linux下mysql忘记密码

前言
今天在服务器安装mysql之后，登录发现密码错误，但是我没有设置密码呀，最后百度之后得知，mysql在5.7版本之后会自动创建一个初始密码。
报错如下:

[root@mytestlnx02 ~]# mysql -u root -p
Enter password: 
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)

修改密码

1. 检查mysql服务是否启动，如果启动，关闭mysql服务
   //查看mysql服务状态

   [root@mytestlnx02 ~]# ps -ef | grep -i mysql
   root 22972 1 0 14:18 pts/0 00:00:00 /bin/sh /usr/bin/mysqld_safe --datadir=/var/lib/mysql --socket=/var/lib/mysql/mysql.sock --pid-file=/var/run/mysqld/mysqld.pid --basedir=/usr --user=mysql
   mysql 23166 22972 0 14:18 pts/0 00:00:00 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --plugin-dir=/usr/lib/mysql/plugin --user=mysql --log-error=/var/log/mysqld.log --pid-file=/var/run/mysqld/mysqld.pid --socket=/var/lib/mysql/mysql.sock
   root 23237 21825 0 14:22 pts/0 00:00:00 grep -i mysql

   //关闭服务
   [root@mytestlnx02 ~]# service mysql stop
   [root@mytestlnx02 ~]#

2. 修改mysql的配置文件my.cnf
   my.cnf配置文件的位置，一般在/etc/my.cnf，有些版本在/etc/mysql/my.cnf

在配置文件中，增加2行代码

[mysqld]

skip-grant-tables

作用是登录mysql的时候跳过密码验证

然后启动mysql服务，并进入mysql

[root@mytestlnx02 ~]# service mysqld start
[root@mytestlnx02 ~]#
[root@mytestlnx02 ~]# mysql -u root 
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
 
mysql>

3. 修改密码
   连接mysql这个数据库，修改用户密码

    mysql> use mysql;
    Reading table information for completion of table and column names
    You can turn off this feature to get a quicker startup with -A
     
    Database changed
    mysql> update mysql.user set authentication_string=password('root_password') where user='root';
    Query OK, 1 row affected, 1 warning (0.00 sec)
    Rows matched: 1  Changed: 1  Warnings: 1
     
    mysql> flush privileges;
    Query OK, 0 rows affected (0.00 sec)
     
    mysql> exit
   

4. 重启mysql服务
   先将之前加在配置文件里面的2句代码注释或删除掉，然后重启mysql服务，就可以使用刚刚设置的密码登录了。

    [root@mytestlnx02 ~]# service mysql start
    [root@mytestlnx02 ~]#
    [root@mytestlnx02 ~]# mysql -u root -p
    Enter password: 
    Welcome to the MySQL monitor.  Commands end with ; or \g.
   

p.s.
在CentOS上的操作方式有所不同。

执行修改密码的命令一直报错

mysql> update user set authentication_string=password('xxxxxxxx') where User='root';       
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '('root_password') where User='root'' at line 1

不可能是语法问题，检查了很多遍，最后发现CentOS下应该这样操作：

查看初始密码

[root@VM_0_8_centos ~]# grep 'temporary password' /var/log/mysqld.log
2018-09-26T04:25:54.927944Z 5 [Note] [MY-010454] [Server] A temporary password is generated for root@localhost: DN34N/=?aIfZ

可以看到初始密码为DN34N/=?aIfZ

使用初始密码登录

[root@VM_0_8_centos ~]# mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.12 MySQL Community Server - GPL

Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.
修改密码

mysql> ALTER USER 'root' IDENTIFIED BY 'xxxxxxxxx';  
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.
mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY 'xxxxxxxx';
Query OK, 0 rows affected (0.11 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.01 sec)

mysql> exit

Bye
重启服务就生效了

[root@VM_0_8_centos ~]# service mysqld stop 
Redirecting to /bin/systemctl stop  mysqld.service
[root@VM_0_8_centos ~]# service mysqld start
Redirecting to /bin/systemctl start  mysqld.service