Reliable way to tell rosetta virtualized vm from inside the guest

[goodwillcoding]

Hi folks,

What's a reliable way to the guest is running a virtualized to know it supports.
Using https://raw.githubusercontent.com/lima-vm/lima/master/examples/experimental/vz.yaml where rosetta is enabled on M* macOS

$ limactl start --name test1 vz.yaml

And uname is not helping

$ limactl shell ubuntu uname -a
Linux lima-ubuntu 6.8.0-31-generic #31-Ubuntu SMP PREEMPT_DYNAMIC Sat Apr 20 02:32:42 UTC 2024 aarch64 aarch64 aarch64 GNU/Linux

What am I missing?

[afbjorklund]

As far as I know, Rosetta is registered using binfmt_misc - so it should be in /proc/sys/fs/binfmt_misc

Note that Rosetta is "only" a binary translator (like qemu-user) and not a hypervisor (like qemu-system)

[afbjorklund]

Actually it will try some heuristics to find Docker and Podman, based on environment files:

https://github.com/systemd/systemd/blob/v255/src/basic/virt.c#L631 (others use $container)

[goodwillcoding]

Note that Rosetta is "only" a binary translator (like qemu-user) and not a hypervisor (like qemu-system)
Right but something is confusing ... is not it translating arm <-> x86 ... so why would the arch for the guest be arm, is the point to run x86 binaries ... which in turn are able to virtualize infra for x86 ...

What am I missing?

[goodwillcoding]

I guess it's limitation of rosetta based on https://kb.parallels.com/129871 ... so it give arm ability to run x86 while staying arm ... I guess that's a lot of scripts to change that use uname (or fake uname)

[afbjorklund]

Just meant that "rosetta" is not the virtualization method, it is called "apple" (Apple's Virtualization.framework, or "VZ")

As you mention, Rosetta is used to run amd64 binaries on arm64. But it can do that both on the host, or in virtualization.

[afbjorklund]

Ah, "Rosetta.Enabled" actually refers to VZLinuxRosettaDirectoryShare (the file system used)

The actual setting is "Rosetta.BinFmt", that enables the binary translation... Good to know. :-)

[afbjorklund]

The file system is mounted under /mnt/lima-rosetta. The handler is /proc/sys/fs/binfmt_misc/rosetta.

They should correspond to the Rosetta.Enabled and Rosetta.Binfmt settings, in the instance configuration

rosetta:
  # Enable Rosetta for Linux (EXPERIMENTAL).
  # Hint: try `softwareupdate --install-rosetta` if Lima gets stuck at `Installing rosetta...`
  # 🟢 Builtin default: false
  enabled: null
  # Register rosetta to /proc/sys/fs/binfmt_misc
  # 🟢 Builtin default: false
  binfmt: null

https://lima-vm.io/docs/config/multi-arch/#fast-mode-2-rosetta-intel-containers-on-arm-vm-on-arm-hostfast-mode-2