The apt-get way don't install the latest stable Ruby (2.1.1), even on Ubuntu 14.04. Instead, I got 1.9.3 that way. RVM can be easy, but to work with Apache I'd need a system-wide installation independent of the RVM environment. So I've decided to install Ruby from source. I had problems around readline, but after seeing this hint, the solution that worked for me is:
on the directory of the unpacked source of Ruby 2.1.1, as root. I suspect there is a more elegant solution out there, but this is enough for me at this time.