Build for merlinxBack to the overview
These instructions will hopefully assist you to start with a stock Xiaomi Redmi Note 9, unlock the bootloader (if necessary), and then download the required tools as well as the very latest source code for PixelExperience (based on Google’s Android operating system) for your device. Using these, you can build both a PixelExperience installation zip and a PixelExperience Recovery image and install them on your device.
It is difficult to say how much experience is necessary to follow these instructions. While this guide is certainly not for the extremely uninitiated, these steps shouldn’t require a PhD in software development either. Some readers will have no difficulty and breeze through the steps easily. Others may struggle over the most basic operation. Because people’s experiences, backgrounds, and intuitions differ, it may be a good idea to read through just to ascertain whether you feel comfortable or are getting over your head.
Remember, you assume all risk of trying this, but you will reap the rewards! It’s pretty satisfying to boot into a fresh operating system you baked at home :). And once you’re an Android-building ninja, there will be no more need to wait for “nightly” builds from anyone. You will have at your fingertips the skills to build a full operating system from code and install it to a running device, whenever you want. Where you go from there– maybe you’ll add a feature, fix a bug, add a translation, or use what you’ve learned to build a new app or port to a new device– or maybe you’ll never build again– it’s all really up to you.
What you’ll need
- A Xiaomi Redmi Note 9.
- A relatively recent 64-bit computer (Linux, macOS, or Windows) with a reasonable amount of RAM and about 200 GB of free storage (more if you enable
ccacheor build for multiple devices). The less RAM you have, the longer the build will take. Aim for 16 GB RAM or more, enabling ZRAM can be helpful. Using SSDs results in considerably faster build times than traditional hard drives.
- A USB cable compatible with the Xiaomi Redmi Note 9.
- A decent internet connection and reliable electricity. :)
- Some familiarity with basic Android operation and terminology. It would help if you’ve installed custom roms on other devices and are familiar with recovery.
It may also be useful to know some basic command line concepts such as
cd, which stands for “change directory”, the concept of directory hierarchies, and that in Linux they are separated by /, etc.
Build PixelExperience and PixelExperience Recovery
Install the platform-tools
If you haven’t previously installed
fastboot, you can download them from Google.
Extract it running:
unzip platform-tools-latest-linux.zip -d ~
Now you have to add
fastboot to your PATH. Open
~/.profile and add the following:
# add Android SDK platform tools to path if [ -d "$HOME/platform-tools" ] ; then PATH="$HOME/platform-tools:$PATH" fi
source ~/.profile to update your environment.
Preparing your system to build
sudo apt install git
Running configuration script:
cd ~/ git clone https://github.com/akhilnarang/scripts cd scripts ./setup/android_build_env.sh
Create the directories
You’ll need to set up some directories in your build environment.
To create them:
mkdir -p ~/bin mkdir -p ~/android/pe
~/bin directory will contain the git-repo tool (commonly named “repo”) and the
~/android/pe directory will contain the source code of PixelExperience.
Enter the following to download the
repo binary and make it executable (runnable):
curl https://storage.googleapis.com/git-repo-downloads/repo > ~/bin/repo chmod a+x ~/bin/repo
~/bin directory in your path of execution
In recent versions of Ubuntu,
~/bin should already be in your PATH. You can check this by opening
~/.profile with a text editor and verifying the following code exists (add it if it is missing):
# set PATH so it includes user's private bin if it exists if [ -d "$HOME/bin" ] ; then PATH="$HOME/bin:$PATH" fi
source ~/.profile to update your environment.
repo requires you to identify yourself to sync Android, run the following commands to configure your
git config --global user.email "firstname.lastname@example.org" git config --global user.name "Your Name"
Initialize the PixelExperience source repository
The following branches can be used to build for the Xiaomi Redmi Note 9:
Enter the following to initialize the repository:
cd ~/android/pe repo init -u https://github.com/PixelExperience/manifest -b branch_name
Download the source code
To start the download of the source code to your computer, type the following:
repo sync -c -j$(nproc --all) --force-sync --no-clone-bundle --no-tags
repo synccommand is used to update the latest source code from PixelExperience. Remember it, as you may want to do it every few days to keep your code base fresh and up-to-date.
Prepare the device-specific code
After the source downloads, ensure you’re in the root of the source code (
cd ~/android/pe), then type:
source build/envsetup.sh lunch aosp_merlinx-userdebug
This will download your device’s necessary dependencies.
Turn on caching to speed up build
Make use of
ccache if you want to speed up subsequent builds by running:
export USE_CCACHE=1 export CCACHE_EXEC=/usr/bin/ccache
and adding that line to your
~/.bashrc file. Then, specify the maximum amount of disk space you want
ccache to use by typing this:
ccache -M 50G
50G corresponds to 50GB of cache. This needs to be run once. Anywhere from 25GB-100GB will result in very noticeably increased build speeds
(for instance, a typical 1hr build time can be reduced to 20min). If you’re only building for one device, 25GB-50GB is fine. If you plan to build
for several devices that do not share the same kernel source, aim for 75GB-100GB. This space will be permanently occupied on your drive, so take this
You can also enable the optional
ccache compression. While this may involve a slight performance slowdown, it increases the number of files that fit in the cache. To enable it, run:
ccache -o compression=true
ccachesize can be lower (aim for approximately 20GB for one device).
if you see build time errors which say something like
ccache: error: Failed to create temporary file for /home/user/.cache/ccache/tmp: Read-only file system, follow this:
first create a new mount point using
sudo mkdir /mnt/ccache
then bind ccache directory to that mount point using
sudo mount --bind /home/<your_account_username>/.cache/ccache /mnt/ccache
<your_account_username> with the appropriate value. After this, add the following
export USE_CCACHE=1 export CCACHE_EXEC=/usr/bin/ccache export CCACHE_DIR=/mnt/ccache
~/.bashrc file instead of what you added in previous step.
set ccache size as done earlier using
ccache -M 50G
Then to make sure this doesnt break after you reboot, we need to add the new mount point to auto mount at login. Edit fstab using
sudo nano /etc/fstab and add
/home/<your_account_username>/.cache/ccache /mnt/ccache none defaults,bind,users,noauto 0 0
save change and add
mount /mnt/ccache to your
~/.profile. You should not see these errors ever again.
Start the build
Time to start building! Now, type:
croot mka bacon -j$(nproc --all)
The build should begin.
Install the build
Assuming the build completed without errors (it will be obvious when it finishes), type the following in the terminal window the build ran in:
There you’ll find all the files that were created. The two files of more interest are:
recovery.img, which is the PixelExperience recovery image.
A zip file whose name starts with ‘PixelExperience_’, which is the PixelExperience installer package.
Success! So… what’s next?
You’ve done it! Welcome to the elite club of self-builders. You’ve built your operating system from scratch, from the ground up. You are the master/mistress of your domain… and hopefully you’ve learned a bit on the way and had some fun too.