Alpha Refresh Available

Sunday, December 29, 2024

Clarification on moss boot management

Frequently in Team Serpent we joke that moss is the “systemd of package managers”. It actually does a whole lot more than is easily visible.. for example:

Content addressable storage for the entire OS
Atomic updates of /usr by renameat2() w/ RENAME_EXCHANGE
Executes transactional triggers in a namespace (container) with RW /usr and RO binds of /etc and /var …
Executes system triggers postblit, with dependency ordering..
Via blsforme, manages the ESP, XBOOTLDR, boot entries, sync and promotion of bootloader, kernel and assets, initrds..
Entirely zero configuration. No /etc/default/grub, no remembering your root={}, it’s determined automatically.
Basically does all the work of OS provisioning, barring disk mounting and partitioning. Our installer, lichen, is basically a thin wrapper of moss.

We’ve had no debugging capabilites around the boot management, so we’ve landed moss boot status command. It’s super primitive but does offer an insight into the introspection capabilites of blsforme. In this simple screenshot, moss/blsforme are supporting the Boot Loader Protocol, querying the systemd-boot entries in efivars. When found, LoaderDevicePartUUID is used to determine the boot ESP, but moss/blsforme will quite happily read the GPT directly (relative to / mount) and find the ESP and XBOOTLDR…

Remember - we happily use systemd-boot. We do not use bootctl or kernel-install. Entries are automatically managed and we’re extending this to support offline rollbacks via boot menu (feel free to extend with /etc/kernel/cmdline.d/*.cmdline drop-in snippets!) Also note we do not allow systemd to automount the ESP or XBOOTLDR via the GPT autogenerator, instead moss/blsforme will automatically discover and if necessary, mount these partitions, when dealing with bootloader or kernel updates.

With this explicit control over the boot management, we’ll happily be landing secure boot and fwupd support in the near future, without the downsides of trying to provide EFI assets to /boot in a package itself. 😬

moss boot status

A note on virtual machine usage

It must be clearly stated that Serpent OS does not support anything other than UEFI booting on x86_64-v2+ capable hardware. Please note that GNOME Boxes will default to BIOS, not UEFI, and will need hand-mangling of the XML file. Also note in other solutions such as VirtualBox you will need to specifically select EFI in the VM settings.

In order to maximise compatibility with other tooling and firmware, we’ve modified the generation of our ISO to include the isolinux MBR/GPT hybrid components, however we deliberately did not include a functioning bootloader for BIOS boot. Instead, you will see a boot failure indicating that ldlinux.c32 could not be found, which is a sure-fire way to know your VM or hardware is incorrectly configured.

Invalid VM configuration

Installer notes

Lichen is due to recieve some love in the next few cycles, so please be aware of the following limitations:

A pre-configured GPT disk is required before lichen is launched
A working internet connection is also required, this is a network installer
A FAT32 formatted EFI System Partition is required (marked as esp in gparted)
For optimal usage, or when your ESP is tiny, please create an XBOOTLDR partition:
- Create an FAT32 partition in gparted of 2GB in size
- Mark it as bls_boot in gparted
Further filesystem support for XBOOTLDR will be added to blsforme when we’ve finished packaging efifs.
XFS or F2FS are strongly recommended for the rootfs, due to the limitations of ext4 with hardlink counts.

COSMIC Desktop

We’ve made the decision to pause our offering of COSMIC Desktop ISOs. We’re huge fans of the project, and we strive to keep it up to date and functional. However, it is very early in alpha, and so are we. It doesn’t make a lot of sense for us to extend our workload to two alpha codebases!

We still offer COSMIC as an option in the installer for those who wish to try it out, and do encourage testing and engaging upstream with the developers. For now, we will offer just the GNOME ISO.

Lichen + COSMIC

Next up

In the new year we’ll be focusing heavily on our tooling to facilitate a scale up of our packaging efforts. We’re quite proud of our tooling, but we’re not oblivious to the warts and issues. The next couple of weeks will be spent improving our documentation (or making it exist!) and making sure that we have the ideal workflow in place to permit large stack updates along with the ABI consistency verification we need. This will also pool work for ent, moss, boulder, by streamlining packaging, and making it trivial to update an entire stack of packages in one go. Eventually this will be an automatic thing, with successful PRs being verified and then merged into the volatile repository.

Don’t forget, versioned repositories are also coming your way, and very soon we’re landing offline rollbacks in the boot menu! blsforme has been significantly restructured for cmdline handling, and understands entries in the context of a distinct system root (ie moss filesystem transaction) - which is the bulk of the work needed to facilitate offline rollbacks. The last piece will be running moss at an early stage in the initrd to swap the /usr pointer to the older transaction, which is instanteous and atomic.

Final thoughts

5 years and no release, and now two alpha ISOs before the end of the year. We’re pretty happy with that, and we’re going to keep surprising you next year with more releases, more features, and more stability. Happy new year from all of us at Team Serpent! 🐍

If you like what we’re doing, please consider sponsoring us - this will allow us to grow our infrastructure and deliver builds quicker. Due to health issues in the last few months, I was forced into a position whereby I had to resign from my job. Any and all contributions to the project are greatly appreciated, and will help us to continue delivering what folks are frequently now calling “the cleanest Linux implementation they’ve ever seen”.

Try it. You might like it. 🚀