texvc does not render latex math in Mediawiki

Question

I have the Math extension installed in my MediaWiki 1.19. After I updated Ubuntu Server from 12.04 to 14.04 something seems to have messed it up and it has stopped working. Basically I get the following error when I try to display anything between the <math> and </math> tags:

 Failed to parse (PNG conversion failed; check for correct installation 
 of latex and dvipng (or dvips + gs + convert))

I have tried the common troubleshooting that one can find online regarding this issue, and have recompiled texvc to check if that fixed the issue. The texvc executable in the extensions/Math/math directory seems to do its job when invoked from the command line. I have obviously checked that all the other executables (latex, dvipng, etc.) work as they should.

When I try to render math from my wiki, the corresponding *.tex file is created in images/tmp with the correct latex code in it, but nothing else happens.

The problem seems to be related to texvc having trouble invoking latex and dvipng.

What could be causing this issue and how can I fix it?

Answer 1

Well, I figured it out. Basically, any shell command is passed by a security filter. So in practice, texvc is executed by Mediawiki through bin/ulimit4.sh:

#!/bin/bash

ulimit -t $1 -v $2 -f $3
eval "$4"

where $4 is the actual texvc command being run and $2 is the amount of memory allowed for this process. The memory that comes by default is 102400 KB (exactly 100MB), which seems to be insufficient for this process to run. The amount of memory can be set in LocalSettings.php with the variable $wgMaxShellMemory. In my case I set it to 300MB, $wgMaxShellMemory = 307200;, which seems to be enough.

Why this small process of generating a png needs so much memory I do not know.

The reason why this stopped working after updating to Ubuntu 14.04 probably has to do with some newly shipped version of either latex, dvipng, convert, etc. requiring more memory than it did with the version that came with Ubuntu 12.04.