getnetgrent

getnetgrent is a function in Unix-like operating systems that retrieves entries from the Network Information Service (NIS) database. NIS, also known as Yellow Pages (YP), is a distributed directory service that allows systems to share configuration data across a network. The getnetgrent function specifically allows applications to iterate through the entries in the 'netgroup' database, which is used to define groups of hosts, users, and domains for access control and network management purposes.

When called, getnetgrent typically returns one netgroup entry at a time. The function manages an internal pointer to keep track of the current position within the database, enabling sequential retrieval of all entries. To start the iteration, a program would call getnetgrent without any arguments. Subsequent calls would continue to fetch the next available netgroup entry. To terminate the iteration and release any associated resources, a separate function, often getnetgrent_end, is typically used.

The 'netgroup' database itself defines relationships between network entities. An entry in the netgroup database can consist of a group name, followed by a list of members. These members can be hosts, users, or other netgroups. This hierarchical structure allows for flexible management of network resources and access permissions. Applications that use getnetgrent can leverage this information to determine whether a given host, user, or domain belongs to a specific netgroup, which is useful for tasks such as authentication, authorization, and setting up network services.