Is there anyway to debug a process running on a Virtual Machine (guest) with Radare2 from the host? I'm currently using VirtualBox. It provides a built in debugger. I'm not sure if it's possible for radare2 to integrate with it.
Radare is able to connect to gdb remote sessions. So if you use something like qemu for your virtualization you would be able to connect to this. The problem will be to find the desired process inside the whole memory. At first you need to understand how your guest operating system handles processes inside it's kernel and then you need to find the kernel inside this memory region.
There are two interesting projects about this topic: zdbg and r2vmi