kmutil

kmutil is a macOS command-line utility that provides low-level management of the kernel and its caching structures. It is used to inspect, rebuild, sign, and install kernel caches and kernel collections, and to influence how the kernel and kernel extensions are loaded at boot. This tool is primarily used by developers, Apple engineers, and experienced administrators when building or debugging macOS images, performing system upgrades, or recovering from boot issues. On Apple Silicon hardware, kmutil operates in the context of the kernel collection mechanism, which consolidates the main kernel, kernel extensions, and system extensions into a boot-time cache that the firmware can load efficiently.

kmutil can report the configuration and status of the current kernel cache, assemble a new cache from the kernel, kexts, and system extensions, and install it to the boot partition. It also handles signing and verification of kernel data to comply with system security policies. The tool interacts with the boot process and, as such, is typically used in development, testing, and troubleshooting scenarios involving kernel-extension changes or system upgrades.

Usage considerations: Because the kernel cache affects the ability of the system to boot, kmutil is a specialized tool that generally requires root privileges and should be used with care. Incorrect usage can render a system unbootable. The tool is documented primarily for developers and IT professionals and is commonly employed during OS development, testing, and troubleshooting of kernel-extension-related changes.

Related topics include kernel extensions (KEXT), kernel cache, kernel collection, and kextcache.