I have an external HDD on which I a collection of video files (too numerous to fit on my laptop's internal HDD). This external HDD connects via USB. I use two Dell laptops, both of which are set up with Kubuntu 14.04 and are configured to boot from (1) CD/DVD, (2) USB, then (3) internal HDD.

Problem is, on one machine, I can have the external HDD plugged in at boot-up and experience no problem at all. But on the other machine, if the external HDD is plugged in, I invariably get the "Invalid partition table" error message, and boot-up fails.

I set up the two machines at different times, probably a couple years apart, but I thought I'd set them up identically. Maybe not. Any ideas what I should look for as a disparity that's causing this difference in behavior?

are the dell laptops same year and model and if not how old what was installed on then when first new?

They were bought as reconditions machines at different times - probably something like two years apart. The elder one is a Dell Latitude E6500; the one newer to me is a Dell Latitude E6430s.

The E6500 came to me with Windows 7 installed, which I over-wrote with several ext3 partitions, creating a dual-boot machine with two variants of Ubuntu operating systems.

The 6430s came to me with Windows 10 installed, which I over-wrote with several ext3 partitions and one NTFS partition, creating a dual-boot machine with one Kubuntu and one Windows 7 operating systems. The NTFS partition has the boot flag; is there something there that is causing the problem?

I suspect that the failing machine is actually trying to boot from that external drive. In the legacy DOS MBR boot code, "Invalid partition table" means that the code did not find exactly one partition marked "active".

That much had been my working assumption, too. My question is: Why is that happening on one machine and not the other, given the same external HDD? The external HDD is an ext3 file-system and does NOT have a boot flag.

I think it's because the BIOS of one laptop is set to boot from the USB drive (before internal hard drive), while the BIOS of the other laptop is not. Look at the BIOS settings on boot priority and also the hard drive boot priority. Unfortunately, some BIOSes will have its own ideas about what hard drive boot priority to assign when a USB hard drive is connected. Usually this will put USB drives at the bottom (which is good for you, but annoying for using thumbdrives for installers or rescue thumbdrives).

IsaacKuo, that in itself cannot be the problem. As I described in my original posting: That is, both machines have the same boot priorities.

Look at the HDD boot priority also. Seriously. The BIOS of many machines see external USB drives as hard drives, so you also have to look at the priority of the hard drives.

You might not be able to change that boot priority. I was setting up a Lenovo desktop for a neighbor, and if an external USB HDD is connected, it insists putting it ahead of the internal HDD in the boot priority. I figured, "No problem. I'll just delete the EFI partition and the UEFI firmware will ignore the drive." No luck -- it still tries to boot the NTFS partition directly. So much for the EFI partition being "required."

You might need to install a boot loader on that drive and configure it to chain back to the internal drive. Good luck getting that to work if you're sharing that external drive among several machines.

Hmm...since there are only two machines, and only one of them is a problem...there's a quick fix:

On the problem machine, use the following commands:

Use this to confirm that the external drive is /dev/sdb. Assuming it's /dev/sdb, then use the following command:

This will install a bootloader on the external USB drive to try and boot from the partition with /boot (specified by UUID).

If you have any other problem machines in the future, you'll have to finagle things so that the UUID is the same in the other problem machine(s). The easiest way to do this is to clone a new install from the other laptop's install using "dd". The steps for best accomplishing this depend on your situation and how hard/easy it is to remove that laptop's hard drive.

Thanks, IsaacKuo" That led me to the solution. In that machine's BIOS, there's a setting (completely apart from the boot sequence settings - under System Configurations > USB Configuration) for an option called "Enable boot support." The explanation (fortunately provided for this ambiguous description) says that enabling this option allows the system to boot from any sort of USB device.

By disabling this option, I can boot with the external HDD attached and not get the error message.

Unfortunately, this means that I cannot boot from a live USB unless I interrupt the boot process (F12) and manually change the setting to allow booting from the USB.

Given the options, however, I'll leave the USB-boot option disabled until I need it. I use the external HDD a lot more often than I need to boot from a USB stick.

Is this before or after the grub boot menu.

edit: never mind must have been posting about the same time, glad you got it sorted out

FWIW, it was before the grub boot menu.