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I have installed Ubuntu 14.04 to a USB stick booting from the install DVD and choosing sdb1 as the boot partition and mount point for the file system root (this is the method described in this answer). The install went without issue and plugging the USB stick to the running system I am able to see the file system structure.

However, whenever I restart a machine with this USB stick plugged in, the system installed there never boots, the boot process always falls back to whatever is internally installed in the machine. I have tried this USB stick in different computers (making sure in all of then the USB is first in the boot order), I have re-installed Ubuntu to it, but I never manage to boot from it.

My best guess is that something might be wrong with the installation, but I have no idea what. Any ideas on what may be amiss?

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    Did you follow the last step carefully? I.e. did you make sure you installed the bootloader on the USB drive (in this case /dev/sdb)? i.stack.imgur.com/Pj1wt.png
    – kos
    Jan 6, 2016 at 9:46
  • Hi kos, this could be the case. Is there any way to check if the bootloader is present without repeating the whole process?
    – Luís de Sousa
    Jan 6, 2016 at 12:55
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    Hmmm I found this. But use sudo dd if=/dev/sdb iflag=fullblock bs=512 count=1 2>/dev/null | strings just to be on the safe side
    – kos
    Jan 6, 2016 at 13:08
  • "Missing operating system", mystery solved. Would you care to file an answer, so I can accept it?
    – Luís de Sousa
    Jan 6, 2016 at 13:13

2 Answers 2

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As it has been determined in the comments, sudo dd if=/dev/sdb iflag=fullblock bs=512 count=1 2>/dev/null | strings showed no trace of GRUB on the device.

So the problem is that the device lacks a bootloader, which explains why trying to boot it didn't avail: the BIOS of the machines in question simply fell back to a bootloader present on another device to boot an OS, which had the effect of booting another OS.

The fix is either installing GRUB on the device or reinstalling Ubuntu on the device making sure that GRUB gets installed to the right device:

s1

On a side note, installing GRUB to another device had the effect of either:

  • Adding an entry for the USB device if the target device had GRUB installed in it already;
  • Installing GRUB if the target device didn't have GRUB installed in it already.

So you might want to fix that as well.

The first problem is easily solvable by removing the relevant entry from GRUB;

For the second problem, have a look at one of these two answers, depending on whether you installed Ubuntu in legacy mode or in UEFI mode:

Legacy: https://askubuntu.com/a/168517/380067

UEFI: https://askubuntu.com/a/304892/380067

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There might be many possibilities:

  1. Your USB stick has a problem: try installing on a new USB stick.
  2. The installation source is not "healthy": check it by installing on the machine or download it again and re-install.
  3. You forgot to choose the right boot device from the boot option: press "ESC" or "F1"...etc to get into the boot menu or modify it from the BIOS.
  4. (less probable) you chose the wrong partition: re-install and choose it carefully.

Above is what I can provide for it. Hope it's just 3...

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  • I have checked all this points and in fact it is none of these things. It just happens the bootloader is missing.
    – Luís de Sousa
    Jan 6, 2016 at 13:18

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