loader.conf(5) — Linux manual page

LOADER.CONF(5)                 loader.conf                LOADER.CONF(5)

NAME

       loader.conf - Configuration file for systemd-boot

SYNOPSIS

       ESP/loader/loader.conf, ESP/loader/entries/*.conf
       XBOOTLDR/loader/entries/*.conf

DESCRIPTION

       systemd-boot(7) will read ESP/loader/loader.conf, and any files
       with the ".conf" extension under ESP/loader/entries/ on the EFI
       system partition (ESP), and XBOOTLDR/loader/entries/ on the
       extended boot loader partition (XBOOTLDR) as defined by Boot
       Loader Specification[1].

       Each of these configuration files must consist of series of
       newline (i.e. ASCII code 10) separated lines, each consisting of
       an option name, followed by whitespace, and the option value.
       "#" may be used to start a comment line. Empty and comment lines
       are ignored. The files use UTF-8 encoding.

       Boolean arguments may be written as "yes"/"y"/"true"/"t"/"on"/"1"
       or "no"/"n"/"false"/"f"/"off"/"0".

OPTIONS

The configuration options supported by ESP/loader/entries/*.conf
and XBOOTLDR/loader/entries/*.conf files are defined as part of
the Boot Loader Specification[1].

The following configuration are supported by the loader.conf
configuration file:

default
A glob pattern to select the default entry. The default entry
may be changed in the boot menu itself, in which case the
name of the selected entry will be stored as an EFI variable,
overriding this option.

If set to "@saved" the chosen entry will be saved as an EFI
variable on every boot and automatically selected the next
time the boot loader starts.

Table 1. Automatically detected entries will use the
following names:
┌───────────────────────────────┬──────────────────────┐
│ Name │ Description │
├───────────────────────────────┼──────────────────────┤
│ auto-efi-default │ EFI Default Loader │
├───────────────────────────────┼──────────────────────┤
│ auto-efi-shell │ EFI Shell │
├───────────────────────────────┼──────────────────────┤
│ auto-osx │ macOS │
├───────────────────────────────┼──────────────────────┤
│ auto-poweroff │ Power Off The System │
├───────────────────────────────┼──────────────────────┤
│ auto-reboot │ Reboot The System │
├───────────────────────────────┼──────────────────────┤
│ auto-reboot-to-firmware-setup │ Reboot Into Firmware │
│ │ Interface │
├───────────────────────────────┼──────────────────────┤
│ auto-windows │ Windows Boot Manager │
└───────────────────────────────┴──────────────────────┘

Supported glob wildcard patterns are "?", "*", and "[...]"
(including ranges). Note that these patterns use the same
syntax as glob(7), but do not support all features. In
particular, set negation and named character classes are not
supported. The matching is done case-insensitively on the
entry ID (as shown by bootctl list).

Added in version 239.

timeout
How long the boot menu should be shown before the default
entry is booted, in seconds. This may be changed in the boot
menu itself and will be stored as an EFI variable in that
case, overriding this option.

If set to "menu-disabled" or "menu-hidden" or "0" (the
default), no menu is shown and the default entry will be
booted immediately. Unless "menu-disabled" is used, the menu
can be shown by pressing and holding a key before
systemd-boot is launched. Setting this to "menu-force"
disables the timeout while always showing the menu.

Added in version 239.

console-mode
This option configures the resolution of the console. This
may be changed in the boot menu itself and will be stored as
an EFI variable in that case, overriding this option.

Takes a number or one of the special values listed below. The
following values may be used:

0
Standard UEFI 80x25 mode

Added in version 239.

1
80x50 mode, not supported by all devices

Added in version 239.

2
the first non-standard mode provided by the device
firmware, if any

Added in version 239.

auto
Pick a suitable mode automatically using heuristics

Added in version 239.

max
Pick the highest-numbered available mode

Added in version 239.

keep
Keep the mode selected by firmware (the default)

Added in version 239.

editor
Takes a boolean argument. Enable (the default) or disable the
editor. The editor should be disabled if the machine can be
accessed by unauthorized persons.

