Install in Ubuntu

Disclaimer

These instructions assume

the user wants to install using the source package instead of distribution provided packaging
access to 'root' account or user with admin permissions
use only distribution release specific instructions
some basic Linux skills
commands aren't copypasted blindly
that the process is stopped in case of errors

Open a terminal and gain root permissions

sudo -s -H

Verify that root has been gained

whoami

which should reply "root".

Install needed development packages

apt-get update
apt-get install make gcc libc6-dev wget libsqlite3-0 libsqlite3-dev

optional additional packages for image output support

apt-get install libgd3 libgd-dev

Get the latest release and extract it

cd /usr/src
wget https://humdi.net/vnstat/vnstat-2.12.tar.gz
tar zxvf vnstat-2.12.tar.gz

Compile and install the binaries

cd vnstat-2.12
./configure --prefix=/usr --sysconfdir=/etc && make && make install

Install the service file and start the daemon

cp -v examples/systemd/vnstat.service /etc/systemd/system/
systemctl enable vnstat
systemctl start vnstat

Verify that daemon process got started

pgrep -c vnstatd

which should reply "1". A reply of "0" indicates that the process has failed to start.