在centOS上安装完mysql, 登录MYSQL时遇到错误
[root@mysql-server Downloads]# mysql -u root
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

关键要用MYSQLD_OPTS="--skip-grant-tables"重新启动mysql服务
[root@mysql-server Downloads]# systemctl stop mysqld
[root@mysql-server Downloads]# systemctl set-enviroment MYSQLD_OPTS="--skip-grant-tables"
Unknown operation 'set-enviroment'.
[root@mysql-server Downloads]# systemctl set-environment MYSQLD_OPTS="--skip-grant-tables"
[root@mysql-server Downloads]# systemctl start mysqld
[root@mysql-server Downloads]# myslq -u root
bash: myslq: command not found...
Similar command is: 'mysql'
[root@mysql-server Downloads]# mysql -u root
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.18 MySQL Community Server (GPL)

Copyright (c) 2000, 2017, 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> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| sys |
+--------------------+
4 rows in set (0.06 sec)

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 user set authentication_string=password('root') where user = 'root';
Query OK, 1 row affected, 1 warning (0.07 sec)
Rows matched: 1 Changed: 1 Warnings: 1

mysql> flush previleges;
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 'previleges' at line 1
mysql> flush priviledges;
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 'priviledges' at line 1
mysql> flush privileges;
Query OK, 0 rows affected (0.11 sec)

mysql> quit
Bye
[root@mysql-server Downloads]# systemctl stop mysqld
[root@mysql-server Downloads]# systemctl unset-environment MYSQLD_OPTS
[root@mysql-server Downloads]# systemctl start mysqld
[root@mysql-server Downloads]# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.18

Copyright (c) 2000, 2017, 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>


参考：https://stackoverflow.com/questions/33510184/change-mysql-root-password-on-centos7