Network Information Services (NIS and NIS+) Guide

NIS Installation and Configuration

For information on installing the Network Information Service (NIS) and the Network File System (NFS), see the AIX 5L Version 5.1 Installation Guide.

Configuring NIS

For each NIS domain you want to configure on your network, do the following:

Decide which hosts on your network you want to include in this domain. Choose a domain name for the domain and make a note of it for use later in the configuration process.
Choose a host that has the characteristics described in Master Servers. Then follow the instructions in Configuring the NIS Master Server.
Decide which hosts, if any, will act as slave servers. Then, for each slave server, follow the instructions in Configuring an NIS Slave Server.
Decide which hosts will be clients in this domain. Then, for each client, follow the instructions in Configuring an NIS Client.

Notes:

If you want non-root users to be able to log into a server, you must configure the server as a NIS client as well.
If the file /var/yp/securenets exists, the server only provides NIS services to the hosts within the Internet Protocol (IP) range specified.

Setting the NIS Domain Name

To set the NIS domain name of a host (whether client or server), use the Web-based System Manager or use one of the following procedures.

Using the System Management Interface Tool (SMIT):
1. Enter the fast path: smit chypdom
2. Enter the domain name in the Domain name of this host field.
3. Specify both in the CHANGE domain name take effect... field.
4. Accept your changes and exit SMIT. The NIS domain name is now set.
Using the command line, enter: chypdom -B newdomainname

Each of these methods perform two actions. First, they run the domainname command, setting the NIS domain name. Second, they modify the /etc/rc.nfs file so that the NIS domain name is set when the system restarts.

Configuring the NIS Master Server

Attention: An NIS record has a maximum size of 1024 bytes. This limitation applies to all NIS map files. For example, a list of users in a group can contain a maximum of 1024 characters in single-byte character set file format. Before doing the following procedure, ensure that no configuration file is beyond this limit. NIS cannot operate correctly with map files that exceed this maximum.

To configure an NIS master server, do the following tasks on the master server host:

Follow the instructions in Preparing a Host for NIS Configuration.
Set the domain name by following the instructions in Setting the NIS Domain Name.
Decide what information you want to manage using NIS. By default, you manage all the information contained in the files listed in NIS Maps. You may want to customize how you manage users, groups, and host names, especially if you have already configured a domain name server. To do so, follow the instructions in Customizing NIS Map Input.

You will now create the directory for this domain, build the NIS maps, and start the NIS daemons. Use the Web-based System Manager or use one of the following procedures.

Using SMIT, enter: smit mkmaster.
- Specify in the HOSTS that will be slave servers field the names of the hosts, if any, that you want to act as slave servers.
- Specify yes in the fields Can existing MAPS for the domain be overwritten? and EXIT on errors, when creating master server? because you will want to know if an error occurs.
- If you want to configure your NIS domain for secure Remote Procedure Call (RPC) networking, specify yes in the START the yppasswdd daemon? and START the ypupdated daemon? fields. You should also configure secure NFS by following the instructions in AIX 5L Version 5.1 System Management Guide: Communications and Networks.
- Specify yes in the START the ypbind daemon? field to configure the master server to use the NIS databases.
- Specify both in the START the master server... field.
- Accept your changes and exit SMIT.
  The system takes a few minutes to perform several tasks. First, it runs the ypinit command. If the ypinit command exits successfully, the system uncomments the entries in the /etc/rc.nfs file for the daemons to which you specified yes above. Finally, the system starts these daemons.
  The ypinit command is a shell script that performs two tasks. First, it creates the directory /var/yp/domainname, where domainname is the domain name you defined above. Second, it runs the make command on the /var/yp/Makefile, which creates all the NIS maps specified in the /var/yp/Makefile.
Using the command line:
1. Enter the ypinit -m command. This command prompts you for various information, including the names of any slave servers, and takes a few minutes to complete.
2. Start the ypserv and ypbind daemons (and the yppasswdd and ypupdated daemons if you want) by following the instructions in Starting and Stopping NIS Daemons.
3. Edit the /etc/rc.nfs file and uncomment the lines that use the startsrc commands to start these daemons (delete the pound signs at the beginning of each line). For example, if the original lines look like the following:
```
#if [ -x /usr/etc/ypserv -a -d /etc/yp/`domainname` ]; then
#       startsrc -s ypserv
#fi
```
  Remove the pound signs so the file looks like:
```
if [ -x /usr/etc/ypserv -a -d /etc/yp/`domainname` ]; then
       startsrc -s ypserv
fi
```

