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All the guides I've read on installing Ubuntu to an external drive strongly recommend unplugging the internal drive before installation. Is there a way around this? I have a Macbook Pro, and I'd really prefer not having to open and take my SSD out.

Given the flexibility of Linux, I would imagine there's a way to ignore the internal drive during the installation.

And I'd at least be interested in the explanation why this isn't possible, if that's the case :)

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The reason people recommend against doing this is just that it would be easy for a non-technical person to accidentally re-format the internal drive, or overwrite the internal drive's MBR (by installing the Grub boot loader) by doing this. If you know not to do this it's fine. – thomasrutter Dec 19 '12 at 6:37
up vote 2 down vote accepted

You can install Ubuntu onto an external (or internal for that matter) drive without removing the internal drive. You just need to make sure you understand how linux identifies drives and where you install grub.

IMO most people who make such recommendations either

  1. Do not understand grub.

  2. Make such recommendations "just in case".

I do not want you to take my advice as dismissive, when installing a operating system, data loss (due to over writing your data) is a mouse click away.

Probably the 2 most important steps for you to take are:

  1. Make a backup.

  2. Read and understand the installation documentation.

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When you get to partitioning Select "Something else"

Confirm "Device for boot loader installation:" is correct, (If you left your internal HDD plugged in make sure the USB drive root is selected - sdb not sdb1).

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<@Tarik> If you get complains about missing drives when you run your external install on another machine (Something like 'Press S to skip mounting or M for manual recovery'), you should have a look at /etc/fstab. Here you can either

  • remove the corresponding lines (no more automatic mount at startup), or

  • add the nobootwait option to them so that they will be automatically skipped if not present.

(More info about fstab here).

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I think the recommendations are really just for safety. You can pick which drive you install onto during the install, so there's no reason you can't just ignore the internal drive and install onto the external, provided you can pick it out of a list.

By removing the internal drive, there's no chance of getting it wrong is the general idea.

You will just have to choose to boot from the external drive after the install is done, in order to get into your Ubuntu install.

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I installed Linux Mint on a USB stick while I already had another installation on the hard drive. As a result, it included the hard drive in the boot menu. I then had to edit grub.cfg to remove the unwanted boot menu options. I still have complains of a missing hard drive during boot which I am trying to figure out how to fix. No detrimental effect otherwise.

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