Boot ISO

qemu-system-x86_64 -boot d -cdrom /path/iso/cdrom.iso  -m <memorySize G>  -smp <#CPU> -enable-kvm -vga virtio


Create a disk

qemu-img create /path/to/debian.img 5G


Install OS

qemu-system-x86_64 -hda /path/to/debian.img -cdrom /path/iso/debian-9.5.0-amd64-netinst.iso -boot d -m 8G -smp 4 -enable-kvm -vga virtio


Run installed system

qemu-system-x86_64 -hda /path/to/debian.img -m 8G -smp 4 -enable-kvm -vga virtio