Once you have your own server, you can of course upload whatever you want. But you're probably asking about booting from an ISO image. As a few other people hav

Once you have your own server, you can of course upload whatever you want. But you're probably asking about booting from an ISO image. As a few other people have said, Hetzner offers a "boot from rescue image" service which apparently lets you boot from an uploaded ISO. I never tried this on my own Hetzner server though. If you're hardcore, you can also do what a friend of mine did: Use the provided Linux system (Debian, Ubuntu, there's a bunch of choices) to fiddle its own boot loader, possibly re-partition the disk, upload your favorite system and reboot into that. You're root, you can do what the hell you want; at worst you might end up bricking your system to the point where you need to re-install from the rescue system.