The build process can be quite long and tedious. The **[F.A.Q.](build_faq.md)** page offers solution for the most common complications. Alternatively, use the [CARLA forum](https://forum.carla.org/c/installation-issues/linux) to post any unexpected issues that may occur.
* __Ubuntu 18.04.__ CARLA provides support for previous Ubuntu versions up to 16.04. **However** proper compilers are needed for UE to work properly. Dependencies for Ubuntu 18.04 and previous versions are listed separatedly below. Make sure to install the ones corresponding to your system.
* __100GB disk space.__ The complete build will require quite a lot of space, especially the Unreal Engine build (around 80GB). Make sure to have around 100GB of free disk space.
* __An adequate GPU.__ CARLA aims for realistic simulations, so the server needs at least a 4GB GPU. A dedicated GPU is highly recommended for machine learning.
* __Two TCP ports and good internet connection.__ 2000 and 2001 by default. Be sure neither the firewall nor any other application block these.
CARLA needs many dependencies to run. Some of them are built automatically during this process, such as *Boost.Python*. Others are binaries that should be installed before starting the build (*cmake*, *clang*, different versions of *Python* and much more). In order to do so, run the commands below in a terminal window.
To avoid compatibility issues between Unreal Engine and the CARLA dependencies, use the same compiler version and C++ runtime library to compile everything. The CARLA team uses clang-8 and LLVM's libc++. Change the default clang version to compile Unreal Engine and the CARLA dependencies.
__1.__ Create a [GitHub](https://github.com/) account. CARLA is organized in different GitHub repositories, so an account will be needed to clone said repositories.
__2.__ Install [git](https://git-scm.com/book/en/v2/Getting-Started-Installing-Git) to manage the repositories via terminal.
__3.__ Create an [Unreal Engine](https://www.unrealengine.com/en-US/feed) account to access the Unreal Engine repositories, which are set to private.
__4.__ Connect both your GitHub and Unreal Engine accounts. Go to your personal settings in there is a section in [Unreal Engine](https://www.unrealengine.com/en-US/)'s website. Click on `Connections > Accounts`, and link both accounts. [Here](https://www.unrealengine.com/en-US/blog/updated-authentication-process-for-connecting-epic-github-accounts) is a brief explanation just in case.
New Unreal Engine accounts need activation. After creating the account, a verification mail will be sent. Check it out, or the UE repository will be shown as non-existent in the following steps.
The current version of CARLA runs on __Unreal Engine 4.24__ only. In this guide, the installation will be done in `~/UnrealEngine_4.24`, but the path can be changed. If your path is different, change the following commands accordingly.
Alternatively to this section, there is another [guide](https://docs.unrealengine.com/en-US/Platforms/Linux/BeginnerLinuxDeveloper/SettingUpAnUnrealWorkflow/index.html) to build UE on Linux. When consulting it, remember that CARLA will need the __4.24 release__, not the latest.
__3.__ Download the patches for Unreal Engine. The first patch fixes some Vulkan visualization issues that may occur when changing the map and the second improves the collision of the wheels with the terrain. Download and install them with the following commands.
Any issues this far are related with Unreal Engine. There is not much CARLA can do about it. However, the [build documentation](https://github.com/EpicGames/UnrealEngine/blob/release/Engine/Build/BatchFiles/Linux/README.md) provided by Unreal Engine may be helpful.
Now the latest state of the simulator, known as `master` branch in the repository, has been copied in local. Here is brief introduction to the most relevant branches of the repository. Remember that you can change and check your branches with the command `git branch`.
*__`dev` branch__ — Latest fixes and features still in development and testing. This branch will be merged with `master` when the time for a new release comes.
Download the assets, as they are necessary to run CARLA. These are stored in a separated package to reduce the size of the build. A script downloads and extracts the latest stable assets automatically. The package is >3GB, so the download may take some time.
The variable should be added to `~/.bashrc` or `~/.profile` to be set persistently session-wide. Otherwise, it will only be accessible from the current shell. To do this, follow these steps.
__1.__ Open `~/.bashrc`.
```sh
gedit ~/.bashrc
```
__2.__ Write the environment variable in the `~/.bashrc` file: `export UE4_ROOT=~/UnrealEngine_4.24`
* __make PythonAPI__ compiles the API client, necessary to grant control over the simulation. It is only needed the first time. Remember to run it again when updating CARLA. Scripts will be able to run after this command is executed.
```sh
make PythonAPI
```
* __make launch__ compiles the server simulator and launches Unreal Engine. Press **Play** to start the spectator view and close the editor window to exit. Camera can be moved with `WASD` keys and rotated by clicking the scene while moving the mouse around.
The project may ask to build other instances such as `UE4Editor-Carla.dll` the first time. Agree in order to open the project. During the first launch, the editor may show warnings regarding shaders and mesh distance fields. These take some time to be loaded and the city will not show properly until then.
Finally, let's test the simulator. Inside `PythonAPI/examples` and `PythonAPI/util` there are some example scripts that may be especially useful for starters. The following commands will spawn some life into the town, and create a weather cycle. Each script should be run in one terminal
If the simulation is running at very low FPS rates, go to `Edit/Editor preferences/Performance` in the UE editor and disable __Use less CPU when in background__.
Read the **[F.A.Q.](build_faq.md)** page or post in the [CARLA forum](https://forum.carla.org/c/installation-issues/linux) for any issues regarding this guide.
Some recommendations after finishing the build. Learn how to update the CARLA build or take your first steps in the simulation, and learn some core concepts.
