Question

I was installing org-mode to my emacs. And a tutorial somewhere online tells me that I should do these steps: c-u 0 m-x byte-recompile-directory<RET>. And I know what I am doing of latter step (m-x byte-recompile-directory<RET>), but what’s the meaning here of "c-u 0"? Thanks!

Answer 1

From the byte-recompile-directory documentation:

If the ‘.elc’ file does not exist, normally this function does not
compile the corresponding ‘.el’ file. However, if the prefix argument
ARG is 0, that means do compile all those files. A nonzero
ARG means ask the user, for each such ‘.el’ file, whether to
compile it. A nonzero ARG also means ask about each subdirectory
before scanning it.

C-u is the usual way to provide a numeric argument to interactive functions. Unless you provide a zero arg with C-u 0, files that don’t already have an .elc file won’t be recompiled.