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.cnf

root@mylnx12:~# locate my.cnf

/etc/alternatives/my.cnf

/etc/mysql/my.cnf

/etc/mysql/my.cnf.fallback

/var/lib/dpkg/alternatives/my.cnf

root@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.cnf

lrwxrwxrwx 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.cnf

auto

/etc/mysql/my.cnf

/etc/mysql/my.cnf.fallback

100

/etc/mysql/mysql.cnf

200

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 -lrt

total 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.cnf

root@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.sock

nice            = 0

[mysqld]

#

# * Basic Settings

#

user            = mysql

pid-file        = /var/run/mysqld/mysqld.pid

socket          = /var/run/mysqld/mysqld.sock

port            = 3306

basedir         = /usr

datadir         = /var/lib/mysql

tmpdir          = /tmp

lc-messages-dir = /usr/share/mysql

skip-external-locking

log_bin        =  mylnx12_bin

server_id      = 0

character-set-server=utf8mb4

collation-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         = 16M

max_allowed_packet      = 100M

thread_stack            = 192K

thread_cache_size       = 8

# This replaces the startup script and checks MyISAM tables if needed

# the first time they are touched

myisam-recover-options  = BACKUP

#max_connections        = 100

#table_cache            = 64

#thread_concurrency     = 10

#

# * Query Cache Configuration

#

query_cache_limit       = 1M

query_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.log

expire_logs_days        = 10

max_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