I think running at install time and caching the output somewhere makes sense for most cases. You can create some documentation on how to re-run it at manually to regenerate that output if you have consciously added another operating system and want to detect it one off.
On Fri, Dec 17, 2021 at 10:03 AM Julian Andres Klode <julian.klode@canonical.com> wrote:
Hi ubuntu-devel,
os-prober is disabled with the grub 2.06 upload, which is
obviously a bit controversial and the outcome is not
necessarily in the best interest of our users.
# Reasons
os-prober is inherently insecure as it mounts all partitions
on your disk using grub-mount to check them for other OS,
which is not a nice thing to do as root as you can exploit
bugs in the filesystem code easily.
# Outcome
1. Users on UEFI are unable to boot other Ubuntu installs,
but can boot other OS via the UEFI bootloader.
Multiple Ubuntu installs are a hack either way, so not
really a huge priority - any Ubuntu install installs
grub to the same location, so your grub just switches
between your Ubuntu installs each time you upgrade it
in one. Ugh.
2. Users on BIOS systems cannot boot any other system
This is highly problematic
# Options
0. Re-enable os-prober
1. Red Hat only runs os-prober during install time, and
instead of regenerating grub.cfg when kernels are installed
writes out drop-in files that are then loaded (it actually
uses the systemd-boot load entries format, which it has
patched into grub)
We could run os-prober during install time, store the
output somewhere and then reuse the cached output in
grub-mkconfig.
2. Can we have an "Other Boot options" entry that goes to the
UEFI boot menu? Or, write a grub module that goes through
the UEFI boot options and creates a submenu, then sets
BootNext and resets the machine when you select an item.
3. Detect the presence of Windows inside grub.cfg and allow
chainloading that, to handle the major dual-boot use case.
4. There was some initial code for a basic os-prober reimplementation
at boot time, which avoids the security issues of running os-prober
at run-time, but also that's a bit meh.
--
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