** Description changed:
As it currently stands grub2 cannot create grub.cfg menu entries that do not
use an initrd image if one is present but the user does not desire to use it.
Furthermore, root= entries only support UUID and LABEL, but neither is an
option if booting the kernel without an initrd.
Suggestion:
Allow grub2 to create configuration files without an "initrd" line and
passing PARTUUID as root= entry by adding configuration knobs.
+
+ [SRU Justification]
+ A lot of time is wasted across the many, many instances of Ubuntu loading
initramfs when booting. It's a measurable savings of CPU time and electricity
to skip loading an initramfs at boot if it's not required.
+
+ [Test case]
+ 1. cp /boot/grub/grub.cfg /tmp/grub.cfg
+ 2. install the grub packages from -proposed.
+ 3. cmp /boot/grub/grub.cfg /tmp/grub.cfg || echo 'fail'
+ 4. as root, configure /etc/default/grub to mount the root disk directly and
bypass the initramfs:
+ echo GRUB_DISABLE_INITRD=true >> /etc/default/grub
+ root=$(awk </etc/fstab '$2 == "/" { print $1 }')
+ case $root in
+ LABEL=*|UUID=*)
+ dev="-l -t $root"
+ ;;
+ *)
+ dev=$root
+ ;;
+ esac
+ partuuid=$(blkid -s PARTUUID -o value $dev)
+ if [ -z "$partuuid" ]; then
+ echo "Error: cannot get partuuid for $root."
+ else
+ echo GRUB_FORCE_PARTUUID=$partuuid >> /etc/default/grub
+ fi
+ 5. If a partuuid has been found, run update-grub. Note that this will only
work if your root device is a partition on a GPT-formatted disk.
+ 6. Check that /boot/grub/grub.cfg now contains entries that don't specify an
initramfs, and do include root=PARTUUID=* on the kernel commandline.
** Description changed:
As it currently stands grub2 cannot create grub.cfg menu entries that do not
use an initrd image if one is present but the user does not desire to use it.
Furthermore, root= entries only support UUID and LABEL, but neither is an
option if booting the kernel without an initrd.
Suggestion:
Allow grub2 to create configuration files without an "initrd" line and
passing PARTUUID as root= entry by adding configuration knobs.
[SRU Justification]
A lot of time is wasted across the many, many instances of Ubuntu loading
initramfs when booting. It's a measurable savings of CPU time and electricity
to skip loading an initramfs at boot if it's not required.
[Test case]
1. cp /boot/grub/grub.cfg /tmp/grub.cfg
2. install the grub packages from -proposed.
3. cmp /boot/grub/grub.cfg /tmp/grub.cfg || echo 'fail'
4. as root, configure /etc/default/grub to mount the root disk directly and
bypass the initramfs:
- echo GRUB_DISABLE_INITRD=true >> /etc/default/grub
- root=$(awk </etc/fstab '$2 == "/" { print $1 }')
- case $root in
- LABEL=*|UUID=*)
- dev="-l -t $root"
- ;;
- *)
- dev=$root
- ;;
- esac
- partuuid=$(blkid -s PARTUUID -o value $dev)
- if [ -z "$partuuid" ]; then
- echo "Error: cannot get partuuid for $root."
- else
- echo GRUB_FORCE_PARTUUID=$partuuid >> /etc/default/grub
- fi
+ echo GRUB_DISABLE_INITRD=true >> /etc/default/grub
+ root=$(awk </etc/fstab '$2 == "/" { print $1 }')
+ case $root in
+ LABEL=*|UUID=*)
+ dev="-l -t $root"
+ ;;
+ *)
+ dev=$root
+ ;;
+ esac
+ partuuid=$(blkid -s PARTUUID -o value $dev)
+ if [ -z "$partuuid" ]; then
+ echo "Error: cannot get partuuid for $root."
+ else
+ echo GRUB_FORCE_PARTUUID=$partuuid >> /etc/default/grub
+ fi
5. If a partuuid has been found, run update-grub. Note that this will only
work if your root device is a partition on a GPT-formatted disk.
6. Check that /boot/grub/grub.cfg now contains entries that don't specify an
initramfs, and do include root=PARTUUID=* on the kernel commandline.
+
+ [Regression potential]
+ This upload introduces no behavior changes unless the user updates
/etc/default/grub to configure the use of the new feature, so there should be
no regressions here. The SRU test case verifies that /boot/grub/grub.cfg
remains unchanged with the new version.
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https://bugs.launchpad.net/bugs/1640878
Title:
grub2 cannot currently generate configuration without initrd
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