# Troubleshooting Equation Images

## General troubleshooting

Try setting `$WeBWorK::PG::ImageGenerator::PreserveTempFiles`

to `1`

(in `webwork2/lib/WeBWorK/Constants.pm`

). 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 `Constants.pm`

.

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. One common cause of dvipng errors is that the `preview.sty`

file is not installed. `preview.sty`

can be found as part of preview-latex in CTAN and many operating systems include a package for it.

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 ImageGenerator.pm 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?