Advanced phone customization/Building your own ROM

Building your ROM is one of the most rewarding experiences you can have. Imagine having your own version of Android on your own phone!

We'll take the popular custom OS LineageOS as a guiding reference.

What you'll needEdit

  • The phone which you need to develop.
  • A relatively recent 64-bit computer (Linux, OS X, or Windows) with a reasonable amount of RAM and about 100 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 8 GB or more). Using SSDs results in considerably faster build times than traditional hard drives.
  • A USB cable compatible with your phone.
  • 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 LineageOS and LineageOS RecoveryEdit

Install the Android SDKEdit

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 ~

Now you have to add adb and fastboot to your PATH. Open ~/.profile and add the following:
<nowiki#</nowiki> 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.

Install the build packagesEdit

Several packages are needed to build LineageOS. You can install these using your distribution’s package manager.
To build LineageOS, you'll need bc bison build-essential ccache curl flex g++-multilib gcc-multilib git gnupg gperf imagemagick lib32ncurses5-dev lib32readline-dev lib32z1-dev liblz4-tool libncurses5-dev libsdl1.2-dev libssl-dev libwxgtk3.0-dev libxml2 libxml2-utils lzop pngcrush rsync schedtool squashfs-tools xsltproc zip zlib1g-dev
(take libwxgtk2.8-dev instead of libwxgtk3.0-dev if you're on older than Ubuntu 16.04)

You'll also need Java. Different versions of LineageOS require different JDK (Java Development Kit) versions.

  • LineageOS 14.1-15.1: OpenJDK 1.8 (install openjdk-8-jdk)
  • LineageOS 11.0-13.0: OpenJDK 1.7 (install openjdk-7-jdk)*

* Ubuntu 16.04 and newer do not have OpenJDK 1.7 in the standard package repositories. See the Ask Ubuntu question “How do I install openjdk 7 on Ubuntu 16.04 or higher?”. Note that the suggestion to use PPA openjdk-r is outdated (the PPA has never updated their offering of openjdk-7-jdk, so it lacks security fixes); skip that answer even if it is the most upvoted.

Create the directoriesEdit

You’ll need to set up some directories in your build environment.

To create them:

mkdir -p ~/bin
mkdir -p ~/android/lineage

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

Install the repo commandEdit

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 executionEdit

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.

Initialize the LineageOS source repositoryEdit

Enter the following to initialize the repository: cd ~/android/lineage repo init -u https://github.com/LineageOS/android.git -b lineage-X

where X is the LineageOS version supported by your device.

Download the source codeEdit

To start the download of the source code to your computer, type repo sync.

The LineageOS manifests include a sensible default configuration for repo, which we strongly suggest you use (i.e. don’t add any options to sync). For reference, our default values are -j 4 and -c. The -j 4 part means that there will be four simultaneous threads/connections. If you experience problems syncing, you can lower this to -j 3 or -j 2. On the other hand, -c will ask repo to pull in only the current branch instead of all branches that are available on GitHub.

Prepare the device-specific codeEdit

This depends on your device.

Turn on caching to speed up buildEdit

Make use of ccache if you want to speed up subsequent builds by running:

export USE_CCACHE=1

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. See more information about ccache on Google’s Android build environment initialization page.

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:

export CCACHE_COMPRESS=1

or add that line to your ~/.bashrc file.

Build it!Edit

Type source ./build/envsetup.sh
Type hmm to get the help text, currently (2020-11-16):

Run "m help" for help with the build system itself.

Invoke ". build/envsetup.sh" from your shell to add the following functions to your environment:
- lunch:      lunch <product_name>-<build_variant>
              Selects <product_name> as the product to build, and <build_variant> as the variant to
              build, and stores those selections in the environment to be read by subsequent
              invocations of 'm' etc.
- tapas:      tapas [<App1> <App2> ...] [arm|x86|mips|arm64|x86_64|mips64] [eng|userdebug|user]
- croot:      Changes directory to the top of the tree, or a subdirectory thereof.
- m:          Makes from the top of the tree.
- mm:         Builds all of the modules in the current directory, but not their dependencies.
- mmm:        Builds all of the modules in the supplied directories, but not their dependencies.
              To limit the modules being built use the syntax: mmm dir/:target1,target2.
- mma:        Builds all of the modules in the current directory, and their dependencies.
- mmma:       Builds all of the modules in the supplied directories, and their dependencies.
- provision:  Flash device with all required partitions. Options will be passed on to fastboot.
- cgrep:      Greps on all local C/C++ files.
- ggrep:      Greps on all local Gradle files.
- jgrep:      Greps on all local Java files.
- resgrep:    Greps on all local res/*.xml files.
- mangrep:    Greps on all local AndroidManifest.xml files.
- mgrep:      Greps on all local Makefiles files.
- sepgrep:    Greps on all local sepolicy files.
- sgrep:      Greps on all local source files.
- godir:      Go to the directory containing a file.
- allmod:     List all modules.
- gomod:      Go to the directory containing a module.
- pathmod:    Get the directory containing a module.
- refreshmod: Refresh list of modules for allmod/gomod.
.... (there's more, omitted for brevity) ...


Running m help outputs:

# m help
The basic Android build process is:
cd /mnt/aosp/lineage
source build/envsetup.sh    # Add "lunch" (and other utilities and variables)
                            # to the shell environment.
lunch [<product>-<variant>] # Choose the device to target.
m -j [<goals>]              # Execute the configured build.
Usage of "m" imitates usage of the program "make".
See /mnt/aosp/lineage/build/make/Usage.txt for more info about build usage and concepts.
Common goals are:
    clean                   (aka clobber) equivalent to rm -rf out/
    checkbuild              Build every module defined in the source tree
    droid                   Default target
    nothing                 Do not build anything, just parse and validate the build structure
    java                    Build all the java code in the source tree
    native                  Build all the native code in the source tree
    host                    Build all the host code (not to be run on a device) in the source tree
    target                  Build all the target code (to be run on the device) in the source tree
    (java|native)-(host|target)
    (host|target)-(java|native)
                            Build the intersection of the two given arguments
    snod                    Quickly rebuild the system image from built packages
                            Stands for "System, NO Dependencies"
    vnod                    Quickly rebuild the vendor image from built packages
                            Stands for "Vendor, NO Dependencies"
    pnod                    Quickly rebuild the product image from built packages
                            Stands for "Product, NO Dependencies"
    psnod                   Quickly rebuild the product_services image from built packages
                            Stands for "ProductServices, NO Dependencies"
    onod                    Quickly rebuild the odm image from built packages
                            Stands for "ODM, NO Dependencies"
So, for example, you could run:
cd /mnt/aosp/lineage
source build/envsetup.sh
lunch aosp_arm-userdebug
m -j java
to build all of the java code for the userdebug variant of the aosp_arm device.
#### build completed successfully (16 seconds) ####

Install the buildEdit

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:

  1. recovery.img, which is the LineageOS recovery image.
  2. lineage-14.1-20180808-UNOFFICIAL-a5y17lte.zip, which is the LineageOS installer package. This will vary depending on your phone and version.

And that's it! You can use your ROM as any other custom ROM that you'll download off the internet.

ReferencesEdit

This article was taken mainly from LineageOS's wiki.