Further Considerations When Using the yppasswd Daemon

If you chose to use a password file other than /etc/passwd to build the passwd map (see Customizing NIS Map Input), you must specify to the yppasswdd daemon the path to that file. By default, the yppasswdd daemon changes passwords for entries in the /etc/passwd file. To change the default password file to another file, do the following:

Edit the /etc/rc.nfs file, and locate the following stanza:

#Uncomment the following lines to start up the NIS
#yppasswd daemon.
DIR=/etc
if [ -x /usr/etc/rpc.yppasswdd -a -f $DIR/passwd ]; then
        start rpc.yppasswdd /usr/lib/netsvc/yp/rpc.yppasswdd
        /etc/passwd ~m
fi

Change the DIR statement so that it specifies the path to your alternate passwd file. For example, if you use the /var/yp/passwd file, the DIR statement should look like:
```
DIR=/var/yp
```
Save the file and exit the editor.

Enter the following three commands:

stopsrc -s yppasswdd
chssys -s yppasswdd -a '/var/yp/passwd -m passwd'
startsrc -s yppasswdd

The yppasswdd daemon will now use your alternate password file.

Configuring an NIS Slave Server

After configuring the master server (see Configuring the NIS Master Server), you must decide which hosts are to act as slave servers. Slave servers keep exact replicas of the master server's maps and share the processing burden by answering queries when the master server is busy or unavailable. The following procedure must be done for each slave server.

Prerequisites

The NIS master server is configured.

Procedure

To configure an NIS slave server, do the following tasks on the slave server host:

Notes:

If you are configuring a slave server that is not on the same IP network, you must configure the new server as an NIS client first (see Configuring an NIS Client). Use the ypset command to explicitly point the new server to the NIS master. For example, ypset 129.23.22.1, where 129.23.22.1 is the IP address of the master server.
When using subnets, a slave server must be configured on each subnet that has NIS clients for the given NIS domain. This allows clients to bind at startup and provides a fall back if the master goes down for any reason.

Follow the instructions in Preparing a Host for NIS Configuration.
Set the domain name by following the instructions in Setting the NIS Domain Name.

You will now create the directory for this domain, start the NIS daemons, and obtain copies of the NIS maps from the master server. Use the Web-based System Manager or use one of the following procedures.

Using SMIT:
1. Enter the fast path: smit mkslave.
2. Specify the hostname of the master server for this domain in the HOSTNAME of the master server field.
3. Specify yes in the fields Can existing MAPS for the domain be overwritten? and Quit if errors are encountered? because you will want to know if an error occurs.
4. Specify both in the START the slave server... field.
5. Accept your changes and exit SMIT.
  The system takes a few minutes to perform several tasks. First, it runs the ypinit command. If the ypinit command exits successfully, the system uncomments the entries in the /etc/rc.nfs file for the ypserv and ypbind daemons. Finally, the system starts these daemons.
  The ypinit command is a shell script that performs two tasks. First, it creates the directory /var/yp/domainname, where domainname is the domain name you defined above. Second, it runs the ypxfr command to obtain the NIS maps from the master server.
  Note: If this NIS slave server is not on same IP network as the NIS master server (that is, a gateway router is positioned between the slave server and the master server), you must explicitly identify the NIS master server by using the ypset command. For example, enter the command:
```
ypset 129.23.22.1
```
  where 129.23.22.1 is the IP address of the NIS master server.
Using the command line:
1. Start the ypbind daemon by following the instructions in Starting and Stopping NIS Daemons to bind to the master server.
2. Enter the ypinit -s mastername command, where mastername is the host name of the master server. This command prompts you for various information and takes a few minutes to complete.
3. Start the ypserv and ypbind daemons by following the instructions in Starting and Stopping NIS Daemons.
  Note: If this NIS slave server is not on same IP network as the NIS master server (that is, a gateway router is positioned between the slave server and the master server), you must explicitly identify the NIS master server by using the ypset command. For example, enter the command:
```
ypset 129.23.22.1
```
  where 129.23.22.1 is the IP address of the NIS master server.
4. Edit the /etc/rc.nfs file and uncomment the lines that use the startsrc commands to start these daemons. Delete the pound signs in the following example:
```
#if [ -x /usr/etc/ypserv -a -d /etc/yp/`domainname` ]; then
#       startsrc -s ypserv
#fi
```
  so it looks like:
```
if [ -x /usr/etc/ypserv -a -d /etc/yp/`domainname` ]; then
       startsrc -s ypserv
fi
```

