programs. The same scheme can be used to prepare OS media for cases where the
firmware includes a boot loader. The target audience for this specification is:
-* Boot loader developers, to write a boot loader that directly reads its configuration at runtime from these drop-in snippets
-* Firmware developers, to add generic boot loading support directly to the firmware itself
-* Distribution and Core OS developers, in order to create these snippets at OS/kernel package installation time
-* UI developers, for implementing a user interface that discovers the available boot options
-* OS Installer developers, to prepare their installation media and for setting up the initial drop-in directory
+* Boot loader developers, to write a boot loader that directly reads its
+ configuration at runtime from these drop-in snippets
+* Firmware developers, to add generic boot loading support directly to the
+ firmware itself
+* Distribution and Core OS developers, in order to create these snippets at
+ OS/kernel package installation time
+* UI developers, for implementing a user interface that discovers the available
+ boot options
+* OS Installer developers, to prepare their installation media and for setting
+ up the initial drop-in directory
## Why is there a need for this specification?
Of course, without this specification things already work mostly fine. But here's why we think this specification is needed:
-* To make the boot more robust, as no explicit rewriting of configuration files is required any more
-* To allow an out of the box boot experience on any platform without the need of traditional firmware mechanisms (e.g. BIOS calls, UEFI Boot Services)
-* To improve dual-boot scenarios. Currently, multiple Linux installations tend to fight over which boot loader becomes the primary one in possession of the MBR, and only that one installation can then update the boot loader configuration of it freely. Other Linux installs have to be manually configured to never touch the MBR and instead install a chain-loaded boot loader in their own partition headers. In this new scheme as all installations share a loader directory no manual configuration has to take place, and all participants implicitly cooperate due to removal of name collisions and can install/remove their own boot menu entries at free will, without interfering with the entries of other installed operating systems.
-* Drop-in directories are otherwise now pretty ubiquitous on Linux as an easy way to extend configuration without having to edit, regenerate or manipulate configuration files. For the sake of uniformity, we should do the same for extending the boot menu.
-* Userspace code can sanely parse boot loader configuration which is essential with modern BIOSes which do not necessarily initialize USB keyboards anymore during boot, which makes boot menus hard to reach for the user. If userspace code can parse the boot loader configuration, too, this allows for UIs that can select a boot menu item to boot into, before rebooting the machine, thus not requiring interactivity during early boot.
-* To unify and thus simplify configuration of the various boot loaders around, which makes configuration of the boot loading process easier for users, administrators and developers alike.
-* For boot loaders with configuration _scripts_ such as grub2, adopting this spec allows for mostly static scripts that are generated only once at first installation, but then do not need to be updated anymore as that is done via drop-in files exclusively.
+* To make the boot more robust, as no explicit rewriting of configuration files
+ is required any more
+* To allow an out of the box boot experience on any platform without the need
+ of traditional firmware mechanisms (e.g. BIOS calls, UEFI Boot Services)
+* To improve dual-boot scenarios. Currently, multiple Linux installations tend
+ to fight over which boot loader becomes the primary one in possession of the
+ MBR, and only that one installation can then update the boot loader
+ configuration of it freely. Other Linux installs have to be manually
+ configured to never touch the MBR and instead install a chain-loaded boot
+ loader in their own partition headers. In this new scheme as all
+ installations share a loader directory no manual configuration has to take
+ place, and all participants implicitly cooperate due to removal of name
+ collisions and can install/remove their own boot menu entries at free will,
+ without interfering with the entries of other installed operating systems.
+* Drop-in directories are otherwise now pretty ubiquitous on Linux as an easy
+ way to extend configuration without having to edit, regenerate or manipulate
+ configuration files. For the sake of uniformity, we should do the same for
+ extending the boot menu.
+* Userspace code can sanely parse boot loader configuration which is essential
+ with modern BIOSes which do not necessarily initialize USB keyboards anymore
+ during boot, which makes boot menus hard to reach for the user. If userspace
+ code can parse the boot loader configuration, too, this allows for UIs that
+ can select a boot menu item to boot into, before rebooting the machine, thus
+ not requiring interactivity during early boot.
+* To unify and thus simplify configuration of the various boot loaders around,
+ which makes configuration of the boot loading process easier for users,
+ administrators and developers alike.
+* For boot loaders with configuration _scripts_ such as grub2, adopting this
+ spec allows for mostly static scripts that are generated only once at first
+ installation, but then do not need to be updated anymore as that is done via
+ drop-in files exclusively.
