Experiences with building a Gentoo virtualisation host

As part of my work to set up infrastructure for a few projects that I hope to launch with some mates in the coming months, I needed to set up a KVM virthost using Gentoo. I decided to write up the process for FOSS Friday! This setup was performed on a Hetzner AMD server running the latest musl stage3, but glibc should be roughly the same.

Hetzner’s AMD offerings are some of the lowest cost dedicated servers with actual support and decent cross connects. All three of these factors are important to the projects that will be using this server.

Gentoo was chosen so that packages could be built with the exact configuration required. There are no extraneous dependencies that can cause vulnerabilities without even being needed or utilised by the actual workload.

The goal is for the host and guest VMs to share the same on-disk kernel. This way, the kernel is only built and updated once. All VMs will automatically boot into the new kernel when the host is rebooted into the new kernel. As such, the guests do not need a /boot or GRUB at all.

Configuring the Host

I decided to have the host and guests share virtually all of their Portage configurations, though I have not set up a centralised Git repository for them to live in just yet. The CPU_FLAGS_X86 are straight from cpuid2cpuflags. USE is “-X -nls -vala verify-sig”, a conservative but useful global-USE for lightweight, hardened infra.

The base hardware additionally needed sys-kernel/linux-firmware for AMD microcode and TCP offloading. Right now, I’m using package.accept_keywords to accept the ~amd64-keyworded version 20240115-r3. It has a significant performance improvement over 20240115 as I tweaked which firmware files are installed using savedconfig.

For package.use, the base settings I find most useful include:

# prefer lighter
app-alternatives/bc -gnu gh
app-alternatives/cpio -gnu libarchive

# trim the fat, what we don’t need on a server
dev-python/pygobject -cairo
net-firewall/ebtables -perl
net-libs/glib-networking -gnome
net-libs/libsoup -brotli
net-misc/netifrc -dhcp
sys-boot/grub -fonts -themes

# eliminate circular dep
dev-libs/libsodium -verify-sig

# would pull CMake into the graph
net-misc/curl -http2

# Required USE for libvirt / virt-install
app-emulation/libvirt lvm
app-emulation/libvirt-glib introspection
net-dns/dnsmasq script
net-libs/gnutls pkcs11 tools
sys-fs/lvm2 lvm
sys-libs/libosinfo introspection

I then did a full world rebuild, followed by emerge -av eix vim sysklogd chrony libvirt virt-install.

Host-side Networking

I created a bridge interface for the guests to use, which will be a private network segment with no access to the outside world. They will still have access to the host itself, which can run a Portage rsync mirror and binpkg/distfiles host as well.

I did the configuration this way because these VMs will contain sensitive data including login information, and I wanted to be extra-paranoid about network traffic going in to them. It’s probably better to use libvirt’s NAT if possible for your use case.

I added the following stanza to my /etc/conf.d/net:

bridge_kvmbr0=""
config_kvmbr0="172.16.11.1/24"

This added an empty bridge interface, and set the guest network subnet as 172.16.11.0/24. The host will use .1. To be extra fancy, you could configure a private DNS server to listen on that IP which would allow guests to resolve each other and communicate via hostname.

Host-side Kernel Configuration

I’m using gentoo-kernel, so there wasn’t any actual Kconfig to be done, but there is the matter of setting up the “hassle-free” automatic update system that I described in the introduction.

What I did was to symlink /boot/vmlinuz-current and /boot/initramfs-current to the present version. We can set the guests to boot that, and simply update the symlinks when the kernel itself is updated.

Configuring the Guests

I used a full-disk LVM volume group on the Hetzner server’s second attached disk for guest storage. I created an LV for each guest machine, and then formatted the LV with XFS. Since the VMs don’t need a boot loader there is no reason to have a partition table at all. You can use your file system of choice; I used XFS for performance and consistency.

# lvcreate -n keycloak -L 40G hostvg
  Logical volume "keycloak" created
# mkfs.xfs /dev/hostvg/keycloak
[...]
# mount /dev/hostvg/keycloak /opt
# curl [stage 3 tarball] | tar -C /opt -xJf -
[Downloading and extracting the tarball]
# cd /opt
# mount -R /dev dev
# mount -t proc none proc
# mount -t sysfs none sys
# chroot /opt

We are now able to configure the guest environment as desired. Since there is no outbound network access, if you want network time you will need to run a network time server on the host. I personally tend to trust virtio’s RTC system as it rarely loses sync in my experience. With the present frequency of kernel and low-level system updates, it isn’t likely that any of these systems will have long enough uptimes to have tiny amounts of drift matter anyway.

