nsswitchconf

nsswitch.conf is the configuration file used by the Name Service Switch (NSS) in many Unix-like operating systems to determine where to obtain information for various system databases, such as user accounts, groups, and hostnames. The file is typically located at /etc/nsswitch.conf and is read by the C library during lookups performed by functions like getpwnam, getpwuid, getgrnam, gethostbyname, and related routines. The sources specified for each database determine the order and the providers consulted to resolve a query.

Format and syntax: Each non-comment line defines a database and a list of sources in decreasing order of priority, separated by spaces after a colon. For example: passwd: files ldap; hosts: files dns. The order matters: the first source that can answer the query is used. Common databases include passwd, group, shadow, hosts, networks, services, protocols, rpc, ethers, and netgroup. Common sources include files (local files such as /etc/passwd and /etc/group), dns, nis, nisplus, ldap, and sss (System Security Services Daemon). Some implementations provide compat mode for interoperability with legacy /etc files.

Notes: Lines beginning with # are comments. The file is system-dependent, and supported databases or sources may vary between Linux, BSD, and other Unix variants. Changes to nsswitch.conf affect NSS-based lookups and do not automatically restart the system; individual applications may implement their own caching.