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Quick HOWTO : Ch30 : Configuring NIS

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介绍

网络信息服务 (NIS) 让你能够创建在网络上所有系统间共享的用户账户。该账户仅能在NIS服务器上创建。NIS 客户机从NIS服务器上下载必要的用户名和密码数据来对每个登录的用户进行确认。

NIS的优点在于用户只需要改变NIS 服务器上的密码,而不是网络上的每个系统。这使得NIS在计算机培训实验室、分散的软件开发工程或者任何其他由团组共享许多不同的电脑的情况下变得普遍。 缺点是NIS不能在每次登录时都将发送的用户名和密码信息进行加密同时所有用户都能接触到储存在NIS上的加密密码。NIS安全性的详尽分析不在本书讨论范围之内,但是建议你限制在高安全性网络中的运用尤其在涉及到非NIS网络的网络中应该严格限制。

轻量级目录访问协议 (LDAP)提供与NIS相似的特性但是有支持无附加软件加密的优点同时支持客户端进入多种网络而不需设置从服务器。 由于这种原因LDAP在类似应用中已经逐渐普及, LDAP在第31章将会详细讨论。"基于LDAP和RADIUS的集中登录".

Scenario

To understand the benefits of NFS, consider an example. A school wants to set up a small computer lab for its students.

  • The main Linux server, bigboy, has a large amount of disk space and will be used as both the NIS server and NFS-based file server for the Linux PCs in the lab.
  • Users logging into the PCs will be assigned home directories on bigboy and not on the PCs themselves.
  • Each user's home directory will be automatically mounted with each user login on the PCs using NFS.
  • The lab instructor will practice with a Linux PC named smallfry before implementing NIS on all the remaining PCs.
  • The suite of NIS RPMs have been installed on the server and client: ypserve and yp-tools are on the server, and ypbind and yp-tools are on the client.

Downloading and installing RPMs isn't hard, as discussed in Chapter 6, "Installing Linux Software". When searching for the RPMs, remember that the filename usually starts with the software package name followed by a version number, as in yp-tools-2.8-3.i386.rpm.

The lab instructor did some research and created an implementation plan:

  1. Configure bigboy as an NFS server to make its /home directory available to the Linux workstations.
  2. Configure smallfry as an NFS client that can access bigboy's /home directory.
  3. Configure bigboy as an NIS server.
  4. Create a user account (nisuser) on bigboy that doesn't exist on smallfry. Convert the account to a NIS user account.
  5. Configure smallfry as an NIS client.
  6. Test a remote login from bigboy to smallfry using the username and password of the account nisuser.

You have the scenario and the plan, it's time to get to work.

Configuring The NFS Server

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.

[[email protected] tmp]# exportfs -a
[[email protected] tmp]#

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

[[email protected] tmp]# chkconfig nfslock on
[[email protected] tmp]# chkconfig nfs on
[[email protected] tmp]# chkconfig portmap on
[[email protected] tmp]# service portmap start
Starting portmapper: [  OK  ]
[[email protected] tmp]# service nfslock start
Starting NFS statd: [  OK  ]
[[email protected] tmp]# service nfs start
Starting NFS services:  [  OK  ]
Starting NFS quotas: [  OK  ]
Starting NFS daemon: [  OK  ]
Starting NFS mountd: [  OK  ]
[[email protected] tmp]#

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

Configuring The NFS Client

You also need to configure the NFS clients to mount their /home directories on the NFS server.

These steps archive the /home directory. In a production environment in which the /home directory would be actively used, you'd have to force the users to log off, backup the data, restore it to the NFS server, and then follow the steps below. As this is a lab environment, these prerequisites aren't necessary.

1. Make sure the required netfs, nfslock, and portmap daemons are running and configured to start after the next reboot.

[[email protected] tmp]# chkconfig nfslock on
[[email protected] tmp]# chkconfig netfs on
[[email protected] tmp]# chkconfig portmap on
[[email protected] tmp]# service portmap start
Starting portmapper: [  OK  ]
[[email protected] tmp]# service netfs start
Mounting other filesystems:  [  OK  ]
[[email protected] tmp]# service nfslock start
Starting NFS statd: [  OK  ]
[[email protected] tmp]#

2. Keep a copy of the old /home directory, and create a new directory /home on which you'll mount the NFS server's directory.

