iRuby notebook can't load rbczmq on ubuntu

Question

I installed the rbczmq and iruby gems to run a Ruby Kernel in Jupyter Notebook, but whenever I try to create a ruby notebook I get You should install rbczmq or ffi_rzmq before running iruby notebook. More completely, I get:

[I 14:28:23.629 NotebookApp] Creating new notebook in 
[W 14:28:24.335 NotebookApp] 404 GET /nbextensions/widgets/notebook/js/extension.js?v=20160509142818 (127.0.0.1) 6.96ms referer=http://localhost:8888/notebooks/Untitled.ipynb?kernel_name=ruby
[I 14:28:24.405 NotebookApp] Kernel started: f4d40465-f404-47da-9bbf-20ace8269861
You should install rbczmq or ffi_rzmq before running iruby notebook. See README.
F, [2016-05-09T14:28:24.546687 #22800] FATAL -- : Kernel died: uninitialized constant IRuby::Kernel::Session
/var/lib/gems/2.3.0/gems/iruby-0.2.9/lib/iruby/kernel.rb:18:in `initialize'
/var/lib/gems/2.3.0/gems/iruby-0.2.9/lib/iruby/command.rb:70:in `new'
/var/lib/gems/2.3.0/gems/iruby-0.2.9/lib/iruby/command.rb:70:in `run_kernel'
/var/lib/gems/2.3.0/gems/iruby-0.2.9/lib/iruby/command.rb:34:in `run'
/var/lib/gems/2.3.0/gems/iruby-0.2.9/bin/iruby:5:in `<top (required)>'
/usr/local/bin/iruby:23:in `load'
/usr/local/bin/iruby:23:in `<main>'
/var/lib/gems/2.3.0/gems/iruby-0.2.9/lib/iruby/kernel.rb:18:in `initialize': uninitialized constant IRuby::Kernel::Session (NameError)
    from /var/lib/gems/2.3.0/gems/iruby-0.2.9/lib/iruby/command.rb:70:in `new'
    from /var/lib/gems/2.3.0/gems/iruby-0.2.9/lib/iruby/command.rb:70:in `run_kernel'
    from /var/lib/gems/2.3.0/gems/iruby-0.2.9/lib/iruby/command.rb:34:in `run'
    from /var/lib/gems/2.3.0/gems/iruby-0.2.9/bin/iruby:5:in `<top (required)>'
    from /usr/local/bin/iruby:23:in `load'
    from /usr/local/bin/iruby:23:in `<main>'

I tried adding a Gemfile like this answer says I should, and that didn't help either. My gem list is:

*** LOCAL GEMS ***

bigdecimal (1.2.8)
bond (0.5.1)
data_uri (0.1.0)
did_you_mean (1.0.0)
ffi (1.9.10)
io-console (0.4.5)
iruby (0.2.9)
json (1.8.3)
libzmq (0.2.0)
mimemagic (0.3.1)
minitest (5.8.4)
multi_json (1.12.0)
net-telnet (0.1.1)
nyaplot (0.1.6)
power_assert (0.3.0, 0.2.7)
psych (2.0.17)
rake (11.1.2, 10.5.0)
rbczmq (1.7.9)
rdoc (4.2.2, 4.2.1)
test-unit (3.1.8, 3.1.7)

So clearly rbczmq is installed. Jupyter works just fine with Python 3, too. I'm using a fresh install of Ubuntu 16.04. Any idea what's wrong?

Answer 1

I figured it out. Installing ffi-rzmq (maybe not necessary) and then ZeroMQ (without libsodium) seems to have solved everything.