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I have an external Seagate HDD that I boot Windows 10 from. I wanted to dual boot from it, so I installed Xubuntu 16.04 alongside Windows 10 using the normal install procedure for Xubuntu (normal installation, not persistent live-USB)

I partitioned the drive into three partitions (Windows, Xubuntu and swap), set the mount point to the Xubuntu partition and installed Xubuntu there.

I believe I set the "device for bootloader installation" to the external HDD in question.

The installation completed sucesfully, and when I browse the Xubuntu partition (from another Linux system), I can see the file structure of Xubuntu, and it looks like a totally sucessful installation.

However, when I try to boot from this HDD, I only get Windows 10 booting automatically, and no Grub bootloader.

This leads me to question whether I actually chose this device for the bootloader, although I could have sworn I did.

Is there any method through which I can confirm that I did indeed install Grub to this HDD?

How can I find out why I don't get Grub while booting from this HDD?

FWIW the computer I used to perform the installation boots just like before and it only had Windows 10 on it.

As requested by @Pilot6, I took my normal Windows/Xubuntu laptop, booted Xubuntu, connected the external HDD in question, and ran sudo parted -l.

Here is the output:

pal@pal-Vostro-3546:~$ sudo parted -l
[sudo] password for pal: 
Model: ATA Hitachi HTS54503 (scsi)
Disk /dev/sda: 320GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags: 

Number  Start   End    Size    Type     File system     Flags
 1      1049kB  525MB  524MB   primary  ntfs            boot
 2      525MB   208GB  207GB   primary  ntfs
 3      208GB   317GB  109GB   primary  ext4
 4      317GB   320GB  3146MB  primary  linux-swap(v1)


Model: Seagate Expansion (scsi)
Disk /dev/sdb: 500GB
Sector size (logical/physical): 512B/4096B
Partition Table: msdos
Disk Flags: 

Number  Start   End    Size    Type     File system     Flags
 1      1049kB  262GB  262GB   primary  ntfs            boot
 2      262GB   498GB  236GB   primary  ext4
 3      498GB   500GB  2097MB  primary  linux-swap(v1)
Fiksdal
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1 Answers1

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You didn't install grub to your external HDD. Connect it to an Ubuntu machine and run:

sudo mount /dev/sdb2 /mnt
sudo grub-install --root-directory=/mnt /dev/sdb
sudo umount /mnt

This will install grub to /dev/sdb.

Pilot6
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  • Alright, I get Grub and Xubuntu boots, but I can no longer boot Windows 10. Grub merely lists "Windows boot manager" and if I select it, I get "error: invalid signature". – Fiksdal Aug 29 '17 at 21:24
  • This is some kind of a Windows problem. I have no idea what signatures they use. Is it a grub error, or a Windows boot loader? – Pilot6 Aug 29 '17 at 21:27
  • I'm not sure, but Windows worked from the external HDD before I installed Grub. – Fiksdal Aug 29 '17 at 21:28
  • How does it look like? Is it on the purple screen? Try to boot on another machine. Win 10 doesn't like when you boot on a wrong one. – Pilot6 Aug 29 '17 at 21:29
  • Alright I booted from another machine and got another error. I think I'll start over with the whole installation, using another computer for the installation process. – Fiksdal Aug 29 '17 at 21:32
  • Make sure grub is on the correct disk. – Pilot6 Aug 29 '17 at 21:33
  • Alright, yeah. Thank you very much for your time and attention! – Fiksdal Aug 29 '17 at 21:33