Title.
I know there are tools to set up a linux distro’s installer on a USB flashdrive. What I’m looking for is slightly different: I want to install a linux distro (a Debian derivative, but am still unsure which) on a USB hard drive, but I want to do it from a running system, rather that have to boot into installer mode.
The rationale is that this is the only active machine I have ATM. I guess this exists since that’s how “live distros” with installers even function in the first place, but I haven’t had much luck searching for information.
I think the most straigthforward solution for you would be to boot the live ISO installer in a virtual machine, and then connect the USB device to it and then install. This is mostly guaranteed to work, since it is already using the actual ISO.
Alternatively, the program that most Linux distro’s use to install nowadays is called calamares. And yes, you can install it on a non-live system.
sudo apt install calamares calamares-settings-debianThis might be easier, but it also might be harder, if say, the installer is not preconfigured with the various settings the live ISO comes with.