xenial - does not ask device to grub-install, finds /dev/vda correctly


~ # pvs
  PV         VG        Fmt  Attr PSize  PFree 
  /dev/vda5  ubuntu-vg lvm2 a--  29.28g 40.00m


~ # vgs
  VG        #PV #LV #SN Attr   VSize  VFree 
  ubuntu-vg   1   2   0 wz--n- 29.28g 40.00m


~ # lvs
  LV     VG        Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  root   ubuntu-vg -wi-ao----  28.29g                                                    
  swap_1 ubuntu-vg -wi-ao---- 976.00m     


~ # ls -lah1 /dev/disk/by-id/
drwxr-xr-x    2     120 Oct  2 17:54 .
drwxr-xr-x    5     100 Oct  2 18:05 ..
lrwxrwxrwx    1      10 Oct  2 18:07 dm-name-ubuntu--vg-root -> ../../dm-0
lrwxrwxrwx    1      10 Oct  2 18:05 dm-name-ubuntu--vg-swap_1 -> ../../dm-1
lrwxrwxrwx    1      10 Oct  2 18:07 dm-uuid-LVM-rKxFFLzSxoQE5R09qa8ztKdfGKZIxktySnE1WunTpz1cKQt8elMkWyzXF25Dhqgt -> ../../dm-0
lrwxrwxrwx    1      10 Oct  2 18:05 dm-uuid-LVM-rKxFFLzSxoQE5R09qa8ztKdfGKZIxktyoOA5IYfjtokmG0cVkmlrLRZfr0gbBZCh -> ../../dm-1


/lib/udev/rules.d # grep -ril lvm * 
55-dm.rules
60-persistent-storage-dm.rules

----

bionic - does not ask device to grub-install, finds /dev/vda correctly


  PV         VG        Fmt  Attr PSize   PFree 
  /dev/vda1  ubuntu-vg lvm2 a--  <30.00g 12.00m


~ # vgs
  VG        #PV #LV #SN Attr   VSize   VFree 
  ubuntu-vg   1   2   0 wz--n- <30.00g 12.00m


~ # lvs
  LV     VG        Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  root   ubuntu-vg -wi-ao----  29.03g                                                    
  swap_1 ubuntu-vg -wi-ao---- 976.00m                                                    


~ # ls -lah1 /dev/disk/by-id/
drwxr-xr-x    2 root     root         120 Oct  2 18:10 .
drwxr-xr-x    6 root     root         120 Oct  2 18:27 ..
lrwxrwxrwx    1 root     root          10 Oct  2 18:27 dm-name-ubuntu--vg-root -> ../../dm-0
lrwxrwxrwx    1 root     root          10 Oct  2 18:27 dm-name-ubuntu--vg-swap_1 -> ../../dm-1
lrwxrwxrwx    1 root     root          10 Oct  2 18:27 dm-uuid-LVM-tuUboqieQsJtu1wB4OyTbAT5pRwXxZj7C8q7wogJHSUaOrIBRvJ2GL7ZcRFz4nCe -> ../../dm-0
lrwxrwxrwx    1 root     root          10 Oct  2 18:27 dm-uuid-LVM-tuUboqieQsJtu1wB4OyTbAT5pRwXxZj7d1U7ckfbgo1bRtQnDa5XQsaoXSpjCvfV -> ../../dm-1


/lib/udev/rules.d # grep -ril lvm *
55-dm.rules
60-persistent-storage-dm.rules
95-dm-notify.rules

----

disco - does not ask, but has only /dev/vda to choose


~ # pvs
  PV         VG        Fmt  Attr PSize   PFree 
  /dev/vda1  ubuntu-vg lvm2 a--  <30.00g 12.00m


~ # vgs
  VG        #PV #LV #SN Attr   VSize   VFree 
  ubuntu-vg   1   2   0 wz--n- <30.00g 12.00m


~ # lvs
  LV     VG        Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  root   ubuntu-vg -wi-ao----  29.03g                                                    
  swap_1 ubuntu-vg -wi-ao---- 976.00m                                                    


~ # ls -lah1 /dev/disk//by-id/
drwxr-xr-x    2 root     root         120 Oct  2 18:09 .
drwxr-xr-x    6 root     root         120 Oct  2 18:27 ..
lrwxrwxrwx    1 root     root          10 Oct  2 18:27 dm-name-ubuntu--vg-root -> ../../dm-0
lrwxrwxrwx    1 root     root          10 Oct  2 18:27 dm-name-ubuntu--vg-swap_1 -> ../../dm-1
lrwxrwxrwx    1 root     root          10 Oct  2 18:27 dm-uuid-LVM-qBHgS7hD0Uk4hjhprGFLVwCUekU0i6OBbMg8u7PfVrnT4mcYKuKXRqI4ehzM7pLX -> ../../dm-0
lrwxrwxrwx    1 root     root          10 Oct  2 18:27 dm-uuid-LVM-qBHgS7hD0Uk4hjhprGFLVwCUekU0i6OBjuHfJCKZ6aVKKmZHq2VxntLeR46xIexG -> ../../dm-1


/lib/udev/rules.d # grep -ril lvm *
55-dm.rules
60-persistent-storage-dm.rules
95-dm-notify.rules


----

eoan - asks device to grub-install and shows /dev/mapper as default


~ # pvs
  PV         VG       Fmt  Attr PSize   PFree 
  /dev/vda1  vgubuntu lvm2 a--  <30.00g 12.00m


~ # vgs
  VG       #PV #LV #SN Attr   VSize   VFree 
  vgubuntu   1   2   0 wz--n- <30.00g 12.00m


~ # lvs
  LV     VG       Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  root   vgubuntu -wi-ao----  29.03g                                                    
  swap_1 vgubuntu -wi-ao---- 976.00m                                                    


~ # ls -lah1 /dev/disk/by-id/
drwxr-xr-x    2 root     root         160 Oct  2 19:25 .
drwxr-xr-x    7 root     root         140 Oct  2 19:25 ..
lrwxrwxrwx    1 root     root          10 Oct  2 19:25 dm-name-vgubuntu-root -> ../../dm-0
lrwxrwxrwx    1 root     root          10 Oct  2 19:25 dm-name-vgubuntu-swap_1 -> ../../dm-1
lrwxrwxrwx    1 root     root          10 Oct  2 19:25 dm-uuid-LVM-uUYPMknWpQfkO3t3oKjW16vWmUeeTItFH9kCscuyNWWYybHdrB9ZENbFXKkJZUfb -> ../../dm-1
lrwxrwxrwx    1 root     root          10 Oct  2 19:25 dm-uuid-LVM-uUYPMknWpQfkO3t3oKjW16vWmUeeTItFfFw10F8npYWNaZWovPClX8tbARfym9zo -> ../../dm-0
lrwxrwxrwx    1 root     root          10 Oct  2 19:25 lvm-pv-uuid-iXIOdp-tXsj-ditG-JaUC-8flA-XV51-RFV778 -> ../../vda1


/lib/udev/rules.d # grep -ril lvm * 
55-dm.rules
56-lvm.rules
60-persistent-storage-dm.rules
69-lvm-metad.rules
95-dm-notify.rules

in 69-lvm-metad.rules:

# Create /dev/disk/by-id/lvm-pv-uuid-<PV_UUID> symlink for each PV
ENV{ID_FS_UUID_ENC}=="?*", SYMLINK+="disk/by-id/lvm-pv-uuid-$env{ID_FS_UUID_ENC}"

That is the difference causing the problem, and installer should NOT have that udev rule in order for not to have to change any logic in init scripts for grub device detection.

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