NIS Minitutorial

Adapted from Wikipedia

The Network Information Service, or NIS (originally called Yellow Pages or YP), is a client–server directory service protocol for distributing system configuration data such as user and host names between computers on a computer network. Sun Microsystems developed the NIS; the technology is licensed to virtually all other Unix vendors.

Because British Telecom PLC owned the name "Yellow Pages" as a registered trademark in the United Kingdom for its paper-based, commercial telephone directory, Sun changed the name of its system to NIS, though all the commands and functions still start with "yp".

A NIS/YP system maintains and distributes a central directory of user and group information, hostnames, e-mail aliases and other text-based tables of information in a computer network. For example, in a common UNIX environment, the list of users for identification is placed in /etc/passwd, and secret authentication hashes in /etc/shadow. NIS adds another "global" user list which is used for identifying users on any client of the NIS domain.

Administrators have the ability to configure NIS to serve password data to outside processes to authenticate users using various versions of the Unix crypt(3) hash algorithms. However, in such cases, any NIS(0307) client can retrieve the entire password database for offline inspection. Kerberos was designed to handle authentication in a more secure manner.

NIS use client server architecture with one master server (and possibly one or several secondary slave servers, necessary for reliability) and many clients. NIS uses several daemons on the server and on all clients to enable the NIS system.

On the NIS master and any NIS slaves, several NIS server daemons should be run.

• On the server the most important of them is ypserv. The ypserv daemon waits for incoming client requests for service, then handles them.
• On the clients, the daemon  ypbind is the most important. It is responsible for connecting with the NIS master when the machine boots and determining any resolution steps necessary to handle logins and other network configuration information handled by NIS. The process of having ypbind connect to the NIS master and establish procedures is called a binding, because the client is bound to the master for requests.

The binding process begins with ypbind sending out a broadcast message for any NIS masters on the network to respond with their IP address and the port number to send requests on. If more than one NIS master responds to the request, only the first received reply is used. If for some reason ypbind finds it isn't getting replies from the NIS master, it assumes that the master has crashed and retransmits a request for a master.

The main daemons involved in the running of an NIS domain are:

• The ypserv daemon
  • Runs on master and slave servers
  • Answers ypbind requests from clients
  • Responds to client information requests
     
• The ypbind daemon runs on all NIS client systems
  • Makes initial client-to-server binding requests
  • Stores binding information in the /var/yp/binding/domain directory
  • Rebinds to another server if the connection is lost with the initial server
  • Requests NIS map information at the library-call level
     
• The yppasswdd daemon
  • Runs on master and slave servers
  • Allows users to change their passwords
  • Updates the passwd and shadow files on the master server
  • Updates the NIS password map
  • Provides or “pushes” the NIS password map to all slave servers
     
• The ypxfrd daemon
  • Runs on the NIS master server only
  • Responds to requests, generated in the slave servers by using the ypxfr command to pull the maps from the master
  • Transfers NIS maps at a high speed

You can find out which NIS master any client machine is bound to with the command ypwhich

Configuring The NFS Server

Adapted from Quick HOWTO Ch30 Configuring NIS - Linux Home Networking

Here are the steps to configure the NFS server in this scenario:

1. Edit the /etc/exports file to allow NFS mounts of the /home directory with read/write access.

/home                   *(rw,sync)

2. Let NFS read the /etc/exports file for the new entry, and make /home available to the network with the exportfs command.

# exportfs -a#

3. Make sure the required nfs, nfslock, and portmap daemons are both running and configured to start after the next reboot.

# chkconfig nfslock on
# chkconfig nfs on
# chkconfig portmap on
# service portmap start
# service nfslock start
# service nfs start

After configuring the NFS server, we have to configure its clients, This will be covered next.

3. Make sure you can mount master's /home directory on the new /home directory you just created. Unmount it once everything looks correct.

[root@node01 tmp]# mount 192.168.1.100:/home /home/
[root@node01 tmp]# ls /home
ftpinstall  nisuser  quotauser  node01  www
[root@node01 tmp]# umount /home
[root@node01 tmp]#

Configuring autofs automounting  on all nodes

Edit your /etc/auto.master file to refer to file /etc/auto.home for mounting information whenever the /home directory is accessed. After five minutes, autofs unmounts the directory.

