Before moving forward, you have to have already installed ROS and Ubuntu 18.04. ROS Melodic Morenia is supported until April 2023, when Ubuntu 18.04 will reach EOL as well. So, you can install ROS Noetic by then. If you want to perform a quick installation, you can follow this documentation. However, keep in mind that not all details are mentioned here. Please, for a detailed description visit here.

Step 1: The first step is adding the ROS repository to your ubuntu sources.list

sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -sc)main" > /etc/apt/sources.list.d/ros-latest.list'

Step 2: Add Official ROS repo keyring

sudo apt-key adv --keyserver 'hkp://keyserver.ubuntu.com:80' --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654

Step 3: And finally, update your packages list

sudo apt update

Step 4: Install ROS Melodic desktop package on Ubuntu 18.04

sudo apt install ros-melodic-desktop-full

Step 5: Let’s configure our environment. This is a very important step, once we have it done, working with ROS will be smooth.

echo "source /opt/ros/melodic/setup.bash" >> ~/.bashrc source ~/.bashrc

We are almost there!

Step 6: To install this tool and other dependencies for building ROS packages, run:

sudo apt install python-rosdep python-rosinstall python-rosinstall-generator python-wstool build-essential

Step 7: With the following, you can initialize rosdep.

sudo apt install python-rosdep sudo rosdep init rosdep update

Now, you have ROS Melodic installed and ready to use!

Step 8:At this point, we must have everything in place. Let’s try some ROS commands to make sure the installation has finished successfully.

roscore

Your terminal must be stuck here, therefore, you can not execute anything else while you have the roscore process there. Roscore is running and ready to serve other ROS processes!