NIS Maps
The information in NIS maps is stored in ndbm format. ypfiles(4) and ndbm(3C) explain the format of the map file.
NIS maps were designed to replace UNIX /etc files, as well as other configuration files, so they store much more than names and addresses. On a network running NIS, the NIS master server for each NIS domain maintains a set of NIS maps for other machines in the domain to query. NIS slave servers also maintain duplicates of the master server's maps. NIS client machines can obtain namespace information from either master or slave servers.
NIS maps are essentially two-column tables. One column is the key and the other column is information related to the key. NIS finds information for a client by searching through the keys. Some information is stored in several maps because each map uses a different key. For example, the names and addresses of machines are stored in two maps: hosts.byname and hosts.byaddr. When a server has a machine's name and needs to find its address, it looks in the hosts.byname map. When it has the address and needs to find the name, it looks in the hosts.byaddr map.
An NIS Makefile is stored in the /var/yp directory of machines designated as an NIS server at installation time. Running make in that directory causes makedbm to create or modify the default NIS maps from the input files.
Note - Always create maps on the master server, as maps created on a slave will not automatically be pushed to the master server.
Default NIS Maps
A default set of NIS maps are provided in the Solaris operating environment. You might want to use all these maps or only some of them. NIS can also use whatever maps you create or add when you install other software products.
Default maps for a NIS domain are located in each server's /var/yp/domainname directory. For example, the maps that belong to the domain test.com are located in each server's /var/yp/test.com directory.
Table 7-3 describes the default NIS maps, information they contain, and whether the software consults the corresponding administrative files when NIS is running.
Table 7-3 NIS Map Descriptions
Map Name | Corresponding NIS Admin File | Description |
|---|---|---|
bootparams | bootparams | Contains path names of files clients need during boot: root, swap, possibly others. |
ethers.byaddr | ethers | Contains machine names and Ethernet addresses. The Ethernet address is the key in the map. |
ethers.byname | ethers | Same as ethers.byaddr, except the key is machine name instead of the Ethernet address. |
group.bygid | group | Contains group security information with group ID as key. |
group.byname | group | Contains group security information with group name as key. |
hosts.byaddr | hosts | Contains machine name, and IP address, with IP address as key. |
hosts.byname | hosts | Contains machine name and IP address, with machine (host) name as key. |
mail.aliases | aliases | Contains aliases and mail addresses, with aliases as key. |
mail.byaddr | aliases | Contains mail address and alias, with mail address as key. |
netgroup.byhost | netgroup | Contains group name, user name and machine name. |
netgroup.byuser | netgroup | Same as netgroup.byhost, except that key is user name. |
netgroup | netgroup | Same as netgroup.byhost, except that key is group name. |
netid.byname | passwd, hosts group | Used for UNIX-style authentication. Contains machine name and mail address (including domain name). If there is a netid file available it is consulted in addition to the data available through the other files. |
netmasks.byaddr | netmasks | Contains network mask to be used with IP submitting, with the address as key. |
networks.byaddr | networks | Contains names of networks known to your system and their IP addresses, with the address as key. |
networks.byname | networks | Same as networks.byaddr, except key is name of network. |
passwd.adjunct. byname | passwd and shadow | Contains auditing information and the hidden password information for C2 clients. |
passwd.byname | passwd and shadow | Contains password information with user name as key. |
passwd.byuid | passwd and shadow | Same as passwd.byname, except that key is user ID. |
protocols.byname | protocols | Contains network protocols known to your network. |
protocols.bynumber | protocols | Same as protocols.byname, except that key is protocol number. |
rpc.bynumber | rpc | Contains program number and name of RPCs known to your system. Key is RPC program number. |
services.byname | services | Lists Internet services known to your network. Key is port or protocol. |
services.byservice | services | Lists Internet services known to your network. Key is service name. |
ypservers | N/A | Lists NIS servers known to your network. |
New ipnodes maps (ipnodes.byaddr and ipnodes.byname) are added to NIS. The maps store both IPv4 and IPv6 addresses. See ipnodes(4). NIS clients and servers can communicate using either IPv4 or IPv6 RPC transports.
Using NIS Maps
NIS makes updating network databases much simpler than with the /etc files system. You no longer have to change the administrative /etc files on every machine each time you modify the network environment.
For example, when you add a new machine to a network running NIS, you only have to update the input file in the master server and run make. This automatically updates the hosts.byname and hosts.byaddr maps. These maps are then transferred to any slave servers and are made available to all of the domain's client machines and their programs. When a client machine or application requests a machine name or address, the NIS server refers to the hosts.byname or hosts.byaddr map as appropriate and sends the requested information to the client.