#/etc/auto.master
/home      /etc/auto.home --timeout 600

5. Edit file /etc/auto.home to do the NFS mount whenever the /home directory is accessed. If the line is too long to view on your screen, you can add a \ character at the end to continue on the next line.

#/etc/auto.home
*   -fstype=nfs,soft,intr,rsize=8192,wsize=8192,nosuid,tcp \
   192.168.1.100:/home/&

6. Start autofs and make sure it starts after the next reboot with the chkconfig command.

[root@node01 tmp]# chkconfig autofs on
[root@node01 tmp]# service autofs restart
Stopping automount:[  OK  ]
Starting automount:[  OK  ]
[root@node01 tmp]#

After doing this, you won't be able to see the contents of the /home directory on master as user root. This is because by default NFS activates the root squash feature, which disables this user from having privileged access to directories on remote NFS servers. You'll be able to test this later after NIS is configured.

All newly added Linux users will now be assigned a home directory under the new remote /home directory. This scheme will make the users feel their home directories are local, when in reality they are automatically mounted and accessed over your network.

Configuring The NIS Server

NFS only covers file sharing over the network. You now have to configure NIS login authentication for the lab students before the job is done. The configuration of the NIS server is not difficult, but requires many steps that you may overlook. There also multiple daemons that all needs to be started in particular order

All the packages required for NIS clients are a standard part of most RHEL/CentOS installations.

You need to add the NIS domain you wish to use in the /etc/sysconfig/network file. For the school, call the domain mycompany.com.  Often people use DNS domain as a name.

#/etc/sysconfig/network
NISDOMAIN="mycompany.com"

NIS servers also have to be NIS clients themselves, so you'll have to edit the NIS client configuration file /etc/yp.conf to list the domain's NIS server as being the server itself or localhost.

# /etc/yp.conf - ypbind configuration file
ypserver 127.0.0.1

Start the necessary NIS daemons in the /etc/init.d directory and use the chkconfig command to ensure they start after the next reboot.

# service portmap start
# service yppasswdd start
# service ypserv start
# chkconfig portmap on
# chkconfig yppasswdd on
# chkconfig ypserv on

Make sure they are all running before continuing to the next step. You can use the rpcinfo command to do this.

# rpcinfo -p localhost | egrep "port|yp"
   program vers proto   port
    100000    2   tcp    111  portmapper
    100000    2   udp    111  portmapper
    100009    1   udp    681  yppasswdd
    100004    2   udp    698  ypserv
    100004    1   udp    698  ypserv
    100004    2   tcp    701  ypserv
    100004    1   tcp    701  ypserv
#

The ypbind and ypxfrd daemons won't start properly until after you initialize the NIS domain. You'll start these daemons after initialization is completed.

Now that you have decided on the name of the NIS domain, you'll have to use the ypinit command to create the associated authentication files for the domain. You will be prompted for the name of the NIS server, which in this case is master.

With this procedure, all nonprivileged accounts are automatically accessible via NIS.

# /usr/lib/yp/ypinit -m
At this point, we have to construct a list of the hosts which will run NIS 
servers.  master is in the list of NIS server hosts.  Please continue to add
the names for the other hosts, one per line.  When you are done with the
list, type a <control D>.
        next host to add:  master
        next host to add:
The current list of NIS servers looks like this:
 
master
 
Is this correct?  [y/n: y]  y
We need a few minutes to build the databases...
Building /var/yp/NISDOMAIN/ypservers...
Running /var/yp/Makefile...
gmake[1]: Entering directory `/var/yp/NISDOMAIN'
Updating passwd.byname...
Updating passwd.byuid...
Updating group.byname...
Updating group.bygid...
Updating hosts.byname...
Updating hosts.byaddr...
Updating rpc.byname...
Updating rpc.bynumber...
Updating services.byname...
Updating services.byservicename...
Updating netid.byname...
Updating protocols.bynumber...
Updating protocols.byname...
Updating mail.aliases...
gmake[1]: Leaving directory `/var/yp/NISDOMAIN'
 
master has been set up as a NIS master server.
 
Now you can run ypinit -s master on all slave server.
#

Note: Make sure portmap is running before trying this step or you'll get errors, such as:

failed to send 'clear' to local ypserv: RPC: Port mapper failureUpdating group.bygid...

