systemd-repart / systemd-sysupdate Example

This repository contains an example of how to use systemd-repart and systemd-sysupdate to build immutable system images that can be updated over the Internet.

See x86.lol for blog posts about this setup:

1. Immutable Systems: NixOS + systemd-repart + systemd-sysupdate
2. Immutable Systems: Cross-Compiling for RISC-V using Flakes

For a more recent implementation exploring the same problem space, also check out the this NixOS appliance images demo by Applicative Systems.

How to Build the System Image

You need Nix with enabled Flakes. After that, you can build the disk image:

$ nix build .

After the build process, there will be a QEMU disk image disk.qcow2 in result/.

Running the Demo

You can boot result/disk.qcow2 produced in the previous step in any virtualization solution that supports UEFI. For simplicity, you can enter a development shell and boot it with the convenience script qemu-efi:

# This will take some time, because it compiles quite a bunch of stuff for
# RISC-V and ARM AArch64.
$ nix develop

$ qemu-efi x86_64 result/disk.qcow2

Experimenting with the Demo

Once you have the demo running, you can see systemd-sysupdate and sysupdate-repart in action:

(I have removed parts of the console output for readability.)

# List the update files.
% ls -lh /var/updates/
total 324M
-r--r--r-- 1 root root  43M Aug 11 15:47 appliance_18.efi.xz
-r--r--r-- 1 root root 282M Aug 11 15:47 store_18.img.xz

# See that systemd-sysupdate has found an update.
% systemd-sysupdate
  VERSION INSTALLED AVAILABLE ASSESSMENT
↻ 18                    ✓     candidate
● 17          ✓               current

# Apply the update.
% systemd-sysupdate update
Selected update '18' for install.
Making room for 1 updates…
Removed no instances.
⤵️ Acquiring /var/updates/appliance_18.efi.xz → /boot/EFI/Linux/appliance_18.efi...
Importing '/var/updates/appliance_18.efi.xz', saving as '/boot/EFI/Linux/.#sysupdateappliance_18.efifce0abb2fdba79a5'.
[...]
Successfully acquired '/var/updates/appliance_18.efi.xz'.
⤵️ Acquiring /var/updates/store_18.img.xz → /proc/self/fd/3p2...
Importing '/var/updates/store_18.img.xz', saving at offset 269484032 in '/dev/sda'.
[...]
Successfully acquired '/var/updates/store_18.img.xz'.
Successfully installed '/var/updates/appliance_18.efi.xz' (regular-file) as '/boot/EFI/Linux/appliance_18.efi' (regular-file).
Successfully installed '/var/updates/store_18.img.xz' (regular-file) as '/proc/self/fd/3p2' (partition).
✨ Successfully installed update '18'.

# Reboot into the new version.
% reboot

Once the system is back up, you can remove the last version. This would also happen automatically when the next version is installed.

% systemd-sysupdate vacuum -m 1

Looking at the partition layout using parted before and after the update is also interesting!