title: jupyter-client has to be installed but “jupyter kernelspec --version” exited with code 127
body: <p>I have already installed Jupyter notebook in my ubuntu 16.04 machine. In jupyter notebook there is by default python installed. Now I want to use R from jupyter notebook. </p>
  
  <p>To do so I followed <a href="https://github.com/IRkernel/IRkernel" rel="noreferrer">IRkernel installation link</a> and run below commands:</p>
  
  <pre><code>install.packages('devtools')
  
  devtools::install_github('IRkernel/IRkernel')
  </code></pre>
  
  <p>But when I run 
  <code>IRkernel::installspec()</code> command it shows below error:</p>
  
  <blockquote>
    <p>jupyter-client has to be installed but “jupyter kernelspec --version” exited with code 127</p>
  </blockquote>
  
  <p>I am now confused why this error occurs.</p>