GRUB_DEFAULT entry

[Robert McBroom]

grub seems to now ignore the settings in /etc/default/grub. What is 
needed to restore the function of setting a specific boot option?

[Jonathan Billings]

On Tue, Jul 06, 2021 at 10:11:01AM -0400, Robert McBroom via users wrote:
> grub seems to now ignore the settings in /etc/default/grub. What is needed
> to restore the function of setting a specific boot option?

I've noticed that GRUB2 on Fedora uses BootLoaderSpec (see this page: 
https://fedoraproject.org/wiki/Changes/BootLoaderSpecByDefault ),
however, if you (or an RPM scriptlet) uses the 'grubby' command to
change the kernel parameters, in the individual /boot/loader/entries/
files, the 'options $kernelopts' line is replaced with the full kernel
options, and they're never updated again even if you change the
/etc/default/grub settings.  FWIW, the nvidia packages use grubby in
an RPM post script, so people who use those often run into this.

It looks like this has been reported:
https://bugzilla.redhat.com/show_bug.cgi?id=1651686

I'm not sure if Fedora needs to do a better job documenting this
behavior, or if it should just be fixed so people aren't confused by
this. Maybe something like "These settings only affect when the system
is loaded and changing them won't affect a running system's grub" in
the /etc/default/grub file?

[Robert McBroom]

On 7/6/21 11:32 AM, Jonathan Billings wrote:
> On Tue, Jul 06, 2021 at 10:11:01AM -0400, Robert McBroom via users wrote:
> > grub seems to now ignore the settings in /etc/default/grub. What is needed
> > to restore the function of setting a specific boot option?
>
> I've noticed that GRUB2 on Fedora uses BootLoaderSpec (see this page:
> https://fedoraproject.org/wiki/Changes/BootLoaderSpecByDefault ),
> however, if you (or an RPM scriptlet) uses the 'grubby' command to
> change the kernel parameters, in the individual /boot/loader/entries/
> files, the 'options $kernelopts' line is replaced with the full kernel
> options, and they're never updated again even if you change the
> /etc/default/grub settings.  FWIW, the nvidia packages use grubby in
> an RPM post script, so people who use those often run into this.
>
> It looks like this has been reported:
> https://bugzilla.redhat.com/show_bug.cgi?id=1651686
>
> I'm not sure if Fedora needs to do a better job documenting this
> behavior, or if it should just be fixed so people aren't confused by
> this. Maybe something like "These settings only affect when the system
> is loaded and changing them won't affect a running system's grub" in
> the /etc/default/grub file?

I typically have several different OS in stanzas in 
/etc/grub.d/06_custom. They don't go through

/boot/loader/entries/

GRUB_DEFAULT

in /etc/default/grub would select the system I wanted to use for a session from the menuentry until edited.
typically these were CENTOS systems that had the legacy support the codes I use needed.
That functionality appears to have been lost.

[Chris Murphy]

On Tue, Jul 6, 2021 at 8:11 AM Robert McBroom via users
 wrote:
> grub seems to now ignore the settings in /etc/default/grub. What is
> needed to restore the function of setting a specific boot option?

Whatever is in /etc/default/grub will be set in each BLS snippet if
you run grub2-mkconfig -o /etc/grub2.cfg

New kernels will get whatever is currently in /proc/cmdline.

If you use grubby with --update-kernel=ALL then all possibilities are
modified regardless of Fedora release version (grubenv or BLS snippets
or grub.cfg as the case may be).

https://fedoraproject.org/wiki/GRUB_2?rd=Grub2#Changing_kernel_command-line_...

--
Chris Murphy