php variable $_SERVER['SERVER_ADDR'] is blank when using crontab -

i have small script gets basic information server ip-, , mac-address of server script running on, posting results mysql database, works fine , code shown below. when use cronjob execute script ip address being stored, reason $_server['server_addr'] blank when being executed cronjob.

this script runs every min, , run on multi raspberry pi's can tell connected share job requests.

$mac_address    = getmaclinux(); $server_ip      = $config['server_ip']; $client_ip      = $_server['server_addr']; $client_name    = $config['client_name'];   $ch = curl_init(); $url = "{$server_ip}/checkin0.php"; echo "url = {$url}"."<br>";  curl_setopt($ch, curlopt_url,$url); curl_setopt($ch, curlopt_post, true); curl_setopt($ch, curlopt_postfields, "client_ip={$client_ip}&client_name={$client_name}&client_mac={$mac_address}"); curl_setopt($ch, curlopt_returntransfer, true); $output = curl_exec ($ch); // execute  curl_close ($ch); // close curl handle  var_dump($output); // show output 

i found following

function getserveraddress() {     if(isset($_server["server_addr"]))     return $_server["server_addr"];     else {     // running cli     if(stristr(php_os, 'win')) {         //  rather hacky way handle windows servers         exec('ipconfig /all', $catch);         foreach($catch $line) {         if(eregi('ip address', $line)) {             // have seen exec return "multi-line" content, hack.             if(count($linecount = split(':', $line)) == 1) {             list($t, $ip) = split(':', $line);                 $ip = trim($ip);             } else {                 $parts = explode('ip address', $line);                 $parts = explode('subnet mask', $parts[1]);                 $parts = explode(': ', $parts[0]);                 $ip = trim($parts[1]);             }             if(ip2long($ip > 0)) {             echo 'ip '.$ip."\n";             return $ip;             } else             ; // todo: handle failure condition.         }         }     } else {         $ifconfig = shell_exec('/sbin/ifconfig eth0');         preg_match('/addr:([\d\.]+)/', $ifconfig, $match);         return $match[1];     }