rpm -qa|grep -i mysql

rpm -ev --nodeps mysql-community-release-el7-5.noarch
rpm -ev --nodeps mysql-community-common-5.6.38-2.el7.x86_64
rpm -ev --nodeps mysql-community-client-5.6.38-2.el7.x86_64
rpm -ev --nodeps mysql-community-libs-5.6.38-2.el7.x86_64
rpm -ev --nodeps community-server-5.6.38-2.el7.x86_64

find / -name mysql

rm -rf 上面查出的文件夹

etc/my.cnf 如果存在的话手动删除，这样mysql就卸载完成了。

centos的yum 源中默认是没有mysql的，所以我们需要先去官网下载mysql的repo源并安装；
网址：https://dev.mysql.com/downloads/repo/yum/ 操作如下：

wget http：//dev.mysql.com/get/Downloads/mysql80-community-release-el7-1.noarch.rpm

安装 yum repo文件并更新 yum 缓存

rpm -ivh mysql57-community-release-el7-11.noarch.rpm

会在/etc/yum.repos.d/目录下生成两个repo文件mysql-community.repo mysql-community-source.repo
更新 yum 命令

yum clean all
 
yum makecache

查看mysql yum仓库中mysql版本，使用如下命令

yum repolist all | grep mysql

使用 yum-config-manager 命令修改相应的版本为启用状态最新版本为禁用状态

yum-config-manager --disable mysql80-community
 
yum-config-manager --enable mysql57-community

安装mysql 命令如下：

yum install mysql-community-server

开启mysql 服务

systemctl start mysqld.service

systemctl start mysqld.service
systemctl restart mysqld
systemctl status mysqld.service

/etc/rc.d/init.d/mysqld: line 239: my_print_defaults: command not found
/etc/rc.d/init.d/mysqld: line 259: cd: /usr/local/mysql: No such file or directory
Starting MySQL ERROR! Couldn't find MySQL server (/usr/local/mysql/bin/mysqld_safe)

my.cnf

[root@izm5eafr6zh39w6kuias38z /]# cd ext
-bash: cd: ext: No such file or directory
[root@izm5eafr6zh39w6kuias38z /]# cd etc
[root@izm5eafr6zh39w6kuias38z etc]# cat my.cnf

For advice on how to change settings please see

http://dev.mysql.com/doc/refman/8.0/en/server-configuration-defaults.html

[mysqld]

Remove leading # and set to the amount of RAM for the most important data

cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.

innodb_buffer_pool_size = 128M

Remove the leading "# " to disable binary logging

Binary logging captures changes between backups and is enabled by

default. It's default setting is log_bin=binlog

disable_log_bin

Remove leading # to set options mainly useful for reporting servers.

The server defaults are faster for transactions and fast SELECTs.

Adjust sizes as needed, experiment to find the optimal values.

join_buffer_size = 128M

sort_buffer_size = 2M

read_rnd_buffer_size = 2M

Remove leading # to revert to previous value for default_authentication_plugin,

this will increase compatibility with older clients. For background, see:

https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_default_authentication_plugin

default-authentication-plugin=mysql_native_password

mysql安装根目录

basedir = /usr/local/mysql

datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock

log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid
[root@izm5eafr6zh39w6kuias38z etc]#

//查看默认密码
grep 'temporary password' /var/log/mysqld.log
／／修改密码　
ALTER user 'root'@'localhost' IDENTIFIED BY 'root123456';

创建用户并指定多IP访问

1. 创建用户并设置密码模式

   CREATE USER '用户名'@'IP' IDENTIFIED WITH mysql_native_password BY '密码';

2.给创建的账号赋权

   GRANT ALL PRIVILEGES ON *.* TO '用户名'@'ip';

   如果需要指定权限，就将ALL改为SELECT DELETE UPDATE INSERT等四种权限任选即可

3.如果还需要设置到另一个ip, 那么就需要重复上面的步骤：

    虽然是重复步骤，但是用户名、密码保持和上面一致,ip改变就可以了

     CREATE USER '用户名'@'IP' IDENTIFIED WITH mysql_native_password BY '密码';

     GRANT ALL PRIVILEGES ON *.* TO '用户名'@'ip';

4.如果创建错了，可以使用下面语句删除用户：
    drop user '用户名'@'ip';

    删除指定ip的用户