I have a dual boot with SSD Windows 10 UEFI + HDD Ubuntu legacy.

I can boot both OSs correctly using BIOS boot order.

Windows does not appear in the grub entries. I tried OS-Prober and grub-update, but it didn't work.

I added a custom Windows 10 menu entry to 40_custom.cfg using blkid to find the uuid of the windows 10 UEFI partition, but when selected in the grub menu: no such device found.

How can I fix this?

lsblk output:

loop0    7:0    0    21M  1 loop /snap/gnome-logs/25
loop1    7:1    0  86,6M  1 loop /snap/core/4486
loop2    7:2    0   140M  1 loop /snap/gnome-3-26-1604/59
loop3    7:3    0   3,3M  1 loop /snap/gnome-system-monitor/36
loop4    7:4    0   1,6M  1 loop /snap/gnome-calculator/154
loop5    7:5    0  12,2M  1 loop /snap/gnome-characters/69
sda      8:0    0 931,5G  0 disk 
└─sda1   8:1    0 931,5G  0 part /
sdb      8:16   0 223,6G  0 disk 
├─sdb1   8:17   0   499M  0 part 
├─sdb2   8:18   0    99M  0 part 
├─sdb3   8:19   0    16M  0 part 
└─sdb4   8:20   0   223G  0 part 
  • Hi Nano, welcome to askubuntu! Include the output of cat /etc/fstab and etc/default/grub and blkid to your post. Further the 40_custom file is without the .cfg extension. Add your /etc/grub.d/40customfile to your post. Did you made a sudo update-grub? – abu_bua Jul 19 '18 at 22:47
  • 1
    Best to re-install ubuntu with uefi boot, i.e., backup data, re-install, then restore data. It's harder to change windows 10 from uefi to legacy and I won't recommend that. I think windows 10 comes with a utility to change from legacy to uefi but not vice versa. – Bernard Wei Jul 19 '18 at 22:47
  • @abu_bua I will edit post when I can, ty – NanoPish Jul 20 '18 at 8:23
  • @Bernard Wei But I think it is possible ot have a dual boot mixing legacy and uefi, am I wrong ? – NanoPish Jul 20 '18 at 8:23
  • @NanoPish Only via UEFI Bios boot selection with legacy support. I don't think it can be done from Grub or Windows bootloader, which is what you wanted right? – Bernard Wei Jul 20 '18 at 17:28

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