## Why not simply rely on the EFI boot menu logic?
system, it provides a boot options logic that can offer similar
functionality. Here's why we think that it is not enough for our uses:
-* The various EFI implementations implement the boot order/boot item logic to different levels. Some firmware implementations do not offer a boot menu at all and instead unconditionally follow the EFI boot order, booting the first item that is working.
-* If the firmware setup is used to reset all data usually all EFI boot entries are lost, making the system entirely unbootable, as the firmware setups generally do not offer a UI to define additional boot items. By placing the menu item information on disk, it is always available, regardless if the BIOS setup data is lost.
-* Harddisk images should be movable between machines and be bootable without requiring explicit EFI variables to be set. This also requires that the list of boot options is defined on disk, and not in EFI variables alone.
-* EFI is not universal yet (especially on non-x86 platforms), this specification is useful both for EFI and non-EFI boot loaders.
-* Many EFI systems disable USB support during early boot to optimize boot times, thus making keyboard input unavailable in the EFI menu. It is thus useful if the OS UI has a standardized way to discover available boot options which can be booted to.
+* The various EFI implementations implement the boot order/boot item logic to
+ different levels. Some firmware implementations do not offer a boot menu at
+ all and instead unconditionally follow the EFI boot order, booting the first
+ item that is working.
+* If the firmware setup is used to reset all data usually all EFI boot entries
+ are lost, making the system entirely unbootable, as the firmware setups
+ generally do not offer a UI to define additional boot items. By placing the
+ menu item information on disk, it is always available, regardless if the BIOS
+ setup data is lost.
+* Harddisk images should be movable between machines and be bootable without
+ requiring explicit EFI variables to be set. This also requires that the list
+ of boot options is defined on disk, and not in EFI variables alone.
+* EFI is not universal yet (especially on non-x86 platforms), this
+ specification is useful both for EFI and non-EFI boot loaders.
+* Many EFI systems disable USB support during early boot to optimize boot
+ times, thus making keyboard input unavailable in the EFI menu. It is thus
+ useful if the OS UI has a standardized way to discover available boot options
+ which can be booted to.
## Technical Details
-Everything described below is located on a placeholder file system `$BOOT`. The installer program should pick `$BOOT` according to the following rules:
+Everything described below is located on a placeholder file system `$BOOT`. The
+installer program should pick `$BOOT` according to the following rules:
* On disks with an MBR partition table:
- * If the OS is installed on a disk with an MBR partition table, and a partition with the type id of 0xEA already exists it should be used as `$BOOT`.
- * Otherwise, if the OS is installed on a disk with an MBR partition table, a new partition with type id of 0xEA shall be created, of a suitable size (let's say 500MB), and it should be used as `$BOOT`.
+ * If the OS is installed on a disk with an MBR partition table, and a
+ partition with the type id of 0xEA already exists it should be used as
+ `$BOOT`.
+ * Otherwise, if the OS is installed on a disk with an MBR partition table, a
+ new partition with type id of 0xEA shall be created, of a suitable size
+ (let's say 500MB), and it should be used as `$BOOT`.
* On disks with GPT (GUID Partition Table)
- * If the OS is installed on a disk with GPT, and an Extended Boot Loader Partition or XBOOTLDR partition for short, i.e. a partition with GPT type GUID of `bc13c2ff-59e6-4262-a352-b275fd6f7172`, already exists, it should be used as `$BOOT`.
- * Otherwise, if the OS is installed on a disk with GPT, and an EFI System Partition or ESP for short, i.e. a partition with GPT type UID of `c12a7328-f81f-11d2-ba4b-00a0c93ec93b`) already exists and is large enough (let's say 250MB) and otherwise qualifies, it should be used as `$BOOT`.
- * Otherwise, if the OS is installed on a disk with GPT, and if the ESP already exists but is too small, a new suitably sized (let's say 500MB) XBOOTLDR partition shall be created and used as `$BOOT`.
- * Otherwise, if the OS is installed on a disk with GPT, and no ESP exists yet, a new suitably sized (let's say 500MB) ESP should be created and used as `$BOOT`.
-
-This placeholder file system shall be determined during _installation time_, and an fstab entry may be created. It should be mounted to either `/boot/` or `/efi/`. Additional locations like `/boot/efi/`, with `/boot/` being a separate file system, might be supported by implementations. This is not recommended because the mounting of `$BOOT` is then dependent on and requires the mounting of the intermediate file system.
