459       'good' state. This means further boot counting for the entry is turned off, as it successfully booted at least
 460       once. The
 461       <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
 462       service moves the currently booted entry from 'indeterminate' into 'good' state when a boot attempt completed
 463       successfully.</para></listitem>
 464     </orderedlist>
 465
 466     <para>Generally, when new entries are added to the boot loader, they first start out in 'indeterminate' state,
 467     i.e. with a 'tries left' counter greater than zero. The boot entry remains in this state until either it managed to
 468     complete a full boot successfully at least once (in which case it will be in 'good' state) — or the 'tries left'
 469     counter reaches zero (in which case it will be in 'bad' state).</para>
 470
 471     <para>Example: let's say a boot loader entry file <filename>foo.conf</filename> is set up for 3 boot tries. The
 472     installer will hence create it under the name <filename>foo+3.conf</filename>. On first boot, the boot loader will
 473     rename it to <filename>foo+2-1.conf</filename>. If that boot does not complete successfully, the boot loader will
 474     rename it to <filename>foo+1-2.conf</filename> on the following boot. If that fails too, it will finally be renamed
 475     <filename>foo+0-3.conf</filename> by the boot loader on next boot, after which it will be considered 'bad'. If the
 476     boot succeeds however the entry file will be renamed to <filename>foo.conf</filename> by the OS, so that it is
 477     considered 'good' from then on.</para>
 478
 479     <para>The boot menu takes the 'tries left' counter into account when sorting the menu entries: entries in 'bad'
 480     state are ordered at the beginning of the list, and entries in 'good' or 'indeterminate' at the end. The user can
 481     freely choose to boot any entry of the menu, including those already marked 'bad'. If the menu entry to boot is
 482     automatically determined, this means that 'good' or 'indeterminate' entries are generally preferred (as the bottom
 483     item of the menu is the one booted by default), and 'bad' entries will only be considered if there are no 'good' or
 484     'indeterminate' entries left.</para>
 485
 486     <para>The <citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry> kernel
 487     install framework optionally sets the initial 'tries left' counter to the value specified in
 488     <filename>/etc/kernel/tries</filename> when a boot loader entry is first created.</para>
 489   </refsect1>
 490
 491   <refsect1>
 492     <title>See Also</title>
 493     <para>
 494       <citerefentry><refentrytitle>bootctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
 495       <citerefentry><refentrytitle>loader.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
 496       <citerefentry><refentrytitle>systemd-bless-boot.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 497       <citerefentry><refentrytitle>systemd-boot-system-token.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 498       <citerefentry><refentrytitle>kernel-install</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
 499       <ulink url="https://systemd.io/BOOT_LOADER_SPECIFICATION">Boot Loader Specification</ulink>,
 500       <ulink url="https://systemd.io/BOOT_LOADER_INTERFACE">Boot Loader Interface</ulink>
 501     </para>
 502   </refsect1>
 503 </refentry>