[[email protected] tmp]# mv /home /home.save
[[email protected] tmp]# mkdir /home
[[email protected] tmp]# ll /
...
...
drwxr-xr-x    1 root   root     11 Nov 16 20:22 home
drwxr-xr-x    2 root   root   4096 Jan 24  2003 home.save
...
...
[[email protected] tmp]#

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

[[email protected] tmp]# mount 192.168.1.100:/home /home/
[[email protected] tmp]# ls /home
ftpinstall  nisuser  quotauser  smallfry  www
[[email protected] tmp]# umount /home
[[email protected] tmp]#

4. Start configuring autofs automounting. 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.

[[email protected] tmp]# chkconfig autofs on
[[email protected] tmp]# service autofs restart
Stopping automount:[  OK  ]
Starting automount:[  OK  ]
[[email protected] tmp]#

After doing this, you won't be able to see the contents of the /home directory on bigboy 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.

Note: This automounter feature doesn't appear to function correctly in my preliminary testing of Fedora Core 3. See Chapter 29, "Remote Disk Access with NFS", for details.

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. Don't worry, we'll review each one in detail.

Note: In the early days, NIS was called Yellow Pages. The developers had to change the name after a copyright infringement lawsuit, yet many of the key programs associated with NIS have kept their original names beginning with yp.

Install the NIS Server Packages

All the packages required for NIS clients are a standard part of most Fedora installations. The ypserv package for servers is not. Install the package according to the steps outlined in Chapter 6,"Installing Linux Software".

Edit Your /etc/sysconfig/network File

You need to add the NIS domain you wish to use in the /etc/sysconfig/network file. For the school, call the domain NIS-SCHOOL-NETWORK.

#/etc/sysconfig/network
NISDOMAIN="NIS-SCHOOL-NETWORK"

Edit Your /etc/yp.conf File

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 Key NIS Server Related Daemons

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

[[email protected] tmp]# service portmap start
Starting portmapper: [  OK  ]
[[email protected] tmp]# service yppasswdd start
Starting YP passwd service: [  OK  ]
[[email protected] tmp]# service ypserv start
Setting NIS domain name NIS-SCHOOL-NETWORK:  [  OK  ]
Starting YP server services: [  OK  ]
[[email protected] tmp]# 

[[email protected] tmp]# chkconfig portmap on
[[email protected] tmp]# chkconfig yppasswdd on
[[email protected] tmp]# chkconfig ypserv on

Table 30.1 lists a summary of the daemon's functions.

Table 30-1 Required NIS Server Daemons

Daemon Name Purpose
portmap The foundation RPC daemon upon which NIS runs.
yppasswdd Lets users change their passwords on the NIS server from NIS clients
ypserv Main NIS server daemon
ypbind Main NIS client daemon
ypxfrd Used to speed up the transfer of very large NIS maps

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

[[email protected] tmp]# rpcinfo -p localhost
   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
[[email protected] tmp]#

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.

Initialize Your NIS Domain

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 bigboy.

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

[[email protected] tmp]# /usr/lib/yp/ypinit -m
At this point, we have to construct a list of the hosts which will run NIS 
servers.  bigboy 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:  bigboy
        next host to add:
The current list of NIS servers looks like this:
 
bigboy
 
Is this correct?  [y/n: y]  y
We need a few minutes to build the databases...
Building /var/yp/NIS-SCHOOL-NETWORK/ypservers...
Running /var/yp/Makefile...
gmake[1]: Entering directory `/var/yp/NIS-SCHOOL-NETWORK'
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/NIS-SCHOOL-NETWORK'
 
bigboy has been set up as a NIS master server.
 
Now you can run ypinit -s bigboy on all slave server.
[[email protected] tmp]#

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/NIS-SCHOOL-NETWORK directory and restart portmap, yppasswd, and ypserv before you'll be able to do this again successfully.

