title: Installing the PostgreSQL gem with 'gem pq' fails with ERROR: Failed to build gem native extension
body: <p>I am learning Ruby on Rails and trying to develop an application.
  In my application I am trying to use the default <strong>SQLite database in the Development Mode</strong> and <strong>PostgreSQL in the Production Mode</strong>.
  But I'm getting the following error while trying to install pg gem using: <code>gem install pg</code></p>
  
  <pre><code>Building native extensions.  This could take a while...
  ERROR:  Error installing pg:
          ERROR: Failed to build gem native extension.
   
      /home/tusharkhatiwada/.rvm/rubies/ruby-2.0.0-p247/bin/ruby extconf.rb
  checking for pg_config... yes
  Using config values from /usr/bin/pg_config
  You need to install postgresql-server-dev-X.Y for building a server-side extension or libpq-dev
   for building a client-side application.
  You need to install postgresql-server-dev-X.Y for building a server-side extension or libpq-dev
   for building a client-side application.
  checking for libpq-fe.h... no
  Can't find the 'libpq-fe.h header
  *** extconf.rb failed ***
  Could not create Makefile due to some reason, probably lack of necessary
  libraries and/or headers.  Check the mkmf.log file for more details.  You may
  need configuration options.
   
  Provided configuration options:
          --with-opt-dir
          --without-opt-dir
          --with-opt-include
          --without-opt-include=${opt-dir}/include
          --with-opt-lib
          --without-opt-lib=${opt-dir}/lib
          --with-make-prog
          --without-make-prog
          --srcdir=.
          --curdir
          --ruby=/home/tusharkhatiwada/.rvm/rubies/ruby-2.0.0-p247/bin/ruby
          --with-pg
          --without-pg
          --with-pg-config
          --without-pg-config
          --with-pg_config
          --without-pg_config
          --with-pg-dir
          --without-pg-dir
          --with-pg-include
          --without-pg-include=${pg-dir}/include
          --with-pg-lib
          --without-pg-lib=${pg-dir}/
   
   
  Gem files will remain installed in /home/tusharkhatiwada/.rvm/gems/ruby-2.0.0-p247@rails4.0.0/g
  ems/pg-0.17.0 for inspection.
  Results logged to /home/tusharkhatiwada/.rvm/gems/ruby-2.0.0-p247@rails4.0.0/gems/pg-0.17.0/ext
  /gem_make.out
  </code></pre>
  
  <p>After that I again tried with <code>gem install pg -- --with-pg-config= '/usr/bin/pg_config'</code>
  and the following error is displayed:</p>
  
  <pre><code>Building native extensions with: '--with-pg-config= /usr/bin/pg_config'
  This could take a while...
  ERROR:  Error installing pg:
          ERROR: Failed to build gem native extension.
   
      /home/tusharkhatiwada/.rvm/rubies/ruby-2.0.0-p247/bin/ruby extconf.rb --with-pg-config= /us
  r/bin/pg_config
  Using config values from 
  sh: 1: : Permission denied
  sh: 1: : Permission denied
  checking for libpq-fe.h... no
  Can't find the 'libpq-fe.h header
  *** extconf.rb failed ***
  Could not create Makefile due to some reason, probably lack of necessary
  libraries and/or headers.  Check the mkmf.log file for more details.  You may
  need configuration options.
   
  Provided configuration options:
          --with-opt-dir
          --without-opt-dir
          --with-opt-include
          --without-opt-include=${opt-dir}/include
          --with-opt-lib
          --without-opt-lib=${opt-dir}/lib
          --with-make-prog
          --without-make-prog
          --srcdir=.
          --curdir
          --ruby=/home/tusharkhatiwada/.rvm/rubies/ruby-2.0.0-p247/bin/ruby
          --with-pg
          --without-pg
          --with-pg-config
          --with-pg-dir
          --without-pg-dir
          --with-pg-include
          --without-pg-include=${pg-dir}/include
          --with-pg-lib
          --without-pg-lib=${pg-dir}/
   
   
  Gem files will remain installed in /home/tusharkhatiwada/.rvm/gems/ruby-2.0.0-p247@rails4.0.0/g
  ems/pg-0.17.0 for inspection.
  Results logged to /home/tusharkhatiwada/.rvm/gems/ruby-2.0.0-p247@rails4.0.0/gems/pg-0.17.0/ext
  /gem_make.out
  </code></pre>