title: Error installing Ruby with RVM: make "-j" argument
body: <p>I have followed the instructions on <a href="https://rvm.io/rvm/install/" rel="nofollow">RVM</a> website to install it on my Ubuntu 12.04 64bit. Now when I try to install Ruby I get a building error:</p>
  
  <pre><code>$ rvm install ruby-1.9.3
  (...)
  ruby-1.9.3-p429 - #compiling...........................................
  Error running 'make -j 4'
  </code></pre>
  
  <p>Reading the make log I found:</p>
  
  <pre><code>make: the `-j' option requires a positive integral argument
  </code></pre>
  
  <p>If I pass it the number of processes, I get the following:</p>
  
  <pre><code>$ rvm install ruby-1.9.3 -j 2
  (...)
  Error running 'make -j 4 -j2'
  </code></pre>
  
  <p>I have tried other versions and get the same error. How can I fix this?</p>