当我使用 OpenType 字体排版文档时，我经常会在文件LuaLaTeX中收到类似这样的消息.log
luaotfload | load : path lookup of "Palatino Linotype.ttf" unsuccessful,
falling back to file:(compiling luc: /usr/local/texlive/2015/texmf-var/luatex-cache/generic/fonts/otf/palatino-linotype.luc)(compiling luc:
/Users/simi/Library/texlive/2015/texmf-var/luatex-cache/generic/fonts/otf/palatino-linotype.luc)(save:
/Users/simi/Library/texlive/2015/texmf-var/luatex-cache/generic/fonts/otf/palatino-linotype.lua)(save:
/Users/simi/Library/texlive/2015/texmf-var/luatex-cache/generic/fonts/otf/palatino-linotype.luc)
luaotfload | load : path lookup of "Palatino Linotype.ttf" unsuccessful, falling back to file: \g__fontspec_family_PalatinoLinotype_int=\count161
luaotfload | load : path lookup of "PalatinoLinotype.ttf" unsuccessful, falling back to file:(compiling luc: /usr/local/texlive/2015/texmf-var/luatex-cache/generic/fonts/otf/palatinolinotype.luc)(compiling luc:
/Users/simi/Library/texlive/2015/texmf-var/luatex-cache/generic/fonts/otf/palatinolinotype.luc)(save: /Users/simi/Library/texlive/2015/texmf-var/luatex-cache/generic/fonts/otf/palatinolinotype.lua)(save: /Users/simi/Library/texlive/2015/texmf-var/luatex-cache/generic/fonts/otf/palatinolinotype.luc)
luaotfload | load : path lookup of "PalatinoLinotype.ttf" unsuccessful, falling back to file:
这件事有几个奇怪的地方：
LuaLaTeX确实使用定义的字体编译了文档。排版不会失败（如果fontspec找不到字体，通常会失败）。/usr/local/texlive/2015/texmf-var/luatex-cache/generic/fonts/otf/palatino-linotype.luc作为第一个后备方案给出的方案并不存在。/Users/simi/Library/texlive/2015/texmf-var/luatex-cache/generic/fonts/otf/palatino-linotype.luc确实存在，但看起来每次都会重新创建。至少，当我在LuaLaTeX运行之前删除此目录时，它会重新创建。- 在此错误消息的最后一部分，根本没有给出路径，只是说
falling back to file:
与给出的错误相反，LuaLaTeX/luaotfload实际上做似乎找不到所需的字体文件。那么这条消息的含义是什么？