Start The ypbind and ypxfrd Daemons

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

[[email protected] tmp]# service ypbind start
Binding to the NIS domain: [  OK  ]
Listening for an NIS domain server.
[[email protected] tmp]# service ypxfrd start
Starting YP map server: [  OK  ]
[[email protected] tmp]# chkconfig ypbind on
[[email protected] tmp]# chkconfig ypxfrd on

Make Sure The Daemons Are Running

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

[[email protected] tmp]# rpcinfo -p localhost
    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
[[email protected] tmp]#

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.

[[email protected] tmp]# useradd -g users nisuser
[[email protected] tmp]# passwd nisuser
Changing password for user nisuser.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
[[email protected] tmp]# cd /var/yp
[[email protected] yp]# make
gmake[1]: Entering directory `/var/yp/NIS-SCHOOL-NETWORK'
Updating passwd.byname...
Updating passwd.byuid...
Updating netid.byname...
gmake[1]: Leaving directory `/var/yp/NIS-SCHOOL-NETWORK'
[[email protected] yp]#

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.

[[email protected] yp]# ypmatch nisuser passwd
nisuser:$1$d6E2i79Q$wp3Eo0Qw9nFD/::504:100::/home/nisuser:/bin/bash
[[email protected] yp]

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.

[[email protected] yp]# getent passwd nisuser
nisuser:x:504:100::/home/nisuser:/bin/bash
[[email protected] yp]#

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.

Run authconfig

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.

[[email protected] 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 NIS-SCHOOL-NETWORK server 192.168.1.100

#/etc/sysconfig/network
NISDOMAIN=NIS-SCHOOL-NETWORK

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: You can also locate a sample NIS nsswitch.conf file in the /usr/share/doc/yp-tools* directory.

Start The NIS Client Related Daemons

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.

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

[[email protected] tmp]# chkconfig ypbind on
[[email protected] tmp]# chkconfig portmap on

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

Verify Name Resolution

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 (smallfry)
#
192.168.1.100    bigboy

 
#
# File: /etc/hosts (bigboy)
#
192.168.1.102    smallfry

Test NIS Access To The NIS Server

You can run the ypcat, ypmatch, and getent commands to make sure communication to the server is correct.

[[email protected] 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
smallfry:$1$qHni9dnR$iKDs7gfyt..BS9Lry3DAq.:501:100::/:/bin/bash
[[email protected] tmp]#

[[email protected] tmp]# ypmatch nisuser passwd
nisuser:$1$d6E2i79Q$wp3Eo0Qw9nFD/:504:100::/home/nisuser:/bin/bash
[[email protected] tmp]#

[[email protected] tmp]# getent passwd nisuser
nisuser:$1$d6E2i79Q$wp3Eo0Qw9nFD/:504:100::/home/nisuser:/bin/bash
[[email protected] 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.

Test Logins via The NIS Server

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.

Logging In Via Telnet

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

[[email protected] tmp]# 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
[[email protected] nisuser]$

Logging In Via SSH

Try logging into the NIS client via SSH.

[[email protected] tmp]# ssh -l nisuser 192.168.1.102
[email protected]'s password:
[[email protected] 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.

[[email protected] root]# service sshd restart
Stopping sshd:[  OK  ]
Starting sshd:[  OK  ]
[[email protected] root]#

NIS Slave Servers

NIS relies a lot on broadcast traffic to operate, which prevents you from having an NIS server on a different network from the clients. You can avoid this problem on your local subnet by using slave servers that are configured to automatically synchronize their NIS data with that of the single master server.

You can also consider placing multiple NIS servers on a single subnet for the sake of redundancy. To do this, configure the NIS clients to have multiple NIS servers for the domain in the /etc/yp.conf file.

Configuring NIS Slave Servers

In this scenario, you need to add an NIS slave server named nisslave (IP address 192.168.1.254) to the NIS-SCHOOL-NETWORK NIS domain. You also must configure the NIS master server, bigboy, to push its database map information to the slave whenever there is an update. Here are the steps you need.


