I am attempting to upgrade Mediawiki 1.5.6 to the latest (1.6.3). I have backed up all files and the MySQL database. I then copied over the original 1.5.6 directory with the new 1.6.3 directory. Next, I ran php -cli ./maintenance/update.php and get the following error:

Fatal error: Call to undefined function socket_sendto() in <MEDIAWIKI>/includes/GlobalFunctions.php on line 1506

I have also tried using the web interface to run the upgrade and the same error message appears. I have also tried just upgrading to Mediawiki 1.6.2and the same isue persists. Below is the versions of applicable software I have:

Mediawiki: 1.5.6 PHP 5.0.5 (apache2handler) MySQL 4.1.15-Max OS: Redhat Enterprise 3AS

I'd really appreciate it if someone can point out what I'm doing wrong and recommend how to complete the upgrade. Thanks in advance!!