NAME

yp — description of the YP/NIS system

SYNOPSIS

DESCRIPTION

The YP subsystem allows network access to directory information hosted by NIS servers. OS X support is provided through the functions getpwent(3), getgrent(3), getfsent(3), getnetgrent(3), gethostent(3), getnetent(3), getrpcent(3), getprotoent(3), getservent(3), ethers(3) and other related functions. Queries to NIS servers are sent by the opendirectoryd daemon. The configuration of NIS clients is further described in the opendirectoryd(8) manual page.

The YP subsystem is started automatically by launchd(8) if an NIS domain is specified in the /etc/defaultdomain configuration file, and if the directory /var/yp exists (which it does in the default distribution).

NIS is an RPC-based client/server system that allows a group of machines within an NIS domain to share a common set of configuration files. This permits a system administrator to set up NIS client systems with only minimal configuration data and add, remove or modify configuration data from a single location.

The canonical copies of all NIS information are stored on a single machine called the NIS master server. The databases used to store the information are called NIS maps. A single NIS server can support several domains at once, therefore it is possible to have several such directories, one for each supported domain. Each domain will have its own independent set of maps.

Client NIS systems receive all NIS data in ASCII form.

There are three main types of NIS systems:

1. NIS clients, which query NIS servers for information.
2. NIS master servers, which maintain the canonical copies of all NIS maps.
3. NIS slave servers, which maintain backup copies of NIS maps that are periodically updated by the master.

OS X systems may be configured as NIS clients, but not as master or slave servers.

A NIS client establishes what is called a binding to a particular NIS server using the ypbind(8) daemon. The ypbind(8) utility checks the system's default domain (as set by the domainname(1) command) and begins broadcasting RPC requests on the local network. These requests specify the name of the domain for which ypbind(8) is attempting to establish a binding. If a server that has been configured to serve the requested domain receives one of the broadcasts, it will respond to ypbind(8), which will record the server's address. If there are several servers available (a master and several slaves, for example), ypbind(8) will use the address of the first one to respond. From that point on, the client system will direct all of its NIS requests to that server. The ypbind(8) utility will occasionally “ping” the server to make sure it is still up and running. If it fails to receive a reply to one of its pings within a reasonable amount of time, ypbind(8) will mark the domain as unbound and begin broadcasting again in the hopes of locating another server.

NIS master and slave servers handle all NIS requests with the ypserv(8) daemon. The ypserv(8) utility is responsible for receiving incoming requests from NIS clients, translating the requested domain and map name to a path to the corresponding database file and transmitting data from the database back to the client. There is a specific set of requests that ypserv(8) is designed to handle, most of which are implemented as functions within the standard system libraries:

yp_order()

check the creation date of a particular map

yp_master()

obtain the name of the NIS master server for a given map/domain

yp_match()

lookup the data corresponding to a given in key in a particular map/domain

yp_first()

obtain the first key/data pair in a particular map/domain

yp_next()

pass ypserv(8) a key in a particular map/domain and have it return the key/data pair immediately following it (the functions yp_first() and yp_next() can be used to do a sequential search of an NIS map)

yp_all()

retrieve the entire contents of a map

There are a few other requests which ypserv(8) is capable of handling (i.e., acknowledge whether or not you can handle a particular domain (YPPROC_DOMAIN), or acknowledge only if you can handle the domain and be silent otherwise (YPPROC_DOMAIN_NONACK)) but these requests are usually generated only by ypbind(8) and are not meant to be used by standard utilities.

HISTORY

The YP subsystem was written from the ground up by Theo de Raadt to be compatible to Sun's implementation. Bug fixes, improvements and NIS server support were later added by Bill Paul. The server-side code was originally written by Peter Eriksson and Tobias Reber and is subject to the GNU Public License. No Sun code was referenced.

OS X NIS client software is derived from FreeBSD.