Mkfontdir For each directory argument, mkfontdir reads all of the font files in the directory searching for properties named "FONT", or (failing that) the name of the file stripped of its suffix. These are used as font names, which are written out to the file "fonts.dir" in the directory along with the name of the font file.
The kinds of font files read by mkfontdir depends on configuration parameters, but typically include SNF (suffix ".snf"), compressed SNF (suffix ".snf.Z"), BDF (suffix ".bdf"), and compressed BDF (suffix ".bdf.Z"). If a font exists in multiple formats, the most efficient format will be used.
The file "fonts.alias" which can be put in any directory of the font-path is used to map new names to existing fonts, and should be edited by hand. The format is straight forward enough, two white-space separated columns, the first containing aliases and the second containing font-name patterns.
When a font alias is used, the name it references is search for in the normal manner, looking through each font directory in turn. This means that the aliases need not mention fonts in the same directory as the alias file.
To embed white-space in either name, simply enclose them in double-quote marks, to embed double-quote marks (or any other character), precede them with back-slash:
"magic-alias with spaces" "\"font\name\" with quotes" regular-alias fixed
If the string "FILE_NAMES_ALIASES" stands alone on a line, each file-name in the directory (stripped of it's .snf suffix) will be used as an alias for that font.
Xserver(1) looks for both "fonts.dir" and "fonts.alias" in each directory in the font path each time it is set (see xset(1)).