it seems it uninstall `node` when install itself.
> "This package will install io.js v1.0.0 and npm v2.1.18 into /usr/local/. The binary /usr/local/bin/iojs will also be symlinked as /usr/local/bin/node."
Go to reinstall nodejs, and that install says a later version is already installed and cancels the install without giving me an option to install anyway.