Quick HOWTO : Ch30 : Configuring NIS/zh
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介绍
网络用户信息服务(NIS)使你可以在你的网络中创建账户并在所有的系统共享。这个账户只能在NIS的服务器上创建。NIS客户端从NIS服务器下载需要的用户名和密码数据来验证用户的登录。
NIS的一个优点是用户只需要在NIS服务器上更改他们的密码，而不必在网络上的每个系统上去更改密码。这使得NIS在计算机实验室很流行，使用在一些分布式软件开发项目和组内成员必须共享很多不同的电脑的情况下。
缺点是NIS没有加密登录时发送到客户端的用户名和密码信息，所有用户有访问在存储NIS服务器加密的密码信息的权限。关于NIS安全细节的分析在这本书的前面部分，但是我建议你限制使用NIS在高安全的网络中，或者有权访问非NIS网络是有很高的限制的网络。
轻量级目录访问协议提供了和NIS相似的特性，但是不依靠额外的软件可以支持加密，并且支持客户端可以不依靠从机访问多重网络。因为这个原因，LDAP在这个应用上十分流行。LDAP更所细节的讨论在31章，"Centralized Logins Using LDAP and RADIUS".
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:
- Configure bigboy as an NFS server to make its /home directory available to the Linux workstations.
- Configure smallfry as an NFS client that can access bigboy's /home directory.
- Configure bigboy as an NIS server.
- Create a user account (nisuser) on bigboy that doesn't exist on smallfry. Convert the account to a NIS user account.
- Configure smallfry as an NIS client.
- 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.
[root@bigboy tmp]# exportfs -a [root@bigboy tmp]#
3. Make sure the required nfs, nfslock, and portmap daemons are both running and configured to start after the next reboot.
[root@bigboy tmp]# chkconfig nfslock on [root@bigboy tmp]# chkconfig nfs on [root@bigboy tmp]# chkconfig portmap on [root@bigboy tmp]# service portmap start Starting portmapper: [ OK ] [root@bigboy tmp]# service nfslock start Starting NFS statd: [ OK ] [root@bigboy tmp]# service nfs start Starting NFS services: [ OK ] Starting NFS quotas: [ OK ] Starting NFS daemon: [ OK ] Starting NFS mountd: [ OK ] [root@bigboy 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.
[root@smallfry tmp]# chkconfig nfslock on [root@smallfry tmp]# chkconfig netfs on [root@smallfry tmp]# chkconfig portmap on [root@smallfry tmp]# service portmap start Starting portmapper: [ OK ] [root@smallfry tmp]# service netfs start Mounting other filesystems: [ OK ] [root@smallfry tmp]# service nfslock start Starting NFS statd: [ OK ] [root@smallfry 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.
[root@smallfry tmp]# mv /home /home.save [root@smallfry tmp]# mkdir /home [root@smallfry 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 ... ... [root@smallfry 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.
[root@smallfry tmp]# mount 192.168.1.100:/home /home/ [root@smallfry tmp]# ls /home ftpinstall nisuser quotauser smallfry www [root@smallfry tmp]# umount /home [root@smallfry 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.
[root@smallfry tmp]# chkconfig autofs on [root@smallfry tmp]# service autofs restart Stopping automount:[ OK ] Starting automount:[ OK ] [root@smallfry 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.
[root@bigboy tmp]# service portmap start Starting portmapper: [ OK ] [root@bigboy tmp]# service yppasswdd start Starting YP passwd service: [ OK ] [root@bigboy tmp]# service ypserv start Setting NIS domain name NIS-SCHOOL-NETWORK: [ OK ] Starting YP server services: [ OK ] [root@bigboy tmp]# [root@bigboy tmp]# chkconfig portmap on [root@bigboy tmp]# chkconfig yppasswdd on [root@bigboy 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.
[root@bigboy 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
[root@bigboy 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.
[root@bigboy 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.
[root@bigboy 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.
[root@bigboy tmp]# service ypbind start Binding to the NIS domain: [ OK ] Listening for an NIS domain server. [root@bigboy tmp]# service ypxfrd start Starting YP map server: [ OK ] [root@bigboy tmp]# chkconfig ypbind on [root@bigboy 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.
[root@bigboy 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
[root@bigboy 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.
[root@bigboy tmp]# useradd -g users nisuser [root@bigboy tmp]# passwd nisuser Changing password for user nisuser. New password: Retype new password: passwd: all authentication tokens updated successfully. [root@bigboy tmp]# cd /var/yp [root@bigboy 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' [root@bigboy 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.
[root@bigboy yp]# ypmatch nisuser passwd nisuser:$1$d6E2i79Q$wp3Eo0Qw9nFD/::504:100::/home/nisuser:/bin/bash [root@bigboy 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.
[root@bigboy yp]# getent passwd nisuser nisuser:x:504:100::/home/nisuser:/bin/bash [root@bigboy 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.
[root@smallfry 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.
