title: Problem installing Sodium package in R on an Ubuntu system
body: <p>I am trying to install a package called <code>sodium</code> in R on an Ubuntu system but I'm getting an error message like the following:</p>
  
  <pre><code>install.packages("sodium", dependencies = T)
  
  ...
  
  * installing *source* package ‘sodium’ ...
  ** package ‘sodium’ successfully unpacked and MD5 sums checked
  Package libsodium was not found in the pkg-config search path.
  Perhaps you should add the directory containing `libsodium.pc'
  to the PKG_CONFIG_PATH environment variable
  No package 'libsodium' found
  Using PKG_CFLAGS=
  Using PKG_LIBS=-lsodium
  ------------------------- ANTICONF ERROR ---------------------------
  Configuration failed because libsodium was not found. Try installing:
   * deb: libsodium-dev (Debian, Ubuntu, etc)
   * rpm: libsodium-devel (Fedora, EPEL)
   * csw: libsodium_dev (Solaris)
   * brew: libsodium (OSX)
  If libsodium is already installed, check that 'pkg-config' is in your
  PATH and PKG_CONFIG_PATH contains a libsodium.pc file. If pkg-config
  is unavailable you can set INCLUDE_DIR and LIB_DIR manually via:
  R CMD INSTALL --configure-vars='INCLUDE_DIR=... LIB_DIR=...'
  --------------------------------------------------------------------
  ERROR: configuration failed for package ‘sodium’
  * removing ‘/R/x86_64-pc-linux-gnu-library/3.4/sodium’
  Warning in install.packages :
    installation of package ‘sodium’ had non-zero exit status
  
  The downloaded source packages are in
      ‘/tmp/Rtmph70q7Q/downloaded_packages’
  </code></pre>
  
  <p>The following code didn't install it either.</p>
  
  <pre><code>install.packages("libsodium-dev", dependencies = T)
  
  Warning in install.packages :
    package ‘libsodium-dev’ is not available (for R version 3.4.4)
  </code></pre>
  
  <p>I also tried <code>install_github</code> but still get an error:</p>
  
  <pre><code>devtools::install_github("jedisct1/libsodium")
  
  Error: Failed to install 'unknown package' from GitHub:
    Timeout was reached: [api.github.com] Resolving timed out after 10000 milliseconds
  </code></pre>
  
  <p>Any idea on how to install this package?</p>
  
  <p>I wish installing packages on an Ubuntu R was as error free as doing it on Windows R.
  If someone could teach me how to avoid package installing errors in Ubuntu R, it'd be great.</p>