前几天刚接手一个 MySQL 数据，操作系统为Ubuntu 16.04.5 LTS， 数据库版本为 5.7.23-0ubuntu0.16.04.1（APT方式安装的MySQL）。这个操作系统下的 MySQL 的配置文件 my.cnf 很多地方都让人有点不适应（跟之前的 MySQL 环境有些出入，之前都是维护 RHEL、CentOS 等操作系统环境下的 MySQL）。遂研究总结了一下。具体如下所示：

root@mylnx12:~# find / -name "my.cnf"/etc/alternatives/my.cnf/etc/mysql/my.cnf/var/lib/dpkg/alternatives/my.cnfroot@mylnx12:~# locate my.cnf/etc/alternatives/my.cnf/etc/mysql/my.cnf/etc/mysql/my.cnf.fallback/var/lib/dpkg/alternatives/my.cnfroot@mylnx12:~# mysql --help | grep my.cnf                      order of preference, my.cnf, $MYSQL_TCP_PORT,/etc/my.cnf /etc/mysql/my.cnf ~/.my.cnf root@mylnx12:~#  mysqld --verbose --help | grep -A 1 'Default options'Default options are read from the following files in the given order:/etc/my.cnf /etc/mysql/my.cnf ~/.my.cnf

从上面这些信息判断，MySQL 的参数文件为 /etc/mysql/my.cnf， 但是其他几个 my.cnf 又是什么情况呢？

root@mylnx12:~# ls -lrt /etc/alternatives/my.cnflrwxrwxrwx 1 root root 20 Sep 28 16:28 /etc/alternatives/my.cnf -> /etc/mysql/mysql.cnf

从上面信息可以看出，/etc/alternatives/my.cnf 其实是一个软连接，指向参数文件 /etc/mysql/mysql.cnf

root@mylnx12:~# cat /var/lib/dpkg/alternatives/my.cnfauto/etc/mysql/my.cnf/etc/mysql/my.cnf.fallback100/etc/mysql/mysql.cnf200

光从上面这些信息，我们还看不出 /var/lib/dpkg/alternatives/my.cnf 与其它配置文件 my.cnf 是什么关系。那么我们先来看看参数文件 /etc/mysql/my.cnf，从下面信息，可以看出 “/etc/mysql/my.cnf” 是全局配置，“~/.my.cnf” 隐藏文件是个人用户设置。

root@mylnx12:~# cat /etc/mysql/my.cnf## The MySQL database server configuration file.## You can copy this to one of:# - "/etc/mysql/my.cnf" to set global options,# - "~/.my.cnf" to set user-specific options.# # One can use all long options that the program supports.# Run program with --help to get a list of available options and with# --print-defaults to see which it would actually understand and use.## For explanations see# http://dev.mysql.com/doc/mysql/en/server-system-variables.html## * IMPORTANT: Additional settings that can override those from this file!#   The files must end with '.cnf', otherwise they'll be ignored.#!includedir /etc/mysql/conf.d/!includedir /etc/mysql/mysql.conf.d/

但是 /etc/mysql/my.cnf 参数文件下面没有任何参数设置，只看到下面两行设置，表示导入这两个目录里面的配置文件。

!includedir /etc/mysql/conf.d/ # 表示包含 /etc/mysql/conf.d/ 这个路径下面的配置文件，前提是必须以为 .cnf 为后缀!includedir /etc/mysql/mysql.conf.d/

表示包含 /etc/mysql/mysql.conf.d/ 这个路径下面的配置文件，前提是必须以为 .cnf 为后缀

其实MySQL的相关配置都位于 mysqld.cnf（/etc/mysql/mysql.conf.d/mysqld.cnf）下面。使用相关参数测试了一下，确实都能生效。这种设置确实有点让刚接触的人有点不适应。暂时先总结到此！

root@mylnx12:~# cd /etc/mysql/mysql.conf.d/root@mylnx12:/etc/mysql/mysql.conf.d# ls -lrttotal 8-rw-r--r-- 1 root root   21 Feb  4  2017 mysqld_safe_syslog.cnf-rw-r--r-- 1 root root 3148 Oct  6 23:34 mysqld.cnfroot@mylnx12:/etc/mysql/mysql.conf.d# cat mysqld.cnf## The MySQL database server configuration file.## You can copy this to one of:# - "/etc/mysql/my.cnf" to set global options,# - "~/.my.cnf" to set user-specific options.# # One can use all long options that the program supports.# Run program with --help to get a list of available options and with# --print-defaults to see which it would actually understand and use.## For explanations see# http://dev.mysql.com/doc/mysql/en/server-system-variables.html# This will be passed to all mysql clients# It has been reported that passwords should be enclosed with ticks/quotes# escpecially if they contain "#" chars...# Remember to edit /etc/mysql/debian.cnf when changing the socket location.# Here is entries for some specific programs# The following values assume you have at least 32M ram[mysqld_safe]socket          = /var/run/mysqld/mysqld.socknice            = 0[mysqld]## * Basic Settings#user            = mysqlpid-file        = /var/run/mysqld/mysqld.pidsocket          = /var/run/mysqld/mysqld.sockport            = 3306basedir         = /usrdatadir         = /var/lib/mysqltmpdir          = /tmplc-messages-dir = /usr/share/mysqlskip-external-lockinglog_bin        =  mylnx12_binserver_id      = 0character-set-server=utf8mb4collation-server=utf8mb4_general_ci## Instead of skip-networking the default is now to listen only on# localhost which is more compatible and is not less secure.bind-address            = 10.21.6.7## * Fine Tuning#key_buffer_size         = 16Mmax_allowed_packet      = 100Mthread_stack            = 192Kthread_cache_size       = 8# This replaces the startup script and checks MyISAM tables if needed# the first time they are touchedmyisam-recover-options  = BACKUP#max_connections        = 100#table_cache            = 64#thread_concurrency     = 10## * Query Cache Configuration#query_cache_limit       = 1Mquery_cache_size        = 16M## * Logging and Replication## Both location gets rotated by the cronjob.# Be aware that this log type is a performance killer.# As of 5.1 you can enable the log at runtime!#general_log_file        = /var/log/mysql/mysql.log#general_log             = 1## Error log - should be very few entries.#log_error = /var/log/mysql/error.log## Here you can see queries with especially long duration#log_slow_queries       = /var/log/mysql/mysql-slow.log#long_query_time = 2#log-queries-not-using-indexes## The following can be used as easy to replay backup logs or for replication.# note: if you are setting up a replication slave, see README.Debian about#       other settings you may need to change.#server-id              = 1#log_bin                        = /var/log/mysql/mysql-bin.logexpire_logs_days        = 10max_binlog_size   = 100M#binlog_do_db           = include_database_name#binlog_ignore_db       = include_database_name## * InnoDB## InnoDB is enabled by default with a 10MB datafile in /var/lib/mysql/.# Read the manual for more InnoDB related options. There are many!## * Security Features## Read the manual, too, if you want chroot!# chroot = /var/lib/mysql/## For generating SSL certificates I recommend the OpenSSL GUI "tinyca".## ssl-ca=/etc/mysql/cacert.pem# ssl-cert=/etc/mysql/server-cert.pem#: ssl-key=/etc/mysql/server-key.pem