title: R Package "rvest" can not install, and the same as in Ubuntu Terminal
body: <p>Recently, I started to learn R language by using Rstudio, but when I tied to install some packages i had some problems.</p>
  
  <p>When I try to install the "rvest" package, it give the errors as following：</p>
  
  <pre><code>    &gt; install.packages("rvest")Installing package into ‘/home/zm/R/x86_64-pc-linux-gnu-library/3.4’
      (as ‘lib’ is unspecified)also installing the dependencies ‘openssl’, ‘httr’
      ??URL’https://cran.rstudio.com/src/contrib/openssl_0.9.7.tar.gz'Content type 'application/x-gzip' length 1243577 bytes (1.2 MB)==================================================downloaded 1.2 MB
      ??URL’https://cran.rstudio.com/src/contrib/httr_1.3.1.tar.gz'Content type 'application/x-gzip' length 147593 bytes (144 KB)==================================================downloaded 144 KB
      ??URL’https://cran.rstudio.com/src/contrib/rvest_0.3.2.tar.gz'Content type 'application/x-gzip' length 1597137 bytes (1.5 MB)==================================================downloaded 1.5 MB
      * installing *source* package ‘openssl’ ...** ???‘openssl’??????MD5???Using PKG_CFLAGS=
      ------------------------- ANTICONF ERROR ---------------------------
      Configuration failed because openssl was not found. Try installing:
       * deb: libssl-dev (Debian, Ubuntu, etc)
       * rpm: openssl-devel (Fedora, CentOS, RHEL)
       * csw: libssl_dev (Solaris)
       * brew: openssl@1.1 (Mac OSX)
      If openssl is already installed, check that 'pkg-config' is in your
      PATH and PKG_CONFIG_PATH contains a openssl.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 ‘openssl’* removing ‘/home/zm/R/x86_64-pc-linux-gnu-library/3.4/openssl’Warning in install.packages :
        installation of package ‘openssl’ had non-zero exit statusERROR: dependency ‘openssl’ is not available for package ‘httr’* removing ‘/home/zm/R/x86_64-pc-linux-gnu-library/3.4/httr’Warning in install.packages :
        installation of package ‘httr’ had non-zero exit statusERROR: dependency ‘httr’ is not available for package ‘rvest’* removing ‘/home/zm/R/x86_64-pc-linux-gnu-library/3.4/rvest’Warning in install.packages :
        installation of package ‘rvest’ had non-zero exit status
  </code></pre>
  
  <p>The downloaded source packages are in
      ‘/tmp/RtmpuOfZU9/downloaded_packages’</p>
  
  <hr>
  
  <p>I think the following is the key point of my problem:</p>
  
  <p>The configuration failed because <code>openssl</code> wasn't found. </p>
  
  <p>I tried to install:</p>
  
  <ul>
  <li>deb: libssl-dev (Debian, Ubuntu, etc)</li>
  <li>rpm: openssl-devel (Fedora, CentOS, RHEL)</li>
  <li>csw: libssl_dev (Solaris)</li>
  <li>brew: openssl@1.1 (Mac OSX)</li>
  </ul>
  
  <p>If openssl is already installed, check that 'pkg-config' is in your
  PATH and PKG_CONFIG_PATH contains a openssl.pc file. </p>
  
  <p>If pkg-config is unavailable, you can set INCLUDE_DIR and LIB_DIR manually via:
  <code>R CMD INSTALL --configure-vars='INCLUDE_DIR=... LIB_DIR=...'</code></p>
  
  <p>I also started to install the packages in Ubuntu. However, I even didn't success to install them in Ubuntu.</p>
  
  <p>And I also tried the following method: <code>export PKG_CONFIG_PATH=/cv/lib:$PKG_CONFIG_PATH</code>
  Without success..</p>
  
  <p>Could somebody help me to figure out what happened, thank you very much!</p>