0、背景
有一些知识很简单，很低频，但是偶尔还是需要使用，故而需要记下来。
开始的时候碰见mysql.sock文件找不到了，不知道什么时候被破坏了，修复了好久，问题一个接着一个，需要急着用，很浪费时间，所以直接选择重装。简单暴力有效。
1、安装
yum安装mysql
# 下载mysql源
wget http://dev.mysql.com/get/mysql57-community-release-el7-8.noarch.rpm
# 添加mysql源
yum localinstall mysql57-community-release-el7-8.noarch.rpm
# 安装mysql
yum install mysql-community-server
检查mysql源是否安装成功
# yum repolist enabled | grep "mysql.*-community.*"
mysql-connectors-community/x86_64 MySQL Connectors Community 141
mysql-tools-community/x86_64 MySQL Tools Community 105
mysql57-community/x86_64 MySQL 5.7 Community Server 404
2、启动
然后就是启动服务
systemctl start mysqld
到这里算是安装、启动完成了
验证下，有下面这个进程，差不多就说明ok了。
# ps -ef | grep mysql
mysql 31427 1 9 10:19 ? 00:16:14 /usr/sbin/mysqld --daemonize --pid-file=/var/run/mysqld/mysqld.pid
3、初始密码
安装完mysql，有一个初始密码，在/var/log/mysqld.log文件中，找到下面这个位置，例如：
[Note] A temporary password is generated for root@localhost: VVwAk;E6y/6a
这里，VVwAk;E6y/6a 就是我的初始密码了，每个人的不一样。
4、修改初始密码
初始密码太复杂，一般都需要修改下。先用初始密码登入：
# mysql -uroot -p123456
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 16
Server version: 5.7.29 MySQL Community Server (GPL)
Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
这里插播一个错误
一般修改密码用这个命令就可以了。
# mysqladmin -u root -p password "abc123"
Enter password:
// 这里abc123是新密码，Enter password:地方输入原密码
但是，新密码强度太弱，不允许设置简单密码，报错信息如下
Warning: Since password will be sent to server in plain text, use ssl connection to ensure password safety.
mysqladmin: unable to change password; error: 'Your password does not satisfy the current policy requirements'
所以，需要降低下密码强度的配置
5、降低初始密码强度配置
# mysql -u root -pXXXXXXX
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 13
Server version: 5.7.29
Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> set global validate_password_policy=0;
Query OK, 0 rows affected (0.00 sec)
mysql> set global validate_password_mixed_case_count=0;
Query OK, 0 rows affected (0.00 sec)
mysql> set global validate_password_number_count=3;
Query OK, 0 rows affected (0.00 sec)
mysql> set global validate_password_special_char_count=0;
Query OK, 0 rows affected (0.00 sec)
mysql> set global validate_password_length=3;
Query OK, 0 rows affected (0.00 sec)
mysql> SHOW VARIABLES LIKE 'validate_password%';
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.
上面最查看时有个错误，意思是需要重设密码，继续如下：（设置新密码为123456）
mysql> SET PASSWORD FOR 'root'@'localhost' = PASSWORD('123456');
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> SHOW VARIABLES LIKE 'validate_password%';
+--------------------------------------+-------+
| Variable_name | Value |
+--------------------------------------+-------+
| validate_password_check_user_name | OFF |
| validate_password_dictionary_file | |
| validate_password_length | 3 |
| validate_password_mixed_case_count | 0 |
| validate_password_number_count | 3 |
| validate_password_policy | LOW |
| validate_password_special_char_count | 0 |
+--------------------------------------+-------+
7 rows in set (0.00 sec)
mysql> exit
OK，到这里密码重新设置完成
6、远程登入配置
mysql允许远程连接的命令就如下2条
mysql> grant all on *.* to root@'%' identified by '123456' with grant option;
mysql> flush privileges;
执行效果如下
# mysql -uroot -p123456
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 16
Server version: 5.7.29 MySQL Community Server (GPL)
Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> grant all on *.* to root@'%' identified by '123456' with grant option;
Query OK, 0 rows affected, 1 warning (0.00 sec)
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
mysql> exit
好了，到这里就可以愉快的使用MySQL了。