Installing ROS

Follow these steps:

• Go to the official ROS installation page (link here). It's same as any other linux distribution, done here.
• Choose the latest distribution supported for the latest LTS release of Ubuntu. As of this writing, it's this one.
• Follow the instructions on the page to install ROS

Congratulations, you've installed ROS on your Raspberry Pi3

Note: We've tried a Desktop-Full install and it worked on a Raspberry Pi3, but other installation types must also work effortlessly.

Additional

Ubuntu MATE

Installation on Raspberry Pi 3

To install Ubuntu MATE on Raspberry Pi3, do the following:

• Go to their official downloads page (link here)
• Select "Raspberry Pi (recommended)" and then select the release "18.04.2 (Bionic)". You may choose any other existing LTS release of Ubuntu as well.
• Download using torrent, magnet or directly using the ".img.xz" option (best)
• After that, download and install Etcher. It's a popular tool used to create bootable drives. We'll use it to create a bootable SD card.
• Insert an SD card (which you choose to use with your Raspberry Pi) into an SD card reader and plug it into a USB port of your system.
• Open Etcher
  • Select the SD card as the drive and the ".img.xz" file as the source file
  • Click burn or flash button and wait till etcher finished unpacking everything into the SD card
• After everything is done, eject the SD card and insert it into the Raspberry Pi
• Connect display, keyboard and mouse and finally the power to the Raspberry Pi
• You'll see Ubuntu MATE's booting logo. Follow the on screen setup instructions.
• Congratulations, you've successfully installed Ubuntu MATE on your Raspberry Pi

Note: This procedure is tested for Raspberry Pi 3B+ but should ideally work for any other Raspberry Pi

At the time of this writing, the latest version is Ubuntu 18.04 (bionic). To check the release version and Codename, run the command lsb_release -rc and see the output. It must show the release to be 18.04 and Codename to be "bionic".

Setting up SSH

In order to setup SSH on Ubuntu MATE, install open ssh using command

sudo apt install openssh-server

And then SSH using any client on the system side. Make sure that the service is enabled on login. Check out this answer if you're facing problems with SSH automatically starting up on boot.