If you use cPanel and you get the following error when calling PING from PEAR:
Warning: popen() has been disabled for security reasons in /usr/lib/php/OS/Guess.php on line 242
Warning: fgets(): supplied argument is not a valid stream resource in /usr/lib/php/OS/Guess.php on line 243
Warning: pclose(): supplied argument is not a valid stream resource in /usr/lib/php/OS/Guess.php on line 252
Warning: exec() has been disabled for security reasons in /home/dev7sof/php/Net/Ping.php on line 243 unable to locate the ping binary
then in WHM -> PHP Configuration -> Switch to Advanced Mode -> remove from disable_functions the functions exec and popen
and save the new configuration.