Persistence of Grub2 menu overrides

[Dave Ulrick]

Every so often I have to boot Linux into single-user mode. I do this by 
waiting for the Grub2 menu, selecting the desired kernel, and pressing 
'e'. Then I select the 'linux' statement, add '<space>1' to the end of 
the line, and boot with <Ctrl-X>.

This still works fine, but since upgrading to Fedora 34 I've noticed 
that the menu overrides I make in this manner are persistent. That is, 
if I add "1" to the end of the boot parameters for one boot, "1" will 
remain in effect until I explicitly remove it: press 'e' from the Grub2 
menu, remove "<space>1", and press <Ctrl-X>.

This was rather scary when I first discovered this behavior. Booting 
into single-user mode without asking to do so is ordinarily associated 
with a serious system issue.

Was this a deliberate change? If so, where is it documented?

I'm not sure I totally like this change. In some situations, it could be 
handy to add a kernel parameter using the Grub2 menu and have it stick 
around from one boot to another, but sometimes the old behavior was good 
for a one-time "failsafe" change that would be reverted just by doing a 
normal reboot.

Contents of /etc/default/grub:

GRUB_TIMEOUT=5
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)"
GRUB_DEFAULT=saved
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="rhgb quiet rd.driver.blacklist=nouveau 
modprobe.blacklist=nouveau nvidia-drm.modeset=1 acpi_enforce_resources=lax"
GRUB_DISABLE_RECOVERY="true"
GRUB_ENABLE_BLSCFG=true

Thanks,
Dave

[stan]

On Tue, 25 Jan 2022 16:04:57 -0600
Dave Ulrick  wrote:
> Every so often I have to boot Linux into single-user mode. I do this
> by waiting for the Grub2 menu, selecting the desired kernel, and
> pressing 'e'. Then I select the 'linux' statement, add '<space>1' to
> the end of the line, and boot with <Ctrl-X>.
>
> This still works fine, but since upgrading to Fedora 34 I've noticed 
> that the menu overrides I make in this manner are persistent. That
> is, if I add "1" to the end of the boot parameters for one boot, "1"
> will remain in effect until I explicitly remove it: press 'e' from
> the Grub2 menu, remove "<space>1", and press <Ctrl-X>.

I don't have an answer, but the last time I edited a boot entry, it did
not have this behavior, the change was temporary.  It sounds like a
bug rather than a feature.  If it was legitimate, it should also change
GRUB_CMDLINELINUX in /etc/default/grub to reflect the change.

I don't recall seeing any discussion of a change like this, but I could
have missed it.

[Tom Horsley]

On Wed, 26 Jan 2022 12:36:00 -0700
stan via users wrote:
> I don't recall seeing any discussion of a change like this, but I could
> have missed it.

I haven't noticed this one either, but I do find a lot of the "helpful"
stuff grub2 desperately tries to do for me annoying, so I have a
script that runs at various points (like right after a dnf update
which may have erased changes I make) to wack the grub.cfg file with
a big hammer and remove all the annoying features.

[greg]

On Wed, Jan 26, 2022 at 8:50 PM Tom Horsley  wrote:
> I haven't noticed this one either...

I noticed this change.
It turns out that

/etc/default/grub - contains default kernel options
/boot/grub2/grubenv - has the entry saved_entry=<id>
which refers to /boot/loader/entries/<id>.conf
which contains kernel options for the entry (which are actually used)
which get modified when editing kernel options via grub menu (thus
becoming persistent)

Also
/etc/default/grub - contains GRUB_ENABLE_BLSCFG=true
which is documented at
https://fedoraproject.org/wiki/Changes/BootLoaderSpecByDefault