Not OP but security and ressource usage are often the main motivators.

For security, GVisor is probably the most widely used userspace-kernel. A userspace kernel may also boot faster and use less resources as it can offload a lot of work to the host (FS drivers etc.)

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qalmakka a day ago | parent [-]

Ok, but Linux UM exists - why can't it be extended and used instead? It should in theory offer better compatibility, right?

	▲	ronsor 21 hours ago \| parent [-]
		User Mode Linux does work, but it can have significant performance issues and isn't actually very portable. Yes, I've tried using it before.