[root@smallfry tmp]# service portmap start Starting portmapper: [ OK ] [root@smallfry tmp]# service ypbind start Binding to the NIS domain: Listening for an NIS domain server. [root@smallfry tmp]# [root@smallfry tmp]# chkconfig ypbind on [root@smallfry 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.
[root@smallfry 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 [root@smallfry tmp]# [root@smallfry tmp]# ypmatch nisuser passwd nisuser:$1$d6E2i79Q$wp3Eo0Qw9nFD/:504:100::/home/nisuser:/bin/bash [root@smallfry tmp]# [root@smallfry tmp]# getent passwd nisuser nisuser:$1$d6E2i79Q$wp3Eo0Qw9nFD/:504:100::/home/nisuser:/bin/bash [root@smallfry tmp]#
Possible sources of error would include:
- Incorrect authconfig setup resulting in errors in the /etc/yp.conf, /etc/sysconfig/network and /etc/nsswitch.conf files
- Failure to run the ypinit command on the NIS server
- NIS not being started on the NIS server or client.
- Poor routing between the server and client, or the existence of a firewall that's blocking traffic
Try to eliminate these areas as sources of error and refer to the syslog /var/log/messages file on the client and server for entries that may provide additional clues.
Test Logins via The NIS Server
Once your basic NIS functionality testing is complete, try to test a remote login. Failures in this area could be due to firewalls blocking TELNET or SSH access and the TELNET and SSH server process not being started on the clients.
Logging In Via Telnet
Try logging into the NIS client via telnet if it is enabled
[root@bigboy tmp]# telnet 192.168.1.201 Trying 192.168.1.201... Connected to 192.168.1.201. Escape character is '^]'. Red Hat Linux release 9 (Shrike) Kernel 2.4.20-6 on an i686 login: nisuser Password: Last login: Sun Nov 16 22:03:51 from 192-168-1-100.simiya.com [nisuser@smallfry nisuser]$
Logging In Via SSH
Try logging into the NIS client via SSH.
[root@bigboy tmp]# ssh -l nisuser 192.168.1.102 [email protected]'s password: [nisuser@smallfry 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@smallfry root]# service sshd restart Stopping sshd:[ OK ] Starting sshd:[ OK ] [root@smallfry 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.
[root@nisslave tmp]# service portmap start Starting portmapper: [ OK ] [root@nisslave tmp]# service ypbind start Binding to the NIS domain: Listening for an NIS domain server. [root@nisslave tmp]# [root@nisslave tmp]# chkconfig portmap on [root@nisslave 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.
[root@nisslave tmp]# service ypxfrd start Starting YP map server: [ OK ] [root@nisslave tmp]# [root@nisslave tmp]# chkconfig ypxfrd on [root@bigboy tmp]# service ypxfrd start Starting YP map server: [ OK ] [root@bigboy tmp]# [root@bigboy 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.
[root@nisslave tmp]# ypwhich -m mail.aliases bigboy group.bygid bigboy passwd.byuid bigboy rpc.bynumber bigboy ... ... [root@nisslave 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.
[root@nisslave 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. [root@nisslave 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.
[root@nisslave tmp]# /usr/lib/yp/ypinit -s bigboy Can't enumerate maps from bigboy. Please check that it is running. [root@nisslave tmp]#
7. Now that the data has been successfully downloaded, it's time to make the slave server serve NIS clients with ypserv.
[root@nisslave tmp]# service ypserv start Starting YP server services: [root@nisslave tmp]# [root@nisslave 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.
[root@bigboy yp]# cd /tmp [root@bigboy tmp]# cd /var/yp/ [root@bigboy 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.
[root@bigboy 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.
[root@bigboy 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' [root@bigboy 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.
[root@nisslave 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 [root@nisslave 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 [root@smallfry tmp]# service ypbind restart Shutting down NIS services: [ OK ] Binding to the NIS domain: [ OK ] Listening for an NIS domain server.. [root@smallfry 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.
[nisuser@bigboy 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. [nisuser@bigboy 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.
[root@bigboy 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. [root@bigboy 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.
[nisuser@smallfry nisuser]$ yppasswd Segmentation fault [nisuser@smallfry nisuser]$ [root@smallfry root]# yppasswd -p nisuser Segmentation fault [root@smallfry 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@smallfry etc]# yppasswd -p nisuser
yppasswd: yppasswdd not running on NIS master host ("bigboy").
[root@smallfry 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.
[root@smallfry tmp]# mkdir /home/nisuser [root@smallfry tmp]# chmod 700 /home/nisuser/ [root@smallfry tmp]# ll /home total 2 drwx------ 2 nisuser users 1024 Aug 4 08:05 nisuser [root@smallfry tmp]# [root@smallfry tmp]# cp /etc/skel/.* /home/nisuser/ cp: omitting directory `/etc/skel/.' cp: omitting directory `/etc/skel/..' cp: omitting directory `/etc/skel/.kde' [root@smallfry tmp]# chown -R nisuser:users /home/nisuser [root@smallfry 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.
[root@bigboy 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
[root@bigboy tmp]#
[root@smallfry 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.
[root@smallfry 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.
