ypfiles(4nis)

ypfiles -- NIS database and directory structure

Description

The Network Information Service (NIS) 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, one has the filename extension .pag and the other has the filename extension .dir. For instance, the database named publickey is implemented by the pair of files publickey.pag and publickey.dir.

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

Files

/var/yp
/var/yp/aliases
/var/yp/Makefile

Usage

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 NIS serves; if the map exists in a given domain, and a client asks about it, 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 privileged user's crontab file on each server. For more information on this topic, see ypxfr(1Mnis).

NIS maps 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 indicates 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(1Mnis) generates both key-value pairs automatically. A map that does not contain both key-value pairs can be served by NIS, but the ypserv process will not be able to return values for ``Get order number'' or ``Get master name'' requests. See ypserv(1Mnis). 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, extra command line switches must be set when it is run.

NIS maps must be generated and modified only at the master server. They are copied to the slaves using ypxfr(1Mnis) 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(1Mnis).

All NIS maps have entries in /var/yp/aliases. Each entry includes the map name and a map nickname. The map name and nickname may be the same depending on the filesystem limitation of the length of filenames.

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. See ypbuild(1Mnis). All system-supplied maps have entries in /var/yp/Makefile; if an NIS map is added, edit this file to support the new map. The makefile uses makedbm(1Mnis) to generate the NIS map on the master, and yppush(1Mnis) 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(1Mnis).

References

dbm(3rpc), domainname(1Mnis), makedbm(1Mnis), ypbuild(1Mnis), ypinit(1Mnis), yppasswdd(1Mnis), yppoll(1Mnis), yppush(1Mnis), ypserv(1Mnis), ypxfr(1Mnis)