Note: If NIS users need to log into an NIS slave server, the slave server must also be configured as a client, and should have the following line as the last line in its /etc/passwd file:
+::::::

Configuring an NIS Client

NIS clients make up the majority of hosts in an NIS domain. Clients do not maintain maps, but rather query servers for information. (Clients do not distinguish between master and slave servers.) If you are configuring a slave server that is not on the same IP network as the master server, you must configure the new server as an NIS client first.

Prerequisites

The NIS master server must be configured. For more information, see Configuring the NIS Master Server.

Procedure

To configure an NIS client, do the following tasks on the client host:

Follow the instructions in Preparing a Host for NIS Configuration.
Set the domain name by following the instructions in Setting the NIS Domain Name.

You then start the client using NIS. Use the Web-based System Manager or use one of the following procedures.

Using SMIT:
1. Enter the fast path: smit mkclient.
2. Specify both in the START the NIS client... field.
3. Accept your changes and exit SMIT.
  The system performs two tasks. First, it starts the ypbind daemon. Second, it uncomments the entry in the /etc/rc.nfs file for the ypbind daemon.
4. Follow the instructions in Setting Up NIS Client Files to Use NIS Services.
Using the command line:
1. Start the ypbind daemon by following the instructions in Starting and Stopping NIS Daemons.
2. Edit the /etc/rc.nfs file and uncomment the lines that use the startsrc command to start this daemon. Specifically, delete the pound signs in the following example:
```
#if [ -x /usr/etc/ypbind ]; then
#       startsrc -s ypbind
#fi
```
  so it looks like:
```
if [ -x /usr/etc/ypbind ]; then
       startsrc -s ypbind
fi
```

Preparing a Host for NIS Configuration

Before you configure NIS on a master server, slave server, or client, do the following:

Verify that the PATH variable in the /.profile file includes the /usr/sbin directory where the NIS commands reside.
Verify that Transmission Control Protocol/Internet Protocol (TCP/IP) is running by entering the command:
```
lssrc -s inetd
```
A message similar to the following displays:
```
Subsystem         Group            PID     Status
 inetd            tcpip            4923    active
```
If the status does not indicate active, follow the instructions in Configuring the inetd Daemon for starting the inetd daemon.
Verify that the portmap daemon is running by entering the command:
```
lssrc -s portmap
```
A message similar to the following displays:
```
Subsystem         Group            PID     Status
 portmap          portmap          14003   active
```
If the status does not indicate active, enter the command:
```
startsrc -s portmap
```

You are now ready to configure NIS on this host. If you are configuring a master server, continue with the following section, Customizing NIS Map Input. If you are configuring a client or slave server, continue with Starting and Stopping NIS Daemons.

Customizing NIS Map Input

The most common customizations made to NIS involve users, groups, and host names. However, you can customize any of the information managed by NIS. Although this discussion focuses on users, groups, and host names, you can use the same techniques to customize input to other maps.

Note: Perform all of these instructions on the master server host.

Users and Groups

Attention: An NIS record has a maximum size of 1024 bytes. This limitation applies to all NIS map files. For example, a list of users in a group can contain a maximum of 1024 characters in single-byte character set file format. Before doing the following procedure, ensure that no configuration file is beyond this limit. NIS cannot operate correctly with map files that exceed this maximum.

By default, NIS uses the /etc/passwd and /etc/group files on the master server as the input for the passwd and group maps. All users and groups on the master server are thus included automatically in the maps. The simplest configuration is to add every user and group in this entire domain to the /etc/passwd and /etc/group files.

Note: It is possible to manage users and groups without using NIS; however, managing users and groups is the primary benefit of NIS. For more secure methods of user and group management, see NIS+ Security Mechanisms.

