nisprefadm defines which servers are to be preferred by NIS+ clients. This information is used by nis_cachemgr(1M) to control the order in which it selects which server to use for a particular domain. On a client system, the cache manager first looks for a local preferred server list in /var/nis. If it doesn't find one, it looks for an entry with its host name in the NIS+ table. Finally, if it doesn't find it there, it looks for an entry for its subnet.

By default, nis_cachemgr puts all servers that are on the same subnet as the client system (that is, local servers) are on the preferred server list. In some cases this default preferred server list is inadequate. For example, if all of the servers for a domain are remote, but some are closer than others, the cache manager should try to select the closer one. Because the cache manager has no reliable way to determine the distance to remote servers, nisprefadm is used to provide this information.

The preferred server information is stored either globally in a NIS+ table (with the -G option) or locally in a file, /var/nis/client_info (with the -L option). It is preferable to store the information globally so that it can be used by all clients on a subnet. The nis_cachemgr process on a client machine reloads the preferred server information periodically, depending on the machine's setup. If the local file is used, the information is reloaded every 12 hours. If the global table is used, the information is reloaded based on the TTL value of the client information table. This TTL value can be changed using nischttl(1). If you want your changes to take effect immediately, use the nisprefadm -F command. When changing local information (-L), nisprefadm automatically forces nis_cachemgr to reload the information.

The cache manager assigns weights to all of the servers on the preferred list. By default, local servers (that is, servers on the same subnet) are given a weight of 0. Other servers are given the weight, "infinite". This can be changed by using the nisprefadm command and giving a weight in parentheses after the server name. When selecting a server for a domain, the cache manager first tries to contact the servers with the lowest weight. If it doesn't get a response, it tries the servers with the next lowest weight, and so on. If it fails to get a response from any of the preferred servers, it tries to contact the non-preferred servers.

The use of weights gives fine control over the server selection process, but care must be given to avoid assigning too many different weights. For example, if weights 0, 1, 2, and 3 are used, but all of the servers with weight 0, 1, and 2, are unavailable, then there will be a noticeable delay in selecting a server. This is because the cache manager waits 5 seconds for a response at each weight level before moving on to the next one. As a general rule, one or two weight levels provides a good balance of server selection control and performance.

When specifying a server name, it is not necessary to fully qualify the name. When the cache manager tries to access a domain, it compares the list of servers for the domain with the list of preferred servers. It will find a match if a preferred server name is a prefix of the name of a server for the domain. If a domain is served by two servers with the same prefix, the preferred server name must include enough of the domain name to distinguish the two.

The nis_cachemgr(1M) process automatically adds local servers (same subnet as the client) to the preferred server list with a weight of 0. Thus, it is not necessary to specify them, though it does no harm.

If you specify a weight for a server, you probably should quote the parentheses to avoid having the shell interpret them. The following command illustrates this:

example% nisprefadm -G -a -C client1 "srv1(2)"

In general, nis_cachemgr does a fairly good job of selecting servers on its own. Therefore, the use of nisprefadm is not usually necessary. Some situations in which it is recommended are:

No local servers, many remote servers

In this case, nis_cachemgr needs to choose one of the remote servers. Because it doesn't have information on which is closest, it sends a ping to all of them and then selects the one that responds fastest. This may not always select the best server. If some of the servers are closer to the client than the others, they should be listed as preferred servers so that nis_cachemgr will try them first. This reduces the amount of network traffic for selecting a server.

Very remote servers

In some networks there are NIS+ servers that are only reachable through very slow network connections. It is usually best to avoid unnecessary traffic over that connection. If the pref_type=pref_only option is set along with preferred servers, then only the preferred servers are contacted for domains they serve. The non-preferred servers are not tried at all; even if all of the preferred servers are unavailable. For domains that are not served by any of the preferred servers, the pref_only option is ignored.

In the SYNOPSIS, when several options are surrounded by braces (that is, by `{' and `}') one of the options must be specified.

-a

Add the specified servers to the preferred server list.

-C client

Store the preferred server information with the key, client. The client can be either a hostname or a subnet number. When a hostname is specified, the preferred server information applies to that host only. When a subnet is specified, the preferred server information applies to all clients on that subnet. The cache manager searches for host specific entries first. It only searches for subnet entries if no host entry is found. If this option is not specified, then the hostname of the machine on which the command is run is used.

-d domain

Specify the domain to which the command is to apply.

-F

Tells nis_cachemgr(1M) to refresh its preferred server information. The program periodically does this anyway, but this option forces it to do the refresh immediately. When updating the local information, nis_cachemgr automatically refreshes the preferred server information.

This option must be executed as root.

-l

List the current preferred server information.

-L | -G

Store the preferred server information locally in the file, /var/nis/client_info (the -L option), or globally in a NIS+ table client.info.org-dir.domain (the -G option). If the information is stored locally, then it only applies to the system on which the command is run. If it is stored globally then it can apply to all systems on a subnet (depending on the value of the -C option).

The -L option must be run as root.

-m

Modify the preferred server list. The server specified by oldserver is replaced by newserver. This is typically used to change the weight for a server.

-o

Specify additional options to control server selection. Currently the only valid option is pref_type, which can have a value of either all (the default) or pref_only. If the value is all, then the cache manager tries to contact non-preferred servers if all of the preferred servers fail to respond. If pref_only is specified, then it won't try non-preferred servers. The only exception to this is when a domain is not served by any of the preferred servers. In this case, the cache manager ignores the option. This is to avoid requiring that preferred servers be defined for every domain.

-r

Remove the specified servers from the preferred server list.

-u

Clear the list of preferred servers and then add the specified servers to the preferred server list.

-x

Remove the preferred server information completely.

nisprefadm returns the following values:

0

On success.

1

On failure.

See attributes(5) for descriptions of the following attributes:

nischttl(1), nis_cachemgr(1M), attributes(5)

NIS+ might not be supported in future releases of the Solaris Operating Environment. Tools to aid the migration from NIS+ to LDAP are available in the Solaris 9 operating environment. For more information, visit http://www.sun.com/directory/nisplus/transition.html.