ypbind

ypbind is a daemon that binds a host to a Network Information Service (NIS, formerly known as YP) domain. It runs on NIS client machines and is responsible for locating an NIS server and establishing a binding so the client can retrieve NIS maps, such as passwd, group, hosts, and other domain data. By binding to a server, the client can fetch and cache the maps needed for user authentication and other name-resolution services.

The binding process begins with determining the NIS domain. ypbind can discover servers by broadcast on the local network or use a configured list of servers provided by the system’s NIS configuration (for example, in /etc/yp.conf on some systems) or via nisdomainname. Once a server is identified, ypbind communicates with the server’s ypserv service using RPC to obtain the server’s address and to establish the binding for the domain. If the chosen server becomes unavailable, ypbind can select a different server from the available set.

Configuration and operation: On most UNIX-like systems, ypbind starts at boot and runs as a background service. The domain is set with system tools such as nisdomainname, and server preferences may be defined in configuration files or via command-line options. Utilities like ypwhich, yppoll, and ypcat are often used to inspect the current binding, the available servers, and the maps provided by the NIS domain.

Security considerations: NIS traffic is unencrypted and relies on network-level trust, making it vulnerable to spoofing and interception. It is typically restricted to trusted networks or VPNs, and many administrators consider migrating to more secure directory services such as LDAP with TLS/Kerberos or other modern authentication mechanisms.

History: ypbind originated with Sun Microsystems as part of the ONC/NIS suite in the 1980s and remains present in many UNIX-like systems, though its use has declined in favor of more secure directory services.