First of all we need to install some version of Linux on our RPi. I tried Ubuntu MATE and it was great. Instructions for downloading and writing it on microSDHC are here: https://ubuntu-mate.org/raspberry-pi/ I preferred the terminal way:

sudo apt-get install gddrescue xz-utils
unxz ubuntu-mate-16.04-desktop-armhf-raspberry-pi.img.xz
sudo ddrescue -D --force ubuntu-mate-16.04-desktop-armhf-raspberry-pi.img /dev/sdx

Once the microSDHC is ready, we can put it on RPi3 and power it on. Of course, we also need to attach a keyboard, mouse and TV display to it. Once it is booted, it will start the configuration of the system (asking for a username and password, etc.). When this is done, we should also resize the partition in order to make full use of the microSHDC card capacity, as described on the page above. I did it from the terminal:

sudo su
echo 'd,2,n,p,2,,,w' | tr ',' '\n' | fdisk /dev/mmcblk0
reboot

The next thing to do is to update/upgrade the system, since there may be any security patches:

sudo su
apt-get update
apt-get upgrade

I also install vim and aptitude on every new system:

apt-get install vim aptitude

A headless computer is one that does not have a monitor and is accessed and managed from the network. For this to work, it needs to have a fixed IP address (instead of a random one given by a DHCP server), so that we know where to access it. Besides this it also needs a SSH server and a VNC server, which allow us to access it remotely.

This article shows how to edit the network connections in order to set a fixed IP: https://funnyvale.com/how-to-set-up-wifi-on-raspberry-pi-3/ On the tab IPv4 Settings you should also set a manual fixed IP, like 192.168.0.200, instead of the dynamic configuration.

From the GUI you can also set a fixed IP for the wired connection. But I prefer to do it from the terminal. I edit the file /etc/network/interfaces and append lines like these:

auto enxb827eb3c62f4
iface enxb827eb3c62f4 inet static
    address 192.168.1.200
    netmask 255.255.255.0
iface enxb827eb3c62f4 inet static
    address 192.168.100.200
    netmask 255.255.255.0

Here enxb827eb3c62f4 is the name of the network interface, which has changed on ubuntu 16.04 (it was something like eth0 previously).

Let's install also openssh-server and tightvncserver.

apt-get install openssh-server
apt-get install tightvncserver

After rebooting, we can access the box through wifi or a cable like this: ssh user@192.168.0.200 (wifi), or ssh user@192.168.1.200 or ssh user@192.168.100.200.

For a headless box (as RPi usually is) we should also disable the GUI: graphical disable and reboot. Dispite this, we can still access its GUI desktop remotely through VNC. This can be done by starting first a vnc server (and setting a password) with the command: vncserver. We can access the vnc desktop with a command like this: vncviewer 192.168.0.200:1. (We may need to install it with aptitude install vncviewer, in case it is not installed.)

I installed Docker following the instructions from this article: http://blog.hypriot.com/post/run-docker-rpi3-with-wifi/

echo "overlay" | sudo tee -a /etc/modules
sudo apt-get install -y apt-transport-https
wget -q https://packagecloud.io/gpg.key -O - | sudo apt-key add -
echo 'deb https://packagecloud.io/Hypriot/Schatzkiste/debian/ wheezy main' | sudo tee /etc/apt/sources.list.d/hypriot.list
sudo apt-get update
sudo apt-get install -y docker-hypriot
sudo systemctl enable docker

Checking the version of docker:

# docker version
Client:
 Version:      1.11.1
 API version:  1.23
 Go version:   go1.4.3
 Git commit:   5604cbe
 Built:        Mon May  9 00:50:14 2016
 OS/Arch:      linux/arm

Server:
 Version:      1.11.1
 API version:  1.23
 Go version:   go1.4.3
 Git commit:   5604cbe
 Built:        Mon May  9 00:50:14 2016
 OS/Arch:      linux/arm

git clone https://github.com/Own-Mailbox/docker omb
cd omb/
./docker.sh build
./docker.sh create
./docker.sh install

Then you can access the web interface at the address http://192.168.0.250

See:

• https://www.own-mailbox.com/alpha-manual.pdf
• https://www.own-mailbox.com/video/Alpha-demo.webm