GNU Emacs Manual. Node: Customization
Chapter 28: Customization
This chapter talks about various topics relevant to adapting the
behavior of Emacs in minor ways. See The Emacs Lisp Reference Manual for how to make more far-reaching changes.
All kinds of customization affect only the particular Emacs session
that you do them in. They are completely lost when you kill the Emacs
session, and have no effect on other Emacs sessions you may run at the
same time or later. The only way an Emacs session can affect anything
outside of it is by writing a file; in particular, the only way to make
a customization ``permanent'' is to put something in your `
file or other appropriate file to do the customization in each session.
See Init File.