一，基本环境

操作系统：Red Hat Enterprise Linux Server release 6.8

mysql版本：mysql-community-server-5.7.21

二，流程

2.1，安装mysql完成后，启动mysql报错

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

2.2，编辑配置文件

    加入参数skip-grant-tables

[root@postgredb etc]# vi my.cnf

# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.7/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 leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# 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
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
skip-grant-tables
# Disabling symbolic-links is recommended to prevent assorted security risks
symbolic-links=0

log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

2.3，重启服务

[root@postgredb etc]# service mysqld stop
停止 mysqld： [确定]
[root@postgredb etc]# service mysqld start
正在启动 mysqld： [确定]

2.4，登陆mysql

    在输入密码阶段，直接回车登陆

[root@postgredb etc]# mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.21 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, 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> 

2.5，修改密码

mysql> update mysql.user set authentication_string=password('tpc1989') where user='root' and host='localhost';
Query OK, 1 row affected, 1 warning (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 1

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

mysql> quit;
Bye
[root@postgredb etc]# 

2.6，去掉参数，重启mysql

    至此，问题等到解决。