Configuring the Network Information Service (NIS)

NIS binding

The action of associating a server with a particular host is called binding that host in the NIS domain. Hosts must be bound for NIS services to be provided. Binding is accomplished at system startup when the ypbind daemon broadcasts for a server to satisfy a process request.

The ypbind daemon remembers information that lets clients' processes on a single node communicate with the ypserv daemon, the NIS database lookup server. Requests are usually to transfer a map, display its contents, or to display information about the NIS domain. Its primary function is to look up information in its local database of NIS maps. Unless the host system crashes or the network administrator intervenes, bindings remain constant in an NIS domain.

NIS services are implemented by the following daemons:

ypxfrd: satisfies requests from slave or copy-only servers to transfer maps. In SCO NIS, maps are transferred only when the identity of the master has been verified by the slave or copy-only server.
yppasswdd: satisfies requests to change passwords of NIS-managed accounts and communicates with the master server to update password information. This service is not available to servers in Secure Mode (see the ``Special NIS password change'' and ``Security limitations on configuration'' sections of this chapter for more information).
yppasswdd must be run only on the master server.

A heterogeneous environment differs from an SCO OpenServer environment with regard to binding:

SCO OpenServer environment
- All hosts are servers that contain both NIS maps and ASCII files derived from them. One exception to this is that copy-only servers store complete ASCII files but only stripped NIS maps.
- Lookups are resolved locally on master or slave servers.
- Clients can resolve some lookups across the network using NIS requests.
- All hosts are bound to themselves by default. That is, the local ypbind binds to the local ypserv, which in turn satisfies all NIS requests originating on that machine.
Heterogeneous environment
- Client hosts possess neither NIS maps nor ASCII files derived from them.
- Lookups are resolved across the network through NIS requests.
- The client's ypbind broadcasts a request for service and binds to the first responding ypserv process.

Applications running on clients may hang when a server is unavailable to answer NIS requests. They will resume when the server is again able to respond. If an NIS client or server requests information from a server that has crashed or is being rebooted, the client or server will send out broadcasts to find another NIS server to which to bind.