1. As you're referring to our servers by their hostnames, you'll have to make sure the names resolve correctly to IP addresses. This can be done either in DNS, when the hosts reside in the same domain, or more simply by editing the /etc/hosts files on both servers as seen in Table 30.2.

Table 30-2 NIS Master / Slave /etc/hosts Files

Master (Bigboy) Slave (Nisslave)
#
# File: /etc/hosts (Bigboy)
#
192.168.1.254    nisslave
#
# File: /etc/hosts (Nisslave)
#
192.168.1.100    bigboy


2. Configure the NIS slave as a NIS client of itself in the /etc/yp.conf file, and configure the NIS domain in the /etc/sysconfig/network file as seen in Table 30.3.

Table 30-3 NIS Master / Slave /etc/yp.conf Files

/etc/yp.conf /etc/sysconfig/network
#
# File: /etc/yp.conf (Bigboy)
#
ypserver 127.0.0.1
#
# File: /etc/sysconfig/network
#
NISDOMAIN="NIS-SCHOOL-NETWORK"


3. On the slave server, run ypbind so the slave can query the master server.

[[email protected] tmp]# service portmap start
Starting portmapper: [  OK  ]
[[email protected] tmp]# service ypbind start
Binding to the NIS domain:
Listening for an NIS domain server.
[[email protected] tmp]#
 
[[email protected] tmp]# chkconfig portmap on
[[email protected] tmp]# chkconfig ypbind on

4. Optimize database map transfers by the NIS map transfer daemon, which should the started on both the master and slave.

[[email protected] tmp]# service ypxfrd start
Starting YP map server: [  OK  ]
[[email protected] tmp]#
[[email protected] tmp]# chkconfig ypxfrd on
 
[[email protected] tmp]# service ypxfrd start
Starting YP map server: [  OK  ]
[[email protected] tmp]#
[[email protected] tmp]# chkconfig ypxfrd on

5. Do a simple database query of the master from the slave using the ypwhich command with the -m (master) switch. You should get a listing of all the tables.

[[email protected] tmp]# ypwhich -m
mail.aliases bigboy
group.bygid bigboy
passwd.byuid bigboy
rpc.bynumber bigboy
...
...
[[email protected] tmp]#

6. Do an initial database download to the slave from the master with the ypinit command using the -s switch for a slave-type operation and specifying server bigboy as the master from which the data is to be obtained. You should see "Trying ypxfrd - success" messages. If the messages say "Trying ypxfrd - not running," then start ypxfrd on both servers.

[[email protected] tmp]# /usr/lib/yp/ypinit -s bigboy
We will need a few minutes to copy the data from bigboy.
Transferring services.byservicename...
Trying ypxfrd ... success
 
Transferring group.byname...
Trying ypxfrd ... success
...
...
 
nisslave's NIS data base has been set up.
If there were warnings, please figure out what went wrong, and fix it.
 
At this point, make sure that /etc/passwd and /etc/group have
been edited so that when the NIS is activated, the data bases you
have just created will be used, instead of the /etc ASCII files.
[[email protected] tmp]#

If your database is corrupt or your /etc/hosts files are incorrect, you'll get map enumeration errors as shown. Use the make command again to rebuild your database on the master when necessary.

[[email protected] tmp]# /usr/lib/yp/ypinit -s bigboy
Can't enumerate maps from bigboy. Please check that it is running.
[[email protected] tmp]#

7. Now that the data has been successfully downloaded, it's time to make the slave server serve NIS clients with ypserv.

[[email protected] tmp]# service ypserv start
Starting YP server services:
[[email protected] tmp]#
[[email protected] tmp]# chkconfig ypxfrd on
 

8. Log on to the master server. Add the slave server to the master server's database map by editing the /var/yp/ypservers file on the master.

[[email protected] yp]# cd /tmp
[[email protected] tmp]# cd /var/yp/
[[email protected] yp]# vi ypservers

Add nisslave to the file.

#
# File: /var/yp/ypservers
#
bigboy
nisslave
 

9. The make file in the /var/yp directory defines how the NIS server will build the database map and how the master will relate to the NIS slave. Make a copy of the master's make file for safekeeping.

