after installing a linux client, you usually wish to have the same users as on your QNAP server. A LDAP server is one useful solution.
This post is certainly obsolete...
on the server side, setup according to: http://web.qnap.com/pro_application.asp?ap_id=847
one note: the domain name is a name you choose for your server (not the domain name of your local network), something useful for the LDAP server to recognise itself (like my-nas.local).
on the client side, there are several HOWTOs, like:
http://doc.ubuntu-fr.org/ldap_client (in french)
it usually takes two minutes if you copy and paste on the client side the information of your NAS server's LDAP page
unfortunately, it failed with "failed to bind to LDAP server ldap://192.168.0.5/: Invalid credentials"
the (undocumented) solution was to:
generate a password on the server side using the slappasswd command
on the client side, copy and paste the generated SHA password instead of the password in clear text in the /etc/ldap.conf configuration file