| Short Answer:
A system running the Linux kernel runs in two states: kernel-space and user-space.
Long Answer:
Many architectures, such as x86, have a handful of processor states, ranging from a 'real' mode with no protection (see: It does wtf you tell it to) to a 'protected' mode. On platforms such as x86 with more than two states, the two extremes are selected for kernel and user space. The kernel ( and all kernel modules ) run in kernel-space, which runs in 'real' mode. Userspace, on the other hand, runs in a protected mode which doesn't just arbitrarily execute code. |