For Debian-based distro's like Ubuntu:
wget https://apt.devkitpro.org/install-devkitpro-pacman
chmod +x ./install-devkitpro-pacman
sudo ./install-devkitpro-pacman
For other distros look here.
echo "export DEVKITARM=/opt/devkitpro/devkitARM
export DEVKITPRO=/opt/devkitpro" >> ~/.bashrc