We configure the guest-side networking to use the subnet we defined in the host bridge. For instance, on this VM I could use config_eth0="172.16.11.2/24". There is no reason to set routes_eth0 because the host system is not going to route packets out for it.

Setting up the Guest

Now it is time to run virt-install for the guest and boot it up. Make sure your SSH keys are installed and the chroot is unmounted first!

# virt-install --boot kernel=/boot/vmlinuz-current,initrd=/boot/initramfs-current,cmdline='console=tty0 console=ttyS0 ro root=/dev/vda net.ifnames=0' --disk /dev/hostvg/keycloak -n auth01 -r 8192 --vcpus=2 --cpuset=10-11 --cpu host --import --osinfo gentoo -w bridge=kvmbr0,mac=52:54:00:04:04:03 --graphics none --autostart

Let’s describe some of the fancier of these options. For a full description of the options used here and additional ones you can try, see the refreshingly coherent man page.

--boot kernel=…,initrd=…,cmdline=…
This sets up the guest to boot from the host kernel, as discussed previously.

--import
This tells virt-instal that we have already installed an OS to the disk provided, so it doesn’t need to perform any installation procedures. We’re “importing” an existing drive into libvirt.

-w bridge=kvmbr0,mac=52:54:00:…
This configures networking to use the bridge we set up previously. Note that the MAC for each guest must be unique, and for KVM VMs it must start with 52:54:00.

Enjoy!

This article showed the overview of how I’ve configured a Gentoo machine to serve as a virthost with a dedicated private LAN segment for guests and a way to have those guests share the same kernel as the host. We also looked at a way to “cheat” on storage by using an actual file system as the attached disk.

In the next set of articles, I plan to review:

  • Setting up WireGuard on the host to have pain-free access to the private LAN segment from my workstation for administration purposes
  • Leveraging the power of Gentoo overlays and profiles to have a consistent configuration for an entire fleet of servers
  • Sharing /var/db/repos and /var/cache/distfiles from the host to each guest, so there is only one copy – saving disk space, bandwidth, and time

Until then, happy hacking!

Dual-booting Windows 11 and Windows 7 on a Haswell

I have a Haskell-era MSI B85-G41 PC Mate motherboard and I decided to use it as a “mid-tier”-ish gaming PC and also as a TV set top box. I already had a WinTV-DCR-2650 dual-tuner CableCARD USB device, and I was gifted a Nvidia GeForce RTX 3070 for the project. The board had 32 GB RAM when I decommissioned it in 2019 as the Adélie x86_64 builder, so memory was not a concern.

My goal is to use Windows 11 for gaming, and Windows 7 Media Centre for the TV support (since Cox Oklahoma uses encryption for virtually all channels).

The problem is that Microsoft dropped support for Windows 7 long before this hardware existed, so it is difficult to boot on it. Also, Windows 11 doesn’t officially support Haswell, either.

Windows 11 was trivial to install in all honesty. I used Rufus to put the installer for Windows 11 on a USB disk, then followed the suggestions from this article in Tom’s Hardware and it installed quite nicely. It is performant, stable, and even still does Windows Update.

Windows 7 was significantly more difficult. I used Rufus again and ensured it used GPT and UEFI. It locked up early in boot. I found the UEFISeven project which seemed to make things somewhat better, but it never finished booting beyond “Starting Windows”. The Windows logo continued to pulse, but after 15 minutes I gave up. I found an issue on the UEFISeven tracker and despite my trepidation on running unknown binaries for booting, putting it in the USB stick managed to boot Windows 7’s installation environment successfully.

Next, while performing the installation, the system had a STOP 0x7E in HIDCLASS.SYS. This appears to be a very classic bug and it’s caused by using a Microsoft Wireless Keyboard/Mouse. (Irony as a MS hardware product crashes MS Windows…) Replacing them with (even more ironically) an Apple Pro Keyboard and Mouse allowed setup to continue.

The next problem was actually dual-booting. If I use the patched Windows 7 boot EFI application as BOOTMGFW.EFI, Windows 11 doesn’t boot; it seems to load all the files, but stays at a black screen. If I use Windows 11’s BOOTMGFW.EFI, Windows 7 no longer boots.

I’ve made a small batch script on the desktop of each one to reboot to the other. The 7->11 script renames BOOTMGFW.EFI to BOOTMGFW.7, then renames BOOTMGFW.11 to BOOTMGFW.EFI. The inverse is done for the 11->7 script. Note that you have to mount the ESP first, which is done (in both OSes) as “MOUNTVOL S: /S”. You can use any available drive letter.

I used LegacyUpdate.net to fetch and install all the needed updates for Windows 7. I still wouldn’t trust it unprotected on the “real” internet, but I’m comfortable enough with it sitting on my home network this way. Kudos to that team for making such a useful and valuable service for all retrocomputing enthusiasts!

