NIS is a hierarchical system of servers. At the top of the hierarchy is the NIS master server. This is the "authoritative" server for the NIS domain.

What is a domain? Well in any organization there may be a number of domains based upon the department one is in, or the seniority in the company, Etc. These are "human" domains.NIS domains are similar. There may be an "ENG" domain for the engineers, a MGMT domain for the management people, and an "ACCT" domain for the accounting people.

The NIS master server has a number of slave servers too. Their jobs are to act as backups to the master servers. If there is a problem with the master, then the slaves will stand in. In addition, a single master server may become inundated by the amount of requests it receives. So clients will be configured to point to the slave servers instead. Therefore, the master will have MUCH less work to do.

However, let's consider NIS, how it works and how to configure it from the client. How do we connect to a NIS server?

There are a number of methods as with everything in Linux. The easiest is probably to run the client configuration utility "authconfig". This will ask you to enter your NIS server as well as your NIS domain. Once done, it will try to start the NIS client. The client is called "ypbind", and if the domain or the server is unavailable, it will give up after a couple of seconds.

The authconfig file modifies a file in /etc called yp.conf. The format of this file can be found in the manual page of ypbind (man 8 ypbind), but here is a brief summary with an example of two:

domain nisdomain server hostname e.g.

domain QEDux server 192.168.1.2
                

domain nisdomain broadcast e.g.

domain QEDux broadcast
                

Then a restart of the ypbind should see you right.

Now, how do we know we are connected? The "domainname" command will return the domain to which we are currently connected.

$ domainname
                

returns,

QEDux
                

(Or whatever your domain name is.)

	Note
	to see the DNS domain name, one needs to use the command "dnsdomainname" rather than just "domainname"

The last thing that needs configuration is the /etc/nsswitch.conf. Remember, this file determines in which order things are looked up. The general order for many things is first FILES, then DNS, then NIS and NISPLUS. Supposing the NIS server has exported their /etc/networks file. To look this up using NIS first, we would need to change the entry in the nsswitch.conf as follows:

networks:   nis files
                

Now, the network information will be looked up first in NIS and then in FILES. Notice too that if the NIS is unavailable, then networks entries will ONLY be looked up in files.

Did this work? Well the way to see that is to run the netstat command.

netstat -r
                

Notice I ommitted the 'n' switch. That would have got me only the numbers, I want the names of the networks too. These names are coming from the NIS server.

I've cited the use in the networks file, or for obtaining an up-to-date list of the public keys of people on you network, but this all seems rather trivial. One of the places NIS is most useful is in the management of user accounts.

Image for a minute you have 100 Linux machines in your environment and each has to have 50 user accounts. I can see you grimacing already! Enter NIS and bingo, we can administer all 50 users, on all 100 machines from a single NIS master server. Simple, efficient and easy. No mess, no fuss.

Linux offers a system for sharing disk space between hosts called the Network File System. NIS or the Network Information Service is a systems of providing information to hosts on the network.

It is a hierarchical system based upon a master-slave configuration. While it is not essential, it beats having to make copies of common files for each user on the system.

The downside of NIS and NFS is that these products are not available to non-Unix based clients so if you are running Windows on your desktop, you can't use NIS to authenticate your Windows desktop back to your Linux server.

While this may seem a problem in Windows heavy environments, is not since you can use LDAP- Light Weight Directory Access Protocol. This is out of the scope of this course but LDAP allows you a way of authenticating users across different platforms.