Name Service Switch
From Wikipedia, the free encyclopedia
The Name Service Switch (NSS) allows replacement of many Unix configuration files (e.g. /etc/passwd, /etc/group, /etc/hosts) with a centralized database or databases, with the mechanisms used to access those databases being configurable. (Earlier Unix systems, with the notable exception of Ultrix which offered nearly identical functionality in /etc/svc.conf, either accessed only the configuration files or had the rules for which files or databases to access hardcoded.) It was first developed by Sun Microsystems for their Solaris operating system, but has been subsequently ported to many other operating systems including FreeBSD, NetBSD, Linux, HP-UX, IRIX and AIX.
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[edit] nsswitch.conf
NSS is usually configured using the file /etc/nsswitch.conf. This lists databases (e.g. group, passwd) and one or more sources for obtaining that information (e.g files for local files, nis for the Network Information Service, or ldap for the Lightweight Directory Access Protocol. For example:
passwd: files nis group: files nis hosts: files dns
The order of the services listed determines in which order NSS will attempt to use those service to resolve queries on the specified database.
[edit] NSS and the C library
NSS requires modifications to the C library so that calls to functions such as getpwent or getgrent will call into the appropriate NSS module. This means that existing applications that use these routines for identity information will not require any changes to work with NSS.
