YPFILES(5)

NAME
ypfiles - the Network Information Service database and directory structure

DESCRIPTION

The Network Information Service (NIS) network lookup service uses a distributed, replicated database of dbm files contained in the /var/yp directory hierarchy on each NIS server. A dbm database consists of two files, created by calls to the ndbm(3) library package. One has the filename extension .pag and the other has the filename extension .dir. For instance, the database named hosts.byname, is implemented by the pair of files hosts.byname.pag and hosts.byname.dir.

A dbm database served by the NIS is called a NIS map. A NIS domain is a subdirectory of /var/yp containing a set of NIS maps. Any number of NIS domains can exist. Each may contain any number of maps.

No maps are required by the NIS lookup service itself, although they may be required for the normal operation of other parts of the system. There is no list of maps which the NIS serves — if the map exists in a given domain, and a client asks about it, the NIS will serve it. For a map to be accessible consistently, it must exist on all NIS servers that serve the domain. To provide data consistency between the replicated maps, an entry to run ypxfr periodically should be made in the super-user's crontab file on each server. More information on this topic is in ypxfr(8).

NIS maps should contain two distinguished key-value pairs. The first is the key YP_LAST_MODIFIED, having as a value a ten-character ASCII order number. The order number should be the system time in seconds when the map was built. The second key is YP_MASTER_NAME, with the name of the NIS master server as a value. makedbm(8) generates both key-value pairs automatically. A map that does not contain both key-value pairs can be served by the NIS, but the ypserv process will not be able to return values for ``Get order number'' or ``Get master name'' requests. See ypserv(8). In addition, values of these two keys are used by ypxfr when it transfers a map from a master NIS server to a slave. If ypxfr cannot figure out where to get the map, or if it is unable to determine whether the local copy is more recent than the copy at the master, you must set extra command line switches when you run it.

NIS maps must be generated and modified only at the master server. They are copied to the slaves using ypxfr(8) to avoid potential byte-ordering problems among NIS servers running on machines with different architectures, and to minimize the amount of disk space required for the dbm files. The NIS database can be initially set up for both masters and slaves by using ypinit(8).

After the server databases are set up, it is probable that the contents of some maps will change. In general, some ASCII source version of the database exists on the master, and it is changed with a standard text editor. The update is incorporated into the NIS map and is propagated from the master to the slaves by running /var/yp/Makefile. All maps supplied with this OS have entries in /var/yp/Makefile; if you add a NIS map, edit this file to support the new map. The makefile uses makedbm(8) to generate the NIS map on the master, and yppush(8) to propagate the changed map to the slaves. yppush is a client of the map ypservers, which lists all the NIS servers. For more information on this topic, see yppush(8).

FILES
/var/yp
/var/yp/Makefile

SEE ALSO
dbm(3X), makedbm(8), rpcinfo(8C), ypinit(8), ypmake(8), yppoll(8), yppush(8), ypserv(8), ypxfr(8),