The Windows Subsystem for Linux (WSL) is a Microsoft technology that allows users to run a Linux environment directly on Windows without the need for a separate virtual machine or dual-boot setup.

Since FLUKA, Flair, and many of its supporting tools are designed for Linux systems, WSL provides a convenient and efficient way to install, configure, and run FLUKA and Flair on Windows while maintaining compatibility with standard Linux-based workflows.

WSL offers a lightweight Linux environment with access to common Linux utilities, compilers, and package managers, while remaining seamlessly integrated with the Windows desktop and file system.

1. Installing WSL on Windows 11

Start the Terminal (Windows PowerShell) as Administrator and run the following command:

wsl --install

This will install all the necessary system components and install the Ubuntu application. During the installation, you will be asked to set a username and password for Ubuntu. They can be anything, as they are not related to your Windows credentials.

When Ubuntu is installed, close the Terminal (Windows PowerShell) running as Administrator.

After the initialization, Ubuntu works just like a native Linux system.

Note 1: If your account doesn't have Administrator rights, then you need to repeat the installation in a Terminal which is not running as Administrator.

Note 2: The windows drives (C:\, D:\, etc.) are automatically mounted at: /mnt/<drive_letter>/...

2. System setup and installing Flair

Download the zip file containing the setup script from here, and extract it to your Downloads folder.

Now you can start Ubuntu in the Terminal by clicking the down-arrow next to the tabs on the top, or in the standalone Ubuntu application in the Start menu.

Then change to the location of the extracted files with:

cd /mnt/c/Users/<YourUserName>/Downloads/cern_fluka_wsl-master/cern_fluka_wsl-master

Note: You need to replace <YourUserName> with your Windows user name.

To check the contents of the directory you can use the command:

ls

If the directory contains the setup_wsl.sh script, run it with:

sudo ./setup_wsl.sh

The script will install the necessary packages and Flair. The setup process will take a few minutes.

Note: The sudo command executes a command with administrator privileges and may prompt for the password created during Ubuntu setup.

3. Installing FLUKA

After registering, you can download FLUKA from the fluka.cern website. Choose the following package for Ubuntu: gfortran>=9, 64 bits (.deb).

The default neutron library shall be downloaded in the .deb format as well.

To install the packages, navigate to your Downloads directory in the Ubuntu window with:

cd /mnt/c/Users/<YourUserName>/Downloads

Note: You need to replace <YourUserName> with your Windows user name.

and use the following command:

sudo apt install ./fluka_4-?.?.x64-Linux-gfor9_amd64.deb ./fluka-pw*

Note: You need to replace `?` characters with the current version numbers, and `*` with the complete filename of the neutron data library.

After the installation, restart Windows or close Ubuntu and run in a Terminal (Windows PowerShell):

wsl --shutdown

4. Running simulations

After starting Ubuntu you can launch Flair with the flair command, or you can run FLUKA from the command line.

See the instructions on fluka.cern

5. Updating FLUKA and Flair

5.1. Updating Flair

To update the whole Ubuntu system (including Flair) use:

sudo apt update && sudo apt upgrade

In case you only want to update Flair use:

sudo apt update && sudo apt upgrade flair flair-geoviewer

5.2. Updating FLUKA

Manually install the latest package of FLUKA as described in section 3.

6. Resetting WSL

If you encounter problems with WSL, you can always reset it to a clean state. To do so, run the following command in the Terminal (Windows PowerShell):

wsl --unregister Ubuntu

Note: This will delete all files in your Ubuntu home directory.

To install Ubuntu again, run:

wsl --install