Userland

A userland is the system utilities that are not a part of the main kernel, but provide a base system. The term userland (or user space) refers to all code that runs outside the operating system's kernel. Userland usually refers to the various programs and libraries that the operating system uses to interact with the kernel: software that performs input/output, manipulates file system objects, application software etc.

Various layers within Linux, also showing separation between the userland and kernel space

User mode	User applications	For example, bash, LibreOffice, Apache OpenOffice, Blender, 0 A.D., Mozilla Firefox, etc.
	Low-level system components:	System daemons: systemd, runit, logind, networkd, soundd, ...	Windowing system: X11, Wayland, Mir, SurfaceFlinger (Android)	Other libraries: GTK+, Qt, EFL, SDL, SFML, FLTK, GNUstep, etc.		Graphics: Mesa, AMD Catalyst, ...
	C standard library	open(), exec(), sbrk(), socket(), fopen(), calloc(), ... (up to 2000 subroutines) glibc aims to be POSIX/SUS-compatible, wp:uClibc targets embedded systems, bionic written for Android, etc.
Kernel mode	Linux kernel	stat, splice, dup, read, open, ioctl, write, mmap, close, exit, etc. (about 380 system calls) The Linux kernel System Call Interface (SCI, aims to be POSIX/SUS-compatible)
		Process scheduling subsystem	IPC subsystem	wp:Memory management subsystem	Virtual files subsystem	Network subsystem
		Other components: ALSA, DRI, wp:evdev, LVM, device mapper, Linux Network Scheduler, Netfilter wp:Linux Security Modules: SELinux, TOMOYO, wp:AppArmor, Smack
Hardware (CPU, [RAM|main memory]], data storage devices, etc.)

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