You can use the ypcat command to display the values in a map. The ypcat basic format is the following.
% ypcat mapname
where mapname is the name of the map you want to examine or its nickname. If a map is composed only of keys, as in the case of ypservers, use ypcat -k. Otherwise, ypcat prints blank lines. The ypcat man page describes more options for ypcat.
You can use the ypwhich command to determine which server is the master of a particular map. Type the following.
% ypwhich -m mapname
where mapname is the name or the nickname of the map whose master you want to find. ypwhich responds by displaying the name of the master server. For complete information, refer to the ypwhich man page.
NIS Map Nicknames
Nicknames are aliases for full map names. To obtain a list of available map nicknames, such as passwd for passwd.byname, type ypcat -x or ypwhich -x.
Nicknames are stored in the /var/yp/nicknames file, which contains a map nickname followed by the fully specified name for the map, separated by a space. This list might be added to or modified. Currently, there is a limit of 500 nicknames.
NIS-Related Commands
The NIS service includes specialized daemons, system programs, and commands, which are summarized in the following table.
Table 7-4 NIS Command Summary
Command | Description |
|---|---|
ypserv | Services NIS clients' requests for information from an NIS map. ypserv is a daemon that runs on NIS servers with a complete set of maps. At least one ypserv daemon must be present on the network for NIS service to function. |
ypbind | Provides NIS server binding information to clients. It provides binding by finding a ypserv process that serves maps within the domain of the requesting client. ypbind must run on all servers and clients. |
ypinit | Automatically creates maps for an NIS server from the input files. It is also used to construct the initial /var/yp/binding/domain/ypservers file on the clients. Use ypinit to set up the master NIS server and the slave NIS servers for the first time. |
make | Updates NIS maps by reading the Makefile (when run in the /var/yp directory). You can use make to update all maps based on the input files or to update individual maps. The ypmake(1M) man page describes the functionality of make for NIS. |
makedbm | makedbm takes an input file and converts it into dbm.dir and dbm.pag files--valid dbm files that NIS can use as maps. You can also use makedbm -u to disassemble a map, so that you can see the key-value pairs that comprise it. |
ypxfr | Pulls an NIS map from a remote server to the local /var/yp/domain directory, using NIS itself as the transport medium. You can run ypxfr interactively, or periodically from a crontab file. It is also called by ypserv to initiate a transfer. |
ypxfrd | Provides map transfers service for ypxfr requests (generally slave servers). It is run only on the master server. |
yppush | Copies a new version of an NIS map from the NIS master server to its slaves. You run it on the master NIS server. |
ypset | Tells a ypbind process to bind to a named NIS server. This is not for casual use and its use is discouraged because of security implications. See the ypset(1M) and ypbind(1M) man pages for information about the ypset and ypsetme options to the ypbind process. |
yppoll | Tells which version of an NIS map is running on a server that you specify. It also lists the master server for the map. |
ypcat | Displays the contents of an NIS map. |
ypmatch | Prints the value for one or more specified keys in an NIS map. You cannot specify which version of the NIS server map you are seeing. |
ypwhich | Shows which NIS server a client is using at the moment for NIS services, or, if invoked with the -m mapname option, which NIS server is master of each of the maps. If only -m is used, it displays the names of all the maps available and their respective master servers. |
NIS Binding
NIS clients get information from an NIS server through the binding process, which can work in one of two modes: server-list or broadcast.
Server-list. In the server-list mode, the ypbind process queries the /var/yp/binding/domain/ypservers list for the names of all of the NIS servers in the domain. The ypbind process binds only to servers in this file. The file is created by running ypinit -c.
Broadcast. The ypbind process can also use an RPC broadcast to initiate a binding. Since broadcasts are only local subnet events that are not routed further, there must be at least one server (master or slave) on the same subnet as the client. The servers themselves might exist throughout different subnets since map propagation works across subnet boundaries. In a subnet environment, one common method is to make the subnet router an NIS server. This allows the domain server to serve clients on either subnet interface.
Server-List Mode
The binding process in server-list mode works as follows:
Any program, running on the NIS client machine that needs information provided by an NIS map, asks ypbind for the name of a server.
ypbind looks in the /var/yp/binding/domainname/ypservers file for a list of NIS servers for the domain.
ypbind initiates binding to the first server in the list. If the server does not respond, ypbind tries the second, and so on, until it finds a server or exhausts the list.
ypbind tells the client process which server to talk to. The client then sends the request directly to the server.
The ypserv daemon on the NIS server handles the request by consulting the appropriate map.
ypserv sends the requested information back to the client.