3 users, 1 folder. Users: vsftpd (FTP server), bobmarley (normal user), www-data (Apache user)
How to unite them and make so that each user can modify any of these user's data, without doing CHMOD 777?
Ex.: bobmarley created a file 'settings.inc.php' www-data tries to access the file, and succeeds. vsftpd user accesses the file and can modify it, too.