yesterday I installed debian on my system. It all went relatively smooth and nice. Today I decided to install Windows 10 alongside Debian.
Unluckily W10 wants a GPT partition table, and Debian installed a MBR (probably asked me if it was ok, I didn't know about the GPT thing...).
So I went ahead and converted the partition table on my disk using gdisk.
I successfully installed windows, there is a new entry on my motherboard "bios" called Windows Boot Manager or something like that, if I set that as first in the boot order, windows starts ok.
Now I'd like my Debian back.
I'm writing this from a Debian live usb, and my disk partition table now looks like this:

root@debian:~# gdisk /dev/sdb
GPT fdisk (gdisk) version 0.8.10

Partition table scan:
 MBR: protective
 BSD: not present
 APM: not present
 GPT: present

Found valid GPT with protective MBR; using GPT.

Command (? for help): p
Disk /dev/sdb: 234441648 sectors, 111.8 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): C30CDFBB-EBFD-4E01-AB9B-31F60867035C
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 234441614
Partitions will be aligned on 2048-sector boundaries
Total free space is 2925 sectors (1.4 MiB)

Number  Start (sector)    End (sector)  Size       Code  Name
 1            2048       112429055   53.6 GiB    8300  Linux filesystem
 2       112429056       113350655   450.0 MiB   2700  Basic data partition
 3       113350656       113555455   100.0 MiB   EF00  EFI system partition
 4       113555456       113588223   16.0 MiB    0C01  Microsoft reserved ...
 5       113588224       224862207   53.1 GiB    0700  Basic data partition
 6       224862208       234440703   4.6 GiB     8200  Linux swap

I think partition 2 is the Windows Recovery (?) and partition 3 was created by Windows too, maybe that's the "windows boot manager" I find in my motherboard boot settings, but I don't know really.
Can you suggest how to proceed from here, possibly without wiping out debian nor windows?


Your linux bootmanager (grub2) has been overwritten by the windows bootloader. The windows bootloader doesn't support booting linux, but grub2 does support booting both. With grub you get a selection menu on boot. (Next time install windows first, then debian!)

You need to boot linux (debian) from CD/DVD/USB and chroot you linux partitions. Reinstall or update grub to make it work again.

Here is a link howto (for ubuntu which should work for debian, too): http://howtoubuntu.org/how-to-repair-restore-reinstall-grub-2-with-a-ubuntu-live-cd

good luck!

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