I am trying a fresh install of Ubuntu 18.04 server, without an internet connection (not Live) on my Dell PowerEdge R640. The machine came with a Boot Optimized Storage SSD (RAID 1), which is where I'm trying to install to. I've wiped the partition clean and chosen "Guided - use entire disk". However, when the installer attempts to install the grub boot loader, I get "Unable to install grub in dummy 'grub-install dummy' failed" and I am unable to progress. Has anyone encountered this and/or know what my issue is?
Since you finished your installation(Please correct) and only pending thing was grub installation, with above error I think it is UEFI system, try to boot from rescue disk and install grub from there.
Hope this will help.