Notes about the iBook G3 Clamshell

I’ve just repaired the hinge on my Indigo Clamshell. While I was in there, I also replaced the aging hard disk with a SD card adaptor. I wanted to write down a few notes about the process, both for posterity and so that others can benefit from my experience.

The standoffs for the hard disk caddy are brittle. I slightly over-tightened one and it snapped right off. Luckily, it snapped in a way that it would still stand solidly and hold the grounding wire of the charging board. When the Service Source manual says do not overtighten, it means it – as soon as there is the slightest resistance, stop: it’s tight.

I burned a copy of the iBook Software Restore CD from the fabulous archivists at the Garden, so that I could put the original software back on the SD card since it was empty. I used Verbatim CD-R 52x media and burned with an LG SP80NB80 on my Mac Studio.

The disc was readable by the iBook’s optical drive, but only barely; it took five minutes to show the Desktop. I’m not sure if it was the speed at which it was burned, the Verbatim media simply not agreeing with the iBook, or something about the power of the laser in the LG.

Errors from attempting to use a burned iBook Software Restore CD.

I regularly received “Some applications could not be quit.” when attempting to use Erase, and received “Restoring the software configuration iBook HD.img to volume Macintosh HD failed.” when attempting to use Restore.

I used my Power Mac G5 to read the CD and copy it to a USB key. Specifically, I used:

sudo dd if=/dev/disk3s1 of=/dev/disk2 bs=1048576

A mere 15 minutes later, I had a functional USB version of the iBook Software Restore. I then used a copy of Puma (Mac OS X 10.1.4) to install on the same partition, allowing me to dual-boot the system in both 9 and X. I have a second partition I plan to use to install Jaguar or Panther. I haven’t decided which one yet.

I’ll close with a photo of the iBook being a happy Puma. Until next time, be well!

My Indigo iBook G3 Clamshell, showing the introduction video from Mac OS X “Puma” 10.1.
Happy as a clam(shell)! 😁

systemd through the eyes of a musl distribution maintainer

Welcome back to FOSS Fridays! This week, I’m covering a real pickle.

I’m acutely aware of the flames this blog post will inspire, but I feel it is important to write nevertheless. I volunteer my time towards helping to maintain a Linux distribution based on the musl libc, and I am writing an article about systemd. This is my take and my take alone. It is not the opinion of the project – or, as far as I am aware, any of the other volunteers working on it.

systemd, as a service manager, is not actually a bad piece of software by itself. The fact it can act as both a service manager and an inetd(8) replacement is really cool. The unit file format is very nice and expressive. Defining mechanism and leaving policy to the administrator is a good design.

Of course, nothing exists in a vacuum. I don’t like the encouragement to link daemons to libsystemd for better integration – all of the useful integrations can be done with more portable measures. And I really don’t like the fact they consider glibc to be “the Linux API” when musl, Bionic, and other libcs exist.

I’d like to dive into detail on the good and the bad of systemd, as seen through my eyes as all of: end user, administrator, and developer.

Service management: Good

Unit files are easy to write by hand, and also easy to generate in an automated fashion. You can write a basic service in a few lines, and grow into using the other features as needs arise – or you can write a very detailed file, dozens of lines long, making it exact and precise.

Parallel service starting and socket activation are first-class citizens as well, which is something very important to making boot-up faster and more reliable.

The best part about it is the concept that this configuration exactly describes the way the system should appear and exist while it is running. This is similar to how network device standards work – see NETCONF and its stepchild RESTCONF. You define how you want the device to look when it is running, apply the configuration, and eventually the device becomes consistent to that configuration.

This is a far cry from OpenRC or SysV init scripts, which focus almost exclusively on spawning processes. It’s a powerful paradigm shift, and one I wholeheartedly welcome and endorse.

Additionally, the use of cgroups per managed unit means that process tracking is always available, without messy pid files or requiring daemons to never fork. This is another very useful feature that not only helps with overall system control, but also helps debugging and even security auditing. When cgroups are used in this way, you always know which unit spawned any process on a fully-managed system.

Lack of competition: Not good

There is no reason that another service manager couldn’t exist with all of these features. In fact, I hope that there will be competition to systemd that is taken seriously by the community. Having a single package being all things for all use cases leads to significant problems. Changes in systemd will necessarily affect every single user – this may seem obvious, but that means it is more difficult for it to evolve. Evolution of the system may, and in some cases already has, break a wide number of use cases and machines.

Additionally, without competition there is no external pressure nudging it towards ideas and concepts that perhaps the maintainers aren’t sure about. GCC and Clang learn from each other’s successes and failures and use that knowledge to make each other better. There is no package doing that with systemd right now. Innovation is stifled where choice is removed.

