Update rbenv --list

gistfile1.txt

$ rbenv install 2.1.2
ruby-build: definition not found: 2.1.2

You can list all available versions with `rbenv install --list'.

If the version you're looking for is not present, first try upgrading
ruby-build. If it's still missing, open a request on the ruby-build
issue tracker: https://github.com/sstephenson/ruby-build/issues
(Fun fact: Recent versions of ruby-build will give you a more helpful error message which just tells you the following.)

On Linux, you probably installed ruby-build as an rbenv plugin. Updating is easy:

COPY
cd ~/.rbenv/plugins/ruby-build
git pull

THANKS !