Editing User space and kernel space (section)

== {{Anchor|USERLAND}}Overview ==
The term '''user space''' (or '''userland''') refers to all code that runs outside the operating system's kernel.<ref>{{cite web
| url = http://www.catb.org/jargon/html/U/userland.html
| title = userland, n.
| work = The [[Jargon File]]
| publisher = [[Eric S. Raymond]]
| access-date = 2016-08-14}}</ref> User space usually refers to the various programs and [[library (computing)|libraries]] that the operating system uses to interact with the kernel: software that performs [[input/output]], manipulates [[file system]] objects, [[application software]], etc.

Each user space [[process (computing)|process]] usually runs in its own [[virtual memory]] space, and, unless explicitly allowed, cannot access the memory of other processes. This is the basis for [[memory protection]] in today's mainstream operating systems, and a building block for [[privilege separation]]. A separate user mode can also be used to build efficient virtual machines – see [[Popek and Goldberg virtualization requirements|Popek and Goldberg's virtualization requirements]]. With enough privileges, processes can request the kernel to map part of another process's memory space to their own, as is the case for [[debugger]]s. Programs can also request [[Shared memory (interprocess communication)|shared memory]] regions with other processes, although other techniques are also available to allow [[inter-process communication]].

{{Linux layers}}
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