Userspace

Userspace / user space means 'done as a regular program'.

It is contrasted with kernel space

We tend to use this term when it may also be reasonable to do the thing in the kernel

'space' refers more to to memory space, e.g. where things are stored, but it is often implied things are also computed in the same place (as the kernel, versus as a user).

Programs are mostly userspace, while e.g. syscalls go into kernel space (almost the definition of a syscall)

For example:

• FUSE (Filesystem in Userspace) - a lot of filesystems are managed by the kernel

FUSE is there because sometimes we can't easily do the thing in kernel space

• NFS servers exist both in-kernel and outside it, and it's useful