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Where does the microvm kernel/initrd come from? How can it be built? I just want a system that's as easy as "docker run ubuntu" but launches as a microvm inste

Where does the microvm kernel/initrd come from? How can it be built? I just want a system that's as easy as "docker run ubuntu" but launches as a microvm instead, without me having to source a kernel or remember hugenormously long qemu incantation lines.

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liquid64 3mo ago
The kernel/initrd come from a regular OCI container image — there's no separate VM image format. Any OCI image containing /boot/vmlinux (and optionally /boot/initramfs.cpio.gz) works as a kernel image.
- spwa4 3mo ago
  And if they don't have a kernel? You just specify kernel + initrd?
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  - pullrun 3mo ago
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  - yakimbo90 3mo ago
    you don't have to source one manually — pullrun kernel install fetches a kata containers kernel into ~/.pullrun/kernels/vmlinux-<version>. One-time setup, then the daemon auto-discovers it.
    - moondev 3mo ago
      If you run an ubuntu image with a kata kernel, do you have difficulty installing some packages? For example if you need linux-headers-$(uname -r) or linux-modules-extra-$(uname -r), it won't exist in canonical apt repos?
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- ktm5j 3mo ago
  I don't think I've ever seen a kernel or initrd in a container image. The whole point of containers is not to duplicate the kernel, and you definitely don't need an initial ram disk since you already have a running operating system.
  - pullrun 3mo ago
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thepoet 3mo ago
We will be soon including this in Tarit, a firecracker alternative https://github.com/instavm/tarit https://github.com/instavm/tarit Currently we have to supply a kernel to run the OCI as a microVM with a warm pool. TARIT_KERNEL=/path/vmlinux taritd image build --oci ubuntu:24.04 --name ubuntu taritd vm create --image ubuntu
jtbaker 3mo ago
I think `smolvm` may fit the bill? I've been using it to run pi.dev in a sandbox. https://smolmachines.com/ https://smolmachines.com/
- ranger_danger 3mo ago
  I tried smolvm, and built several single binaries with it for different distros. Less than a month later, those same binaries now silently exit with code 0 and I have absolutely no idea what's wrong or how to diagnose.
v_elem 3mo ago
Looks like everyone is converging on the same idea these days :-) You might be interested in my project then: https://github.com/virtkit-dev/virtkit https://github.com/virtkit-dev/virtkit (also inspired by smolvm and similar projects). Default kernel included, but can also boot a custom kernel if necessary. I built it at work to replace years of accumulated tooling around complex multi-stage docker/docker-compose builds. The same workloads now run more securely, often faster, and with much less disk space. Also acts as a Gitlab executor to run CI jobs in microvms :-) Obviously built with AI (this would otherwise have been a multi-year effort... and therefore not exist at all!) but I think the design is not bad. Still beta and under-documented, but already quite usable. Edit: it's not just a runtime, it also replaces docker build with its own native build engine — the build steps themselves run inside microVMs (not "docker inside a VM"). I haven't seen any other tool actually do that, that's quite fun ;-)
sureglymop 3mo ago
You can do this with libkrun. I use it as a podman backend which works exactly as you describe here. podman run --rm -it --runtime=krun ubuntu sh
- ranger_danger 3mo ago
  Error: default OCI runtime "krun" not found: invalid argument
  - sureglymop 3mo ago
    Oh, you do need to install it. e.g. on arch: https://archlinux.org/packages/extra/x86_64/krun/ https://archlinux.org/packages/extra/x86_64/krun/
    - ranger_danger 3mo ago
      I do have both podman and crun installed, but I don't see any krun or libkrun packages for ubuntu unfortunately :/
      - sureglymop 3mo ago
        That's unfortunate. I'm sorry, I should have checked that before recommending. Looks like your only option from an ubuntu host is to build from source.
      - pullrun 3mo ago
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liquid64 3mo ago

The kernel/initrd come from a regular OCI container image — there's no separate VM image format. Any OCI image containing /boot/vmlinux (and optionally /boot/initramfs.cpio.gz) works as a kernel image.

spwa4 3mo ago
And if they don't have a kernel? You just specify kernel + initrd?
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- pullrun 3mo ago
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- yakimbo90 3mo ago
  you don't have to source one manually — pullrun kernel install fetches a kata containers kernel into ~/.pullrun/kernels/vmlinux-<version>. One-time setup, then the daemon auto-discovers it.
  - moondev 3mo ago
    If you run an ubuntu image with a kata kernel, do you have difficulty installing some packages? For example if you need linux-headers-$(uname -r) or linux-modules-extra-$(uname -r), it won't exist in canonical apt repos?
    - deleted 3mo ago
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    - pullrun 3mo ago
      [flagged]
ktm5j 3mo ago
I don't think I've ever seen a kernel or initrd in a container image. The whole point of containers is not to duplicate the kernel, and you definitely don't need an initial ram disk since you already have a running operating system.
- pullrun 3mo ago
  [flagged]

thepoet 3mo ago

We will be soon including this in Tarit, a firecracker alternative https://github.com/instavm/tarit https://github.com/instavm/tarit Currently we have to supply a kernel to run the OCI as a microVM with a warm pool. TARIT_KERNEL=/path/vmlinux taritd image build --oci ubuntu:24.04 --name ubuntu taritd vm create --image ubuntu

jtbaker 3mo ago

I think `smolvm` may fit the bill? I've been using it to run pi.dev in a sandbox. https://smolmachines.com/ https://smolmachines.com/

ranger_danger 3mo ago
I tried smolvm, and built several single binaries with it for different distros. Less than a month later, those same binaries now silently exit with code 0 and I have absolutely no idea what's wrong or how to diagnose.

v_elem 3mo ago

Looks like everyone is converging on the same idea these days :-) You might be interested in my project then: https://github.com/virtkit-dev/virtkit https://github.com/virtkit-dev/virtkit (also inspired by smolvm and similar projects). Default kernel included, but can also boot a custom kernel if necessary. I built it at work to replace years of accumulated tooling around complex multi-stage docker/docker-compose builds. The same workloads now run more securely, often faster, and with much less disk space. Also acts as a Gitlab executor to run CI jobs in microvms :-) Obviously built with AI (this would otherwise have been a multi-year effort... and therefore not exist at all!) but I think the design is not bad. Still beta and under-documented, but already quite usable. Edit: it's not just a runtime, it also replaces docker build with its own native build engine — the build steps themselves run inside microVMs (not "docker inside a VM"). I haven't seen any other tool actually do that, that's quite fun ;-)

sureglymop 3mo ago

You can do this with libkrun. I use it as a podman backend which works exactly as you describe here. podman run --rm -it --runtime=krun ubuntu sh

ranger_danger 3mo ago
Error: default OCI runtime "krun" not found: invalid argument
- sureglymop 3mo ago
  Oh, you do need to install it. e.g. on arch: https://archlinux.org/packages/extra/x86_64/krun/ https://archlinux.org/packages/extra/x86_64/krun/
  - ranger_danger 3mo ago
    I do have both podman and crun installed, but I don't see any krun or libkrun packages for ubuntu unfortunately :/
    - sureglymop 3mo ago
      That's unfortunate. I'm sorry, I should have checked that before recommending. Looks like your only option from an ubuntu host is to build from source.
    - pullrun 3mo ago
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