What's the correct term for the approach (pattern) that Linux uses to load multiple configuration files in a directory?

Question

It seems to me that Linux systems frequently load (and sometimes merges) multiple text configuration files in a directory, in order to build an aggregated configuration structure for a daemon, application, service, etc.

Eg, all the configuration files in /linux/etc/apt/apt.conf.d or in /etc/init.d/ are read and applied to the configuration.

What is the name of the pattern used for this approach of aggregating configuration files? (I'm looking to the term used for this approach in system architecture.)

I'm simply interested to read more about it and about its advantages and disadvantages.

Answer 1

I'm not sure if this design pattern even has one well-known, official name or not, but drop-in configuration files and drop-in configuration directory are terms I've seen used to describe it. If a configuration file syntax has an include directive that can take wildcards, it can be implemented even without modifying the program in question at all.

In a nutshell, it enables automated administration by allowing software packages and/or automation tools to drop in individual configuration snippets as needed instead of trying to programmatically modify one single configuration file. It can also benefit human system administrators by allowing settings to be grouped by purpose.

Note that /etc/init.d does not exactly follow this pattern, but a well-known, somewhat more complex pattern known as SysVinit startup/shutdown scripts: the scripts in /etc/init.d are not simply all incorporated to the start-up process, but there are separate directories of symbolic links (/etc/rc.d/rc[0-6].d/) that are used to determine which scripts will be called and in which order. Some more modern implementations generate and manage the symlinks in these directories automatically based on specially-formatted comments at the beginning of the scripts in /etc/init.d/... but this is a later extension, not an original part of the SysVinit startup/shutdown script pattern.