The CiviMember UpdateMembershipRecord.php script updates membership statuses and optionally sends renewal reminders. Emailed renewal reminders are currently disabled. To enable them, edit /home/yournec.org/sites/all/modules/civicrm/bin/UpdateMembershipRecord.php and uncomment the lines starting at about 226. Also CiviCRM needs to be configured to know where the Drupal users table is, via civicrm >> administer >> configure >> global settings >> cms integration.
The script can be run manually via the following URL, but it's also set as a cron job to run once a day. (Manage cron jobs via http://panel.dreamhost.com.)
Notice that this URL includes a login ID, password and a site key. The 'memberadmin' ID belongs to the 'memberadmin' group that has very limited permissions... only enough to run this script. So that's all that this ID is used for.
Other CiviCRM command-line scripts are listed here: http://wiki.civicrm.org/confluence/display/CRMDOC40/Command-line+Script+Configuration