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Network Information Service (NIS) is a client-server directory service protocol used for distributed systems to maintain consistent data and configuration files throughout a network. It was initially developed by Sun Microsystems to centralize the administration of Unix systems. It later developed into an industry standard that was adopted by all major Unix vendors.
A network information system is a remote-procedure-call-based client-server system that permits a group of machines within an NIS domain to share a common set of configuration files. This allows system administrators to set up NIS client systems with the least configuration data and add, remove or alter configuration data from a single location.
The network information service environment involves clients and servers logically grouped together in a domain with specific characteristics defined in databases or maps that specify information such as usernames, passwords and host names. The three types of hosts in a network information service are master servers, client servers and clients. The servers act as a central repository for host configuration information. Master servers have the master copy of the information, while slave servers mirror this information for redundancy. The servers are shared, and clients depend on them for information. The host files, master password and groups are shared through the network information service. The client queries the NIS server when it requires information found in the local files.
The master server may be accessed by the system administrator. Master servers are extremely stable, so that the systems that depend on them may be assured of uninterrupted service. They are also accessible from most systems on the network. If there is a large number of hosts, the master server may be overloaded; if there are only a few hosts, each host can easily access the master server directly.
In case of network or master server failure, slave servers take up the role of backup. The greater the number of slave servers, the less time the client is required to wait for a response from a server. Every domain has at least one slave server. The slave servers are balanced to get the required level of availability and response time, without adding the expense of copying data to many systems. To ensure load balance, additional hosts may be designated as slave servers.
Most of the hosts in an NSI domain are clients. They run the ypbind daemon, enabling the client process to obtain information from servers, query servers to receive user and system account information, and make use of remote procedure calls to access system information within a map. The server searches the local database based on the request and returns the required information. An NIS server locates a server by broadcasting on networks connected to the client machine. The network speed affects the response time.