-
-**Note:** _`$BOOT` should be considered **shared** among all OS installations of a system. Instead of maintaining one `$BOOT` per installed OS (as `/boot/` was traditionally handled), all installed OS share the same place to drop in their boot-time configuration._
+ * If the OS is installed on a disk with GPT, and an Extended Boot Loader
+ Partition (or XBOOTLDR partition for short), i.e. a partition with GPT type
+ GUID of `bc13c2ff-59e6-4262-a352-b275fd6f7172`, already exists, it should
+ be used as `$BOOT`.
+ * Otherwise, if the OS is installed on a disk with GPT, and an EFI System
+ Partition (or ESP for short), i.e. a partition with GPT type UID of
+ `c12a7328-f81f-11d2-ba4b-00a0c93ec93b` already exists and is large enough
+ (let's say 250MB) and otherwise qualifies, it should be used as `$BOOT`.
+ * Otherwise, if the OS is installed on a disk with GPT, and if the ESP
+ already exists but is too small, a new suitably sized (let's say 500MB)
+ XBOOTLDR partition shall be created and used as `$BOOT`.
+ * Otherwise, if the OS is installed on a disk with GPT, and no ESP exists
+ yet, a new suitably sized (let's say 500MB) ESP should be created and used
+ as `$BOOT`.
+
+This placeholder file system shall be determined during _installation time_,
+and an fstab entry may be created. It should be mounted to either `/boot/` or
+`/efi/`. Additional locations like `/boot/efi/` (with `/boot/` being a separate
+file system) might be supported by implementations. This is not recommended
+because the mounting of `$BOOT` is then dependent on and requires the mounting
+of the intermediate file system.
+
+**Note:** _`$BOOT` should be considered **shared** among all OS installations
+of a system. Instead of maintaining one `$BOOT` per installed OS (as `/boot/`
+was traditionally handled), all installed OS share the same place to drop in
+their boot-time configuration._
For systems where the firmware is able to read file systems directly, `$BOOT`
must be a file system readable by the firmware. For other systems and generic
We define two directories below `$BOOT`:
-* `$BOOT/loader/` is the directory containing all files needed for Type #1 entries
-* `$BOOT/loader/entries/` is the directory containing the drop-in snippets. This directory contains one `.conf` file for each boot menu item.
+* `$BOOT/loader/` is the directory containing all files needed for Type #1
+ entries
-**Note:** _In all cases the `/loader/` directory should be located directly in the root of the file system. Specifically, if `$BOOT` is the ESP, then `/loader/` directory should be located directly in the root directory of the ESP, and not in the `/EFI/` subdirectory._
+* `$BOOT/loader/entries/` is the directory containing the drop-in
+ snippets. This directory contains one `.conf` file for each boot menu item.
+
+**Note:** _In all cases the `/loader/` directory should be located directly in
+the root of the file system. Specifically, if `$BOOT` is the ESP, then
+`/loader/` directory should be located directly in the root directory of the
+ESP, and not in the `/EFI/` subdirectory._
Inside the `$BOOT/loader/entries/` directory each OS vendor may drop one or
more configuration snippets with the suffix ".conf", one for each boot menu
In order to maximize compatibility with file system implementations and
restricted boot loader environments, and to minimize conflicting character use
-with other programs, file names shall be chosen from a restricted character set:
-ASCII upper and lower case characters, digits, "+", "-", "_" and ".". Also, the
-file names should have a length of at least one and at most 255 characters
-(including file name suffix).
-
-These configuration snippets shall be Unix-style text files (i.e. line separation with a single newline character), in the UTF-8 encoding. The configuration snippets are loosely inspired on Grub1's configuration syntax. Lines beginning with '#' shall be ignored and used for commenting. The first word of a line is used as key and shall be separated by one or more spaces from its value. The following keys are known:
-
-* `title` shall contain a human readable title string for this menu item. This will be displayed in the boot menu for the item. It is a good idea to initialize this from the `PRETTY_NAME` of `/etc/os-release`. This name should be descriptive and does not have to be unique. If a boot loader discovers two entries with the same title it is a good idea to show more than just the raw title in the UI, for example by appending the `version` field. This field is optional. Example: "Fedora 18 (Spherical Cow)".
-* `version` shall contain a human readable version string for this menu item. This is usually the kernel version and is intended for use by OSes to install multiple kernel versions at the same time with the same `title` field. This field shall be in a syntax that is useful for Debian-style version sorts, so that the boot loader UI can determine the newest version easily and show it first or preselect it automatically. This field is optional. Example: `3.7.2-201.fc18.x86_64`.
