diff --git a/docs/bootloaders.md b/docs/bootloaders.md new file mode 100644 index 00000000..c5e51296 --- /dev/null +++ b/docs/bootloaders.md @@ -0,0 +1,40 @@ +--- +nav_order: 11 +--- + +# Bootloaders +{: .no_toc } + +1. TOC +{:toc} + +## OSTree and bootloaders + +The intended design of OSTree is that it just writes new files into `/boot/loader/entries`. There is a legacy GRUB script (shipped on Fedora as `ostree-grub2`) that is intended only for the cases where the system GRUB does not support the `blscfg` verb. + +In the happy path then, the flow of an OS update is just: + +- ostree writes a new set of files in `/boot/loader/entries` (during `ostree-finalize-staged.service` on system shutdown) +- On system start, GRUB reads those files + +And that's it. + +## OSTree and grub + +For historical reasons, OSTree defaults to detecting the bootloader; if some GRUB files are present then OSTree will default to executing `grub2-mkconfig`. + +[Commented out for now, as this can lead to the system not booting in some cases.]: # +[This can be avoided by setting `sysroot.bootloader=none` (except this should not be set on s390x).]: # + +## GRUB and os-prober + +A specific component of GRUB that can significantly impede the reliability of OS updates is the `os-prober` aspect, which scans all system block devices. If one doesn't care about dual booting, avoiding this is a good idea. + +## Anaconda + +Until very recently, the Anaconda project only supported setting up the bootloader (e.g. GRUB) on its own, which requires `grub2-mkconfig` etc. As of recently, Anaconda now [supports bootupd](https://github.com/rhinstaller/anaconda/pull/5298). + +## bootupd + +As of recently, [the bootupd project](https://github.com/coreos/bootupd/) ships [static grub configs](https://github.com/coreos/bootupd/tree/main/src/grub2) and in this case, the `sysroot.bootloader` should be set to `none` (except on s390x). +And assuming that the system grub has the `blscfg` support, which it does on Fedora derivatives per above.