关于MetaPost的label无法显示、无法编译的文章网上已经有一大堆了，但还是没有一个能解决我的问题……于是研究了两天，得出了又一种解法。

我的问题是：有label的MetaPost文件可以编译，但是编译完的东西无法显示，无论是用Evince还是ghostscript命令都不行，随便找个文件用ghostscript试一下就会得到如下信息：

GPL Ghostscript 9.10 (2013-08-30)
Copyright (C) 2013 Artifex Software, Inc.  All rights reserved.
This software comes with NO WARRANTY: see the file PUBLIC for details.
Error: /undefined in cmsy10
Operand stack:
   (p)
Execution stack:
   %interp_exit   .runexec2   --nostringval--   --nostringval--   --nostringval--   2   %stopped_push   --nostringval--   --nostringval--   --nostringval--   false   1   %stopped_push   1916   1   3   %oparray_pop   1915   1   3   %oparray_pop   1899   1   3   %oparray_pop   1787   1   3   %oparray_pop   --nostringval--   %errorexec_pop   .runexec2   --nostringval--   --nostringval--   --nostringval--   2   %stopped_push   --nostringval--
Dictionary stack:
   --dict:1171/1684(ro)(G)--   --dict:0/20(G)--   --dict:77/200(L)--
Current allocation mode is local
Current file position is 1066
GPL Ghostscript 9.10: Unrecoverable error, exit code 1

下面是解决方法。

首先根据搜索结果，在MetaPost源文件的开头添加如下一行：

prologues := 1;

之后重新编译一下那个文件，再用ghostscript查看。虽然可以显示，但还是会得到如下错误信息，并且其中的字体也不正常。

GPL Ghostscript 9.10 (2013-08-30)
Copyright (C) 2013 Artifex Software, Inc.  All rights reserved.
This software comes with NO WARRANTY: see the file PUBLIC for details.

   **** Warning: Some of the BoundingBox for the EPS file will be clipped.
                 Use -dEPSCrop or -dEPSFitPage to avoid clipping.

Can't find (or can't open) font file /usr/share/ghostscript/9.10/Resource/Font/CMSY10.
Can't find (or can't open) font file CMSY10.
Querying operating system for font files...
Can't find (or can't open) font file /usr/share/ghostscript/9.10/Resource/Font/CMSY10.
Can't find (or can't open) font file CMSY10.
Didn't find this font on the system!
Substituting font Courier for CMSY10.
Loading NimbusMonL-Regu font from /usr/share/fonts/type1/gsfonts/n022003l.pfb... 3935012 2454367 6881384 3120799 2 done.
Can't find (or can't open) font file /usr/share/ghostscript/9.10/Resource/Font/CMMI10.
Can't find (or can't open) font file CMMI10.
Didn't find this font on the system!
Substituting font Courier for CMMI10.
>>showpage, press <return> to continue<<

其中几行代码显示了字体保存路径，到那里去看看，就会发现那里有一堆字体，把TeX用到的字体文件复制过去就行了。注意大小写。

另外似乎现在TeX的字体不是bluesky，我的字体是在这个路径找到的：/usr/local/texlive/2014/texmf-dist/fonts/type1/public/amsfonts/cm（我用的是TeXLive发行版）。