I get "failed to build gem native extension." when I'm trying to install mysql2 (OSX)

Question

When I'm trying to install mysql2 I get error mysql.h is missing. But when I try to install mysql (needed mysql-devel) then I get warning "mysql is already installed". So why I get the error message? THX for reply! (RoR 2.0.0)

sudo gem install mysql2 -v '0.3.11'
Building native extensions.  This could take a while...
ERROR:  Error installing mysql2:
   ERROR: Failed to build gem native extension.

/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/bin/ruby extconf.rb
checking for rb_thread_blocking_region()... yes
checking for rb_wait_for_single_fd()... yes
checking for mysql.h... no
checking for mysql/mysql.h... no
-----
mysql.h is missing.  please check your installation of mysql and try again.
-----
*** 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
--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=/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/bin/ruby
--with-mysql-config
--without-mysql-config


Gem files will remain installed in /Users/michaljurnik/.rvm/gems/ruby-1.9.3-    p448/gems/mysql2-0.3.11 for inspection.
Results logged to /Users/michaljurnik/.rvm/gems/ruby-1.9.3-p448/gems/mysql2-0.3.11/ext/mysql2/gem_make.out

And installation of mysql

brew install mysql
Warning: mysql-5.6.12 already installed

mkmf.log:

have_func: checking for rb_thread_blocking_region()... -------------------- yes

"/usr/local/bin/gcc-4.2 -o conftest -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1/x86_64-darwin12.4.0 -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1/ruby/backward -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -I/usr/local/opt/libyaml/include -I/usr/local/opt/readline/include -I/usr/local/opt/libksba/include -I/usr/local/opt/openssl/include  -O3 -ggdb -Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wshorten-64-to-32 -Wimplicit-function-declaration  -fno-common -pipe conftest.c  -L. -L/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/readline/lib -L/usr/local/opt/libksba/lib -L/usr/local/opt/openssl/lib -L. -L/usr/local/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/readline/lib -L/usr/local/opt/libksba/lib -L/usr/local/opt/openssl/lib      -lruby.1.9.1  -lpthread -ldl -lobjc "
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: int main(int argc, char **argv)
4: {
5:   return 0;
6: }
/* end */

"/usr/local/bin/gcc-4.2 -o conftest -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1/x86_64-darwin12.4.0 -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1/ruby/backward -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -I/usr/local/opt/libyaml/include -I/usr/local/opt/readline/include -I/usr/local/opt/libksba/include -I/usr/local/opt/openssl/include  -O3 -ggdb -Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wshorten-64-to-32 -Wimplicit-function-declaration  -fno-common -pipe conftest.c  -L. -L/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/readline/lib -L/usr/local/opt/libksba/lib -L/usr/local/opt/openssl/lib -L. -L/usr/local/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/readline/lib -L/usr/local/opt/libksba/lib -L/usr/local/opt/openssl/lib      -lruby.1.9.1  -lpthread -ldl -lobjc "
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: /*top*/
 4: int t() { void ((*volatile p)()); p = (void ((*)()))rb_thread_blocking_region; return 0; }
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     printf("%p", &t);
 9:   }
10: 
11:   return 0;
12: }
/* end */

--------------------

have_func: checking for rb_wait_for_single_fd()... -------------------- yes

"/usr/local/bin/gcc-4.2 -o conftest -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1/x86_64-darwin12.4.0 -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1/ruby/backward -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -I/usr/local/opt/libyaml/include -I/usr/local/opt/readline/include -I/usr/local/opt/libksba/include -I/usr/local/opt/openssl/include  -O3 -ggdb -Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wshorten-64-to-32 -Wimplicit-function-declaration  -fno-common -pipe conftest.c  -L. -L/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/readline/lib -L/usr/local/opt/libksba/lib -L/usr/local/opt/openssl/lib -L. -L/usr/local/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/readline/lib -L/usr/local/opt/libksba/lib -L/usr/local/opt/openssl/lib      -lruby.1.9.1  -lpthread -ldl -lobjc "
conftest.c: In function ‘t’:
conftest.c:4: error: ‘rb_wait_for_single_fd’ undeclared (first use in this function)
conftest.c:4: error: (Each undeclared identifier is reported only once
conftest.c:4: error: for each function it appears in.)
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: /*top*/
 4: int t() { void ((*volatile p)()); p = (void ((*)()))rb_wait_for_single_fd; return 0; }
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     printf("%p", &t);
 9:   }
10: 
11:   return 0;
12: }
/* end */

"/usr/local/bin/gcc-4.2 -o conftest -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1/x86_64-darwin12.4.0 -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1/ruby/backward -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -I/usr/local/opt/libyaml/include -I/usr/local/opt/readline/include -I/usr/local/opt/libksba/include -I/usr/local/opt/openssl/include  -O3 -ggdb -Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wshorten-64-to-32 -Wimplicit-function-declaration  -fno-common -pipe conftest.c  -L. -L/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/readline/lib -L/usr/local/opt/libksba/lib -L/usr/local/opt/openssl/lib -L. -L/usr/local/lib -L/usr/local/opt/libyaml/lib -L/usr/local/opt/readline/lib -L/usr/local/opt/libksba/lib -L/usr/local/opt/openssl/lib      -lruby.1.9.1  -lpthread -ldl -lobjc "
conftest.c: In function ‘t’:
conftest.c:4: warning: implicit declaration of function ‘rb_wait_for_single_fd’
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: /*top*/
 4: int t() { rb_wait_for_single_fd(); return 0; }
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     printf("%p", &t);
 9:   }
10: 
11:   return 0;
12: }
/* end */

--------------------

have_header: checking for mysql.h... -------------------- no

"/usr/local/bin/gcc-4.2 -E -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1/x86_64-darwin12.4.0 -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1/ruby/backward -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -I/usr/local/opt/libyaml/include -I/usr/local/opt/readline/include -I/usr/local/opt/libksba/include -I/usr/local/opt/openssl/include -I/usr/local/Cellar/mysql/5.6.12/include  -Wno-null-conversion -Os -g -fno-strict-aliasing  -O3 -ggdb -Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wshorten-64-to-32 -Wimplicit-function-declaration  -fno-common -pipe  conftest.c -o conftest.i"
cc1: error: unrecognized command line option "-Wno-null-conversion"
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: #include <mysql.h>
/* end */

--------------------

have_header: checking for mysql/mysql.h... -------------------- no

"/usr/local/bin/gcc-4.2 -E -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1/x86_64-darwin12.4.0 -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1/ruby/backward -I/Users/michaljurnik/.rvm/rubies/ruby-1.9.3-p448/include/ruby-1.9.1 -I. -D_XOPEN_SOURCE -D_DARWIN_C_SOURCE   -I/usr/local/opt/libyaml/include -I/usr/local/opt/readline/include -I/usr/local/opt/libksba/include -I/usr/local/opt/openssl/include -I/usr/local/Cellar/mysql/5.6.12/include  -Wno-null-conversion -Os -g -fno-strict-aliasing  -O3 -ggdb -Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wshorten-64-to-32 -Wimplicit-function-declaration  -fno-common -pipe  conftest.c -o conftest.i"
cc1: error: unrecognized command line option "-Wno-null-conversion"
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: #include <mysql/mysql.h>
/* end */

--------------------

Answer 1

Try to install only mysql without the "2":

gem install mysql

Answer 2

The solution is using sudo apt-get install libmysqlclient-dev, because it requires mysql development libraries to be installed on the server.