SyntaxHighlight does not add the HTML to highlight code, simply adding a <pre> tag around the code block which is meant to be highlighted and erroneously adding the 'Pages with syntax highlighting errors' category to the page.
The Debug console reports a Warning : Failed to invoke Pygments: env: python: No such file or directory
The log shows the following stacktrace:
[error] [154a08a1] /wiki/FreeBSD_Mail_Server ErrorException from line 300 of /usr/local/www/mediawiki/includes/debug/MWDebug.php: PHP Notice: Failed to invoke Pygments: env: python: No such file or directory
[Called from SyntaxHighlight_GeSHi::highlight in /usr/local/www/mediawiki/extensions/SyntaxHighlight_GeSHi/SyntaxHighlight_GeSHi.class.php at line 296][error-json]
{"id":"154a08a1","type":"ErrorException","file":"/usr/local/www/mediawiki/includes/debug/MWDebug.php","line":300,"message":"PHP Notice: Failed to invoke Pygments: env: python: No such file or directory\n [Called from SyntaxHighlight_GeSHi::highlight in /usr/local/www/mediawiki/extensions/SyntaxHighlight_GeSHi/SyntaxHighlight_GeSHi.class.php at line 296]","code":0,"url":"/wiki/FreeBSD_Mail_Server","backtrace":[{"function":"handleError","class":"MWExceptionHandler","type":"::","args":["integer","string","string","integer","array"]},
{"file":"/usr/local/www/mediawiki/includes/debug/MWDebug.php","line":300,"function":"trigger_error","args":["string","integer"]},
{"file":"/usr/local/www/mediawiki/includes/debug/MWDebug.php","line":155,"function":"sendMessage","class":"MWDebug","type":"::","args":["string","array","string","integer"]},
{"file":"/usr/local/www/mediawiki/includes/GlobalFunctions.php","line":1209,"function":"warning","class":"MWDebug","type":"::","args":["string","integer","integer","string"]},
{"file":"/usr/local/www/mediawiki/extensions/SyntaxHighlight_GeSHi/SyntaxHighlight_GeSHi.class.php","line":296,"function":"wfWarn","args":["string"]},
{"file":"/usr/local/www/mediawiki/extensions/SyntaxHighlight_GeSHi/SyntaxHighlight_GeSHi.class.php","line":127,"function":"highlight","class":"SyntaxHighlight_GeSHi","type":"::","args":["string","string","array"]},
{"function":"parserHook","class":"SyntaxHighlight_GeSHi","type":"::","args":["string","array","Parser","PPFrame_DOM"]},
{"file":"/usr/local/www/mediawiki/includes/parser/Parser.php","line":4234,"function":"call_user_func_array","args":["array","array"]},
{"file":"/usr/local/www/mediawiki/includes/parser/Preprocessor_DOM.php","line":1262,"function":"extensionSubstitution","class":"Parser","type":"->","args":["array","PPFrame_DOM"]},
{"file":"/usr/local/www/mediawiki/includes/parser/Parser.php","line":3342,"function":"expand","class":"PPFrame_DOM","type":"->","args":["PPNode_DOM","integer"]},
{"file":"/usr/local/www/mediawiki/includes/parser/Parser.php","line":1239,"function":"replaceVariables","class":"Parser","type":"->","args":["string"]},
{"file":"/usr/local/www/mediawiki/includes/parser/Parser.php","line":439,"function":"internalParse","class":"Parser","type":"->","args":["string"]},
{"file":"/usr/local/www/mediawiki/includes/content/WikitextContent.php","line":331,"function":"parse","class":"Parser","type":"->","args["string","Title","ParserOptions","boolean","boolean","integer"]},
{"file":"/usr/local/www/mediawiki/includes/content/AbstractContent.php","line":497,"function":"fillParserOutput","class":"WikitextContent","type":"->","args":["Title","integer","ParserOptions","boolean","ParserOutput"]},
{"file":"/usr/local/www/mediawiki/includes/poolcounter/PoolWorkArticleView.php","line":140,"function":"getParserOutput","class":"AbstractContent","type":"->","args"["Title","integer","ParserOptions"]},
{"file":"/usr/local/www/mediawiki/includes/poolcounter/PoolCounterWork.php","line":123,"function":"doWork","class":"PoolWorkArticleView","type":"->","args":[]},
{"file":"/usr/local/www/mediawiki/includes/page/Article.php","line":676,"function":"execute","class":"PoolCounterWork","type":"->","args":[]},
{"file":"/usr/local/www/mediawiki/includes/actions/ViewAction.php","line":44,"function":"view","class":"Article","type":"->","args":[]},
{"file":"/usr/local/www/mediawiki/includes/MediaWiki.php","line":490,"function":"show","class":"ViewAction","type":"->","args":[]},
{"file":"/usr/local/www/mediawiki/includes/MediaWiki.php","line":287,"function":"performAction","class":"MediaWiki","type":"->","args":["Article","Title"]},
{"file":"/usr/local/www/mediawiki/includes/MediaWiki.php","line":714,"function":"performRequest","class":"MediaWiki","type":"->","args":[]},
{"file":"/usr/local/www/mediawiki/includes/MediaWiki.php","line":508,"function":"main","class":"MediaWiki","type":"->","args":[]},
{"file":"/usr/local/www/mediawiki/index.php","line":41,"function":"run","class":"MediaWiki","type":"->","args":[]}]}
This is on MediaWiki 1.26.2 with PHP 5.6.20
Invoking pygmentize from the commandline works and produces the correct output, as does invoking it with PHP proc_open() and via Symfony\Components\Process\ProcessBuilder.