CentOS

#ipconfig command not found

Well, ipconfig is a Windows command.

Linux has pretty much deprecated the ifconfig command, which may have been what you wanted. In some minimal installs, depending upon distribution, instead of the old ifconfig command, you're supposed to use the ip command.
I have a small page on it, with a link to other cheatsheets.

http://srobb.net/ip.html

You can also do a yum install net-tools to get ifconfig back.