yp

yp, short for Yellow Pages, is a distributed directory service used to share system and network configuration information across Unix-like systems. It originated as part of the Network Information Service (NIS) developed by Sun Microsystems in the 1980s and was historically called Yellow Pages. The term is still used in contexts referring to the NIS/YP system, though several distributions simply call it YP or NIS.

Architecture and data model: yp provides a centralized repository of maps that describe resources such as user accounts, groups, host names, and services. Within an NIS domain, one server acts as the master for each map and one or more slave servers replicate it. Clients running ypbind contact these servers to retrieve information. Data are organized into maps with keys and values, for example passwd.byname or hosts.byaddr. Updates to maps are typically made on the master server and propagated to slaves through the NIS infrastructure, often using specialized commands or make-based workflows during maintenance.

Administration and deployment: Setting up YP involves configuring an NIS domain, initializing the master and slaves, and populating maps from source files (such as /etc/passwd and /etc/group) on the master. Common tools include ypinit, ypserver/ypserv, ypbind, yppasswd, and ypupdate. It is commonly used in heterogeneous networks to provide uniform authentication and name resolution across machines, though modern deployments frequently migrate to alternative directory services such as LDAP.

Security and relevance: YP originally offered limited security, with data transmitted without strong encryption and limited authentication. Because of these concerns, many networks place YP behind trusted networks or replace it with more secure solutions. Today, YP remains of historical interest and is found in legacy environments, with continued use primarily in specific, controlled deployments.