今天在折腾MySQL的参数文件时，突然发现MySQL 5.6.20-enterprise-commercial-advanced-log这个版本数据库的参数文件my.cnf的位置有点奇怪，如下所示：
[root@DB-Server ~]# mysql --help | grep my.cnf
order of preference, my.cnf, $MYSQL_TCP_PORT,
/etc/my.cnf /etc/mysql/my.cnf /usr/etc/my.cnf ~/.my.cnf
[root@DB-Server ~]# ls -lrt /etc/my.cnf /etc/mysql/my.cnf /usr/etc/my.cnf ~/.my.cnf
ls: /etc/my.cnf: No such file or directory
ls: /etc/mysql/my.cnf: No such file or directory
ls: /usr/etc/my.cnf: No such file or directory
ls: /root/.my.cnf: No such file or directory
[root@DB-Server ~]# locate my.cnf
/usr/my.cnf
[root@DB-Server ~]# find / -name "my.cnf"
/usr/my.cnf
我们知道MySQL启动的时候，会先去读取参数文件my.cnf中的参数去初始化，默认情况下，MySQL会按一定的顺序来读取参数文件，这个顺序为/etc/my.cnf /etc/mysql/my.cnf /usr/etc/my.cnf ~/.my.cnf 但是，在这个MySQL版本中my.cnf 参数文件位于/usr/my.cnf下，Why？ 一头懵逼！ 然后我测试了一下其它版本，例如mysql-community-server-5.7.18，确实都是位于指定的目录，如下所示
[root@gettestlnx02 ~]# locate my.cnf
/etc/my.cnf
/etc/my.cnf.d
[root@gettestlnx02 ~]# strace mysql ";" 2>&1 | grep my.cnf
stat64("/etc/my.cnf", {st_mode=S_IFREG|0644, st_size=979, ...}) = 0
open("/etc/my.cnf", O_RDONLY|O_LARGEFILE) = 3
stat64("/etc/mysql/my.cnf", 0xffc0f4a0) = -1 ENOENT (No such file or directory)
stat64("/usr/etc/my.cnf", 0xffc0f4a0) = -1 ENOENT (No such file or directory)
stat64("/root/.my.cnf", 0xffc0f4a0) = -1 ENOENT (No such file or directory)
[root@gettestlnx02 ~]# rpm -qf /etc/my.cnf
mysql-community-server-5.7.18-1.el6.i686
[root@gettestlnx02 ~]#
后面搜索了一下，发现这居然是一个bug来着。具体参考下面链接
https://bugs.mysql.com/bug.php?id=68318
https://bugs.mysql.com/bug.php?id=71600
With recent MySQL 5.6 versions, the RPM installation generate a non-standard /usr/my.cnf file overriding the sql_mode set in /etc/my.cnf as per: https://bugs.mysql.com/bug.php?id=71600
This occurs during upcp when minor MySQL updates are installed and breaks some sites due to "STRICT_TRANS_TABLES".
Please add the flag --keep-my-cnf when executing mysql_install_db or otherwise remove the /usr/my.cnf file after MySQL upgrade during upcp to remove this unexpected change.
参考资料：
https://features.cpanel.net/topic/disable-creation-of-usrmy-cnf-when-mysql-is-installed
https://bugs.mysql.com/bug.php?id=71600