** Description changed:
+ [Impact]
+ This issue makes it impossible for UEFI users to access to boot menu and
choose their kernel if /boot is installed on LVM.
+
+ [Test case]
+ 1) Install Ubuntu on UEFI; put /boot on a LVM LV.
+ 2) Reboot after the install
+ 3) Verify that you will get a GRUB menu at boot.
+
+ [Regression potential]
+ Give particular attention to boot behavior on different disk setups: failure
to show the menu on LVM or other disk setups when holding the SHIFT key, or
showing the menu at every boot unnecessarily on other types of disk
configurations: /boot on a physical partition, etc.
+
+ ---
+
Because EFI does not support instantaneous read of modifier keys (i.e.
holding down shift at boot), the only way to reliably show a boot menu
is by letting the system boot, interrupting the boot, and letting the
menu be displayed because 'recordfail' has been set.
If /boot/grub is on LVM, recordfail does not work, because grub doesn't
have write support on LVM, so saveenv doesn't work. Indeed, from the
grub.cfg on such a system, the recordfail function is written as:
function recordfail {
- set recordfail=1
- # GRUB lacks write support for lvm, so recordfail support is disabled.
+ set recordfail=1
+ # GRUB lacks write support for lvm, so recordfail support is disabled.
}
The interaction of these two limitations means that systems with
/boot/grub on LVM cannot reliably get a grub menu, ever.
While I think that in the long term we should always put /boot/grub on
the ESP (which means it will always be writable by grub), which is in
fact what we did for Ubuntu Core, in the meantime I believe what we need
to do here is always show the boot menu if we are booted under EFI and
we have a non-writable grubenv.
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https://bugs.launchpad.net/bugs/1800722
Title:
EFI booting + /boot on LVM == inaccessible boot menu
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