passthru gives error in httpd/error_log

I'm trying to run a super simple command through passthru. Here's my test.php file: <html><body> <? passthru('ls -l'); ?> </body></html> It works if run directly with "php test.php". When this is run from the browser, there is no output, and the following error is logged in /var/log/httpd/error_log : sh: /ls: No such file or directory What does this mean ? Any command I try instead of "ls -l", gives a similar error. The funky thing is that it HAS worked, but now it doesn't, and I have no idea what happened. Any clues and hints are much appreciated. /Jesper