Build for merlinx

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Note: This page is auto-generated for the Xiaomi Redmi Note 9, based on the device’s information, located here. You can find similar instructions for every officially-supported device on this wiki.

Introduction

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, preferably a recent version of ubuntu) with a reasonable amount of RAM and about 200 GB of free storage (more if you enable ccache or 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.

Tip: If you are not accustomed to using Linux, this is an excellent chance to learn. It’s free – just download and run a virtual machine (VM) such as VirtualBox, then install a Linux distribution such as Ubuntu (AOSP vets Ubuntu as well). Any recent 64-bit version should work great, but the latest Long Term Support (LTS) version is recommended. There are plenty of instructions on setting up VirtualBox to run Ubuntu, so we’ll leave that to you.

Let’s begin!

Build PixelExperience and PixelExperience Recovery

Note: You only need to do these steps once. If you have already prepared your build environment and downloaded the source code, skip to Prepare the device-specific code

Install the platform-tools

If you haven’t previously installed adb and fastboot, you can download them from Google. Extract it running:

unzip platform-tools-latest-linux.zip -d ~

Tip: The file may not be named identically to what stands in this command, so adjust accordingly.

Now you have to add adb and 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

Then, run source ~/.profile to update your environment.

Preparing your system to build

Tip: This guide assumes that you have Ubuntu 18 (or higher) installed.

Installing git:

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

The ~/bin directory will contain the git-repo tool (commonly named “repo”) and the ~/android/pe directory will contain the source code of PixelExperience.

Install the `repo` command

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

Put the `~/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

Then, run source ~/.profile to update your environment.

Configure git

Given that repo requires you to identify yourself to sync Android, run the following commands to configure your git identity:

git config --global user.email "you@example.com"
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:

thirteen (discontinued)
thirteen-plus (discontinued)
twelve (discontinued)
twelve-plus (discontinued)

Enter the following to initialize the repository:

Note: Make sure the branch you enter here is the one you wish to build!

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

Note: This may take a while, depending on your internet speed. Go and have a beer/coffee/tea/nap in the meantime!

Tip: The repo sync command 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

where 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 into consideration.

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

Note: If compression is enabled, the ccache size 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

replace <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

to your ~/.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:

cd $OUT

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.

To get assistance

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