QEMU comes in two variants: system mode for full machine emulation, and user mode for single-binary emulation. Install with apt install qemu-system qemu-user-static on Debian/Ubuntu.
qemu-system-arm -M versatilepb -kernel zImage -nographic # full machine qemu-arm ./binary # single binary
System mode (qemu-system-*) emulates an entire machine—CPU, memory, disk, peripherals—and boots a full OS. User mode (qemu-arm, qemu-riscv64, etc.) emulates only CPU instructions for a single process, translating syscalls to the host kernel. User mode is lighter weight when you just need to run one foreign-architecture binary.
Common flags across both modes:
-M machine machine/board type (versatilepb, virt, etc.) -kernel file load kernel image -dtb file load device tree -append "args" kernel command-line arguments -nographic no GUI, use serial console on terminal -m size memory (e.g., -m 512M, -m 4G) -smp N number of CPUs
User mode is invoked transparently via binfmt_misc when qemu-user-static is installed. A foreign-architecture binary executes as if native; QEMU intercepts syscalls and translates them.
System mode typically runs headless with -nographic for embedded testing. Remove -nographic to open a GUI window (useful for desktop OS testing, but slower over SSH).