Userland

Userland, also called user space, is the portion of a computer's software that runs with non-privileged permissions, distinct from the operating system kernel, which runs in kernel mode with full privileges. In most modern operating systems, the kernel provides core services such as process management, memory management, and I/O, while applications, libraries, and runtime environments run in userland. The separation protects the kernel from faults in untrusted code and allows the system to remain stable even when user programs crash or misbehave.

Userland comprises executable programs, shared libraries, shells, scripting runtimes, and user-mode services. It communicates with the kernel through system calls and inter-process communication; transiting to kernel mode occurs during system calls or interrupts.

In some designs, userland networking stacks or user-mode device drivers are used for modularity or security. In unikernel or minimal-kernel environments, the distinction can be blurred, with application logic running directly on top of a small kernel or runtime but still conceptually in userland.

The term is informal but widely used in operating-system discussions to describe the boundary between privileged kernel-space and unprivileged user-space.