Ubuntu Manpage: loader.conf - Configuration file for systemd-boot

Provided by: systemd-boot_256.5-2ubuntu4_amd64

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

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

EXAMPLE

SEE ALSO

NOTES