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doc: document charset to use for bootspec entry names

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Prompted-by: https://github.com/systemd/systemd/issues/12572#issuecomment-711074702
This commit is contained in:
Lennart Poettering 2020-10-19 14:19:52 +02:00
parent e9f4a596a2
commit d9067aba40
1 changed files with 21 additions and 1 deletions
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22
docs/BOOT_LOADER_SPECIFICATION.md
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@ -114,7 +114,23 @@ We define two directories below `$BOOT`:
**Note:** _In all cases the `/loader/` directory should be located directly in the root of the file system. Specifically, if `$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 `$BOOT/loader/entries/` directory each OS vendor may drop one or more configuration snippets with the suffix ".conf", one for each boot menu item. The file name of the file is used for identification of the boot item but shall never be presented to the user in the UI. The file name may be chosen freely but should be unique enough to avoid clashes between OS installations. More specifically it is suggested to include the machine ID (`/etc/machine-id` or the D-Bus machine ID for OSes that lack `/etc/machine-id`), the kernel version (as returned by `uname -r`) and an OS identifier (The ID field of `/etc/os-release`). Example: `$BOOT/loader/entries/6a9857a393724b7a981ebb5b8495b9ea-3.8.0-2.fc19.x86_64.conf`.
Inside the `$BOOT/loader/entries/` directory each OS vendor may drop one or
more configuration snippets with the suffix ".conf", one for each boot menu
item. The file name of the file is used for identification of the boot item but
shall never be presented to the user in the UI. The file name may be chosen
freely but should be unique enough to avoid clashes between OS
installations. More specifically it is suggested to include the machine ID
(`/etc/machine-id` or the D-Bus machine ID for OSes that lack
`/etc/machine-id`), the kernel version (as returned by `uname -r`) and an OS
identifier (The ID field of `/etc/os-release`). Example:
`$BOOT/loader/entries/6a9857a393724b7a981ebb5b8495b9ea-3.8.0-2.fc19.x86_64.conf`.
In order to maximize compatibility with file system implementations and
restricted boot loader environments, and to minimize conflicting character use
with other progams, 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:
@ -171,6 +187,10 @@ extension `.efi`. Support for images of this type is of course specific to
systems with EFI firmware. Ignore this section if you work on systems not
supporting EFI.
Type #2 file names should be chosen from the same restricted character set as
Type #1 described above (but use a different file name suffix of `.efi` instead
of `.conf`).
Images of this type have the advantage that all metadata and payload that makes
up the boot entry is monopolized in a single PE file that can be signed
cryptographically as one for the purpose of EFI SecureBoot.