* 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 moveable 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.
+* 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.
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 MBR disk labels
- * If the OS is installed on a disk with MBR disk label, and a partition with the MBR type id of 0xEA already exists it should be used as `$BOOT`.
- * Otherwise, if the OS is installed on a disk with MBR disk label, a new partition with MBR type id of 0xEA shall be created, of a suitable size (let's say 500MB), and it should be used as `$BOOT`.
-* On disks with GPT disk labels
- * If the OS is installed on a disk with GPT disk label, and a partition with the GPT type GUID of `bc13c2ff-59e6-4262-a352-b275fd6f7172` already exists, it should be used as `$BOOT`.
- * Otherwise, if the OS is installed on a disk with GPT disk label, and an ESP partition (i.e. with the GPT type UID of `c12a7328-f81f-11d2-ba4b-00a0c93ec93b`) already exists and is large enough (let's say 250MB) and otherwise qualifies, it should be used as `$BOOT`.
- * Otherwise, if the OS is installed on a disk with GPT disk label, and if the ESP partition already exists but is too small, a new suitably sized (let's say 500MB) partition with GPT type GUID of `bc13c2ff-59e6-4262-a352-b275fd6f7172` shall be created and it should be used as `$BOOT`.
- * Otherwise, if the OS is installed on a disk with GPT disk label, and no ESP partition exists yet, a new suitably sized (let's say 500MB) ESP should be created and should be used as `$BOOT`.
+* 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`.
+* 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 partition already exists but is too small, a new suitably sized (let's say 500MB) XBOOTLDR partition shall be created and used as `$BOOT`.
+ * Otherwise, if the OS is installed on a disk with GPT, and no ESP partition exists yet, a new suitably sized (let's say 500MB) ESP should be created and used as `$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 `$BOOT` is then dependent on and requires the mounting of the intermediate file system.
this specification. This specification only defines semantics of the `/loader/`
directory inside the file system (see below), but it doesn't intend to define
ownership of the whole file system exclusively. Boot loaders, firmware, and
-other software implementating this specification may choose to place other
+other software implementing this specification may choose to place other
files and directories in the same file system. For example, boot loaders that
implement this specification might install their own boot code into the `$BOOT`
partition. On systems where `$BOOT` is the ESP this is a particularly common
## Links
+[GUID Partition Table](https://en.wikipedia.org/wiki/GUID_Partition_Table)<br>
+[Boot Loader Interface](https://systemd.io/BOOT_LOADER_INTERFACE)<br>
+[Discoverable Partitions Specification](https://systemd.io/DISCOVERABLE_PARTITIONS)<br>
[systemd-boot(7)](https://www.freedesktop.org/software/systemd/man/systemd-boot.html)<br>
-[bootctl(1)](https://www.freedesktop.org/software/systemd/man/bootctl.html)
+[bootctl(1)](https://www.freedesktop.org/software/systemd/man/bootctl.html)<br>
+[systemd-gpt-auto-generator(8)](https://www.freedesktop.org/software/systemd/man/systemd-gpt-auto-generator.html)
projects / thirdparty / systemd.git / blobdiff