Hmm.. this one is a little bit tricky.

I do something like this:
system ("/usr/bin/ssh -l someuser somehost /path/somescr.pl", $return);

Executing that command (from the same user as apache runs) back EVERY TIME correct retval.

But, when called from Apache+PHP (no matter if safe_mode is enabled nor disabled) and if somescr.pl outputs something on STDOUT, retval randomly vary (0 or 255).

somescr.pl is:

#! /usr/bin/perl
print "OK";
exit 0;

Tried exec() and passthru (), results are the same.