Why SWUpdate?

Field updates are inevitable. SWUpdate provides a robust, modular solution for updating firmware, root filesystems, and application layers — all with built-in rollback capability.
It’s open source, well documented, and integrates seamlessly with an A/B partition layout.

Web browser GUI for SWUpdate

Architecture overview

SWUpdate consists of several key components:

  • Update daemon (swupdate) — runs on the device and applies updates
  • Update handlers — define what to update (rootfs, files, scripts, etc.)
  • Client interfaces — web interface, REST API, or local CLI
  • sw-description file — defines the structure and logic of the update package

Example update flow

  1. Build an update package (.swu) that contains:
    • A new root filesystem image
    • The sw-description file
    • Optional scripts (for customization or verification)
  2. swupdate writes the update to the defined devices.
  3. A post-update script confirms success or triggers a rollback if necessary.

Example

In this example, we split an official Raspberry Pi OS Trixie image into two files:

  • 2025-10-01-raspios-trixie-arm64.boot.vfat
  • 2025-10-01-raspios-trixie-arm64.root.ext4

These files are referenced in the sw-description file to create the .swu package:

software =
{
    version = "0.1.0";
    description = "Firmware update for XXXXX Project";

    hardware-compatibility: [ "1.0", "1.2", "1.3"];

    images: (
        {
            filename = "2025-10-01-raspios-trixie-arm64.boot.vfat";
            device = "/dev/mmcblk0p1";
            compressed = "zlib";
            installed-directly = true;
        },
        {
            filename = "2025-10-01-raspios-trixie-arm64.root.ext4";
            device = "/dev/mmcblk0p2";
            compressed = "zlib";
            installed-directly = true;
        }
    );

    scripts: (
        {
          type: "lua",
          filename: "repair-disk-uuid.lua"
        }
    ),
}

The following Lua script adjusts partition UUIDs in cmdline.txt and fstab after flashing:

#!/usr/bin/lua

-- helper: run shell command and capture output
function run(cmd)
  local f = io.popen(cmd)
  local out = f:read("*a")
  f:close()
  return (out:gsub("%s+$", ""))
end

-- detect PARTUUIDs
local root_part = "/dev/mmcblk0p2"
local boot_part = "/dev/mmcblk0p1"
local root_uuid = run("blkid -s PARTUUID -o value " .. root_part)
local boot_uuid = run("blkid -s PARTUUID -o value " .. boot_part)

print("Rootfs PARTUUID: " .. root_uuid)
print("Boot   PARTUUID: " .. boot_uuid)

-- mount points
os.execute("mkdir -p /mnt/root /mnt/boot")
os.execute("mount " .. root_part .. " /mnt/root")
os.execute("mount " .. boot_part .. " /mnt/boot")

-- update cmdline.txt
local cmdline_path = "/mnt/boot/cmdline.txt"
local file = io.open(cmdline_path, "r")
local text = file:read("*a")
file:close()

text = text:gsub("root=PARTUUID=[^ ]+", "root=PARTUUID=" .. root_uuid)

file = io.open(cmdline_path, "w")
file:write(text)
file:close()

-- update /etc/fstab
local fstab_path = "/mnt/root/etc/fstab"
local fstab = io.open(fstab_path, "r")
local content = fstab:read("*a")
fstab:close()

-- replace root line
content = content:gsub("PARTUUID=[^%s]+%s+/%s", "PARTUUID=" .. root_uuid .. " /")
-- replace boot line (/boot or /boot/firmware)
content = content:gsub("PARTUUID=[^%s]+%s+/boot", "PARTUUID=" .. boot_uuid .. " /boot")

fstab = io.open(fstab_path, "w")
fstab:write(content)
fstab:close()

os.execute("sync")
os.execute("umount /mnt/boot")
os.execute("umount /mnt/root")

print("All PARTUUIDs updated successfully.")

Use swugenerator to bundle the update:(https://github.com/sbabic/swugenerator).

Apply the update

To test the generated .swu file:

  1. Boot the CM5 into the rescue system.
  2. Create a mount point, for example:
sudo mkdir -p /mnt/update
  1. Mount an NFS share containing the update file:
sudo mount -t nfs :/path/to/share /mnt/update
  1. Apply the update:
sudo swupdate -i /mnt/update/update.swu

Integration possibilities

Trigger updates from a local UI or backend API

  • Sign and verify updates for enhanced security
  • Use SWUpdate’s web interface for testing or debugging
  • Combine with systemd services to automate recovery and rollbacks

Why it fits this stack

Together with rpi-image-gen and rpi-sb-provisioner, SWUpdate completes the picture:

  • Build → rpi-image-gen (Image creation)
  • Deploy → rpi-sb-provisioner (Device provisioning)
  • Maintain → SWUpdate (OTA updates and lifecycle management)

The result is a flexible, open, and maintainable embedded Linux platform — one that evolves with your product, without the overhead of Yocto.

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