第一次再centos7的系统下配置MySQL，遇到的坑不少，一一记录下，避免下次再犯
默认安装好mysql之后，数据存储的路径在/var/lib/mysql下面，下面我们修改数据的存储路径
编辑/etc/my.cnf配置文件
1、先停止数据库的运行
systemctl stop mariadb //mysql在centos7名字变成了mariadb
2、创建新的数据存储目录
mkdir /data/mysql/
给这个目录加上读写权限：
chmod 777 /mysqldata
把 /var/lib/mysql 整个目录复制到 /data/mysql/
cp -r /var/lib/mysql/* /data/mysql/
/var/log/mariadb/复制到/data/log/mariadb
cp -a /var/log/mariadb/ /data/log/mariadb
2、修改mysql配置文件，把[mysqld]下的配置项datadir注释掉（以防有问题再改回来），新加行改为新的数据存储路径
[mysqld]
#datadir=/var/lib/mysql
datadir=/mysqldata
socket=/var/lib/mysql/mysql.sock
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0
# Settings user and group are ignored when systemd is used.
# If you need to run mysqld under a different user or group,
# customize your systemd unit file for mariadb according to the
# instructions in http://fedoraproject.org/wiki/Systemd
[mysqld_safe]
#log-error=/var/log/mariadb/mariadb.log
log-error=/mysqldata/log/mariadb/mariadb.log
pid-file=/var/run/mariadb/mariadb.pid
#
# include all files from the config directory
#
3、保存文件退出。
修改 /datamysql 目录的拥有者
chown -R mysql:mysql /datamysql
4、启动 Mariadb 服务
systemctl start mariadb.service
重启的时候，报错
[root@localhost www]# systemctl start mariadb
Job for mariadb.service failed because the control process exited with error code. See "systemctl status mariadb.service" and "journalctl -xe" for details.
然后执行systemctl status mariadb.service查看状态，如下
[root@localhost www]# systemctl status mariadb.service
● mariadb.service - MariaDB database server
Loaded: loaded (/usr/lib/systemd/system/mariadb.service; enabled; vendor preset: disabled)
Active: failed (Result: exit-code) since 三 2020-01-08 09:18:40 CST; 3s ago
Process: 17001 ExecStartPost=/usr/libexec/mariadb-wait-ready $MAINPID (code=exited, status=1/FAILURE)
Process: 17000 ExecStart=/usr/bin/mysqld_safe --basedir=/usr (code=exited, status=0/SUCCESS)
Process: 16965 ExecStartPre=/usr/libexec/mariadb-prepare-db-dir %n (code=exited, status=0/SUCCESS)
Main PID: 17000 (code=exited, status=0/SUCCESS)
1月 08 09:18:39 localhost.localdomain systemd[1]: Starting MariaDB database server...
1月 08 09:18:39 localhost.localdomain mariadb-prepare-db-dir[16965]: Database MariaDB is probably initialized in /www/data already, nothing is done.
1月 08 09:18:39 localhost.localdomain mariadb-prepare-db-dir[16965]: If this is not the case, make sure the /www/data is empty before running mariadb-prepare-db-dir.
1月 08 09:18:39 localhost.localdomain mysqld_safe[17000]: 200108 09:18:39 mysqld_safe Logging to '/www/log/mariadb/mariadb.log'.
1月 08 09:18:39 localhost.localdomain mysqld_safe[17000]: 200108 09:18:39 mysqld_safe Starting mysqld daemon with databases from /www/data
1月 08 09:18:40 localhost.localdomain systemd[1]: mariadb.service: control process exited, code=exited status=1
1月 08 09:18:40 localhost.localdomain systemd[1]: Failed to start MariaDB database server.
1月 08 09:18:40 localhost.localdomain systemd[1]: Unit mariadb.service entered failed state.
1月 08 09:18:40 localhost.localdomain systemd[1]: mariadb.service failed.
然后进入到mysql的日志，有一句警告
200108 9:18:39 [Warning] Can't create test file /www/data/localhost.lower-test百度之后，通过下面的方法执行命令之后，在执行启动mysql命令，问题解决
**setenforce 0
但最好使用一个永久方法，以便在重启后继续不要这货。
修改/etc/selinux/config文件中设置SELINUX=disabled ，然后重启或等待下次重启。**