Windows 10 does not show in grub menu (separate disk installation)

Question

I was using windows 10 installed on a SSD plus an HHD for storage. Recently, I have added another ssd where I have installed Ubuntu 18.04.2 LTS

My problem is that neither os-prober nor grub can find windows 10. However, I am able to boot in windows 10 from the UEFI boot menu. I read all the posts about it but could not solve the problem. Can you please help me?

Here is the output from boot info Boot Info Script 0.61 [1 April 2012]

============================= Boot Info Summary: ===============================

 => Windows is installed in the MBR of /dev/sda.
 => Windows is installed in the MBR of /dev/sdb.
 => Windows is installed in the MBR of /dev/sdc.

sda1: __________________________________________________________________________

File system:       ntfs
Boot sector type:  Windows Vista/7: NTFS
Boot sector info:  No errors found in the Boot Parameter Block.
Operating System:  
Boot files:        /bootmgr /Boot/BCD /Windows/System32/winload.exe

sda2: __________________________________________________________________________

File system:       ntfs
Boot sector type:  Windows Vista/7: NTFS
Boot sector info:  No errors found in the Boot Parameter Block.
Operating System:  
Boot files:        

sdb1: __________________________________________________________________________

File system:       
Boot sector type:  -
Boot sector info: 
Mounting failed:   mount: /tmp/BootInfo-OmyD6Lmf/sdb1: unknown filesystem type ''.

sdb2: __________________________________________________________________________

File system:       ntfs
Boot sector type:  Windows Vista/7: NTFS
Boot sector info:  No errors found in the Boot Parameter Block.
Operating System:  
Boot files:        

sdc1: __________________________________________________________________________

File system:       vfat
Boot sector type:  FAT32
Boot sector info:  No errors found in the Boot Parameter Block.
Operating System:  
Boot files:        /efi/BOOT/fbx64.efi /efi/ubuntu/fwupx64.efi 
                   /efi/ubuntu/grubx64.efi /efi/ubuntu/mmx64.efi 
                   /efi/ubuntu/shimx64.efi

sdc2: __________________________________________________________________________

File system:       ext4
Boot sector type:  -
Boot sector info: 
Operating System:  Ubuntu 18.04.2 LTS
Boot files:        /boot/grub/grub.cfg /etc/fstab

============================ Drive/Partition Info: =============================

Drive: sda _____________________________________________________________________

Disk /dev/sda: 111,8 GiB, 120034123776 bytes, 234441648 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos

Partition  Boot  Start Sector    End Sector  # of Sectors  Id System

/dev/sda1    *          2,048   233,517,055   233,515,008   7 NTFS / exFAT / HPFS
/dev/sda2         233,517,056   234,438,655       921,600  27 Hidden NTFS (Recovery Environment)

Drive: sdb _____________________________________________________________________

Disk /dev/sdb: 931,5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt

Partition  Boot  Start Sector    End Sector  # of Sectors  Id System

/dev/sdb1                   1 4,294,967,295 4,294,967,295  ee GPT

/dev/sdb1 ends after the last sector of /dev/sdb

GUID Partition Table detected.

Partition    Start Sector    End Sector  # of Sectors System
/dev/sdb1              34       262,177       262,144 Microsoft Reserved Partition (Windows)
/dev/sdb2         264,192 1,953,523,711 1,953,259,520 Data partition (Windows/Linux)

Drive: sdc _____________________________________________________________________

Disk /dev/sdc: 223,6 GiB, 240057409536 bytes, 468862128 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt

Partition  Boot  Start Sector    End Sector  # of Sectors  Id System

/dev/sdc1                   1   468,862,127   468,862,127  ee GPT


GUID Partition Table detected.

Partition    Start Sector    End Sector  # of Sectors System
/dev/sdc1           2,048     1,050,623     1,048,576 EFI System partition
/dev/sdc2       1,050,624   468,860,927   467,810,304 Data partition (Linux)

"blkid" output: ________________________________________________________________

Device           UUID                                   TYPE       LABEL

/dev/loop0                                              squashfs   
/dev/loop1                                              squashfs   
/dev/loop10                                             squashfs   
/dev/loop11                                             squashfs   
/dev/loop12                                             squashfs   
/dev/loop13                                             squashfs   
/dev/loop14                                             squashfs   
/dev/loop15                                             squashfs   
/dev/loop16                                             squashfs   
/dev/loop17                                             squashfs   
/dev/loop2                                              squashfs   
/dev/loop3                                              squashfs   
/dev/loop4                                              squashfs   
/dev/loop5                                              squashfs   
/dev/loop6                                              squashfs   
/dev/loop7                                              squashfs   
/dev/loop8                                              squashfs   
/dev/loop9                                              squashfs   
/dev/sda1        6EAEC608AEC5C933                       ntfs       Fisso
/dev/sda2        34D8E21FD8E1DEDC                       ntfs       
/dev/sdb1                                                          
/dev/sdb2        1688449A884479EF                       ntfs       Fisso exp
/dev/sdc1        3BCC-705C                              vfat       
/dev/sdc2        b64bdc97-1ec9-4a7f-a4f6-7e0e51b54f2d   ext4  

================================ Mount points: =================================

Device           Mount_Point              Type       Options

/dev/sdc1        /boot/efi                vfat       (rw,relatime,fmask=0077,dmask=0077,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)
/dev/sdc2        /                        ext4       (rw,relatime,errors=remount-ro)

=========================== sdc2/boot/grub/grub.cfg: ===========================

Answer 1

Windows is in legacy mode, so to run it from grub, you would need to boot grub in legacy mode, but you installed it in UEFI mode. Easiest just to reinstall Ubuntu in legacy mode. How you boot the install media (legacy vs. UEFI) is how it installs

Your Windows 10 installation is on a dos partitioned (vs gpt) disk, so that alone implies a legacy installation. Its disk also has an MBR boot setup, and no EFI partition, so those are other clues it's a legacy install. Ubuntu works in either mode (legacy/UEFI) on any disk partition type (dos/gpt), but usually for UEFI uses the more more modern gpt, but its disk (sdc) does have an EFI partition with the Ubunu bootloaders, so a UEFI install was done. If you want a legacy install on that disk, you will need to either:

1. Add a grub-bios 2M unformatted partition (since grub cannot tuck it's code between the partitions on a gpt disk) or
2. Repartition the disk using a DOS partition table (no grub-bios partition needed in this case).