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Prevent accidental push of yp maps from slave servers
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nis_intro(7) Miscellaneous Information Manual nis_intro(7) NAME
nis_intro - Network Information Service (NIS) introductory information DESCRIPTION
The Network Information Service (NIS) is a distributed name service that allows participating hosts to share access to a common set of sys- tem and network files. NIS allows the system administrator to manage these shared files on a single system. NIS is intended for use in a secure environment only, where gateways do not allow outside Internet access to the NIS protocol. NIS Maps Information distributed by NIS is stored in database files called maps. Most of the NIS maps represent files that were traditionally stored in the /etc directory. These files include the following: aliases group hosts netgroups networks passwd protocols rpc services In a secure environment, you can run NIS in a secure mode, thereby creating secure and nonsecure versions of the NIS maps. See the Secu- rity guide for more information. You can also use NIS to distribute files used by Automount or AutoFS, or to distribute other user-defined files. Each NIS map contains a set of keys and associated values. For example, as keys, the hosts map contains all host names on a network, and as values, the corresponding Internet addresses. Each NIS map has a map name, used by programs to access data in the map. NIS Domains A named set of NIS maps is called a domain. A system's "domain name" or "NIS domain" corresponds to the set of NIS maps that the system can access. You can think of an NIS domain as a set of systems that share the same set of NIS maps. A system's domain name is set at the time the system is booted by the /sbin/init.d/nis script using an entry in the /etc/rc.config.common file. System administrators can use the nissetup script to place entries in this file. The nissetup script is described in the Network Administration manual. You can determine your system's NIS domain using the domainname command. Refer to domainname(1). A domain name is required for retrieving data from an NIS database. NIS Client-Server Model NIS follows the client-server model of distributed services. There are two types of NIS servers - master and slave. The master server stores the master copy of the NIS maps for its domain; these are the only NIS maps that can be modified. Each domain has only one master server. Slave servers store copies of the master server's NIS maps. NIS slave servers can be spread throughout a network. Whenever an NIS map is updated on the master server, the master propagates the changes to each slave server in its domain. If the master is unavailable for any reason, the slave servers continue to make the NIS maps available to the NIS clients. Clients are all of the systems that can access NIS maps. When a client requires NIS information, it makes a remote procedure call (RPC) to one of the NIS servers to obtain the information. NIS Data Storage The data in NIS maps is stored as databases in dbm/ndbm, btree, or hash format. For example, the NIS map for the /etc/hosts file in the domain market might be stored in these dbm/ndbm files: /var/yp/mar- ket/hosts.byaddr.dir /var/yp/market/hosts.byaddr.pag /var/yp/market/hosts.byname.dir /var/yp/market/hosts.byname.pag The makedbm command takes an ASCII file such as /etc/hosts and converts it into dbm/ndbm files suitable for use by NIS. However, system administrators use the Makefile script in the /var/yp directory to create NIS map files and specify file format. The Makefile script then calls makedbm. Refer to the Network Administration manual for details on the Makefile script, specifying different formats, and other NIS management information. RELATED INFORMATION
Commands: domainname(1), svcsetup(8), ypbind(8), yppasswdd(8), ypserv(8), ypxfr(8) Files: svc.conf(4) Network Administration delim off nis_intro(7)
