I'm automating an install of Ubuntu 14.04 and later 18.04 with Ansible. I have the 14.04 root file system on sdb1. I can mount it and it all looks good. I'm running Ubuntu 18.04 live CD to install grub.
sda1 is a data drive and the bios is set to boot sda1. There are many installations in the field like this and I cannot change it.
In grub-rescue mode, ls (hd1,1) displays unknown filesystem.
Auto-detection of a filesystem of /dev/sdb1 failed.
address@hidden:/# /usr/sbin/grub-probe --device-map="/boot/grub/device.map" --target=fs -v /boot/grub
/usr/sbin/grub-probe: info: cannot open `/boot/grub/device.map'.
/usr/sbin/grub-probe: info: Scanning for dmraid_nv RAID devices on disk hd0.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: Scanning for dmraid_nv RAID devices on disk hd1.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: Scanning for dmraid_nv RAID devices on disk hd2.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: scanning hd0 for LVM.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: no LVM signature found.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: scanning hd1 for LVM.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: no LVM signature found.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: scanning hd2 for LVM.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: no LVM signature found.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: Scanning for mdraid09 RAID devices on disk hd0.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: Scanning for mdraid09 RAID devices on disk hd1.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: Scanning for mdraid09 RAID devices on disk hd2.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: Scanning for mdraid1x RAID devices on disk hd0.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: Scanning for mdraid1x RAID devices on disk hd1.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: Scanning for mdraid1x RAID devices on disk hd2.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: Scanning for mdraid09 RAID devices on disk hd0.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: Scanning for mdraid09 RAID devices on disk hd0,msdos2.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: Scanning for mdraid09 RAID devices on disk hd0,msdos1.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: Scanning for mdraid09 RAID devices on disk hd1.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: Scanning for mdraid09 RAID devices on disk hd1,msdos2.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: Scanning for mdraid09 RAID devices on disk hd1,msdos1.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: Scanning for mdraid09 RAID devices on disk hd2.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: Scanning for mdraid09 RAID devices on disk hd2,msdos1.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: Scanning for mdraid1x RAID devices on disk hd0.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: Scanning for mdraid1x RAID devices on disk hd0,msdos2.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: Scanning for mdraid1x RAID devices on disk hd0,msdos1.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: Scanning for mdraid1x RAID devices on disk hd1.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: Scanning for mdraid1x RAID devices on disk hd1,msdos2.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: Scanning for mdraid1x RAID devices on disk hd1,msdos1.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: Scanning for mdraid1x RAID devices on disk hd2.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: Scanning for mdraid1x RAID devices on disk hd2,msdos1.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: scanning hd0 for LVM.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: no LVM signature found.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: scanning hd0,msdos2 for LVM.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: no LVM signature found.
/usr/sbin/grub-probe: info: scanning hd0,msdos1 for LVM.
/usr/sbin/grub-probe: info: the size of hd0 is 1953525168.
/usr/sbin/grub-probe: info: no LVM signature found.
/usr/sbin/grub-probe: info: scanning hd1 for LVM.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: no LVM signature found.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: scanning hd1,msdos2 for LVM.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: no LVM signature found.
/usr/sbin/grub-probe: info: scanning hd1,msdos1 for LVM.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: no LVM signature found.
/usr/sbin/grub-probe: info: scanning hd2 for LVM.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: no LVM signature found.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: scanning hd2,msdos1 for LVM.
/usr/sbin/grub-probe: info: the size of hd2 is 7827456.
/usr/sbin/grub-probe: info: no LVM signature found.
/usr/sbin/grub-probe: info: /dev/sdb1 starts from 2048.
/usr/sbin/grub-probe: info: opening the device hd1.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: info: Partition 0 starts from 2048.
/usr/sbin/grub-probe: info: opening hd1,msdos1.
/usr/sbin/grub-probe: info: the size of hd1 is 125045424.
/usr/sbin/grub-probe: error: unknown filesystem.