MySQL的安装
我因为新的项目用的 gem 'mysql2', '0.4.5'，与我的 MySQL 5.7 不兼容，就重装了MySQL。
但执行 mysql -uroot，报错 ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)
执行 ln -s /usr/local/var/mysql/mysql.sock /tmp/mysql.sock后，
再执行 mysql -uroot，报错ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/usr/local/var/mysql/mysql.sock' (2)
去/usr/local/var/mysql 目录查看，发现根本没有 mysql.sock 文件。所以，不只是没有软链接的问题。
又Google到了各种答案，各种尝试后都还是不行。
最终搜到了以下答案，直接彻底删除之前的MySQL，然后重装：brew install mysql on mac os
brew remove mysql
brew cleanup
launchctl unload -w ~/Library/LaunchAgents/homebrew.mxcl.mysql.plist
rm ~/Library/LaunchAgents/homebrew.mxcl.mysql.plist
sudo rm -rf /usr/local/var/mysql
brew install mysql #安装最新版本
brew install [email protected] #安装指定版本
unset TMPDIR
mysql.server start
mysql -uroot
我自己一开始的重装出错的原因，应该就是没有彻底删除之前的MySQL。
执行 rails console时，若报错： Library not loaded: /usr/local/opt/mysql/lib/libmysqlclient.20.dylib (LoadError)， 说明是重装了MySQL，rails 找不到 mysql的相关文件了。这时需要依次执行：
gem uninstall mysql2
gem install mysql
安装 gem mysql2 的指定版本
比如Rails项目的Gemfile中使用的是 gem mysql2 0.3.18 版本，执行 gem install mysql2 -v '0.3.18',报错：
Building native extensions. This could take a while...
ERROR: Error installing mysql2:
ERROR: Failed to build gem native extension.
/Users/huazai/.rvm/rubies/ruby-2.1.1/bin/ruby 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
-----
Using mysql_config at /usr/local/bin/mysql_config
-----
checking for mysql.h... yes
checking for errmsg.h... yes
checking for mysqld_error.h... yes
-----
Setting rpath to /usr/local/Cellar/mysql/8.0.15/lib
-----
creating Makefile
make "DESTDIR=" clean
make "DESTDIR="
compiling client.c
client.c:431:3: error: use of undeclared identifier 'my_bool'
my_bool res = mysql_read_query_result(client);
^
client.c:433:19: error: use of undeclared identifier 'res'
return (void *)(res == 0 ? Qtrue : Qfalse);
^
client.c:762:3: error: use of undeclared identifier 'my_bool'
my_bool boolval;
^
client.c:793:7: error: use of undeclared identifier 'boolval'
boolval = (value == Qfalse ? 0 : 1);
^
client.c:794:17: error: use of undeclared identifier 'boolval'
retval = &boolval;
^
client.c:797:10: error: use of undeclared identifier 'MYSQL_SECURE_AUTH'; did you mean 'MYSQL_DEFAULT_AUTH'?
case MYSQL_SECURE_AUTH:
^~~~~~~~~~~~~~~~~
MYSQL_DEFAULT_AUTH
/usr/local/Cellar/mysql/8.0.15/include/mysql/mysql.h:188:3: note: 'MYSQL_DEFAULT_AUTH' declared here
MYSQL_DEFAULT_AUTH,
^
client.c:798:7: error: use of undeclared identifier 'boolval'
boolval = (value == Qfalse ? 0 : 1);
^
client.c:799:17: error: use of undeclared identifier 'boolval'
retval = &boolval;
^
client.c:830:38: error: use of undeclared identifier 'boolval'
wrapper->reconnect_enabled = boolval;
^
client.c:1196:38: error: use of undeclared identifier 'MYSQL_SECURE_AUTH'; did you mean 'MYSQL_DEFAULT_AUTH'?
return _mysql_client_options(self, MYSQL_SECURE_AUTH, value);
^~~~~~~~~~~~~~~~~
MYSQL_DEFAULT_AUTH
/usr/local/Cellar/mysql/8.0.15/include/mysql/mysql.h:188:3: note: 'MYSQL_DEFAULT_AUTH' declared here
MYSQL_DEFAULT_AUTH,
^
10 errors generated.
make: *** [client.o] Error 1
make failed, exit code 2
是因为 和 mysql 的高版本不兼容。需要卸载 MySQL重装兼容的版本，比如 MySQL 5.7版。
但安装5.7版后再执行 gem install mysql2 -v '0.3.18' --source 'https://gems.ruby-china.com/ 又报错：
Building native extensions. This could take a while...
ERROR: Error installing mysql2:
ERROR: Failed to build gem native extension.
/Users/huazai/.rvm/rubies/ruby-2.1.1/bin/ruby 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
checking for main() in -lm... yes
checking for mysql_query() in -lmysqlclient... no
checking for main() in -lz... yes
checking for mysql_query() in -lmysqlclient... no
checking for main() in -lsocket... no
checking for mysql_query() in -lmysqlclient... no
checking for main() in -lnsl... no
checking for mysql_query() in -lmysqlclient... no
checking for main() in -lmygcc... no
checking for mysql_query() in -lmysqlclient... no
*** 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=/Users/huazai/.rvm/rubies/ruby-2.1.1/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
--with-mlib
--without-mlib
--with-mysqlclientlib
--without-mysqlclientlib
--with-zlib
--without-zlib
--with-mysqlclientlib
--without-mysqlclientlib
--with-socketlib
--without-socketlib
--with-mysqlclientlib
--without-mysqlclientlib
--with-nsllib
--without-nsllib
--with-mysqlclientlib
--without-mysqlclientlib
--with-mygcclib
--without-mygcclib
--with-mysqlclientlib
--without-mysqlclientlib
extconf failed, exit code 1
也搜到了各种方法，都没解决问题。可能是我重装之前删掉了一些不该删除的文件。不知道以后还会不会带来灾难，哈哈哈哈哈哈哈哈哈哈哈
我是最后通过执行gem install mysql2 -v '0.3.18' --source 'https://gems.ruby-china.com/' -- --with-mysql-config=/usr/local/Cellar/[email protected]/5.7.25/bin/mysql_config 才安装成功了。
执行 rails console时，若报错：Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2) (Mysql2::Error)，执行ln -s /usr/local/var/mysql/mysql.sock /tmp/mysql.sock ，如果报错 ln: /tmp/mysql.sock: File exists ，可先将文件/tmp/mysql.sock删除，再执行 ln -s /usr/local/var/mysql/mysql.sock /tmp/mysql.sock