Php-fpm does not work me exec or shell_exec

I have OpenBSD 5.6 and php-fpm, nginx.

Is chrooted by default on /var/www

I try:(test.php)

<?php
if(function_exists('exec')) {
    echo "exec is enabled";
}else{
   // it's not
echo "exec is disabled";
}
echo "<br>";
if( ini_get('safe_mode') ){
   // safe mode is on
echo "safe_mode is enabled";
}else{
   // it's not
echo "safe_mode is disabled";
}
echo "<br>";
echo exec('whoami');
?>

browser only prints:

exec is enabled 
safe_mode is disabled

I tried to change:

echo exec('whoami');

to

echo exec('/usr/bin/whoami');

but exec does not work

I've tried in the terminal;

# sudo -u www php-5.5 test.php
exec is enabled<br>safe_mode is disabled<br>www

So I think the whole problem is in php-fpm.

Would I could help?