passthru()/exec()/system() Errors

I can do passthru("ls -la"), etc. just fine. but I am unable to do a passthru("fping .") Fping is a very useful utility, and I'd very much like to use it in my PHP scripts but am currently unable to. Via command line, it works perfectly. But through Apache, I get no output. <?php passthru("fping -sdC 1 localhost"); ?> # php test2.php localhost : 0.37 1 targets 1 alive 0 unreachable 0 unknown addresses 0 timeouts (waiting for response) 1 ICMP Echos sent 1 ICMP Echo Replies received 0 other ICMP received 0.37 ms (min round trip time) 0.37 ms (avg round trip time) 0.37 ms (max round trip time) 0.503 sec (elapsed real time) localhost : [0], 84 bytes, 0.37 ms (0.37 avg, 0% loss) Browser: <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; charset=iso-8859-1"></HEAD> <BODY></BODY></HTML> (Nothing) Fping is in /usr/sbin, but I've also tried moving it to /sbin, /bin, the same dir as the PHP script, chown'ing to nobody, etc. Any suggestions? I've had many problems with permissions in my command executions, but never this much. - Robert