[[email protected] yp]# cp Makefile Makefile.old
 

10. Edit the make file to allow the master to push maps to the slave.

#
# File: /var/vp/Makefile
#
 
#
# Allow the master to do database pushes to the slave
#
NOPUSH=false
 

11. Use the make command to rebuild the database. The make command automatically pushes database updates to the servers listed in the /var/yp/servers file.

[[email protected] yp]# make
gmake[1]: Entering directory `/var/yp/NIS-SCHOOL-NETWORK'
Updating ypservers...
YPPUSH: gethostbyname(): Success
YPPUSH: using not FQDN name
gmake[1]: Leaving directory `/var/yp/NIS-SCHOOL-NETWORK'
gmake[1]: Entering directory `/var/yp/NIS-SCHOOL-NETWORK'
Updating netid.byname...
YPPUSH: gethostbyname(): Success
YPPUSH: using not FQDN name
gmake[1]: Leaving directory `/var/yp/NIS-SCHOOL-NETWORK'
[[email protected] yp]#

12. On the slave server, create a cron file in the /etc/crond.d directory, in this case named nis_sync, that will run periodic database downloads from the master server. This helps to ensure that the slave servers have current databases even if they miss updates from the master in the event the school goes offline for maintenance. Restart the cron daemon so that the configuration in this file becomes active.

[[email protected] yp]# vi /etc/cron.d/nis_sync
 
#
# File: /etc/cron.d/nis_sync
#
20 *    * * *    /usr/lib/yp/ypxfr_1perhour
40 6    * * *    /usr/lib/yp/ypxfr_1perday
55 6,18 * * *    /usr/lib/yp/ypxfr_2perday
 
[[email protected] yp]# service crond restart

That's a lot of work but it's still not over. There is one final configuration step that needs to be done on the NIS clients before you're finished.

Configuring NIS Clients With Slaves

Edit the /etc/yp.conf file on all the clients to include nisslave, and restart ypbind.

#
# File: /etc/yp.conf (Smallfry)
#
domain NIS-SCHOOL-NETWORK server 192.168.1.100
domain NIS-SCHOOL-NETWORK server 192.168.1.254

 
[[email protected] tmp]# service ypbind restart
Shutting down NIS services: [  OK  ]
Binding to the NIS domain: [  OK  ]
Listening for an NIS domain server..
[[email protected] tmp]#

Changing Your NIS Passwords

You should also test to make sure your users can change their NIS passwords from the NIS clients with the yppasswd command. The process is different whether there is only a single NIS master or a master-slave server relationship.

When There Is Only An NIS Master

When there is only a single NIS server, password changes can be made only on the NIS server using the yppasswd command.

Users Changing Their Own Passwords

Users can change their passwords by logging into the NIS server and issuing the yppasswd command.

[[email protected] nisuser]$ yppasswd
Changing NIS account information for nisuser on bigboy.my-site.com.
Please enter old password:
Changing NIS password for nisuser on bigboy.my-site.com.
Please enter new password:
Please retype new password:
 
The NIS password has been changed on bigboy.my-site.com.
 
[[email protected] nisuser]$

User "Root" Changing Passwords

The root user can change other users' passwords issuing the yppasswd command with the -p switch that specifies the username that needs the change.

[[email protected] tmp]# yppasswd -p nisuser
Changing NIS account information for nisuser on bigboy.my-site.com.
Please enter root password:
Changing NIS password for nisuser on bigboy.my-site.com.
Please enter new password:
Please retype new password:
 
The NIS password has been changed on bigboy.my-site.com.

[[email protected] tmp]#

When There Is A NIS Master / Slave Pair

With an NIS master and slave pair configuration, passwords can be changed on the NIS clients or the NIS slave, but not on the NIS master.

Possible Password Errors

There are a number of unexpected errors you may find when changing passwords - errors that have nothing to do with bad typing.

Segmentation Faults

Running the yppasswd command on the wrong client or server depending on your NIS master and slave configuration can cause segmentation fault errors. (Make sure you follow the chapter's guidelines for password changes!) Here are some sample password change failures on an NIS client with only one NIS master server.