Either for security, accounting, or performance reasons, you may not want certain users to log into the master server. If so, you can build the passwd and group maps from other files, such as /var/yp/passwd and /var/yp/group, that are for NIS users and groups only. With this, /etc/passwd and /etc/group can contain only the minimum necessary entries. (Using a separate password file also affects the yppasswdd daemon. See Configuring the NIS Master Server for more information.) To configure the master server in this way, do the following:

Create the new file to be used instead of the /etc/group file (for example, assume that you name the file /var/yp/group) by entering the following command:
```
cp /etc/group /var/yp/group
```
You can use a copy of any machine's /etc/group file, not just the /etc/group file on the master server. Then, using an editor, remove from the /etc/group file all the non-local entries, and add the NIS escape sequence (+:) as the last line in the file.
Create the new file to be used instead of the /etc/passwd file (for example, assume that you name the file /var/yp/passwd). Again, you can use a copy of any machine's /etc/passwd file, not just the /etc/passwd file on the master server. Also, you can use the password information from another NIS domain by entering ypcat passwd > passwd at the command line of a client in the other domain. Then, copy the passwd file into the /var/yp directory of the master server in this domain.
You can either preserve the current passwords or reset the passwords.
- If you want to preserve existing passwords, use the mrgpwd command to merge the /etc/passwd file with the /etc/security/passwd file, where the encrypted passwords are stored. This step is actually two commands, as shown below:
```
cd /var/yp
/usr/sbin/mrgpwd > passwd
```
  mrgpwd takes its input from the /etc/passwd and /etc/security/passwd files only.
- If you want to reset all the passwords, enter the following command:
```
cp /etc/passwd /var/yp/passwd
```
  Then, using an editor, remove the ! (exclamation point) from the password field in each entry in the /var/yp/passwd file. Finally, using an editor, remove from the /etc/passwd file all the non-local entries, and add the NIS escape sequence (+::0:0:::) as the last line in the file.
  
  Note: User IDs (UIDs) created in this way initially contain no passwords.
Change the /var/yp/Makefile file to reflect the new locations of the input files. You can do so using one of two methods:
- Locate only the /etc/passwd and /etc/group files in /var/yp. Using an editor, open the /var/yp/Makefile file and create a new variable called PWDIR=/var/yp. In the passwd.time and group.time stanzas, replace every occurrence of the DIR variable with PWDIR.
- Locate all the /etc files in /var/yp. Edit the Makefile file to modify the default DIR variable. Change DIR=/etc (the default configuration) to DIR=/var/yp. In contrast to the first method, you do not have to edit any of the Makefile stanzas.
  
  Note: The Web-based System Manager or the SMIT fast paths smit mkuser and smit mkgroup can be used to create users and groups only in the /etc/passwd and /etc/group files.

Host Names

By default, NIS only uses the /etc/hosts file to build the hosts map. If you have configured a domain name server in your network, you can configure NIS to include domain name system (DNS) information as well as /etc/hosts information in the hosts map. (Including DNS information in the hosts map eliminates re-entering all this information in the /etc/hosts file.) To do so, use an editor to change the /var/yp/Makefile file as follows:

Locate the hosts.time stanza in the /var/yp/Makefile file.

Change the two lines containing the word MAKEDBM:

...
| $(MAKEDBM) - $(YPDBDIR)/$(DOM)/hosts.byname; \
...
| $(MAKEDBM) - $(YPDBDIR)/$(DOM)/hosts.byaddr; \
...

so that they look like:

...
| $(MAKEDBM) -b - $(YPDBDIR)/$(DOM)/hosts.byname; \
...
| $(MAKEDBM) -b - $(YPDBDIR)/$(DOM)/hosts.byaddr; \
...

In other words, add the -b flag, with a space before and after, to both lines.

The ypserv and ypxfrd daemons use the file /var/yp/securenets, if it exists, and only respond to the IP addresses listed in the netmask netaddr pairs within that file.

Starting and Stopping NIS Daemons

Use Web-based System Manager, SMIT, or the following procedure to start or stop NIS daemons.

Prerequisites

NFS must be installed on your system.

