Re: 'error: invalid signature' when booting Windows 10

[Pascal Hambourg]

Le 20/12/2018 à 17:21, David Collier a écrit :
> I added the entry to mount Windows EFI partition, so /boot/efi has the EFI
> directory entry in it now.
(...)
> update-grub finds the windows partition now and adds it to the menu. but
> running grub-install still fails:
>
> > grub-install
> Installing for x86_64-efi platform.
> grub-install: warning: disk does not exist, so falling back to partition
> device /dev/sdb3.
> grub-install: warning: disk does not exist, so falling back to partition
> device /dev/sdb3.
> grub-install: warning: disk does not exist, so falling back to partition
> device /dev/sdb3.
> grub-install: error: disk `hostdisk//dev/sdb3' not found.

/dev/sdb3 is the EFI partition on the Windows disk, isn't it ?

Does /boot/grub/device.map exist, and what does it contain ?
Does it help if you run grub-mkdevicemap before grub-install, or run 
grub-install with --recheck ?

> when booting from the USB stick in EFI mode the new menu item boots windows
> successfully, but if I boot from the SSD the same menu shows, but windows
> does not boot.

The SSD boots GRUB in BIOS mode but the Windows menu entry in grub.cfg 
is intended only for EFI mode, as in your original post.