#查看MySQL默认密码
sudo vim /etc/mysql/debian.cnf 

#进入数据库
mysql -udebian-sys-maint -p

#修改root用户密码
use mysql;

alter user 'root'@'localhost' identified with mysql_native_password by "rootpass";
flush privileges;

#新增用户
create user 'newuser'@'%' identified with mysql_native_password by "newpass";
flush privileges;

#给新用户授权
grant all privileges on *.* to 'newuser'@'%' with grant option;