MuntsOS Embedded Linux

CHANGELOG.txt  454539Jun 17 14:54:21 2024
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This framework supports Linux on several single board microcomputers. The goal of the MuntsOS project is to deliver a turnkey, RAM resident Linux operating system for very low cost single board microcomputers. With MuntsOS installed, such microcomputers can treated as components, as Linux microcontrollers, and integrated into other projects just like traditional single chip microcontrollers.


Quick Setup Instructions for the Impatient

Instructions for installing the MuntsOS cross-toolchain development environment onto a host computer are found in Application Note #1 and Application Note #2. Or just download and run one of the following quick setup scripts:


Instructions for installing MuntsOS to a target computer are found in Application Note #3 and Application Note #15.


The documentation for MuntsOS (mostly application notes) is available online at:

Embedded Linux Distribution in a Kernel

MuntsOS is a stripped down Linux distribution that includes a small compressed root file system within the kernel image binary itself. At boot time the root file system is unpacked into RAM and thereafter the system runs entirely in RAM.

Each kernel release tarball contains a kernel image file (.img), which may be common to several different microcomputer boards, and one or more device tree files (.dtb) that are specific to particular microcomputer boards. Some kernel release tarballs also contain one or more device tree overlay files (.dtbo) that can make small changes to the device tree at boot time.

Prebuilt MuntsOS kernel release tarballs are available at:


The MuntsOS root file system can be extended at boot time using any of three mechanisms:

First, if /boot/tarballs exists, any gzip'ed tarball files (.tgz) in it will be extracted on top of the root file system. Typically you would use this mechanism for customized /etc/passwd, .ssh/authorized_keys, and similiar system configuration files.

Secondly, if /boot/packages exists, any Debian package files (.deb) in it will be installed into the root file system. Note that packages from the Debian project will probably not work; they must be built specifically for MuntsOS. The startup script that installs .deb packages also installs .rpm and .nupkg packages.

The GPIO Server extension package demonstrates how to build a Debian package that adds application specific software to MuntsOS.

Thirdly, the system startup script /etc/rc can be configured via a kernel command line option to search for a subdirectory called autoexec.d in various places, such as SD card, USB flash drive, USB CD-ROM or NFS mount. If an autoexec.d subdirectory is found, each executable program or script in it will be executed when the system boots.

The idea is to build a MuntsOS kernel (which takes a long time) once and install it to the target platform. Then application specific software can be built after the fact and installed as tarball files in /boot/tarballs; Debian, RPM, and NuGet package files in /boot/packages; or executable programs and scripts in /boot/autoexec.d.

Prebuilt MuntsOS extension packages are available at:

Thin Servers

Boot Files + Kernel Files + Extensions = Thin Server

The Thin Server is a system design pattern that is little more than a network interface for a single I/O device. Ideally, a Thin Server will be built from a cheap and ubiquitous network microcomputer like the Raspberry Pi. The software must be easy to install from a user's PC or Mac without requiring any special programming tools. It must be able to run headless, administered via the network. It must be able to survive without orderly shutdowns, and must not write much to flash media. It must provide a network based API (Application Programming Interface) using HTTP as a lowest common denominator.

MuntsOS, with its operating system running entirely from RAM, serves well for the Thin Server, and the two concepts have evolved together over the past few years. The simplest way to use MuntsOS is to download one of the prebuilt Thin Server .zip files and extract it to a freshly formatted FAT32 SD card. You can then modify autoexec.d/00-wlan-init on the SD card to pre-configure it for your wireless network environment, if desired, before inserting it in the target board. After booting MuntsOS, log in from the console or via SSH (user "root", password "default") and run sysconfig to perform more system configuration.

Note: Some platforms require the boot flag to be set on the FAT32 boot partition on the SD card or on-board eMMC. The ROM boot loader in the CPU will ignore any partitions that are not marked as bootable.

MuntsOS Application Notes 3 and 15 contain more detailed instructions about how to install a MuntsOS Thin Server.

Prebuilt MuntsOS Thin Servers are at available at:


Raspberry Pi

The Raspberry Pi is a family of low cost Linux microcomputers selling for USD $15 to $80, depending on model. There have been five generations of Raspberry Pi microcomputers, each using a successively more sophisticated Broadcom ARM core CPU. The first two generations (32-bit ARMv6 Raspberry Pi 1 and 32-bit ARMv7 Raspberry Pi 2) are now obsolete.

Some Raspberry Pi models have an on-board Bluetooth radio that uses the serial port signals that are brought out to the expansion header. By default, MuntsOS port disables the on-board Bluetooth radio, in favor of the serial port on the expansion header.

Raspberry Pi 3

The 64-bit Raspberry Pi 2 Model B Revision 1.2 with the 900 MHz BCM2710 ARMv8 Cortex-A53 quad-core CPU can be treated as a power conserving Raspberry Pi 3 Model B− and is useful for industrial applications where wired Ethernet is preferred.

