新安装完并启动 Mysql 5.7 后，你会发现无法直接使用 Mysql 命令进入，原因是 5.7 版本已经为你生成了默认的 root 用户密码，该密码可以在 /var/log/mysqld.log 里找到或通过以下命令：
grep -i temporary /var/log/mysqld.log
可以看到类似以下：
A temporary password is generated for root@localhost: 6PmM/L,QiJ;B
找到密码就可以登录 Mysql 了
登陆 Mysql 后，发现无法查询数据库，无法创建数据库等操作。这个时候需要你修改 root 的登陆密码，而且要注意的是 Mysql 5.7 版本对密码的安全要求很高，如果使用安全度过低的密码有可能修改失败。修改密码参考如下：
[root@imweb ~]# mysql_secure_installation
Securing the MySQL server deployment.
Enter password for user root:
The existing password for the user account root has expired. Please set a new password.
New password:
Re-enter new password:
... Failed! Error: Your password does not satisfy the current policy requirements
New password:
Re-enter new password:
The 'validate_password' plugin is installed on the server.
The subsequent steps will run with the existing configuration
of the plugin.
Using existing password for root.
Estimated strength of the password: 100
Change the password for root ? ((Press y|Y for Yes, any other key for No) : y
New password:
Re-enter new password:
Estimated strength of the password: 100
Do you wish to continue with the password provided?(Press y|Y for Yes, any other key for No) : y
By default, a MySQL installation has an anonymous user,
allowing anyone to log into MySQL without having to have
a user account created for them. This is intended only for
testing, and to make the installation go a bit smoother.
You should remove them before moving into a production
environment.
Remove anonymous users? (Press y|Y for Yes, any other key for No) : y
Success.
Normally, root should only be allowed to connect from
'localhost'. This ensures that someone cannot guess at
the root password from the network.
Disallow root login remotely? (Press y|Y for Yes, any other key for No) : y
Success.
By default, MySQL comes with a database named 'test' that
anyone can access. This is also intended only for testing,
and should be removed before moving into a production
environment.
Remove test database and access to it? (Press y|Y for Yes, any other key for No) : y
- Dropping test database...
Success.
- Removing privileges on test database...
Success.
Reloading the privilege tables will ensure that all changes
made so far will take effect immediately.
Reload privilege tables now? (Press y|Y for Yes, any other key for No) : y
Success.
All done!或者使用以下命令来修改这里同样需要注意密码的安全度要够强：
SET PASSWORD FOR ‘root’@’localhost’ = PASSWORD(‘Yourpassword’);
修改完密码就可以正常操作 Mysql 了！
安装 Mysql 5.7 版本，请参考：Centos Linux 安装最新版本 mysql 5.7