Basically, there is no restriction how font files for groff are
named and how long font names are; however, to make the font family
mechanism work (see Font Families), fonts within a family should
start with the family name, followed by the shape. For example, the
Times family uses ‘T’ for the family name and ‘R’, ‘B’,
‘I’, and ‘BI’ to indicate the shapes ‘roman’, ‘bold’,
‘italic’, and ‘bold italic’, respectively. Thus the final font names
are ‘TR’, ‘TB’, ‘TI’, and ‘TBI’.
All font files are kept in the font directories, which constitute
the font path. The file search functions always append the
directory devname, where name is the name of the
output device. Assuming, say, DVI output, and /foo/bar as a font
directory, the font files for grodvi must be in
/foo/bar/devdvi.
The elements of the search path for font files are (in that order):
gtroff’s or groff’s
-F command-line option. All device drivers and some
preprocessors also have this option.
GROFF_FONT_PATH environment variable.
/usr/local/share/groff/site-font /usr/local/share/groff/1.23.0/font
assuming that the version of groff is 1.23.0, and the
installation prefix was /usr/local. It is possible to fine-tune
those directories during the installation process.