The portmap daemon must be active. To check this, use the following command:

lssrc -s portmap

The result looks similar to the following:

Subsystem         Group          PID          Status
 portmap          portmap        4388         active

Procedure

The five NIS daemons are controlled by the System Resource Controller (SRC). As illustrated in the following table, four of the daemons have the SRC group name yp:

SRC Controlled NIS Daemons
Daemon Name	Subsystem Name	Group Name
keyserv	keyserv	keyserv
ypbind	ypbind	yp
yppasswdd	yppasswdd	yp
ypserv	ypserv	yp
ypupdated	ypupdated	yp

To start or stop NIS daemons, use the Web-based System Manager or use one of the following procedures.

Using SMIT:
- Enter the SMIT smit ypstartstop fast path.
  Select a menu option, depending on whether you want to start or stop the ypserv, ypbind, yppasswdd, or ypupdated daemon. Once you make your selection, the daemon you specified will be started or stopped.
- To start the keyserv daemon, use the SMIT smit mkkeyserv fast path.
- To stop the keyserv daemon, use the SMIT smit rmkeyserv fast path.
Using the command line to start or stop the NIS daemons, run the startsrc or stopsrc command. You can start or stop the daemons individually or as a group. For example:
- To start all the daemons (not including the keyserv daemon), enter:
```
startsrc -g yp
```
- To stop all the daemons, enter:
```
stopsrc -g yp
```
- To start a single daemon, enter:
```
startsrc -s daemon_name
```
- To stop a single daemon, enter:
```
stopsrc -s daemon_name
```

Setting Up NIS Client Files to Use NIS Services

In this procedure, you specify which NIS maps that this client will use by adding a special NIS marker to various system files. In general, the system configuration files on an NIS client should have a minimum number of entries because the client should rely primarily on a server for its information. However, you may want to configure a few local entries that you do not want defined throughout the entire domain.

Actually, NIS handles client configuration files in two ways. Some configuration files are completely ignored once the ypbind daemon starts, and other files are appended to. If NIS ignores a particular file, the client will only know what its server's map contains. If NIS appends map information to a file, the client can use local information that no other host knows as well as NIS map information.

Files that NIS Ignores

Once the ypbind daemon is running, the client relies solely on the following NIS maps instead of their corresponding files:

Maps Used by the ypbind Daemon Instead of Files
Map	Nickname	File
hosts.byaddr	hosts	/etc/hosts
hosts.byname
ethers.byaddr	ethers	/etc/ethers
ethers.byname
networks.byaddr	networks	/etc/networks
networks.byname
rpc.bynumber		/etc/rpc
services.byname	services	/etc/services
protocols.byname	protocols	/etc/protocols
protocols.bynumber
netgroup		/etc/netgroup
netgroup.byhost
netgroup.byuser
publickey.byname		/etc/publickey
netid.byname		/etc/passwd
		/etc/group
		/etc/hosts
		/etc/netid
netmasks.byaddr		/etc/netmasks

You do not need to perform any configuration on the above files in order to use their corresponding NIS maps; the ypbind daemon does this automatically. However, the /etc/hosts file should have entries for the local loopback name and client's host name. Use either an editor or the smit hosts fast path to verify that the /etc/hosts file has these entries. For example, the client's /etc/hosts file should look similar to this example:

127.1         localhost   # local loopback name
200.10.2.101  zepher      # client's host name

The /etc/hosts file is accessed at boot time before NIS is available. After the system is running and the ypbind daemon is started, NIS ignores the /etc/hosts file.

Files where NIS Appends Map Information

Each of the following subheadings explains how to configure a client's configuration files to use a particular NIS map. You may choose to use all the available maps, or only a few. Many NIS installations use all the available maps, especially the passwd and group maps.

passwd.byname and passwd.byuid map

These two maps together are referred to by the nickname passwd. Using either an editor or the smit lsuser fast path, verify that the /etc/passwd file contains entries for the root user and the other primary users on the machine (in other words, the entries supplied in the default /etc/passwd file). Then, using an editor, add the NIS escape entry, + (plus sign), to enable the NIS password service. For example, the client's /etc/passwd file should look similar to the following:

root:!.k:0:1:/:/usr/bin/csh
nobody:*:-2:-2::/:
daemon:*:1:1::/:
sys:*:2:2::/:/usr/bin/csh
bin:*:3:3::/usr/bin:
uucp:*:4:4::/var/spool/uucppublic:
news:*:6:6::/var/spool/news:/usr/bin/csh
+::0:0:::

The NIS entry (the last line) instructs library routines to use the NIS password service after examining the local entries. So, when a program examines the /etc/passwd file, it first finds the local entries, and then it requests that NIS provide the password information.