You will have to delete the /var/yp/NISDOMAIN directory and restart portmap, yppasswd, and ypserv before you'll be able to do this again successfully.

You can now start the ypbind and the ypxfrd daemons because the NIS domain files have been created.

# service ypbind start
# service ypxfrd start
# chkconfig ypbind on
# chkconfig ypxfrd on

All the NIS daemons use RPC port mapping and, therefore, are listed using the rpcinfo command when they are running correctly.

# rpcinfo -p localhost | egrep "port|yp|nfs"
    program vers proto   port
     100000    2   tcp    111  portmapper
     100000    2   udp    111  portmapper
     100003    2   udp   2049  nfs
     100003    3   udp   2049  nfs
     100021    1   udp   1024  nlockmgr
     100021    3   udp   1024  nlockmgr
     100021    4   udp   1024  nlockmgr
     100004    2   udp    784  ypserv
     100004    1   udp    784  ypserv
     100004    2   tcp    787  ypserv
     100004    1   tcp    787  ypserv
     100009    1   udp    798  yppasswdd
  600100069    1   udp    850  fypxfrd
  600100069    1   tcp    852  fypxfrd
     100007    2   udp    924  ypbind
     100007    1   udp    924  ypbind
     100007    2   tcp    927  ypbind
     100007    1   tcp    927  ypbind
#

Adding New NIS Users

New NIS users can be created by logging into the NIS server and creating the new user account. In this case, you'll create a user account called nisuser and give it a new password.

Once this is complete, you then have to update the NIS domain's authentication files by executing the make command in the /var/yp directory.

This procedure makes all NIS-enabled, nonprivileged accounts become automatically accessible via NIS, not just newly created ones. It also exports all the user's characteristics stored in the /etc/passwd and /etc/group files, such as the login shell, the user's group, and home directory.

# useradd -g users nisuser
# passwd nisuser
Changing password for user nisuser.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
# cd /var/yp
[root@ypmaster]# make
gmake[1]: Entering directory `/var/yp/NISDOMAIN'
Updating passwd.byname...
Updating passwd.byuid...
Updating netid.byname...
gmake[1]: Leaving directory `/var/yp/NISDOMAIN'
[root@ypmaster]#

You can check to see if the user's authentication information has been updated by using the ypmatch command, which should return the user's encrypted password string.

[root@ypmaster]# ypmatch nisuser passwd
nisuser:$1$d6E2i79Q$wp3Eo0Qw9nFD/::504:100::/home/nisuser:/bin/bash
[root@ypmaster]

You can also use the getent command, which has similar syntax. Unlike ypmatch, getent doesn't provide an encrypted password when run on an NIS server, it just provides the user's entry in the /etc/passwd file. On a NIS client, the results are identical with both showing the encrypted password.

[root@ypmaster]# getent passwd nisuser
nisuser:x:504:100::/home/nisuser:/bin/bash
[root@ypmaster]#

NOTE:

To set password you need to use yppasswd utility not passwd
 

See Changing Passwords

From root use

yppasswd -p user_name

Configuring The NIS Client

Now that the NIS server is configured, it's time to configure the NIS clients. There are a number of related configuration files that you need to edit to get it to work. Take a look at the procedure.

The authconfig or the authconfig-tui program automatically configures your NIS files after prompting you for the IP address and domain of the NIS server.

[root@node01 tmp]# authconfig-tui

Once finished, it should create an /etc/yp.conf file that defines, amongst other things, the IP address of the NIS server for a particular domain. It also edits the /etc/sysconfig/network file to define the NIS domain to which the NIS client belongs.

# /etc/yp.conf - ypbind configuration file
domain mycompany.com server 192.168.1.100

#/etc/sysconfig/network
NISDOMAIN=mycompany.com

In addition, the authconfig program updates the /etc/nsswitch.conf file that lists the order in which certain data sources should be searched for name lookups, such as those in DNS, LDAP, and NIS. Here you can see where NIS entries were added for the important login files.

#/etc/nsswitch.conf
passwd:     files nis
shadow:     files nis
group:      files nis

Note: There is a sample NIS nsswitch.conf file in the /usr/share/doc/yp-tools* directory.

