https://fedoraproject.org/wiki/Changes/UnifyGrubConfig
== Summary ==
This change makes the GRUB configuration files layout to be consistent
across all the supported architectures. Currently EFI is a special
case since the GRUB configuration file and environment variables block
are stored in the EFI System Partition (ESP) instead of the boot
partition (or `/boot` directory if no boot partition is used).
== Owner ==
* Name: [[User:Javierm|Javier Martinez Canillas]]
* Email: javi...@redhat.com
* Name: [[User:Gicmo|Christian Kellner]]
* Email: ckell...@redhat.com
== Detailed Description ==
The GRUB configuration files layout on EFI platforms is not consistent
with the other non-EFI platforms (e.g: x86 with legacy BIOS, ppc64le
with Open Firmware). On platforms using EFI the GRUB configuration
file (`grub.cfg`) and environment variables block (`grubenv`) are
stored in the EFI System Partition (ESP) while for non-EFI platforms
these are stored in the boot partition (or `/boot` directory if not
boot partition is used).
The reason for this is that the path where the GRUB bootloader
searches for its configuration file varies depending on the firmware
interface used. In most cases, GRUB searches for it in the path set in
the `$prefix` variable. The device is not specified in that case, GRUB
just searches for a configuration in this path for every detected
device. But on EFI, a special `$fw_path` variable is used instead.
This variable specifies both the device and path from where the GRUB
bootloader was loaded and these are used to search for the
configuration file. This is done for security reasons, to make sure
that the correct GRUB configuration file is used and not just the
first one found in one of the detected devices.
Since the GRUB binary is located in the ESP, it expects to find the
configuration file in that location as well. But this creates the
mentioned inconsistency, because the GRUB configuration file has to be
stored in `/boot/efi/EFI/fedora/grub.cfg` while for non-EFI platforms
it has to be stored in `/boot/grub2/grub.cfg`.
This leads to a GRUB configuration layout that is confusing for users
and error prone, since either the tools that are used to manage these
files have to be aware of the differences or symbolic links used to
hide the fact that the pats differ depending on the platform. Also, it
creates artificial constraints on the OS installation due the
differences in the configuration layout used. A system installed when
using EFI won't be bootable if the firmware configuration is changed
to boot using legacy BIOS instead, for example enabling the EFI
Compatibility Support Module or moving the disk to a BIOS machine.
The proposal is to always store the `grub.cfg` and `grubenv` files in
the `/boot/grub2/` directory, making `/boot/efi/EFI/fedora/grub.cfg`
to only be a small configuration file that sets a different `$prefix`
variable and loads the configuration file stored in
`/boot/grub2/grub.cfg`.
The `$prefix` variable will be set to the device partition where
`/boot/grub2/grub.cfg` is stored, using the partition filesystem's
Universally Unique IDentifier (UUID). That way the correct GRUB
configuration file will be loaded, making it as secure as the current
approach where the configuration file in the ESP is used.
A drawback of the new approach is that the GRUB configuration will now
depend on the boot partition (or `/boot` directory if no boot
partition is used). But since the kernel and initramfs images are
stored there too, the bootloader configuration already has this
dependency anyways.
Note that the proposed configuration files layout is already used by
the Fedora CoreOS Assembler (COSA) and OSBuild image builders. So this
will make the systems installed with Anaconda to be consistent with
the images generated by these.
== Benefit to Fedora ==
This change will not only simplify and make less confusing the GRUB
configuration but also allow the following improvements:
* To have a consistent configuration across all the architectures using GRUB.
* Allow the same installation to be booted with either EFI or legacy BIOS.
* Use the same documentation and commands for all architectures
instead of having EFI as a special case.
* Make GRUB configuration tools more robust by not relying on symbolic
links to be created and not having to handle platform specific cases.
* Align with images generated by COSA and OSBuild on how the GRUB
configuration files are used.
* Align with other Linux distributions on how the GRUB configuration
files are used.
== Scope ==
* Proposal owners:
** Modify Anaconda to generate the `grub.cfg` and `grubenv` files in
`/boot/grub2/` instead of `/boot/efi/EFI/fedora/` for EFI platforms.
** Make Anaconda to generate the minimal GRUB config file in the ESP
that sets the `$prefix` variable and loads the configuration file
located in `/boot/grub2/grub.cfg`.
** Modify the grub2 package scriptlets to not generate the
`/boot/grub2/grubenv` and `/etc/grub2-efi.cfg` symbolic links since
these will not be needed anymore.
** Make any changes needed in tools that use these configuration files
(`grubby`, `kernel-install` scripts, etc).
* Other developers:
** The Anaconda developers will need to review and merge the patches
to change where the GRUB configuration files are created.
** Test and watch for regressions.
* Release engineering:
**
[[Fedora_Program_Management/ReleaseBlocking/Fedora{{FedoraVersionNumber|next}}|List
of deliverables]]: N/A
* Policies and guidelines: The policies and guidelines do not need to
be updated.
* Trademark approval: No changes needed.
== Upgrade/compatibility impact ==
The changes will only be for new installations, existing systems will
not be impacted and will continue using the grub.cfg and grubenv files
that are located in the ESP.
== How To Test ==
* Install Fedora 34 and verify that the GRUB configuration is correct.
* Check that the `/boot/efi/EFI/fedora/grub{.cfg,env}` files are not present.
* Check that the `/boot/grub2/grub{.cfg,env}` files are present.
* Enter the GRUB prompt by pressing 'c' from the GRUB boot menu and
execute the following command:
<pre>echo $prefix</pre>
and verify that the prefix is set to the partition that contains the
`/boot/grub2` directory.
* Re-generate the GRUB configuration file with:
<pre>grub2-mkconfig -o /boot/grub2/grub.cfg</pre>
and verify that the GRUB configuration is still correct.
== User Experience ==
No visible changes are expected other than the configuration files
being present in a different path. This should improve the overall
user experience.
== Dependencies ==
None
== Contingency Plan ==
* Contingency mechanism: Revert the Anaconda and grub2 package
scriptlets changes.
* Contingency deadline: Beta Freeze
* Blocks release? No
* Blocks product? None
== Documentation ==
* Fedora CoreOS assembler script that creates the GRUB config file for
EFI: https://github.com/coreos/coreos-assembler/blob/master/src/create_disk.sh
* OSBuild org.osbuild.grub2 stage that creates the GRUB config file
for EFI: https://github.com/osbuild/osbuild/blob/main/stages/org.osbuild.grub2
--
Ben Cotton
He / Him / His
Senior Program Manager, Fedora & CentOS Stream
Red Hat
TZ=America/Indiana/Indianapolis
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