QEMU
Load kernel and initrd
qemu-system-i386 -kernel bzImage -initrd rootfs.cpio
Load kernel and initrd with serial terminal
qemu-system-i386 -kernel bzImage -initrd rootfs.cpio -nographic -append 'console=ttyS0'
Create qcow2 disk image
qemu-img create -f qcow2 example.qcow2 5G
Boot from qcow2 disk image
qemu-system-x86_64 -enable-kvm -m 4096 -cpu host -smp 4 -drive file=example.qcow2,format=qcow2 -vga virtio -display type=sdl
Boot from ISO image
qemu-system-x86_64 -enable-kvm -m 4096 -cpu host -smp 4 -vga virtio -display type=sdl -cdrom example.iso