Ubuntu Minimal 18.04 + i3-gaps

gistfile1.txt

You only need to install xorg and lightdm if you have installed Ubuntu Minimal.
If you installed a regullar Ubuntu desktop, just skip to the i3-gaps section.

xorg
====

# Xorg provides a base for a graphical environment
sudo apt install xorg

lightdm
=======

# login manager
sudo apt install lightdm

i3-gaps
=======

# Dependencies
sudo apt install libxcb1-dev libxcb-keysyms1-dev libpango1.0-dev libxcb-util0-dev libxcb-icccm4-dev libyajl-dev libstartup-notification0-dev libxcb-randr0-dev libev-dev libxcb-cursor-dev libxcb-xinerama0-dev libxcb-xkb-dev libxkbcommon-dev libxkbcommon-x11-dev autoconf libxcb-xrm0 libxcb-xrm-dev automake

# Clone the repository
git clone https://www.github.com/Airblader/i3 .i3-gaps
cd .i3-gaps

# Compile & install
autoreconf --force --install
rm -rf build/
mkdir -p build && cd build/

# Disabling sanitizers is important for release versions!
# The prefix and sysconfdir are, obviously, dependent on the distribution.
../configure --prefix=/usr --sysconfdir=/etc --disable-sanitizers
make -j8
sudo make install

reboot
======

# now reboot your system by run this on terminal
reboot

# on login screen, click on a little button in the login box/dialog and select i3
# if you've got "failed to start session" message, click that button again and 
# select the other option and then i3 (just change to something else and back to i3)
# try to login again. If a black screen appears, just reboot your system and everything will work fine.