[[email protected] nisuser]$ yppasswd
Segmentation fault
[[email protected] nisuser]$
 
[[email protected] root]# yppasswd -p nisuser
Segmentation fault
[[email protected] 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.

[[email protected] etc]# yppasswd -p nisuser
yppasswd: yppasswdd not running on NIS master host ("bigboy").
[[email protected] 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.

Considerations For A Non NFS Environment

In many cases NFS, isn't used to create a centralized home directory for users and, therefore, you'll have to create it on each NIS client and not on the server.

This example creates the home directory for the NIS client, smallfry. After doing this, you have to copy a BASH login profile file into it and modify the ownership of the directory and all the files to user nisuser.

Logins should proceed normally once this has been done and all the other steps have been followed.

[[email protected] tmp]# mkdir /home/nisuser
[[email protected] tmp]# chmod 700 /home/nisuser/
[[email protected] tmp]# ll /home
total 2
drwx------    2 nisuser users        1024 Aug  4 08:05 nisuser
[[email protected] tmp]#
[[email protected] tmp]# cp /etc/skel/.* /home/nisuser/
cp: omitting directory `/etc/skel/.'
cp: omitting directory `/etc/skel/..'
cp: omitting directory `/etc/skel/.kde'
[[email protected] tmp]# chown -R nisuser:users /home/nisuser
[[email protected] tmp]#

NIS Troubleshooting

Troubleshooting is always required as any part of your daily routine, NIS is no exception. Here are some simple steps to follow to get it working again.

1. The rpcinfo provides a list of TCP ports that your NIS client or server is using. Make sure you can TELNET to these ports from the client to the server and vice versa. If this fails, make sure all the correct NIS daemons are running and that there are no firewalls blocking traffic on the network or on the servers themselves. These ports change from time to time, so memorizing them won't help much.

The example tests from the client to the server.

[[email protected] tmp]# rpcinfo -p
    program vers proto   port
     100000    2   tcp    111  portmapper
     100000    2   udp    111  portmapper
     100024    1   udp  32768  status
     100024    1   tcp  32768  status
     391002    2   tcp  32769  sgi_fam
     100009    1   udp   1018  yppasswdd
     100004    2   udp    611  ypserv
     100004    1   udp    611  ypserv
     100004    2   tcp    614  ypserv
     100004    1   tcp    614  ypserv
     100007    2   udp    855  ypbind
     100007    1   udp    855  ypbind
     100007    2   tcp    858  ypbind
     100007    1   tcp    858  ypbind
  600100069    1   udp    874  fypxfrd
  600100069    1   tcp    876  fypxfrd
[[email protected] tmp]#
 
 
[[email protected] tmp]# telnet 192.168.1.100 858
Trying 10.41.32.71...
Connected to 10.41.32.71.
Escape character is '^]'.
^]
telnet> quit
Connection closed.
[[email protected] tmp]#

2. Always use the ypmatch, getent, and ypwhich commands to check your NIS connectivity. If there is any failure, check your steps over again and you should be able to find the source of your problem.

3. Do not fail to create a user's home directory, set its permissions, and copy the /etc/skel files correctly. If you forget, which is a common error, your users may have incorrect login prompts and no ability to create files in their home directories.

It can never be overemphasized that one of the best places to start troubleshooting is by looking in your error log files in the /var/log directory. You'll save a lot of time and effort if you always refer to them whenever the problem doesn't appear to be obvious.

Conclusion

NIS is a very useful tool for centralized login management, but it has two shortcomings: NIS clients are typically limited to Unix or Linux operating systems, and the password information passes over the network unencrypted.

Newer authentication schemes overcome these issues. For example, LDAP, which is discussed in Chapter 31, "Centralized Logins Using LDAP and RADIUS", provides both encryption and the ability to be used on varied types of equipment. Unfortunately older operating systems don't support it, making NIS the preferred option in some cases.

As always, explore your options when deciding on a centralized login scheme. A wrong decision could haunt you for a long time.