The configuration files in this directory are intended to control the standard initialization scripts found in /etc/init.d (known as init scripts), or the way various system libraries behave. They contain environment variable definitions that are used by system libraries or in the init scripts, to control execution options, software module loading, and anything else that can be controlled dynamically.
In the case of definitions used by the init scripts, the variables usually include a definition of command line options to be used. In some cases, setting one of the variables modifies the behavior of the script. For example, setting RESOLVCONF to anything but no in /etc/default/bind9 will cause the init script to use the resolvconf utility to add an appropriate resolver line for the localloopback interface during initialization (and remove it during shutdown).
For those scripts that apply to system libraries, they generally define default behavior for commands or software that the libraries affect. A good example of this is /etc/ default/nss, which controls how the Name Service Switch (NSS) functions in the GNU C library. In particular, it controls what information the library will consider authoritative for NSS calls, as well as the behavior of certain function calls.
In special cases, the default definition file may not be a single file, but " a subdirectory of /etc/default. TItis is done to split information into groups of related variables, both for ease of update, and to allow local modifications that won't be overwritten when configuration files are replaced.
