A “Hello World” virtual machine running the Hurd

Jan Nieuwenhuizen, Ludovic Courtès — 2020-04-08

Hello GNU World!

There’s been a bit of speculation as to whether our April 1st post was a joke. Part of it was a joke: we’re not deprecating Linux-libre, fear not! But when we published it, it was already April 2nd in Eastern parts of the world and thus, not surprisingly, the remainder of the post was less of a joke.

Getting to a bootable system

For all you who tried our April 1st image and ran guix we sure hope you had a good laugh. We set out to cross-build that virtual machine (VM) image using Guix and while we made some good progress on Wednesday, in the end we decided to cheat to make the release deadline.

What we got stuck on for a while was to get past the ext2fs translator (the user-land process that implements the ext2 file system) seemingly freezing on boot, saying:

start ext2fs:

and then nothing... Running ext2fs cross-built with Guix on Debian GNU/Hurd would hang similarly. The kernel debugger would show an intriguing backtrace in ext2fs suggesting that ext2fs was not handling page fault messages. Long story short: we eventually realized that the server interfaces were compiled with a 64-bit MiG whereas we were targeting a 32-bit platform. From there on, we embarked on a delightful hacking journey ensuring the Hurd boot process would correctly run in our VM up to a proper login prompt.

Today we have a humble gift for you: On the wip-hurd-vm branch (Update: this has now been merged!) we have an initial hurd.scm system description that can be used to cross build a VM running the Hurd.

Running:

./pre-inst-env guix build -f gnu/system/hurd.scm

cross-compiles all the relevant packages for GNU/Hurd—specifically the i586-pc-gnu triplet—and produces a VM image:

/gnu/store/yqnabv1zmlkviwzikc23w9qvfnyfwvj7-qemu-image

You can build it and start it from your GNU/Linux machine with this command:

qemu-system-i386 -enable-kvm -m 512 -snapshot -hda \
  $(./pre-inst-env guix build -f gnu/system/hurd.scm)

and voilà:

Woohoo! (Actually we already have more stuff not shown here, such as guix itself running… for a future post! :-))

Why bother?

Why bother with the Hurd anyway? Isn’t it a pipe dream or “vaporware”, depending on one’s perspective? There’s some unquestionable truth in that: we know that Hurd development started in the early 90’s, months before Linux development started, and yet it still lacks so much in terms of hardware support, even though significant progress was made in recent years in particular with the use of Rump kernels.

The more we witness how new features are retrofitted in the kernel Linux, the more we think the Hurd’s design is better suited to today’s needs. Linux namespaces, the foundation of “containers”, are such an example of an afterthought; unprivileged user namespaces, which allow unprivileged users to benefit from lightweight “container” virtualization, are still often disabled by distros due to a lack of confidence. This is in sharp contrast with the Hurd’s inherent unrestricted support for fine-grain virtualization: a PID namespace is just another proc server, and file system name space is just another root file system server, and so on. Container-like lightweight virtualization is native on the Hurd.

Last but not least, with an eye on the security and transparency of free software systems, a microkernel-based systems seems to naturally lend itself well to bootstrapping from a reduced trusted base. This is one of the topics we discussed on the last Reproducible Builds Summit.

The question is not so much whether 2020 or 2021 will be the year of the Hurd. It’s more about the kind of systems we want to build. A lot of work remains to be done, but we think, in 2020 more than ever, that this is a promising approach for the betterment of the security of our systems and the freedom of users.

We also have to admit that this is an amazing system to hack on, even more so when combined with Guix, so… happy hacking! :-)

About GNU Guix

GNU Guix is a transactional package manager and an advanced distribution of the GNU system that respects user freedom. Guix can be used on top of any system running the Hurd or the Linux kernel, or it can be used as a standalone operating system distribution for i686, x86_64, ARMv7, and AArch64 machines.

In addition to standard package management features, Guix supports transactional upgrades and roll-backs, unprivileged package management, per-user profiles, and garbage collection. When used as a standalone GNU/Linux distribution, Guix offers a declarative, stateless approach to operating system configuration management. Guix is highly customizable and hackable through Guile programming interfaces and extensions to the Scheme language.

About the GNU Hurd

The GNU Hurd is the GNU project's replacement for the Unix kernel. It is a collection of servers that run on the Mach microkernel to implement file systems, network protocols, file access control, and other features that are implemented by the Unix kernel or similar kernels (such as Linux). More info.

The mission of the GNU Hurd project is to create a general-purpose kernel suitable for the GNU operating system, which is viable for everyday use, and gives users and programs as much control over their computing environment as possible.