Installing Debian to an external HDD

Question

I had a laptop that ceased to turn on one day due to (what I presume to be) a hardware malfunction. I successfully managed to extract the hard drive from that laptop and place it in an USB adapter. I can now navigate the hard drive’s content from any new computer. I want to install Debian on that now external hard drive and boot from it on another laptop. Would that be possible? If «yes», how?

There are instruction for installing to and booting from an external USB drive, but I don't know, if these same instructions are applicable to an external HDD.

Answer 1

Short answer is «yes», it is possible.

The Debian installer will check for all connected drives to your computer. If the external hard drive is connected via USB, you can choose to have Debian installed on it without fear of damaging the data on your internal hard drive that boots your current operating system (typically Windows or macOS). You can even install from a USB drive to an external HDD.

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It is possible that your BIOS (UEFI settings to be precise) has secure boot enabled and is missing an administrator password that won't let you boot the installer from a USB (or other media) as a security policy. In which case you do the following from your BIOS/UEFI settings:

1. Disable secure boot.
2. Set an administrator password.

After the installation is complete you must either

1. Reset your BIOS/UEFI settings to default.
2. Re-disable secure boot.

or just

1. Clear the administrator password.

The point is secure boot must be left as is («unsecured») so that it may boot Debian from the external HDD after installation.