You need to supply full path, as long as you're not superuser, and you have permissions to execute - sbin is not in your $PATH environment. If you log in as root and type 'ifconfig' you'll get the response. Nmap is extremely good tool, but it is a bazooka and I think you're trying to kill a fly with it
Use "netstat" to get generic ports information, but if this is not what you need, please specify your request.
For reverse lookup you can either use 'nslookup' or 'host'. Or even 'dig'.