Start the ypbind NIS client, and portmap daemons in the /etc/init.d directory and use the chkconfig command to ensure they start after the next reboot. Remember to use the rpcinfo command to ensure they are running correctly.

[root@node01 tmp]# service portmap start
Starting portmapper: [  OK  ]
[root@node01 tmp]# service ypbind start
Binding to the NIS domain:
Listening for an NIS domain server.
[root@node01 tmp]#

[root@node01 tmp]# chkconfig ypbind on
[root@node01 tmp]# chkconfig portmap on

Note: Remember to use the rpcinfo -p localhost command to make sure they all started correctly.

As the configuration examples refer to the NIS client and server by their hostnames, you'll have to make sure the names resolve correctly to IP addresses. This can be configured either in DNS, when the hosts reside in the same domain, or more simply by editing the /etc/hosts file on both Linux boxes.

#
# File: /etc/hosts (node01)
#
192.168.1.100    master

 
#
# File: /etc/hosts (master)
#
192.168.1.102    node01

You can run the ypcat, ypmatch, and getent commands on the nodes served by the NIS master to make sure communication to the server is correct.

[root@node01 tmp]# ypcat passwd
nisuser:$1$Cs2GMe6r$1hohkyG7ALrDLjH1:505:100::/home/nisuser:/bin/bash
quotauser:!!:503:100::/home/quotauser:/bin/bash
ftpinstall:$1$8WjAVtes$SnRh9S1w07sYkFNJwpRKa.:502:100::/:/bin/bash
www:$1$DDCi/OPI$hwiTQ.L0XqYJUk09Bw.pJ/:504:100::/home/www:/bin/bash
node01:$1$qHni9dnR$iKDs7gfyt..BS9Lry3DAq.:501:100::/:/bin/bash
[root@node01 tmp]#

[root@node01 tmp]# ypmatch nisuser passwd
nisuser:$1$d6E2i79Q$wp3Eo0Qw9nFD/:504:100::/home/nisuser:/bin/bash
[root@node01 tmp]#

[root@node01 tmp]# getent passwd nisuser
nisuser:$1$d6E2i79Q$wp3Eo0Qw9nFD/:504:100::/home/nisuser:/bin/bash
[root@node01 tmp]#

Possible sources of error would include:

• Incorrect authconfig setup resulting in errors in the /etc/yp.conf, /etc/sysconfig/network and /etc/nsswitch.conf files
• Failure to run the ypinit command on the NIS server
• NIS not being started on the NIS server or client.
• Poor routing between the server and client, or the existence of a firewall that's blocking traffic

Try to eliminate these areas as sources of error and refer to the syslog /var/log/messages file on the client and server for entries that may provide additional clues.

Once your basic NIS functionality testing is complete, try to test a remote login. Failures in this area could be due to firewalls blocking TELNET or SSH access and the TELNET and SSH server process not being started on the clients.

Try logging into the NIS client via telnet if it is enabled

# telnet 192.168.1.201
Trying 192.168.1.201...
Connected to 192.168.1.201.
Escape character is '^]'.
Red Hat Linux release 9 (Shrike)
Kernel 2.4.20-6 on an i686
login: nisuser
Password:
Last login: Sun Nov 16 22:03:51 from 192-168-1-100.simiya.com
[nisuser@node01 nisuser]$

Try logging into the NIS client via SSH.

# ssh -l nisuser 192.168.1.102
[email protected]'s password:
[nisuser@node01 nisuser]$

In some versions of Linux, the NIS client's SSH daemon doesn't re-read the /etc/nsswitch.conf file you just modified until SSH is restarted. SSH logins, therefore, won't query the NIS server until this is done. Restart SSH on the NIS client.

[root@node01 root]# service sshd restart
Stopping sshd:[  OK  ]
Starting sshd:[  OK  ]
[root@node01 root]#

Daemon Errors

The yppasswdd daemon must be running on both the client and server for password changes to work correctly. When they aren't running, you'll get errors.

[root@node01 etc]# yppasswd -p nisuser
yppasswd: yppasswdd not running on NIS master host ("master").
[root@node01 etc]#

You'll also get a similar error if you attempt to change an NIS password on an NIS master server in a master and slave configuration.

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Last modified: March, 12, 2019