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The consensus for installing an 100% independent Linux on an external HDD, without having any boot record etc interference with any other OSes on any other HDDs, is to unplug all your HDDs, plug in only the live CD/USB and the destination HDD or flash drive, and install.

Because every time I see a guide for doing it without unplugging the rest of the HDDs, it is riddled with comments of how it backfired (exhibit A, exhibit B, plus I tried it a couple of times and gave myself huge headaches and a lot of work afterwards).

I have a Windows laptop that I can't open up, and I don't have access to any PCs. So I will ask, clearly how else can I, what's the actual way to, easily, with minimal risk of screwing up, with minimal steps, install Ubuntu without corrupting my main system or leaving any other traces or dependencies in it?

I would love it if there just was a button for "install everything to this HDD clearly labeled as 'MY External HDD'". OR to download a 16GB pre-installed sector-by-sector Ubuntu HDD image that I could "recover" to my external HDD and then resize the data partition accordingly. Because that guarantees not messing anything up big time, and it also doesn't require any OS restarts or ISO boots for the process.

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Well, hello.

I have a dual boot (from 2 different drives) Debian/Windows desktop. I suppose the installation process is quite similar in Ubuntu if not identical.

Follow these steps:

  • Burn your .iso in a thumb drive or a CD/DVD
  • Boot from it (you should read on MBR/GPT on that)
  • Fire up the OS installer (click install)
  • When prompted to select an installation option choose "Something Else" (other options are "Erase disk and install Linux", "Install Linux alongside X", etc.)
  • In "Something Else" you are required to partition the hard drive you're going to use and set a swap partition as well. (Take extra time & care in this step as formating the wrong drive means data loss)
  • IMPORTANT: In the end of the OS installation process, you'll be promted to install/setup Grub (bootloader). Once Grub is installed you'll be asked on which drive you want boot info saved (this defaults to /dev/sda but you most likely don't want it there, you want Grub to install and save it's config ONLY on your external hard drive which means when the drive is connected Grub fires up, and when it's not Windows Bootloader does).

If all of the above is done properly you'll be able boot in both Linux & Windows without losing any of your data.

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  • Long story short, no foolproof way. It's quite simple though and hard to fail, once you fully understand exactly what you're trying to do and how it's done. Feel free to comment for further clarification. – nic3ts Jan 5 '19 at 13:56
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    This works well for BIOS installs, but not at all for UEFI installs. Just installed 19.04 to sdb drive and it did not install grub to sdb drive's ESP. So still not fixed for UEFI. See bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1396379 & bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1229488 & bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1173457 I always partition in advance and include an ESP on every drive. And then back up sda's ESP. After new install, copy to new drive's ESP & restore backed up ESP to sda. Reset fstab for new efi partition & reinstall grub. – oldfred Jan 5 '19 at 16:07
  • Thanks for the heads-up! I think I will wait a sec for a laptop I can destroy or use a neighbour's PC for now. – Spectraljump Jan 6 '19 at 22:14
  • And UEFI is such a pain. It took me a long time to figure out how to even be able to boot from USB. Had to enable some kind of "legacy mode" for UEFI, but also disable secure boot (which on one of my laptops' bioses doesn't even exist it seems) to allow usb boot, otherwise it just does what it wants to protect you the sweet innocent user, or lock you out of your own product depending on how you look at it :) – Spectraljump Jan 6 '19 at 22:14

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