Simple question which I haven't found an explanation for yet while searching on google. What is sources.list.d for as opposed to sources.list? What does the d stand for?
(I know that sources.list holds links to repositories where debian can download software).
While google finds a ton of information, you don't need google for that. The manual page is mentioning it:
man sources.list
SOURCES.LIST.D
The /etc/apt/sources.list.d directory provides a way to add sources.list entries in separate files. The format is the same as for the regular sources.list file. File names need to end with .list and may only contain letters (a-z and A-Z), digits (0-9), underscore (_), hyphen (-) and period (.) characters. Otherwise APT will print a notice that it has ignored a file if the file doesn't match a pattern in the Dir::Ignore-Files-Silently configuration list - in this case it will be silently ignored.
This means all files in that directory are "merged" together with the main sources list and build together the collection of repositories.
While you can still just put all repositories into one file, there are advantages for maintainability if you spread the list into several files. When you want to disable a repository you can just remove a file instead of manipulating the main list. This is especially good for automation.
