title: Cannot install mysql2 gem for Rails project
body: <p>I've looked at and tried just about everything on the topic here at Stackoverflow.com and still can't figure this out...</p>
  
  <p>When I 'gem install mysql2' I get a permissions error. when I 'sudo gem install mysql2' I get the following:</p>
  
  <pre><code>    Teds-MacBook-Pro:~ tedmartin$ sudo gem install mysql2
  Building native extensions.  This could take a while...
  ERROR:  Error installing mysql2:
      ERROR: Failed to build gem native extension.
  
      current directory: /Users/tedmartin/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/mysql2-0.4.5/ext/mysql2
  /Users/tedmartin/.rbenv/versions/2.4.1/bin/ruby -r ./siteconf20170420-50202-1nekuvd.rb extconf.rb
  checking for rb_absint_size()... yes
  checking for rb_absint_singlebit_p()... yes
  checking for ruby/thread.h... yes
  checking for rb_thread_call_without_gvl() in ruby/thread.h... yes
  checking for rb_thread_blocking_region()... no
  checking for rb_wait_for_single_fd()... yes
  checking for rb_hash_dup()... yes
  checking for rb_intern3()... yes
  checking for rb_big_cmp()... yes
  -----
  Using mysql_config at /usr/local/bin/mysql_config
  -----
  checking for mysql.h... yes
  checking for SSL_MODE_DISABLED in mysql.h... yes
  checking for SSL_MODE_PREFERRED in mysql.h... yes
  checking for SSL_MODE_REQUIRED in mysql.h... yes
  checking for SSL_MODE_VERIFY_CA in mysql.h... yes
  checking for SSL_MODE_VERIFY_IDENTITY in mysql.h... yes
  checking for errmsg.h... yes
  checking for mysqld_error.h... yes
  -----
  Don't know how to set rpath on your system, if MySQL libraries are not in path mysql2 may not load
  -----
  -----
  Setting libpath to /usr/local/Cellar/mysql-connector-c/6.1.9/lib
  -----
  creating Makefile
  
  current directory: /Users/tedmartin/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/mysql2-0.4.5/ext/mysql2
  make "DESTDIR=" clean
  
  current directory: /Users/tedmartin/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/mysql2-0.4.5/ext/mysql2
  make "DESTDIR="
  compiling client.c
  compiling infile.c
  compiling mysql2_ext.c
  compiling result.c
  compiling statement.c
  linking shared-object mysql2/mysql2.bundle
  ld: library not found for -l-lpthread
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  make: *** [mysql2.bundle] Error 1
  
  make failed, exit code 2
  
  Gem files will remain installed in /Users/tedmartin/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/gems/mysql2-0.4.5 for inspection.
  Results logged to /Users/tedmartin/.rbenv/versions/2.4.1/lib/ruby/gems/2.4.0/extensions/x86_64-darwin-15/2.4.0-static/mysql2-0.4.5/gem_make.out
  </code></pre>
  
  <p>Anyone who has an idea, suggestion, tip, fix, etc... I'd be really grateful.</p>
  
  <p>Thanks!</p>