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Comment by qmarchi | Hacker News Reader

Small note, that's not true for Google Cloud, which runs on top of Linux, though modified.

Disclaimer: Former Googler, Cloud Support

Another Xoogler here: any idea what they mean by it's not Linux at the bottom for other providers? Like, surely it's _some_ common OS? Either my binaries wouldn't run or AWS is reimplementing Linux so they can, which seems odd.

Or are they just saying that the VM my binary runs on might be some predictable Linux version, but the underlying thing launching the VM could be anything?

Old AWS used to be Xen, Nitro afaik uses customised VMM and I don't recall if it's not a custom OS or hosted on top of something.

Azure is Hyper-V underneath IIRC, a custom variant at least (remember Windows Server Nano? IIRC it was the closest you could get to running it), with sometimes weird things like network cards running Linux and integrating with Windows' built-in SDN facility.

Rest of the bigger ones is mainly Linux with occasional Xen and such, but sometimes you can encounter non-trivial VMware deployments.

Nitro is supposed to be this super customized version of KVM.

When your programs are running on a VM, the linux that loads and runs your binaries is not at the bottom; that linux image runs inside a virtual machine which is constructed and supervised by a hypervisor which sits underneath it all. That hypervisor may run on the bare machine (or what passes for a bare machine what with all the sub-ring-zero crud out there), or may run on top of another OS which could be linux or something else. And even if there is linux in the middle and linux at the bottom they could be completely different versions of linux from releases made years apart.

> Or are they just saying that the VM my binary runs on might be some predictable Linux version, but the underlying thing launching the VM could be anything?

Yup. eg with Xen the hypervisor wasn't Linux, even if the privileged management VM (dom0) was Linux (or optionally NetBSD in the early days). The very small Xen hypervisor running on the bare metal was not a general purpose OS, and didn't expose any interface itself - it was well hidden and relied on dom0 for administration.

Azure runs a version of Windows, see:

https://techcommunity.microsoft.com/t5/windows-os-platform-b...

Correct, that the Hypervisor isn't running Linux.

I think the only provider where that would make sense would be Microsoft, where they have their own OS.

As I understand it, there's linux running on the Google Cloud hardware but the virtualized networking and storage stacks in Google Cloud are google proprietary and largely bypass linux -- in the case of networking see the "Snap: a Microkernel Approach to Host Networking" paper.

In contrast, it appears that Oxide is committing to open-source the equivalent pieces of their virtualization platform.

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