# Create an interactive shell for Zephyr RTOS on Arm Cortex-M

## In this learning path

- [Introduction](https://learn.arm.com/learning-paths/embedded-and-microcontrollers/zephyr_shell/)
- [Set up the Zephyr shell development environment](https://learn.arm.com/learning-paths/embedded-and-microcontrollers/zephyr_shell/1_installation/)
- [Understand the Zephyr shell subsystem and backends](https://learn.arm.com/learning-paths/embedded-and-microcontrollers/zephyr_shell/2_overview/)
- [Build and run the Zephyr MQTT shell on Arm Cortex-M](https://learn.arm.com/learning-paths/embedded-and-microcontrollers/zephyr_shell/3_mqtt_shell/)
- [Build and run the Zephyr UART shell on Arm Cortex-M](https://learn.arm.com/learning-paths/embedded-and-microcontrollers/zephyr_shell/4_uart_shell/)
- [Next Steps](https://learn.arm.com/learning-paths/embedded-and-microcontrollers/zephyr_shell/_next-steps/)

## About this Learning Path

|  |  |
| --- | --- |
| Skill level: | Introductory |
| Reading time: | 30 min |
| Last updated: | 13 Aug 2026 |

| Authors:          |                            |
|-------------------|----------------------------|
|                   | Ayoub Bourjilat, Ac6      |
|                   | Odin Shen, Arm            |
|                   | Akash Malik, Arm          |

|  |  |
| --- | --- |
| Authors: | Ayoub Bourjilat , Ac6<br>[GitHub](https://github.com/Bourjilat)<br>[LinkedIn](https://linkedin.com/in/ayoub-bourjilat-a55b58165/)<br>[ac6.fr](https://www.ac6.fr/en/)<br>Odin Shen , Arm<br>[GitHub](https://github.com/odincodeshen)<br>[LinkedIn](https://linkedin.com/in/odin-shen-lmshen)<br>Akash Malik , Arm<br>[GitHub](https://github.com/akashmalik19973)<br>[LinkedIn](https://linkedin.com/in/akash-malik-a65bab219) |
| Arm IP: | [Cortex-M](https://support.arm.com/?tab=compute-ip&Product%20Type=Microcontrollers) |
| Tags: | [RTOS Fundamentals](https://learn.arm.com/tag/rtos-fundamentals) [RTOS](https://learn.arm.com/tag/rtos) [Zephyr](https://learn.arm.com/tag/zephyr) [C](https://learn.arm.com/tag/c) |

### Who is this for?

This is an introductory topic for embedded developers who want to add an interactive command-line shell to a Zephyr RTOS application on Arm Cortex-M.

### What will you learn?

After completing this Learning Path, you'll be able to perform the following tasks:

- Enable and tailor Zephyr shell (Kconfig/prj.conf) to produce a minimal CLI footprint
- Build and flash shell-enabled Zephyr apps using MQTT and UART shell backends on an Arm Cortex-M board
- Use the Zephyr shell for board bring-up, diagnostics, and interactive testing

### Prerequisites

Before starting, you'll need the following prerequisites:

- Basic familiarity with embedded C programming
- Visual Studio Code with the Workbench for Zephyr extension installed and configured
- Docker Desktop, Docker Engine, or another Docker-compatible runtime installed on your host computer (for the MQTT shell example, if you’re not installing Mosquitto on host)
- A Zephyr-supported Arm Cortex-M board (for example, NXP FRDM-MCXN947)

### Summary

You’ll enable and configure the Zephyr shell on an Arm Cortex-M board with Workbench for Zephyr. First, you’ll update `prj.conf` for the shell and selected MQTT or UART backend. Then, you’ll build and flash from Visual Studio Code, verify the shell prompt, and use built-in modules for bring-up and diagnostics over Ethernet or USB serial.

### Frequently asked questions

**How do I know the Zephyr shell is enabled and working after I flash the board?**

You should see a shell prompt on the selected backend after boot. Run a built-in command such as `kernel version` to confirm the shell responds.

**Do I need to add networking code in main.c for the MQTT shell example?**

No. The MQTT example starts the shell, network stack, DHCP client, and MQTT shell backend from configuration options in `prj.conf`.

**Which backend should I use if I want to interact locally during bring-up?**

Use the UART shell backend. It maps shell input and output to the active UART console over the board’s USB serial interface and doesn’t require network connectivity.

**What should I check if I don’t see any shell output over UART?**

Verify that the UART shell backend is enabled in `prj.conf` and that you’re connected to the board’s USB serial interface selected as the active console. Use a serial terminal application supported on your host OS to view the console.

**What should I check if the MQTT shell doesn't connect to the broker?**

Confirm `CONFIG_SHELL_BACKEND_MQTT` is enabled and that required networking options are set in `prj.conf` so the device can obtain network connectivity. Ensure the MQTT broker is reachable from the board over Ethernet.