Name Service Switch

The Name Service Switch (NSS) connects the computer with a variety of sources of common configuration databases and name resolution mechanisms. These sources include local operating system files (such as /etc/passwd, /etc/group, and /etc/hosts), the Domain Name System (DNS), the Network Information Service (NIS, NIS+), and LDAP.

This operating system mechanism, used in billions of computers, including all Unix-like operating systems, is indispensable to functioning as part of the networked organization and the Internet. Among other things, it is invoked every time a computer user clicks on or types a website address in the web browser or responds to the password challenge to be authorized access to the computer and the Internet.