-* `machine-id` shall contain the machine ID of the OS `/etc/machine-id`. This is useful for boot loaders and applications to filter out boot entries, for example to show only a single newest kernel per OS, or to group items by OS, or to maybe filter out the currently booted OS in UIs that want to show only other installed operating systems. This ID shall be formatted as 32 lower case hexadecimal characters (i.e. without any UUID formatting). This key is optional. Example: `4098b3f648d74c13b1f04ccfba7798e8`.
-* `linux` refers to the Linux kernel to spawn and shall be a path relative to the `$BOOT` directory. It is recommended that every distribution creates a machine id and version specific subdirectory below `$BOOT` and places its kernels and initial RAM disk images there. Example: `/6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/linux`.
-* `initrd` refers to the initrd to use when executing the kernel. This also shall be a path relative to the `$BOOT` directory. This key is optional. This key may appear more than once in which case all specified images are used, in the order they are listed. Example: `6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/initrd`.
-* `efi` refers to an arbitrary EFI program. This also takes a path relative to `$BOOT`. If this key is set, and the system is not an EFI system this entry should be hidden.
-* `options` shall contain kernel parameters to pass to the Linux kernel to spawn. This key is optional and may appear more than once in which case all specified parameters are used in the order they are listed.
+with other programs, file names shall be chosen from a restricted character
+set: ASCII upper and lower case characters, digits, "+", "-", "_" and
+".". Also, the file names should have a length of at least one and at most 255
+characters (including file name suffix).
+
+These configuration snippets shall be Unix-style text files (i.e. line
+separation with a single newline character), in the UTF-8 encoding. The
+configuration snippets are loosely inspired on Grub1's configuration
+syntax. Lines beginning with '#' shall be ignored and used for commenting. The
+first word of a line is used as key and shall be separated by one or more
+spaces from its value. The following keys are known:
+
+* `title` shall contain a human readable title string for this menu item. This
+ will be displayed in the boot menu for the item. It is a good idea to
+ initialize this from the `PRETTY_NAME` of `/etc/os-release`. This name should
+ be descriptive and does not have to be unique. If a boot loader discovers two
+ entries with the same title it is a good idea to show more than just the raw
+ title in the UI, for example by appending the `version` field. This field is
+ optional. Example: "Fedora 18 (Spherical Cow)".
+* `version` shall contain a human readable version string for this menu
+ item. This is usually the kernel version and is intended for use by OSes to
+ install multiple kernel versions at the same time with the same `title`
+ field. This field shall be in a syntax that is useful for Debian-style
+ version sorts, so that the boot loader UI can determine the newest version
+ easily and show it first or preselect it automatically. This field is
+ optional. Example: `3.7.2-201.fc18.x86_64`.
+* `machine-id` shall contain the machine ID of the OS `/etc/machine-id`. This
+ is useful for boot loaders and applications to filter out boot entries, for
+ example to show only a single newest kernel per OS, or to group items by OS,
+ or to maybe filter out the currently booted OS in UIs that want to show only
+ other installed operating systems. This ID shall be formatted as 32 lower
+ case hexadecimal characters (i.e. without any UUID formatting). This key is
+ optional. Example: `4098b3f648d74c13b1f04ccfba7798e8`.
+* `linux` refers to the Linux kernel to spawn and shall be a path relative to
+ `$BOOT`. It is recommended that every distribution creates a machine id and
+ version specific subdirectory below `$BOOT` and places its kernels and
+ initial RAM disk images there. Example:
+ `/6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/linux`.
+* `initrd` refers to the initrd to use when executing the kernel. This also
+ shall be a path relative to `$BOOT`. This key is optional. This key may
+ appear more than once in which case all specified images are used, in the
+ order they are listed. Example:
+ `6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.x86_64/initrd`.
+* `efi` refers to an arbitrary EFI program. This also takes a path relative to
+ `$BOOT`. If this key is set, and the system is not an EFI system this entry
+ should be hidden.
+* `options` shall contain kernel parameters to pass to the Linux kernel to
+ spawn. This key is optional and may appear more than once in which case all
+ specified parameters are used in the order they are listed.
* `devicetree` refers to the binary device tree to use when executing the
-kernel. This also shall be a path relative to the `$BOOT` directory. This
-key is optional. Example: `6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.armv7hl/tegra20-paz00.dtb`.
