how to solve "ruby installation is missing psych" error?

I used rvm to install ruby 1.9.3. even though it was successfully installed, it complained about libyaml. and now every time i wanna install a gem (say rails) this warning shows up:

It seems your ruby installation is missing psych (for YAML output). To eliminate this warning, please install libyaml and reinstall your ruby.

I use Mac os X 10.7 (Lion).

Solution 1:

In my case

rvm pkg install libyaml

and

rvm reinstall ruby-1.9.3-p125

solved the problem.

For people using Ubuntu, make sure that libtool is installed prior to the steps above:

sudo apt-get install libtool

For macOS users (with homebrew):

rm -rf /usr/local/lib/ruby/gems/ && brew reinstall ruby

Solution 2:

for ubuntu and rvm

sudo apt-get install libtool
rvm pkg install libyaml
rvm reinstall 1.9.3

worked