Ubuntu 18.04になって早速、octopress環境をセットアップしようとruby 2.3.1をインストールしようとした。

Octopressをセットアップするのとおり、

git clone https://github.com/sstephenson/rbenv.git ~/.rbenv
git clone https://github.com/sstephenson/ruby-build.git ~/.rbenv/plugins/ruby-build
echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bashrc
echo 'eval "$(rbenv init -)"' >> ~/.bashrc
source ~/.bashrc
sudo apt-get install gcc build-essential libssl-dev libreadline-dev zlib1g-dev
rbenv install 2.3.1

rbenv install 2.3.1したら

BUILD FAILED (Ubuntu 18.04 using ruby-build 20180424)

Inspect or clean up the working tree at /tmp/ruby-build.20180429220407.5386
Results logged to /tmp/ruby-build.20180429220407.5386.log

Last 10 log lines:
installing rdoc:              /home/arimasou16/.rbenv/versions/2.3.1/share/ri/2.3.0/system
installing capi-docs:         /home/arimasou16/.rbenv/versions/2.3.1/share/doc/ruby
The Ruby openssl extension was not compiled.
ERROR: Ruby install aborted due to missing extensions
Try running `apt-get install -y libssl-dev` to fetch missing dependencies.

Configure options used:
	--prefix=/home/arimasou16/.rbenv/versions/2.3.1
	LDFLAGS=-L/home/arimasou16/.rbenv/versions/2.3.1/lib 
	CPPFLAGS=-I/home/arimasou16/.rbenv/versions/2.3.1/include 

libssl-devはインストール済なのに、どうして…

GitHub - rbenv/ruby-build: Compile and install Rubyを見て、

cd "$(rbenv root)"/plugins/ruby-build && git pull

ruby-buildをアップグレードしても最新。

Home · rbenv/ruby-build Wiki · GitHubの Suggested build environmentを見て

sudo apt-get install autoconf bison build-essential libssl-dev libyaml-dev libreadline6-dev zlib1g-dev libncurses5-dev libffi-dev libgdbm3 libgdbm-dev

しても駄目。

答えはここにあった Can’t build on Ubuntu 18.04 (bionic64) · Issue #1199 · rbenv/ruby-build · GitHub

Ruby < 2.4 is not compatible with openssl 1.1.
You need to install libssl1.0-dev.

arimasou16@Lemur:~$ openssl version
OpenSSL 1.1.0g  2 Nov 2017

ruby2.4未満はopenssl 1.1と互換性がない。

sudo apt install libssl1.0-dev

これで解決。