Thanks for considering helping with this issue!

I am struggling to get an external USB-SSD to boot (Ubuntu and grub installed on it) on my Dell XPS 15 l501x Laptop.

The issue there is that the external Disk is powered by the USB ports only a few seconds after the bios has scaned for bootable media. Afterwards, the drive's partitions can be used as storage.

There is no reason why this wouldn't work. It works flawlessly on my PC. It did work a few times on the Laptop (each of these times way immediately after playing around with the bios settings or the USB cable (got a Y-cable to make sure there really is be enough power)) but fails 99% of the time.

I tried many combinations of bios setting, switched each setting on and of individually but no success.

The Laptop's battery is broken but it is plugged into the wall. I don't think that the small amount of extra power needed for the USB-SSD exceeds the power supply (I also tried with the internal HDD disconnected which should then have freed up enough power).

Since this problem can probably not be solved directly, is there a way to make grub (on the internal drive) re-scan for external drives and then boot from them? I tried just adding

set root(hd1,7)

but grub only finds hd0 so it would probably have to re-scan.

So, I really don't have any idea what else to try and therefore need your ideas and knowledge to find the solution for this. I am so grateful for any help you can provide!

  • I'm not sure your hypothesis is correct. Type usb at the GRUB prompt and see what it outputs.
    – jdwolf
    Dec 25, 2017 at 2:31

1 Answer 1


We have had similar issues with external HDDs. Sometimes the USB port cannot supply enough power to the external device. Should be 5 Volts. The solution is a powered USB hub between the laptop USB port and the external device. The hub has a separate power supply such as an AC adapter. Maybe your Y-cable should work, but I don't know exactly what your hardware setup is. Myself, I would verify it. I boot Ubuntu from a USB memory (memory stick) in a laptop for years without problem.

  • Alternatively, an external battery on one of the Y-cable's ends works as well. Thanks for giving me this idea! Dec 25, 2017 at 11:32

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