以which命令尋mysql于何處：
which mysql得徑：
/usr/bin/mysql以此徑尋配置文件:
/usr/bin/mysql --verbose --help | grep -A 1 'Default options'顯示信息：
Default options are read from the following files in the given order:
/etc/mysql/my.cnf /etc/my.cnf ~/.my.cnf 其意為：
服务器先讀/etc/mysql/my.cnf，如不存在則讀/etc/my.cnf，仍不存在則讀~/.my.cnf文件
打開/etc/mysql/my.cnf：
除末兩行，他行皆注釋，而我竟不知“！”號何意？
#
# 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/于其中 mysqld.cnf文件見datadir值更為"/mnt/mysql"