Added in version 239.

auto-entries
Takes a boolean argument. Enable (the default) or disable
entries for other boot entries found on the boot partition.
In particular, this may be useful when loader entries are
created to show replacement descriptions for those entries.

Added in version 239.

auto-firmware
A boolean controlling the presence of the "Reboot Into
Firmware Interface" entry (enabled by default). If this is
disabled, the firmware interface may still be reached by
using the f key.

Added in version 239.

beep
Takes a boolean argument. If timeout enabled beep every
second, otherwise beep n times when n-th entry in boot menu
is selected (default disabled). Currently, only x86 is
supported, where it uses the PC speaker.

Added in version 251.

secure-boot-enroll
Danger: this feature might soft-brick your device if used
improperly.

Controls enrollment of secure boot keys found on the ESP if
the system is in setup mode:

off
No action is taken.

Added in version 253.

manual
Boot entries for found secure boot keys are created that
allow manual enrollment.

Added in version 253.

if-safe
Same behavior as manual, but will try to automatically
enroll the key "auto" if it is considered to be safe.
Currently, this is only the case if the system is running
inside a virtual machine.

Added in version 253.

force
Always enroll the "auto" key if found. Note that a
warning message with a timeout will still be shown if
this operation is unknown to be safe.

Added in version 253.

The different sets of variables can be set up under
/loader/keys/NAME where NAME is the name that is going to be
used as the name of the entry. This allows one to ship
multiple sets of Secure Boot variables and choose which one
to enroll at runtime.

Supported Secure Boot variables are one database for
authorized images, one for the key exchange key (KEK) and one
for the platform key (PK). For more information, refer to the
UEFI specification[2], under Secure Boot and Driver Signing.
Another resource that describe the interplay of the different
variables is the EDK2 documentation[3].

A complete set of UEFI variable includes db.auth, KEK.auth
and PK.auth. Note that these files need to be authenticated
UEFI variables. See below for an example of how to generate
them from regular X.509 keys.

uuid=$(systemd-id128 new --uuid)
for key in PK KEK db; do
openssl req -new -x509 -subj "/CN=${key}/" -keyout "${key}.key" -out "${key}.pem"
openssl x509 -outform DER -in "${key}.pem" -out "${key}.der"
sbsiglist --owner "${uuid}" --type x509 --output "${key}.esl" "${key}.der"
done

# See also: Windows Secure Boot Key Creation and Management Guidance[4]
curl --location \
"https://go.microsoft.com/fwlink/p/?linkid=321192" -o ms-db-2011.der \
"https://go.microsoft.com/fwlink/p/?linkid=321185" -o ms-kek-2011.der \
"https://go.microsoft.com/fwlink/p/?linkid=321194" -o ms-uefi-db-2011.der \
"https://go.microsoft.com/fwlink/p/?linkid=2239776" -o ms-db-2023.der \
"https://go.microsoft.com/fwlink/p/?linkid=2239775" -o ms-kek-2023.der \
"https://go.microsoft.com/fwlink/p/?linkid=2239872" -o ms-uefi-db-2023.der
sha1sum -c <<END
580a6f4cc4e4b669b9ebdc1b2b3e087b80d0678d ms-db-2011.der
31590bfd89c9d74ed087dfac66334b3931254b30 ms-kek-2011.der
46def63b5ce61cf8ba0de2e6639c1019d0ed14f3 ms-uefi-db-2011.der
45a0fa32604773c82433c3b7d59e7466b3ac0c67 ms-db-2023.der
459ab6fb5e284d272d5e3e6abc8ed663829d632b ms-kek-2023.der
b5eeb4a6706048073f0ed296e7f580a790b59eaa ms-uefi-db-2023.der
END
for key in ms-*.der; do
sbsiglist --owner 77fa9abd-0359-4d32-bd60-28f4e78f784b --type x509 --output "${key%der}esl" "${key}"
done

