nss_directories

nss_directories is a set of C library extensions which allow a directory
full of files to be used as a primary source of user, group, protocol, and
service information instead of or in addition to flat files or NIS.

nss_files	nss_directories
=========	===============
/etc/passwd	/etc/passwd.d/*
/etc/shadow	/etc/shadow.d/*
/etc/group	/etc/group.d/*
/etc/services	/etc/services.d/*
/etc/protocols	/etc/protocols.d/*