Very quick review:
- please use escapeshellarg() where ever exec is used... - unless it would break things.. (then at least make notes to such)
- try using System::which() to discover /usr/sbin/iwconfig etc... in the constructor
(normally for something like this I would have done
var $cmds = array( 'ifconfig' => ..... , 'iwconfig' => .....)
Groups related variables together , and concentrates code and documentation in a smaller more relivent group.