title: Cannot install R packages within WRDS Interactive R session
body: <p>I would like to install the R package 'rstan' in an interactive R session on the WRDS server, but cannot manage to install it, or any other packages.</p>
  
  <p>I have tried specifying the CRAN mirrors directly in the install.packages() command.</p>
  
  <p>I have tried the following within an interactive WRDS session:</p>
  
  <pre><code>install.packages("rstan", dep= T)
  </code></pre>
  
  <p>Actual results:</p>
  
  <pre><code>install.packages("rstan", dep= T)
  </code></pre>
  
  <p>Installing package into ‘/usr/local/sas/grid/R-3.5.1-linux-library’
  (as ‘lib’ is unspecified)
  Warning in install.packages("rsta", dep = T) :
    'lib = "/usr/local/sas/grid/R-3.5.1-linux-library"' is not writable
  Would you like to use a personal library instead? (yes/No/cancel)</p>
  
  <pre><code>yes
  </code></pre>
  
  <p>--- Please select a CRAN mirror for use in this session ---</p>
  
  <p>Then after I pick any mirror, I get:</p>
  
  <p>Warning: unable to access index for repository <a href="http://wbc.upm.edu.my/cran/src/contrib" rel="nofollow noreferrer">http://wbc.upm.edu.my/cran/src/contrib</a>:
    cannot open URL '<a href="http://wbc.upm.edu.my/cran/src/contrib/PACKAGES" rel="nofollow noreferrer">http://wbc.upm.edu.my/cran/src/contrib/PACKAGES</a>'
  Warning messages:
  1: In download.file(url, destfile = f, quiet = TRUE) :
    URL '<a href="https://cran.r-project.org/CRAN_mirrors.csv" rel="nofollow noreferrer">https://cran.r-project.org/CRAN_mirrors.csv</a>': status was 'Couldn't connect to server'
  2: package ‘rstan’ is not available (for R version 3.5.1) </p>