Misnaming glibc as “the Linux API”: Bad

I am also unhappy about systemd’s lack of musl libc support. That is probably a blessing for me, because it’s an easy reason to avoid trying to ship it in Adélie. While I have just spent five paragraphs noting how great systemd is at service management, it is really bad at a lot of other things. This is where most articles go off the deep end, but I want to provide some constructive criticism on some of the issues I’ve personally faced and felt while using systemd-based machines.

The Journal: Very bad

journald is my least-favourite feature of systemd, bar none. While I understand the reasons why it was designed the way it was, I do not appreciate that it is the only way to log on a systemd system. Sure, you can ForwardToSyslog and set the journal to be in-memory-only with a small size, and pretend journald doesn’t exist. However, that is not only excess processor power and memory usage for negative gain, it’s also an additional attack surface. It would be great if there were a “stub” journald that was strictly a forwarder with no other code.

I am also unhappy with how the journal tries to “eat” core files. While the Linux default setting of “putting a file named ‘core’ in $CWD” is absolutely unusable for development and production, the weird mixture of FS and binary journal makes things needlessly complex. The documentation even explicitly calls out that core files may exist without corresponding journal entries, and journal entries may point to core files that no longer exist. Yet they use xattrs to put “some metadata” in the core files. Why not just have a sidecar file (maybe [core file name].info or .json or .whatever) that contains all the information from the journal, and have a single journal entry that points to that file if the administrator is interested in more information about the crash?

resolved: A solution looking for a problem

resolved might a decent idea on its own, but there are already other packages that can provide a local caching resolver without the many problems of resolved. Moreover, the very idea of a DNS resolver being part of “the system layer” seems ill-advised to me.

DNSSEC support is experimental and not handled correctly, and they readily admit that. It’s fine to know your limitations, but DNSSEC is something that is incredibly valuable to have on endpoints. I don’t really think resolved can be taken seriously without it. It’s beyond me how no one has contributed this feature to such a widely-used package.

There are odd issues with local domain search. This is made more complicated on home networks where a lot of what it does is overkill. On enterprise networks, it’s likely a bad fit anyway, which makes me question why it supports everything it does.

Lastly, and relatedly, in my opinion resolved tries to shoehorn too many odd features and protocols without having the basics done first. mDNS is better taken care of by a dedicated package like Avahi. LLMNR support has been deprecated by its creator Microsoft in favour of mDNS for over a year. As LLMNR has always been a security risk, I’m not sure why the support was added in the first place.

nspawn: Niche tool for niche uses

Any discussion including resolved would be remiss without mentioning the main reason it exists, and that is nspawn. It’s an interesting take on being “in between” chroot and a full container like Docker. It has niche uses, and I don’t have any real qualms with it, but I’ve never found it useful in any of my work so I don’t have a lot of experience with it. Usually when I am grabbing for chroot I want shared state between host and container, so nspawn wouldn’t make sense there. And when I grab for Podman, I want full isolation, which I feel more comfortable handing to a package that has more tooling around it.

Ancillary tools: Why in the system layer?

networkd is immature, doesn’t have a lot of support for advanced use cases, and has no GUI for end users. I don’t know why they want to stuff networking into the “system layer” when NetworkManager exists and keeps all the networking goop out of the system layer.

timedated seems like a cute way to allow users to change timezones via a PolicyKit action but otherwise seems like something that would be better taken care of by a “real” NTP client like Chrony or NTP. And again, I don’t know why it should live in the system layer.

systemd-boot only supports EFI, which makes it non-portable and inflexible. You won’t find EFI on Power or Z, and I have plenty of ARM boards that don’t support mainline U-Boot as well. This really isn’t a problem with systemd-boot, as it’s totally understandable to only want to deal with a single platform’s idiosyncrasies. What is concerning is the fact that distros like Fedora are pivoting away from GRUB in favour of it, which means they are losing even more portability.

In conclusion: A summary

What I really want to make clear with this article is:

  • I don’t blindly hate systemd, and in fact I really admire many of its qualities as an actual service manager. What I dislike is its attempt to take over what they term the “system layer”, when there are no alternatives available.
  • The problems I have with systemd are tangible and not just hand-wavy “Unix good, sysd bad”.
  • If there was an effort to have systemd separate from all of the other tentacles it has grown, I would genuinely push to have it be available as a service manager in Adélie. I feel that as a service manager – and only as a service manager – it would provide a fantastic user experience that cannot be rivaled by other existing solutions.

Thank you for reading. Have a great day, and please remember that behind every keyboard is a real person with real feelings.