I've successfully installed rbenv (along with the build tools) on my Ubuntu 14.04 desktop, and that appears to be working fine, but as soon as I try to install ruby 2.1.1, the build fails:
daniel@grape:~$ rbenv install 2.1.1
Downloading yaml-0.1.6.tar.gz...
-> http://dqw8nmjcqpjn7.cloudfront.net/5fe00cda18ca5daeb43762b80c38e06e
Installing yaml-0.1.6...
Installed yaml-0.1.6 to /home/daniel/.rbenv/versions/2.1.1
Downloading ruby-2.1.1.tar.gz...
-> http://dqw8nmjcqpjn7.cloudfront.net/e57fdbb8ed56e70c43f39c79da1654b2
Installing ruby-2.1.1...
BUILD FAILED
Inspect or clean up the working tree at /tmp/ruby-build.20140418142258.3543
Results logged to /tmp/ruby-build.20140418142258.3543.log
Last 10 log lines:
installing default ripper libraries
compiling ossl_pkcs7.c
compiling ossl_ssl.c
installing default openssl libraries
linking shared-object openssl.so
make[2]: Leaving directory `/tmp/ruby-build.20140418142258.3543/ruby-2.1.1/ext/openssl'
linking shared-object ripper.so
make[2]: Leaving directory `/tmp/ruby-build.20140418142258.3543/ruby-2.1.1/ext/ripper'
make[1]: Leaving directory `/tmp/ruby-build.20140418142258.3543/ruby-2.1.1'
make: *** [build-ext] Error 2
The contents of the log file can be found here: http://pastebin.com/SXxTeCJY
I've done some searching for help with this issue, including following what is said here: https://github.com/sstephenson/ruby-build/wiki - but I've not had any joy.
UPDATE: Use Ruby 2.1.2, it fixes this issue.
14.04 is probably shipping with readline 6.3, which uses rl_hook_func_t instead of Function.
This bug has already been reported and fixed in Ruby (https://bugs.ruby-lang.org/issues/9578), but not released yet.
Until Ruby 2.1.2 comes out (which I assume will contain this fix), you can use a patch to properly support the new rl_hook_func_t method. Use this to install Ruby 2.1.1:
curl -fsSL https://gist.github.com/mislav/a18b9d7f0dc5b9efc162.txt | rbenv install --patch 2.1.1
(Source: http://gorails.com/setup/ubuntu/14.04)