In addition to using the entire passwd map, you can explicitly include (with a plus entry) and exclude (with a minus entry) NIS password information about specific users and groups.

The following are the types of + (plus) and - (minus) entries that you may define:

A + (plus) by itself means to include the entire contents of the NIS passwd map.
A + (plus) with a name means to include that name from the NIS map.
A + (plus) followed by a @ and a netgroup (that is +@netgroup_name) means to insert the entries for all the members of the netgroup netgroup_name at that point.
The - (minus) entries mean exclude the user or netgroup specified.

If the + (plus) entry contains data in one of the colon-separated fields (except for the user ID, or UID, and group ID, or GID, fields) of the password entry, that data overrides what is in the NIS map. Also, earlier entries in the file take precedence over later entries with the same user name or user ID. The following are some examples:

To remove the NIS password entry for a user, enter:

-user

To remove the NIS password for users in a netgroup, enter:

-@netgroup

The line that subtracts the netgroup or user must appear before any other /etc/passwd file entry that includes the netgroup or user. For example, to remove password entries for user cliffc and users in the bad-users netgroup, the password file entry must contain the user name, UID, and GID:

-cliffc:*:218:201::
-@bad-users
+::0:0:::

If user cliffc is a member of the good-users netgroup, the following example does not remove user cliffc from the /etc/passwd file:

+@good-users
-cliffc:*:218:201::
+::0:0:::

Once the routines that read the password's file find a match for cliffc, they stop parsing the file. Therefore, the -cliffc entry will never be found, because the good-users netgroup includes user cliffc.

group.byname and group.bygid maps

These two maps together are referred to by the nickname group. Using either an editor or the smit lsgroup fast path, verify that the /etc/group file contains entries for the system and other primary groups on the machine (in other words, the entries supplied in the default /etc/group file). Then, using an editor, add the NIS escape entry (+, plus sign) to enable the NIS group service. For example, the client's /etc/group file should look similar to the following:

system:!:0:root
staff:!:1:root
bin:!:2:root,bin
sys:!:3:root,su,bin,sys
adm:!:4:root,su,bin,adm
uucp:!:5:root,uucp
mail:!:6:root,su
security:!:7:root
cron:!:8:root
printq:!:9:root
audit:!:10:root
+:

mail.aliases and mail.byaddr maps

These two maps together are referred to by the nickname aliases. To enable use of the NIS aliases mapping:

Uncomment O AliasFile in the sendmail.cf file and specify the map name for NIS aliases.
Recompile the sendmail.cf file with the command sendmail -bz.
Recompile the alias database with the command sendmail -bi.

netgroup.byhost and netgroup.byuser maps

As noted in Files that NIS Ignores, NIS uses these two maps automatically. However, you can configure two other system files to reference these maps, specifically, the /etc/hosts.equiv file and the /.rhosts file. Doing so can help you control remote logins more effectively.

For example, you can edit the /etc/hosts.equiv file and add a single line, with only the + (plus) character on it. This allows anyone to log into the machine because all further entries are retrieved from NIS rather than the local file. Or, for more control over logins, add a list of trusted hosts to the /etc/hosts.equiv file. For example:

+@trusted_group1
+@trusted_group2
-@distrusted_group

The names to the right of the @ (at sign) should be netgroup names defined in the netgroup map.

You can also add a list of trusted hosts to the /.rhosts file. For example:

+@trusted_group1
+@trusted_group2
-@distrusted_group

Because this file controls remote root access to the local machine, unrestricted access is not recommended. You cannot use aliases for host names in the /.rhosts, hosts.equiv, or netgroup files, because they all enable local machines to access remote machines. You can, however, use aliases for host names in the /etc/hosts file.

Note: If none of the escape sequences are added to the /etc/hosts.equiv or /.rhosts files, NIS is not used when a program examines these files.