# Optionally add Microsoft Windows certificates (needed to boot into Windows).
cat ms-db-*.esl >>db.esl

# Optionally add Microsoft UEFI certificates for firmware drivers / option ROMs and third-party
# boot loaders (including shim). This is highly recommended on real hardware as not including this
# may soft-brick your device (see next paragraph).
cat ms-uefi-*.esl >>db.esl

# Optionally add Microsoft KEK certificates. Recommended if either of the Microsoft keys is used as
# the official UEFI revocation database is signed with this key. The revocation database can be
# updated with fwupdmgr(1).
cat ms-kek-*.esl >>KEK.esl

attr=NON_VOLATILE,RUNTIME_ACCESS,BOOTSERVICE_ACCESS,TIME_BASED_AUTHENTICATED_WRITE_ACCESS
sbvarsign --attr "${attr}" --key PK.key --cert PK.pem --output PK.auth PK PK.esl
sbvarsign --attr "${attr}" --key PK.key --cert PK.pem --output KEK.auth KEK KEK.esl
sbvarsign --attr "${attr}" --key KEK.key --cert KEK.pem --output db.auth db db.esl

This feature is considered dangerous because even if all the
required files are signed with the keys being loaded, some
files necessary for the system to function properly still
won't be. This is especially the case with Option ROMs (e.g.
for storage controllers or graphics cards). See Secure Boot
and Option ROMs[5] for more details.

Added in version 252.

reboot-for-bitlocker
Caveat: This feature is experimental, and is likely to be
changed (or removed in its current form) in a future version
of systemd.

Work around BitLocker requiring a recovery key when the boot
loader was updated (disabled by default).

Try to detect BitLocker encrypted drives along with an active
TPM. If both are found and Windows Boot Manager is selected
in the boot menu, set the "BootNext" EFI variable and restart
the system. The firmware will then start Windows Boot Manager
directly, leaving the TPM PCRs in expected states so that
Windows can unseal the encryption key. This allows
systemd-boot(7) to be updated without having to provide the
recovery key for BitLocker drive unlocking.

Note that the PCRs that Windows uses can be configured with
the "Configure TPM platform validation profile for native
UEFI firmware configurations" group policy under "Computer
Configuration\Administrative Templates\Windows
Components\BitLocker Drive Encryption". When Secure Boot is
enabled, changing this to PCRs "0,2,7,11" should be safe. The
TPM key protector needs to be removed and then added back for
the PCRs on an already encrypted drive to change. If PCR 4 is
not measured, this setting can be disabled to speed up
booting into Windows.

Added in version 251.

EXAMPLE

           # /boot/efi/loader/loader.conf
           timeout 0
           default 01234567890abcdef1234567890abdf0-*
           editor no

       The menu will not be shown by default (the menu can still be
       shown by pressing and holding a key during boot). One of the
       entries with files with a name starting with
       "01234567890abcdef1234567890abdf0-" will be selected by default.
       If more than one entry matches, the one with the highest priority
       will be selected (generally the one with the highest version
       number). The editor will be disabled, so it is not possible to
       alter the kernel command line.

NOTES

        1. Boot Loader Specification
           https://uapi-group.org/specifications/specs/boot_loader_specification

        2. UEFI specification
           https://uefi.org/specifications

        3. EDK2 documentation
           https://edk2-docs.gitbook.io/understanding-the-uefi-secure-boot-chain/secure_boot_chain_in_uefi/uefi_secure_boot

        4. Windows Secure Boot Key Creation and Management Guidance
           https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/windows-secure-boot-key-creation-and-management-guidance

        5. Secure Boot and Option ROMs
           https://github.com/Foxboron/sbctl/wiki/FAQ#option-rom

COLOPHON

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       ⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
       This page was obtained from the project's upstream Git repository
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systemd 257~devel                                         LOADER.CONF(5)

Pages that refer to this page: systemd-boot(7), systemd.directives(7), systemd.index(7)

...
https://man7.org/linux/man-pages/man5/loader.conf.5.html

loader.conf(5) — Linux manual page

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

EXAMPLE

SEE ALSO

NOTES

COLOPHON