rbenv install error (2.1.2)

temp > rm -rf `RBENV_VERSION=2.1.2 rbenv prefix`
temp > rbenv install -f 2.1.2
Downloading ruby-2.1.2.tar.gz...
-> http://dqw8nmjcqpjn7.cloudfront.net/f22a6447811a81f3c808d1c2a5ce3b5f5f0955c68c9a749182feb425589e6635
Installing ruby-2.1.2...

BUILD FAILED

Inspect or clean up the working tree at /var/folders/zb/f74m1x7x7pn4ptqdr5gqnx900000gn/T/ruby-build.20140919101325.68381
Results logged to /var/folders/zb/f74m1x7x7pn4ptqdr5gqnx900000gn/T/ruby-build.20140919101325.68381.log

Last 10 log lines:
                              io-console 0.4.2
                              json 1.8.1
                              minitest 4.7.5
                              psych 2.0.5
                              rake 10.1.0
                              rdoc 4.1.0
                              test-unit 2.1.2.0
installing rdoc:              /Users/kent/.rbenv/versions/2.1.2/share/ri/2.1.0/system
installing capi-docs:         /Users/kent/.rbenv/versions/2.1.2/share/doc/ruby
The Ruby openssl extension was not compiled. Missing the OpenSSL lib?
temp > 

sudo apt install libssl1.0-dev will solve your problem