MacOS’s Activity Monitor will give you a list of all the apps you’re running, which is useful for closing down CPU-hungry processes. But it also throws in a bunch of system process, some of which may not be safe to quit. Here’s how to tell the difference.
Who Are All These Users?
First, you should look at who owns the process. Processes in macOS (and any other Unix-like operating system, including Linux) have owners, tying each process to the user account that started the process. And while you will recognize your user account, there’s a lot of other users on your computer, most of which are managed by the system.
You can see here, on a standard installation of macOS, there are over 250 users managed by the system, most of which start with an underscore:
Macs have so many user accounts because of the way permissions work in macOS, and each user has specific permissions. For example, _dock would have permission to access files related to the dock and not much else. This keeps your system more secure by keeping low-level system processes in their own containers.
Important: Since most of these are purely system processes, it’s best never to quit any process whose owner starts with an underscore.
It’s probably safe to close all processes under your user account name since most of them will automatically restart if they’re needed. However, you shouldn’t go too crazy closing everything to save on system performance, as the vast majority of the processes running on your machine are idle. It’s a lot better to leave them there for when they’re needed, instead of spending extra resources having to open them up again.