Troubleshooting Equation Images

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Revision as of 16:01, 21 February 2008 by Sam (Talk | contribs)
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Try setting $WeBWorK::PG::ImageGenerator::PreserveTempFiles to 1 (in webwork2/lib/WeBWorK/ After that, you should see directories like ImageGenerator.xxxxxx accumulating in webwork2/tmp/. These contain files that ImageGenerator uses in generating each equation image:

  • equation.tex - TeX source file
  • equation.log - log file written by LaTeX
  • equation.dvi - DVI file generated by LaTeX
  • latex.out, latex.err - messages written to STDOUT and STDERR by LaTeX
  • dvipng.out, dvipng.err - messages written to STDOUT and STDERR by dvipng
  • If latex.out and latex.err don't exist, this indicates that LaTeX was never invoked. I'm not sure what would cause this.
  • If equation.log doesn't exist, then LaTeX was invoked, but probably never ran. Check for a properly installed latex and make sure that the path to latex in global.conf is correct.
  • Check equation.log, latex.out, and latex.err for errors. These might indicate problems in the TeX code being sent to LaTeX for processing. The errors might be in the equation itself in the PG file, or in the TexPreamble or TexPostamble, which are defined in
  • if equation.dvi does not exist, then LaTeX was not able to interpret its input successfully. Read equation.log, latex.out, and latex.err for errors.
  • Open equation.dvi in a DVI viewer and see if it contains a properly rendered equation.
  • Check dvipng.out and dvipng.err for errors.

The PNG file that dvipng produces is moved from the ImageGenerator.xxxxxx directory and renamed, so you'll have to look at the HTML source of the problem page to find its name. It'll be something like e40d5b21c65856b95bbc6f4dfced571.png. (That's the SHA-1 hash of the TeX equation followed by 1.png.) Make sure that file exists in webwork2/htdocs/tmp/equations/. Check its permissions. Make sure it is web-accessible (check http://yourserver/webwork2_files/tmp/equations/filename.png). See if it's a valid PNG, and see if it contains the proper equation image.

Inappropriate ioctl for device

This seems to occur when very old versions of dvipng are in use, and the easiest way to resolve it is to upgrade to the latest version. If that is not possible, try the following:

[In I] had [to] use the command

    my $dvipngCommand = "cd $wd && $dvipng " . $DvipngArgs . " equation.dvi > dvipng.out 2> dvipng.err";

i.e. pass it equation.dvi rather than equation. Probably my old version of
dvipng requires this. There certainly can't be any harm in this, correct? The
newer versions of dvipng must accept this, correct?
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