Introduction: The Power of Custom Kernels and AnyKernel3

Custom kernels are the heart of advanced Android customization, offering performance boosts, improved battery life, and device-specific features not available in stock firmware. However, distributing and flashing these kernels across various devices and Android versions can be a complex task. This is where AnyKernel3 comes into play: a universal flashable ZIP solution that simplifies the process of packaging and flashing custom kernels via custom recoveries like TWRP. This expert-level guide will walk you through the process of building your own custom kernel flasher using AnyKernel3, making your kernels easily distributable and installable.

Prerequisites for Your Kernel Flasher Project

Before diving in, ensure you have the following:

• A Linux-based operating system (Ubuntu or Debian recommended) for kernel compilation and packaging.
• Android SDK Platform Tools (ADB and Fastboot) installed and configured on your system.
• A cross-compilation toolchain (e.g., AOSP Clang or GCC) set up to compile your kernel. This guide assumes you already have a compiled kernel image.
• The kernel source code for your target Android device, specific to its SoC and Android version.
• The AnyKernel3 repository cloned from GitHub.
• Basic understanding of shell scripting and Android file systems.

We’ll assume you have successfully compiled your custom kernel and have the necessary output files, typically an Image.gz-dtb or Image, and potentially kernel modules (.ko files).

Getting Started with AnyKernel3

First, obtain the AnyKernel3 framework. Navigate to your desired directory and clone the repository:

git clone https://github.com/osm0sis/AnyKernel3.git your_kernel_flasher

Now, change into the newly created directory:

cd your_kernel_flasher

Explore the directory structure:

• anykernel.sh: The main script that handles flashing logic. This is where most of your customization will occur.
• ramdisk-patch/: Contains binaries and scripts for ramdisk modifications.
• tools/: Utility binaries (e.g., magiskboot).
• modules/: An empty directory where you will place your compiled kernel modules.
• META-INF/: Contains the updater script that tells TWRP what to do (usually you won’t need to modify this).

Configuring anykernel.sh: The Core Logic

The anykernel.sh script is the brain of your kernel flasher. Open it in your favorite text editor. Here are the key sections and variables you’ll need to understand and modify:

1. Kernel File and Ramdisk Compression

Locate the following variables and set them according to your kernel build:

kernel_file=Image.gz-dtb # Or just Image, or boot.img, etc., depending on your build system. Often Image.gz-dtb for modern kernels.modules_path=/vendor/lib/modules # Or /system/lib/modules, /lib/modules, etc. Check your device's module path.ramdisk_compression=auto # Or gzip, lz4, zstd, etc. 'auto' is usually sufficient.

2. Device and Android Version Detection

AnyKernel3 provides robust detection mechanisms. You can use conditional logic to apply specific patches or flash different files based on the device model or Android version. For instance, to detect a specific device:

# Device check (example for a Pixel 5)if [ -f /sys/block/sda/device/model ] && grep -q "Pixel 5" /sys/block/sda/device/model; then  ui_print "- Detected Pixel 5 device..."  # Perform Pixel 5 specific actionsfi# Android version check (example for Android 13)if [ $(file_getprop /system/build.prop ro.build.version.release) -ge 13 ]; then  ui_print "- Detected Android 13 or newer..."  # Apply Android 13 specific patchesfi

3. The Main Flashing Functions

The most critical functions in anykernel.sh are dump_boot, flash_boot, and optionally flash_dtbo. These are usually called at the end of the script’s main execution block.

# Main execution block# 1. Back up the original boot.imgdump_boot; # This extracts the current boot.img to work with# 2. Add any ramdisk patches (optional, often handled by AnyKernel3 automatically)#    Example: Forcing SELinux permissive (use with caution!)#    patch_fstab /vendor/etc/fstab.qcom disable_dm_verity,avb_enable=1 # Example, adjust as needed# 3. Flash the new kernel and ramdiskflash_boot; # This flashes the modified boot.img# Optional: If your device uses a separate DTBO partitionflash_dtbo;

Ensure your kernel_file (e.g., Image.gz-dtb) is placed in the root of the your_kernel_flasher directory before running flash_boot.

4. Kernel Module Installation

If your kernel compiles with external modules (.ko files), you’ll need to copy them into the modules/ directory, maintaining their original path structure relative to the kernel’s root. For example, if your kernel output has drivers/usb/typec/typec.ko, you’d place it in modules/lib/modules/KERNEL_VERSION/kernel/drivers/usb/typec/typec.ko.

AnyKernel3 automatically handles module installation based on the modules_path variable and the contents of the modules/ directory. After placing your modules, add this line in anykernel.sh if it’s not already there:

# Install kernel modulesinstall_modules;

Adding Your Kernel Image and Modules

Once your kernel is compiled, copy your kernel image to the root of your AnyKernel3 directory:

cp /path/to/your/compiled/kernel/Image.gz-dtb ./

If you have kernel modules, create the necessary subdirectories under `modules/` and copy them:

# Example: assuming KERNEL_VERSION is 5.10.66mkdir -p modules/lib/modules/5.10.66/kernel/drivers/cp /path/to/your/compiled/kernel/drivers/usb/typec/typec.ko modules/lib/modules/5.10.66/kernel/drivers/usb/typec/

Repeat for all relevant modules, ensuring the `modules_path` in `anykernel.sh` matches the base path on the device.

Building the Flashable ZIP

With your anykernel.sh configured and kernel files in place, you’re ready to create the flashable ZIP. Navigate back to the parent directory containing your_kernel_flasher:

cd ..zip -r9 [Device]-[KernelName]-AnyKernel3.zip your_kernel_flasher/* -x your_kernel_flasher/.git your_kernel_flasher/.gitignore

Replace `[Device]` and `[KernelName]` with appropriate identifiers (e.g., `Pixel5-MyAwesomeKernel-AnyKernel3.zip`). The `-x` flag excludes the Git metadata from the final ZIP.

Flashing Your Custom Kernel

Now, transfer the generated ZIP file to your Android device (either via ADB sideload or by copying it to internal storage/SD card).

adb push [Device]-[KernelName]-AnyKernel3.zip /sdcard/

Reboot your device into TWRP or your preferred custom recovery. From the main menu, select