Samba - add users

Go root:

sudo bash

First, add users to the system, its necessary:

adduser <username>

Fill in the password and some credentials.

Add the user to Samba:

smbpasswd -a <username>

Then edit the user line in /etc/passwd

The line looks like this:

username:x:123:123:Username,,,:/home/username:/bin/bash

Edit it so it does not have any home and will be logged 
out directly if trying to login on a terminal:

username:x:123:123:Username,,,:/nonexistent:/bin/false

Then remove the home of the user, be careful here to not make a typo:

rm -rf /home/username

Also edit /etc/samba/smb.conf and give user access if needed.

Restart Samba, may not be necessary:

service smbd restart