Kernel extension

Kernel extensions, also known as "kexts", are deprecated modifications to the kernel of Mac OS X to add low-level functionality. These are referred to as "s" in other operating systems.

Description
Kexts filled the role of extensions previously used in classic Mac OS, but with greater stability under the Unix-based architecture of Mac OS X. After startup, problematic processes can be viewed and sometimes quit through the Activity Monitor utility.

Deprecation and replacement
Kexts were later deemed to be a security risk without a straighforward graphical user interface to manage them. Starting with macOS High Sierra (10.13) in 2017, installation of kexts was limited to users with administrator privileges, though this did not affect pre-existing kexts during an upgrade.

Apple introduced system extensions in macOS Catalina (10.15) in 2019 as a more secure alternative that would only operate in. These modern system extensions can be managed through the Extensions pane of System Preferences. Starting in macOS 10.15.4, the continued use of kernel extensions would trigger a warning to the user. Support for kexts would start to be phased out in macOS Big Sur except for Apple-approved enterprise developers. Any legacy kexts still installed would require user approval to be loaded.