libnss-mysql-bg provides a Name Service Switch module that allows MySQL to act as a name service. . Its configuration is very flexible by allowing to set an SQL query per NSS call (getpwnam, getpwuid, ...). You would use it instead of the other "libnss-mysql" package for building an NSS over an existing database (used for another purpose like groupware, ...). . It currently supports storage of passwd, group and shadow informations.