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I tried to install 18.04 Ubuntu unsuccessfully twice and then formatted and installed 17.10. Windows 10 is on the separate SSD while the ubuntu disk looks like this:

sda:

  • [sda1 Ubuntu root and boot 100 GB]
  • [unallocated space 400 GB]
  • [sda2 NTFS data rest of the disk]

After whole installation adventure grub shows 17.10 ubuntu on sda1 and some kind of dos on sda2, while there is nothing on sda2 except data. Choosing this option leads to prompt asking to disconnect all drives without OS on them and Ctrl+Alt+Del to restart.

Booting through bios directly to windows boot loader or SSD disk with windows leads directly to grub, so no way to boot into windows.

Here is boot info: http://paste.ubuntu.com/p/g2wBYm77qk/ It seems to correctly see that windows actually on sdb1.

Os-prober too sees that nonexistent dos OS, but fails to detect actual windows 10.

How do I restore windows boot and add it to grub?

  • You have older BIOS with MBR(msdos) partitioning. Since main partition of Windows is first partition of sdb, it probably had its boot partition of 100MB with two essential boot files in it on sda, now gone. Separate boot partition is not required & you can repair sdb1 to directly boot Windows. First add boot flag to sdb1. Then use a Windows repair tool to run full set of repairs. You are missing BCD & bootmgr which need to be added to sdb1. It will not run repairs without boot flag. May be best to disconnect sda so Windows does not try to use it. – oldfred Apr 25 '18 at 3:44
  • @oldfred so how do I add boot flag? As you may read in the comment to the Paul Benson's answer I tried booting sdb1 separately but it wouldn't. – Virgileo Apr 25 '18 at 17:15
  • Probably easiest to use gparted and right click, set boot flag on. You can use Disks, command line, and in Windows, its command line set active on after selecting drive & partition. Your Windows will not boot without adding the missing two boot files bootmgr & BCD which you should be able to fix with Windows repairs, but it will not even repair it without boot flag. – oldfred Apr 25 '18 at 19:37
  • Well adding bootable flag changed nothing. You keep mentioning some kind of repair - what is it? Is it built in win 10 feature or do I need some kind of external software? – Virgileo Apr 25 '18 at 20:24
  • That said if you mean windows 10 installation USB drive, I don't currently have large enough drive to put it on, though I have win8 DVD, would it suffice? – Virgileo Apr 25 '18 at 20:34
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The info is useful but points to a to a bodge, regarding important mounting points and a possible BIOS config issue. You do need to know what you're doing when it comes to setting up Ubuntu, let alone a dual boot. The some kind of DOS on sda2 suggests you have an MBR disk and that partition points to your data file, not your W10 system so that shouldn't even be in there as a GRUB option.

For now I'd concentrate on getting Windows back. Power down, disconnect your HDD (the one with Ubuntu on it), then start up and see if W10 will boot. If it doesn't then your MBR and maybe your BCD file are messed up. Both can be repaired externally without the need for a re-install, but that's another subject. Meanwhile I suggest have a good read of this first before attempting another dual boot installation.

  • So I tried to boot only sdb and in the boot menu there were three related entries: ssd itself, win bootloader and ubuntu (?) - all of them leading to the following prompt: "Reboot and Select proper Boot device or Insert Boot Media in selected Boot device and press a key" The comment by oldfred advises to add boot flag to the sdb, should I do it or something else? – Virgileo Apr 25 '18 at 14:42
  • Did you install Ubuntu from a UFD?? If so, plug it in. Restart (go into BIOS boot manager again) and reboot from UFD.. Select Try Ubuntu and boot into live Ubuntu. Open terminal then type following: sudo apt-get repository ppa:yannubuntu/boot-repair. When that's finished type sudo apt-get update then sudo apt-get install boot-repair. Follow instructions then Restart computer. – Paul Benson Apr 25 '18 at 18:14
  • So i did that, here is output: image, boot-info It did remove weird stuff like dos OS thingy, but no windows to be seen. – Virgileo Apr 25 '18 at 20:05
  • I also tried adding boot flag to sdb as was advised by @oldfred but it changed nothing. Booting from windows boot loader and from sdb directly just leads to grub with lonely ubuntu there. – Virgileo Apr 25 '18 at 20:27
  • But can you boot into Ubuntu yet on sda?I see Windows option is missing from grub.cfg. Did you try as suggested and disconnect sda drive and then try to boot up Windows separately from BIOS boot menu? Other than re-installing W10, it sounds like you are going to have to repair your BCD and maybe your MBR on sdb. – Paul Benson Apr 25 '18 at 21:44

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