Create_boot_multiple_kernel.md

docs/boot_multiple_kernel.md

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+# Using Multiple Kernels on SBC with Armbian via SD Cards
+
+A common and effective way to use multiple kernels on a single-board computer (SBC) running Armbian is to use separate SD cards. This method is especially useful for testing new kernels, different versions of a kernel, or different Linux distributions without risking your primary, stable system. It also simplifies the process by leveraging the standard SBC boot sequence, which typically checks for a bootable SD card first.  
+
+This tutorial will walk you through the process of setting up multiple SD cards with different Armbian kernels.
+
+---
+
+## Prerequisites
+
+Before you begin, you'll need a few things:
+
+- **Your SBC**: A compatible single-board computer (e.g., Orange Pi, Rock Pi, Odroid).  
+- **Multiple SD cards**: One for each kernel or system you want to run. Use reliable, high-speed cards from a reputable brand.  
+- **A computer** to write the images to the SD cards.  
+- **A reliable power supply** for your SBC.  
+- **Armbian images**: The specific Armbian images for your board, each with the desired kernel version (`current`, `edge`, or `legacy`). You can download these from the [official Armbian website](https://www.armbian.com/download/).  
+
+---
+
+## Step 1: Prepare the SD Cards 💾
+
+Each SD card must be flashed with a different Armbian image.
+
+1. **Download the Images**  
+   Go to the official Armbian download page and find the images for your specific SBC model.  
+   Example: one with the `current` kernel and another with the `edge` kernel.  
+
+2. **Flash the SD Cards**  
+   Use a flashing tool like **BalenaEtcher** or the `dd` command-line utility.
+
+   ### Using BalenaEtcher
+   - Insert an SD card into your computer.  
+   - Open Etcher, select the downloaded Armbian image file.  
+   - Select your SD card from the list of drives.  
+   - Click **Flash!** to start the process.  
+   - Repeat for each SD card and image.  
+
+   ### Using `dd` (Linux/macOS users)
+   - Unzip the Armbian image file (`.xz`).  
+   - Identify your SD card's device name with `lsblk` or `diskutil list`.  
+   - Run:  
+     ```bash
+     sudo dd if=/path/to/armbian-image.img of=/dev/sdX bs=1M status=progress && sync
+     ```  
+     Replace `/path/to/armbian-image.img` and `/dev/sdX` with the correct path and device name.  
+   - **Be extremely careful** to select the right device to avoid data loss.  
+
+---
+
+## Step 2: Initial Boot and Configuration ⚙️
+
+After flashing, each SD card is a self-contained, bootable system.
+
+1. **Insert and Boot**  
+   Insert one SD card into your SBC and connect power. The SBC’s bootloader (usually U-Boot) will detect and boot from it.  
+
+2. **Initial Setup**  
+   On first boot, Armbian will:  
+   - Resize the filesystem  
+   - Prompt for a root password  
+   - Prompt to create a new user  
+
+   Complete these steps for each SD card.  
+
+3. **Shut Down and Swap**  
+   - Power down the SBC.  
+   - Remove the first SD card.  
+   - Insert the second SD card.  
+   - Repeat the boot and setup process.  
+
+---
+
+## Step 3: Managing and Using Different Kernels 🧑💻
+
+Now you have multiple independent systems on separate SD cards.
+
+- **Swapping SD Cards**  
+  To switch kernels, power down, swap SD cards, and power back up. The bootloader handles everything automatically.  
+
+- **Testing and Development**  
+  - Use one SD card for a stable, “production” kernel.  
+  - Use another for experimental or development kernels.  
+  - If something fails, swap back to your stable card instantly.  
+
+- **Kernel Version Management**  
+  While Armbian’s `armbian-config` tool allows kernel management inside a single installation, using separate SD cards gives **full isolation**.  
+  This prevents conflicts between kernel versions and ensures a clean test environment.  
+
+---