Setting Up Red Hat Linux as an NIS Client

Defining an NIS domain name

You can set your Red Hat Linux computer's NIS domain name using the domainname command. For example, if your NIS domain name were trident, you could set it by typing the following as the root user from the shell:

# domainname trident

To verify that your NIS domain name is set, simply type domainname and you will see the name. Unfortunately, you're not done yet. Running domainname doesn't set the NIS domain name permanently. As soon as you reboot the computer, it is gone. (You can verify this by typing domainname again after a reboot.)

To make the NIS domain name permanent, you need to have the domainname command run automatically each time your system boots. There are many ways to do this. What I did was add the command line (domainname trident) to a run-level script that runs before the ypbind daemon is started. I edited the /etc/init.d/network file and added the following lines just after the first set of comment lines (about line number 9).

# Set the NIS domain name.
domainname trident

This caused my NIS domain name to be set each time my Red Hat Linux system booted. When you add this entry, make sure you spell the NIS domain name properly (including upper- and lowercase letters). If you get it slightly wrong, you will see ypbind failure messages when you boot.

Setting up the /etc/yp.conf file

The ypbind daemon needs information about your NIS domain and NIS servers for it to work. That information is set up in your /etc/yp.conf file. The first entries define your NIS domain name and NIS servers. For example, if you had an NIS domain called trident and a master server called maple, you would have the following entry in your /etc/yp.conf file:

domain trident server maple

If you had other slave NIS servers named oak and pine, for example, you could also have the following entries:

domain trident server oak
domain trident server pine

You can also set your computer to broadcast to the local network for your NIS server. If your domain were named trident, for example, you would use the domain/broadcast option as follows:

domain trident broadcast

If the address of your NIS server is contained in your /etc/hosts file, you can specify that ypbind look in that file to find the server's IP address. For example, if your NIS master server is named maple, you would add the following entry:

ypserver maple

When ypbind starts, all the information in this file is read. It is then used to contact the appropriate NIS server.

Configuring NIS client daemons

After your NIS client information is all set up, all you need to do to run NIS as a client is start the ypbind and ypwhich daemons. The ypbind daemon runs continuously as two processes: The master ypbind process handles requests for information from your NIS server, and the slave ypbind process checks the bindings from time to time. The ypwhich daemon finds your NIS master server.

Getting these daemons running is pretty easy. You can set up an existing run-level script called ypbind to start automatically at boot time. To do this, you can run the following command (as root user from a Terminal window):

# chkconfig ypbind on

To start the ypbind daemon immediately, type:

# /etc/init.d/ypbind start

Checking that NIS is working

To check that your NIS client is communicating with your NIS master server, follow the instructions in this section.

From the NIS client computer, type the following command to make sure that you are communicating with the NIS server:

# ypwhich
maple

The output shown above indicates that the NIS client is bound to the NIS server named maple. Next, check that the maps are being shared using the ypcat command. (To see what files are being shared from the NIS server, look in the server's /var/yp/nisdomain directory, where nisdomain is replaced by your NIS domain name.) Type one of the files shown in that directory along with the ypcat command. Here's an example:

# ypcat hosts
10.0.0.45      ash
10.0.0.46      pine
10.0.0.47      maple

If you are communicating with the NIS server and able to access map files, you can now define which maps the NIS client uses of those shared map files.

Using NIS maps

For the information being distributed by the NIS server to be used by the NIS client, you must configure the /etc/nsswitch.conf file to include nis in the search path for each file you want to use.

The following is a listing from the /etc/nsswitch.conf file showing valid values that can be in the search paths for accessing different configuration files.

# Legal entries are:
#
#   nisplus or nis+    Use NIS+ (NIS version 3)
#   nis or yp          Use NIS (NIS version 2), also called YP
#   dns                Use DNS (Domain Name Service)
#   files              Use the local files
#   db                 Use the local database (.db) files
#   compat             Use NIS on compat mode
#   hesiod             Use Hesiod for user lookups
#   [NOTFOUND=return]  Stop searching if not found so far
#

For our purposes, we want to add nis into the paths for the files we want to distribute from our NIS server to this NIS client. In most cases, only the local files are checked (files). The following are examples of how some entries appear:

passwd:     files
shadow:     files
group:      files
hosts:      files dns

For each of these entries, the original files are checked first (/etc/passwd, /etc/shadow, and so on). For host names, the DNS server is checked after the local hosts file. For our purposes, we can add nis to access the maps being shared from the NIS server. (Linux NIS servers only implement nis and not nisplus.) The lines would then appear as follows:

passwd:     files nis
shadow:     files nis
group:      files nis
hosts:      files nis dns

As soon as the /etc/nsswitch file is changed, the data from the NIS maps are accessible. No need to restart the NIS service. You can go through and change any of the files listed in the /etc/nsswitch file so that it is configured to let your system access the NIS maps being shared.