# 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 need

* 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 Recovery
### Install the Android SDK

If you haven’t previously installed adb and fastboot, you can download them from Google. Extract it running:
Now you have to add adb and fastboot to your PATH. Open ~/.profile and add the following:
Then, run source ~/.profile to update your environment.

### Install the build packages

Several packages are needed to build LineageOS. You can install these using your distribution’s package manager.
In arch linux you can install all the needed packages by installing lineageos-devel from the AUR. 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)
(libwxgtk3.0-dev Was changed to libwxgtk3.0-gtk3-dev in Ubuntu 20.04)
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 directories

You’ll need to set up some directories in your build environment.
To create them:
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 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):
Then, run source ~/.profile to update your environment.
In arch linux do the same but name the file ~/.bashrc

### Initialize the LineageOS source repository

Enter the following to initialize the repository:
cd ~/android/lineage
repo init -u https://github.com/LineageOS/android.git -b lineage-X --git-lfs
where X is the LineageOS version supported by your device.
You need to initialize git for this to work:
git config --global user.name "abc"
git config --global user.email "abc@example.com"

### Download the source code

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 code

This depends on your device.

### Turn on caching to speed up build

Make use of ccache if you want to speed up subsequent builds by running:
and adding that line to your ~/.bashrc file. Then, specify the maximum amount of disk space you want ccache to use by typing this:
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:
or add that line to your ~/.bashrc file.

### Build it!

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

## 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 LineageOS recovery image.
* 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.

## References

This article was taken mainly from LineageOS's wiki.