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model, either a DNS or a hybrid NIS/DNS model for managing hosts works (such as via the technical rules listed in Section 5.3 earlier in this chapter). If the individual groups are using DNS to the exclusion of the NIS hosts map, then there is little work for the central committee other than to maintain the mapping of subdomains to subdomain name servers. The central committee, of course, is responsible for adding or deleting subdomains. If the individual groups use NIS for local hostname information, then the central committee would maintain the entire DNS infrastructure by periodically gathering host map information from each group. This could be done automatically.

Complete decentralization

Each system administration group has the autonomy to modify its NIS host maps as well as the authority to modify the common DNS database. Such a system will not scale as the number of subdomains and system administration groups rises. With too many authorized players, it will be hard to track down problems caused by mistakes, not to mention avoiding duplicate efforts.

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[1] Soft administraton includes everything that does not require onsite personnel. An example of something that is not soft administration would be replacing a disk drive.

Migrating from NIS to DNS for host naming

By now you should have a good handle on the differences between NIS and DNS as they impact host naming. If you are considering migrating from NIS to DNS, you need to decide what you want to do about unqualified versus qualified hostnames. By going from NIS to DNS, you are exposing your users to a hierarchical (qualified) naming scheme versus the flat (unqualified) one they knew under NIS. While you don't want to continue a flat naming scheme for accessing hosts outside the user's subdomain, you may want to temporarily or permanently support a flat naming scheme for hosts within each user's subdomain, using techniques described earlier. Such an approach also gives you more time to find all references to unqualified hostnames in configuration files and in software packages and correct them to be qualified.

What next?

The Network Information Service provides an easy-to-manage general purpose distributed database system. When used in conjunction with a source code control system and local tools, it solves many problems with configuration file management by providing audit trails and a single point of administration. The single biggest advantage of NIS is that it adds consistency to a network. Getting all hosts to agree on usernames, uid and gid values, and hostnames and host addresses is a prerequisite for adding other distributed services such as NFS.

Chapter 6. System Administration Using the Network File System

The Network File System (NFS) is a distributed filesystem that provides transparent access to remote disks. Just as NIS allows you to centralize administration of user and host information, NFS allows you to centralize administration of disks. Instead of duplicating common directories such as /usr/local on every system, NFS provides a single copy of the directory that is shared by all systems on the network. To a host running NFS, remote filesystems are indistinguishable from local ones. For the user, NFS means that he or she doesn't have to log into other systems to access files. There is no need to use rcp or tapes to move files onto the local system. Once NFS has been set up properly, users should be able to do all their work on their local system; remote files (data and executables) will appear to be local to their own system. NFS and NIS are frequently used together: NIS makes sure that configuration information is propagated to all hosts, and NFS ensures that the files a user needs are accessible from these hosts.

NFS is also built on the RPC protocol and imposes a client-server relationship on the hosts that use it. An NFS server is a host that owns one or more filesystems and makes them available on the network; NFS clients mount filesystems from one or more servers. This follows the normal client-server model