Ubuntu下麵MySQL的參數文件my.cnf淺析

前幾天剛接手一個MySQL數據，操作系統為Ubuntu 16.04.5 LTS，  資料庫版本為5.7.23-0ubuntu0.16.04.1（APT方式安裝的MySQL）。這個操作系統下的MySQL的配置文件my.cnf很多地方都讓人有點不適應（跟之前的MySQL環境有些出入，之前都是維護RHEL、CentOS等操作系統環境下的MySQL）。遂研究總結了一下。具體如下所示：

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 

從上面這些信息判斷，MySQL的參數文件為/etc/mysql/my.cnf， 但是其他幾個my.cnf又是什麼情況呢？

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

從上面信息可以看出，/etc/alternatives/my.cnf 其實是一個軟連接，指向參數文件/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

光從上面這些信息，我們還看不出/var/lib/dpkg/alternatives/my.cnf與其它配置文件my.cnf是什麼關係。那麼我們先來看看參數文件/etc/mysql/my.cnf,從下麵信息，可以看出“/etc/mysql/my.cnf”是全局配置，“~/.my.cnf”隱藏文件是個人用戶設置.

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參數文件下麵沒有任何參數設置，只看到下麵兩行設置，表示導入這兩個目錄裡面的配置文件。

!includedir /etc/mysql/conf.d/     

#表示包含/etc/mysql/conf.d/這個路徑下麵的配置文件，前提是必須以為.cnf為尾碼

!includedir /etc/mysql/mysql.conf.d/

#表示包含/etc/mysql/mysql.conf.d/這個路徑下麵的配置文件，前提是必須以為.cnf為尾碼

其實MySQL的相關配置都位於mysqld.cnf（/etc/mysql/mysql.conf.d/mysqld.cnf）下麵。使用相關參數測試了一下，確實都能生效。這種設置確實有點讓剛接觸的人有點不適應。暫時先總結到此！

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

#