1.ERROR: While executing gem ... (Gem::Exception) Unable to require openssl, install OpenSSL and rebuild ruby (preferred) or use non-HTTPS sources
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方法：
进入ruby源码解压包，进入ruby 源码包下的 ext/openssl ，用ruby自带的openssl编译，而不是yum 的openssl
cd /root/ruby-2.1.5/ext/openssl ruby extconf.rb 成功... make 报错.... make: *** No rule to make target `/thread_native.h', needed by `ossl.o'. Stop. 解决方法： 打开Makefile vim Makefile 加入第三行路径，也就是【top_srcdir = /root/ruby-2.1.5】 srcdir = . topdir = /usr/local/ruby/include/ruby-2.1.0 top_srcdir = /root/ruby-2.1.5 hdrdir = $(topdir) 保存退出，make clean， 重新make,成功， make install 成功 [root@MySQL openssl]# make linking shared-object openssl.so [root@mysql openssl]# make install /usr/bin/install -c -m 0755 openssl.so /usr/local/ruby/lib/ruby/site_ruby/2.1.0/x86_64-linux installing default openssl libraries
2.
gem install mysql2
Fetching: mysql2-0.4.3.gem (100%)
Building native extensions. This could take a while...
ERROR: Error installing mysql2:
ERROR: Failed to build gem native extension.
/usr/local/ruby/bin/ruby -r ./siteconf20160321-3049-192s9jh.rb extconf.rb
checking for ruby/thread.h... yes
checking for rb_thread_call_without_gvl() in ruby/thread.h... yes
checking for rb_thread_blocking_region()... yes
checking for rb_wait_for_single_fd()... yes
checking for rb_hash_dup()... yes
checking for rb_intern3()... yes
checking for mysql_query() in -lmysqlclient... no
-----
mysql client is missing. You may need to 'apt-get install libmysqlclient-dev' or 'yum install mysql-devel', and try again.
-----
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers. Check the mkmf.log file for more details. You may
need configuration options.
Provided configuration options:
--with-opt-dir
--without-opt-dir
--with-opt-include
--without-opt-include=${opt-dir}/include
--with-opt-lib
--without-opt-lib=${opt-dir}/lib
--with-make-prog
--without-make-prog
--srcdir=.
--curdir
--ruby=/usr/local/ruby/bin/ruby
--with-mysql-dir
--without-mysql-dir
--with-mysql-include
--without-mysql-include=${mysql-dir}/include
--with-mysql-lib
--without-mysql-lib=${mysql-dir}/lib
--with-mysql-config
--without-mysql-config
--with-mysql-dir
--without-mysql-dir
--with-mysql-include
--without-mysql-include=${mysql-dir}/include
--with-mysql-lib
--without-mysql-lib=${mysql-dir}/lib
--with-mysqlclientlib
--without-mysqlclientlib已经讲的很清楚了，安装mysql-devel
yum install mysql-devel
