Errors Installing mysql2 gem via the Bundler

I am trying to install the mysql2 gem via the Bundler, but it keeps dying with the following error:

** executing command
/home/cc_rails/.rvm/rubies/ruby-1.9.2-p0/lib/ruby/1.9.1/rubygems/installer.rb:483:in 'rescue in block in build_extensions': 
ERROR: Failed to build gem native extension. (Gem::Installer::ExtensionBuildError)

/home/cc_rails/.rvm/rubies/ruby-1.9.2-p0/bin/ruby extconf.rb --with-mysql-config=/usr/bin/mysql_config
checking for rb_thread_blocking_region()... 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
--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/cc_rails/.rvm/rubies/ruby-1.9.2-p0/bin/ruby
--with-mysql-config
Gem files will remain installed for inspection.

Most things I found via Googling recommended passing the --with-mysql-config parameter to fix it. So, based on:

$ which mysql_config
/usr/bin/mysql_config

I added the following to the Bundler's config:

$ bundle config build.mysql2 --with-mysql-config='/usr/bin/mysql_config'

However, still no luck -- same crash as above.

Since it's dying with the error mysql.h is missing, I checked for that, and it's allegedly around, just can't be found by the Bundler.

$ find / -name mysql.h
/usr/include/mysql5/mysql/mysql.h

Any thoughts?

Answer was similar to the one Wrikken posted -- here's what I did to fix it for the sake of future readers.

(This is for RHEL 5.5 -- similar but different commands apply for Ubuntu/Debian/etc.)

Doing sudo yum list installed will print out all installed packages on your machine (note: yum on RHEL requires you add a Red Hat Network repository [I use EPEL], and run it via sudo).

I had mysql and mysql-server, which explained why MySQL worked fine for every pre-existing app, but no mysql-devel, which is necessary to fix that mysql.h is missing error and similar other build errors.

Long story short, after a mysqldump -u root -ppassword --all-databases > full-dump.sql for safety, it was fixed with a simple

sudo yum install mysql-devel

For Ubuntu have to install following. libmysqlclient-dev libmysqlclient16

For Mac with a brew install of mysql the following solution fixed the problem for me:

I edited the mysql_config file in /usr/local/Cellar/mysql/5.6.12/bin and removed the W-compiler options -Wno-null-conversion and -Wno-unused-private-field for cflags and cxxflags.

This solved the problem with "gem install mysql2".

Reference: http://www.randomactsofsentience.com/2013/05/gem-install-mysql2-missing-mysqlh-on-os.html