The Rasbperry Pi 3 Model B has a 1200 MHz BCM2710 ARMv8 Cortex-A53 quad-core CPU and has 1 GB of RAM along with on-board Bluetooth and WiFi radios.

The Raspberry Pi 3 Model A+ has the same form factor as the Raspberry Pi 1 Model A+, with only one USB host port and no wired Ethernet. It has a 1400 MHz BCM2710 ARMv8 Cortex-A53 quad-core CPU and has 512 MB of RAM along with on-board Bluetooth and WiFi radios.

The Raspberry Pi 3 Model B+ has a 1400 MHz BCM2710 ARMv8 Cortex-A53 quad-core CPU and has improved power management and networking components.

The Raspberry Pi Zero 2 W has the same form factor as the Raspberry Pi Zero W, with a 1000 MHz BCM2710 ARMv8 Cortex-A53 quad core CPU and 512 MB of RAM along with on-board Bluetooth and WiFi radios.

All Raspberry Pi 3 models use the same AArch64 toolchain and ARMv8 kernels, but different device trees.

Raspberry Pi 4

The Raspberry Pi 4 Model B has a 1500 MHz BCM2711 ARMv8 Cortex-A72 quad-core CPU and is available with 1 to 8 GB of RAM. It diverged significantly from the Raspberry Pi 1 B+ form factor, with the USB and Ethernet ports reversed, two micro-HDMI connectors instead of a single full size HDMI connector, and a USB-C power connector instead of micro-USB. Two of the USB ports are 3.0 and two are 2.0. A major improvement is a Gigabit Ethernet controller connected via PCI Express instead of the USB connected Ethernet used for all earlier models. The Raspberry Pi 4 Model B uses the same wireless chip set as the 3+.

There are also a myriad of Raspberry Pi 4 Compute Modules, with varying combinations of wireless Ethernet, RAM and eMMC.

All Raspberry Pi 4 models use the same AArch64 toolchain and ARMv8 kernels, but different device trees.

Raspberry Pi 5

The Raspberry Pi 5 yields another 2-3x increase in performance over the Raspberry Pi 4, at the expense of greater power consumption. It has a 2400 MHz BCM2712 ARMv8 Cortex-A76 quad-core CPU and is available with 4 or 8 GB of RAM. The Ethernet socket and USB ports have swapped sides, so it has a form factor that is sort of a cross between the Raspberry Pi 1 B+ (same grouping of Ethernet and USB ports) and the Raspberry Pi 4 (same dual micro-HDMI sockets and USB-C power socket). It uses the same AArch64 toolchain as all of the other 64-bit Raspberry Pi models, but a separate kernel and device tree.

The Raspberry Pi 5 introduced a breaking GPIO API change. See Application Note #11 for more information.

The Raspberry Pi 5 also introduced a breaking PWM API change. It has four hardware PWM outputs, but the pin mapping has changed as well. Notably, channel 2 is mapped to GPIO18 instead of channel 0 on previous Raspberry Pi boards. See RP1 Peripherals page 15 for more information.

Raspberry Pi USB Gadget Kernels

MuntsOS also provides Raspberry Pi kernels with dedicated USB Gadget support enabled. These kernels run on 3 A+, CM3, Zero 2 W, 4 B, and CM4. You can supply power to and communicate with a compatible Raspberry Pi solely through the USB port. This kernel supports USB Network, Raw HID, and Serial Port gadgets, selected by bits in the OPTIONS word passed on the kernel command line. The USB Gadget Thin Servers have USB Network Gadget selected by default.

The absolute minimum possible usable Raspberry Pi kit consists of a Raspberry Pi Zero 2 W, a micro-USB cable, and a micro-SD card with one of the MuntsOS Raspberry Pi 3 USB Gadget Thin Servers installed.


I build a custom Ada/C/C++/Fortran/Go/Modula-2 GCC cross-toolchain for each MuntsOS platform family. Each GCC cross-toolchain requires a number of additional software component libraries, which are packaged and distributed separately but installed into the same directory tree as the parent cross-toolchain. I also build Free Pascal cross-compilers. Each of these rely on the libraries contained in the corresponding GCC cross-toolchain package.

Cross-toolchain packages built for Debian Linux (x86-64 and ARM64) development host computers are available at either: (Debian package repository) or (just the package files).

x86-64 RPM packages containing the exact same binaries and known to work on Fedora 40 and RHEL 9.1 and its derivatives are available at:

Debian Package Repository

Prebuilt cross-toolchain packages for Debian Linux are available at:

File Repository

Prebuilt binaries for MuntsOS are available at:

Git Repository

The source code for MuntsOS is available at:

Use the following command to clone it:

git clone

Questions or comments to Philip Munts