In order to build ChromiumOS from source, you will need to have a virtual machine or server with the following minimum hardware and software specifications.
Officially Ubuntu is the only supported operating system for building ChromiumOS from source however it is technically possible to build ChromiumOS from other 64 bit linux distributions such as Debian or other distribution. This guide will assume you are using Ubuntu and if you are using a different distribution of Linux, you will need to modify the instructions based on your distribution of choice. You can verify that you are running a 64 bit distribution by running the following command.
You should get "x86_64" as a result if you are running a 64 bit distribution.
If you are using a virtual machine, it is critical that the virtual machine itself has the minimum resources specified above, it is not enough that the host machine or hypervisor has the minimum requirements, the virtual machine itself must as well. Furthermore if a virtual machine is being used, it is important that your choice of virtualization allows you to access files in /proc /sys and /dev, this means technologies such as WSL(Windows Subsystem for Linux), OpenVZ, Docker Containers and LXC containers will not work. It is strongly advised to use KVM virtual machines if you choose to use a virtual machine.
The number of CPU cores dedicated to your build environment has a direct impact of the speed of your build. Generally the more CPU cores you have assigned to your build environment, the faster your build will be. The build system uses a threaded process to batch up individual build tasks, the number of tasks per batch is limited by your CPU thread count.