+ kernel. This also shall be a path relative to `$BOOT`. This key is
+ optional. Example:
+ `6a9857a393724b7a981ebb5b8495b9ea/3.8.0-2.fc19.armv7hl/tegra20-paz00.dtb`.
* `devicetree-overlay` refers to a list of device tree overlays that should be
-applied by the boot loader. Multiple overlays are separated by spaces and
-applied in the same order as they are listed. This key is optional but depends
-on the `devicetree` key. Example:
-`/6a9857a393724b7a981ebb5b8495b9ea/overlays/overlay_A.dtbo
-/6a9857a393724b7a981ebb5b8495b9ea/overlays/overlay_B.dtbo`
-* `architecture` refers to the architecture this entry is defined for. The argument should be an architecture identifier, using the architecture vocabulary defined by the EFI specification (i.e. `IA32`, `x64`, `IA64`, `ARM`, `AA64`, …). If specified and this does not match (case insensitively) the local system architecture this entry should be hidden.
-
-Each configuration drop-in snippet must include at least a `linux` or an `efi` key and is otherwise not valid. Here's an example for a complete drop-in file:
+ applied by the boot loader. Multiple overlays are separated by spaces and
+ applied in the same order as they are listed. This key is optional but
+ depends on the `devicetree` key. Example:
+ `/6a9857a393724b7a981ebb5b8495b9ea/overlays/overlay_A.dtbo
+ /6a9857a393724b7a981ebb5b8495b9ea/overlays/overlay_B.dtbo`
+* `architecture` refers to the architecture this entry is defined for. The
+ argument should be an architecture identifier, using the architecture
+ vocabulary defined by the EFI specification (i.e. `IA32`, `x64`, `IA64`,
+ `ARM`, `AA64`, …). If specified and this does not match (case insensitively)
+ the local system architecture this entry should be hidden.
+
+Each configuration drop-in snippet must include at least a `linux` or an `efi`
+key and is otherwise not valid. Here's an example for a complete drop-in file:
# /boot/loader/entries/6a9857a393724b7a981ebb5b8495b9ea-3.8.0-2.fc19.x86_64.conf
title Fedora 19 (Rawhide)
which are not don't make unnecessary assumption on the underlying firmware,
i.e. don't hard depend on legacy BIOS calls or UEFI boot services.
-Note that these configuration snippets may only reference kernels (and EFI programs) that reside on the same file system as the configuration snippets, i.e. everything referenced must be contained in the same file system. This is by design, as referencing other partitions or devices would require a non-trivial language for denoting device paths. If kernels/initrds are to be read from other partitions/disks the boot loader can do this in its own native configuration, using its own specific device path language, and this is out of focus for this specification. More specifically, on non-EFI systems configuration snippets following this specification cannot be used to spawn other operating systems (such as Windows).
+Note that these configuration snippets may only reference kernels (and EFI
+programs) that reside on the same file system as the configuration snippets,
+i.e. everything referenced must be contained in the same file system. This is
+by design, as referencing other partitions or devices would require a
+non-trivial language for denoting device paths. If kernels/initrds are to be
+read from other partitions/disks the boot loader can do this in its own native
+configuration, using its own specific device path language, and this is out of
+focus for this specification. More specifically, on non-EFI systems
+configuration snippets following this specification cannot be used to spawn
+other operating systems (such as Windows).
### Type #2 EFI Unified Kernel Images
A valid unified kernel image must contain two PE sections:
* `.cmdline` section with the kernel command line
-* `.osrel` section with an embedded copy of the [os-release](https://www.freedesktop.org/software/systemd/man/os-release.html) file describing the image
+* `.osrel` section with an embedded copy of the
+ [os-release](https://www.freedesktop.org/software/systemd/man/os-release.html)
+ file describing the image
-The `PRETTY_NAME=` and `VERSION_ID=` fields in the embedded os-release file are used the same as `title` and `version` in the "boot loader specification" entries. The `.cmdline` section is used instead of the `options` field. `linux` and `initrd` fields are not necessary, and there is no counterpart for the `machine-id` field.
+The `PRETTY_NAME=` and `VERSION_ID=` fields in the embedded os-release file are
+used the same as `title` and `version` in the "boot loader specification"
+entries. The `.cmdline` section is used instead of the `options` field. `linux`
+and `initrd` fields are not necessary, and there is no counterpart for the
+`machine-id` field.
