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116 lines
4.8 KiB
Markdown
116 lines
4.8 KiB
Markdown
---
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title: systemd-boot UEFI Boot Manager
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category: Documentation for Developers
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layout: default
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SPDX-License-Identifier: LGPL-2.1-or-later
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---
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# systemd-boot UEFI Boot Manager
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systemd-boot is a UEFI boot manager which executes configured EFI images. The default entry is selected by a configured pattern (glob) or an on-screen menu.
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systemd-boot operates on the EFI System Partition (ESP) only. Configuration file fragments, kernels, initrds, other EFI images need to reside on the ESP.
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Linux kernels need to be built with CONFIG\_EFI\_STUB to be able to be directly executed as an EFI image.
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systemd-boot reads simple and entirely generic boot loader configuration files; one file per boot loader entry to select from. All files need to reside on the ESP.
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Pressing the Space key (or most other keys actually work too) during bootup will show an on-screen menu with all configured loader entries to select from.
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Pressing Enter on the selected entry loads and starts the EFI image.
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If no timeout is configured, which is the default setting, and no key pressed during bootup, the default entry is executed right away.
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All configuration files are expected to be 7-bit ASCII or valid UTF8. The loader configuration file understands the following keywords:
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| Config |
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|---------|------------------------------------------------------------|
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| default | pattern to select the default entry in the list of entries |
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| timeout | timeout in seconds for how long to show the menu |
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The entry configuration files understand the following keywords:
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| Entry |
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|--------|------------------------------------------------------------|
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| title | text to show in the menu |
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| version | version string to append to the title when the title is not unique |
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| machine-id | machine identifier to append to the title when the title is not unique |
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| efi | executable EFI image |
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| options | options to pass to the EFI image / kernel command line |
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| linux | linux kernel image (systemd-boot still requires the kernel to have an EFI stub) |
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| initrd | initramfs image (systemd-boot just adds this as option initrd=) |
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Examples:
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```
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/boot/loader/loader.conf
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timeout 3
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default 6a9857a393724b7a981ebb5b8495b9ea-*
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/boot/loader/entries/6a9857a393724b7a981ebb5b8495b9ea-3.8.0-2.fc19.x86_64.conf
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title Fedora 19 (Rawhide)
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version 3.8.0-2.fc19.x86_64
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machine-id 6a9857a393724b7a981ebb5b8495b9ea
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linux /6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/linux
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initrd /6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/initrd
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options root=UUID=f8f83f73-df71-445c-87f7-31f70263b83b quiet
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/boot/loader/entries/custom-kernel.conf
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title My kernel
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efi /bzImage
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options root=PARTUUID=084917b7-8be2-4e86-838d-f771a9902e08
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/boot/loader/entries/custom-kernel-initrd.conf
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title My kernel with initrd
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linux /bzImage
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initrd /initrd.img
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options root=PARTUUID=084917b7-8be2-4e86-838d-f771a9902e08 quiet`
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```
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While the menu is shown, the following keys are active:
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| Keys |
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|--------|------------------------------------------------------------|
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| Up/Down | Select menu entry |
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| Enter | boot the selected entry |
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| d | select the default entry to boot (stored in a non-volatile EFI variable) |
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| t/T | adjust the timeout (stored in a non-volatile EFI variable) |
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| e | edit the option line (kernel command line) for this bootup to pass to the EFI image |
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| Q | quit |
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| v | show the systemd-boot and UEFI version |
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| P | print the current configuration to the console |
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| h | show key mapping |
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Hotkeys to select a specific entry in the menu, or when pressed during bootup to boot the entry right-away:
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| Keys |
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|--------|------------------------------------------------------------|
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| l | Linux |
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| w | Windows |
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| a | macOS |
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| s | EFI Shell |
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| 1-9 | number of entry |
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Some EFI variables control the loader or exported the loaders state to the started operating system. The vendor UUID `4a67b082-0a4c-41cf-b6c7-440b29bb8c4f` and the variable names are supposed to be shared across all loaders implementations which follow this scheme of configuration:
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| EFI Variables |
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|---------------|------------------------|-------------------------------|
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| LoaderEntryDefault | entry identifier to select as default at bootup | non-volatile |
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| LoaderConfigTimeout | timeout in seconds to show the menu | non-volatile |
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| LoaderEntryOneShot | entry identifier to select at the next and only the next bootup | non-volatile |
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| LoaderDeviceIdentifier | list of identifiers of the volume the loader was started from | volatile |
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| LoaderDevicePartUUID | partition GPT UUID of the ESP systemd-boot was executed from | volatile |
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Links:
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[https://github.com/systemd/systemd](https://github.com/systemd/systemd)
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[https://uapi-group.org/specifications/specs/boot_loader_specification/](https://uapi-group.org/specifications/specs/boot_loader_specification/)
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