On EFI, any such images shall be added to the list of valid boot entries.
### Additional notes
-Note that these configurations snippets do not need to be the only configuration source for a boot loader. It may extend this list of entries with additional items from other configuration files (for example its own native configuration files) or automatically detected other entries without explicit configuration.
+Note that these configurations snippets do not need to be the only
+configuration source for a boot loader. It may extend this list of entries with
+additional items from other configuration files (for example its own native
+configuration files) or automatically detected other entries without explicit
+configuration.
-To make this explicitly clear: this specification is designed with "free" operating systems in mind, starting Windows or macOS is out of focus with these configuration snippets, use boot-loader specific solutions for that. In the text above, if we say "OS" we hence imply "free", i.e. primarily Linux (though this could be easily be extended to the BSDs and whatnot).
+To make this explicitly clear: this specification is designed with "free"
+operating systems in mind, starting Windows or macOS is out of focus with these
+configuration snippets, use boot-loader specific solutions for that. In the
+text above, if we say "OS" we hence imply "free", i.e. primarily Linux (though
+this could be easily be extended to the BSDs and whatnot).
-Note that all paths used in the configuration snippets use a Unix-style "/" as path separator. This needs to be converted to an EFI-style "\\" separator in EFI boot loaders.
+Note that all paths used in the configuration snippets use a Unix-style "/" as
+path separator. This needs to be converted to an EFI-style "\\" separator in
+EFI boot loaders.
## Logic
file is also private property of the kernel package and should be removed along
with it.
-A _UI application_ intended to show available boot options shall operate similar to a boot loader, but might apply additional filters, for example by filtering out the booted OS via the machine ID, or by suppressing all but the newest kernel versions.
+A _UI application_ intended to show available boot options shall operate
+similar to a boot loader, but might apply additional filters, for example by
+filtering out the booted OS via the machine ID, or by suppressing all but the
+newest kernel versions.
-An _OS installer_ picks the right place for `$BOOT` as defined above (possibly creating a partition and file system for it) and pre-creates the `/loader/entries/` directory in it. It then installs an appropriate boot loader that can read these snippets. Finally, it installs one or more kernel packages.
+An _OS installer_ picks the right place for `$BOOT` as defined above (possibly
+creating a partition and file system for it) and pre-creates the
+`/loader/entries/` directory in it. It then installs an appropriate boot loader
+that can read these snippets. Finally, it installs one or more kernel packages.
## Out of Focus
There are a couple of items that are out of focus for this specification:
-* If userspace can figure out the available boot options, then this is only useful so much: we'd still need to come up with a way how userspace could communicate to the boot loader the default boot loader entry temporarily or persistently. Defining a common scheme for this is certainly a good idea, but out of focus for this specification.
-* This specification is just about "Free" Operating systems. Hooking in other operating systems (like Windows and macOS) into the boot menu is a different story and should probably happen outside of this specification. For example, boot loaders might choose to detect other available OSes dynamically at runtime without explicit configuration (like `systemd-boot` does it), or via native configuration (for example via explicit Grub2 configuration generated once at installation).
-* This specification leaves undefined what to do about systems which are upgraded from an OS that does not implement this specification. As the previous boot loader logic was largely handled by in distribution-specific ways we probably should leave the upgrade path (and whether there actually is one) to the distributions. The simplest solution might be to simply continue with the old scheme for old installations and use this new scheme only for new installations.
+* If userspace can figure out the available boot options, then this is only
+ useful so much: we'd still need to come up with a way how userspace could
+ communicate to the boot loader the default boot loader entry temporarily or
+ persistently. Defining a common scheme for this is certainly a good idea, but
+ out of focus for this specification.
+* This specification is just about "Free" Operating systems. Hooking in other
+ operating systems (like Windows and macOS) into the boot menu is a different
+ story and should probably happen outside of this specification. For example,
+ boot loaders might choose to detect other available OSes dynamically at
+ runtime without explicit configuration (like `systemd-boot` does it), or via
+ native configuration (for example via explicit Grub2 configuration generated
+ once at installation).
+* This specification leaves undefined what to do about systems which are
+ upgraded from an OS that does not implement this specification. As the
+ previous boot loader logic was largely handled by in distribution-specific
+ ways we probably should leave the upgrade path (and whether there actually is
+ one) to the distributions. The simplest solution might be to simply continue
+ with the old scheme for old installations and use this new scheme only for
+ new installations.
## Links
projects / thirdparty / systemd.git / commitdiff
