问：


Been banging my head agains the wall for awhile now. My Xcode project went a little haywire while refactoring, and refused to build. I've squashed all the other errors, except one last linktime error:
Framework not found AudioUnit


I have the AudioUnit headers, the AudioUnit.framework is included in my project as it was before (Targets > Get Info > General > Linked Libraries > + ), but I cannot figure out why it does not work now. AudioToolbox.framework is
 also included.


回答1：Remove AudioUnit.framework and add CoreAudio.framework

回答2：And
 make sure that your import for CoreAudio is #import <CoreAudio/CoreAudioTypes.h>

回答3：To
 those arriving from Google: You may also find it necessary to add AudioToolkit.framework instead of or in addition to CoreAudio.framework

输入命令
systemctl start mysql.service
要启动MySQL数据库是却是这样的提示
Failed to start mysqld.service: Unit not found
解决方法如下:
首先需要安装mariadb-server
yum install -y mariadb-server
启动服务
systemctl start mariadb.service
添加到开机启动
systemctl enable mariadb.service
进行一些安全设置，以及修改数据库管理员密码
[zhaojq@localhost]$ mysql_secure_installation
mysql给root开启远程访问权限
use mysql；
select  User,authentication_string,Host from user；
GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' IDENTIFIED BY '123456';
flush privileges;

异常：Failed to start mysql.server.service: Unit not found.
[root@fa35eaa48320 /]# service mysql start
Redirecting to /bin/systemctl start mysql.service
Failed to start mysql.service: Unit not found.

解决方法如下:
首先需要安装mariadb-server

    [root@fa35eaa48320 /]# yum install -y mariadb-server

　　启动服务

　　[root@fa35eaa48320 /]# systemctl start mariadb.service

　　添加到开机启动

　　[root@fa35eaa48320 /]# systemctl enable mariadb.service

原因：

MariaDB代替了mysql数据库，MariaDB数据库管理系统是MySQL的一个分支，主要由开源社区在维护，采用GPL授权许可。开发这个分支的原因之一是：甲骨文公司收购了MySQL后，有将MySQL闭源的潜在风险，因此社区采用分支的方式来避开这个风险。

如果你按上述操作后：
[root@fa35eaa48320 /]# mysql
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MariaDB connection id is 3
Server version: 5.5.60-MariaDB MariaDB Server

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MariaDB [(none)]> show tables;
ERROR 1046 (3D000): No database selected
MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| test               |
+--------------------+

这里可以看出MariaDB 就是mysql

很多人对本博客的方法提出了质疑，在此我解释一下：
由于MySQL在CentOS7中收费了，所以已经不支持MySQL了，取而代之在CentOS7内部集成了mariadb，而安装MySQL的话会和MariaDB的文件冲突。所以本文建议直接安装mariadb。
具体讨论的详情大家可以参考知乎讨论：https://www.zhihu.com/question/41832866，本文不再赘述。
输入命令
 systemctl start mysql.service

要启动MySQL数据库是却是这样的提示
Failed to start mysqld.service: Unit not found

解决方法如下:
首先需要安装mariadb-server
yum install -y mariadb-server

启动服务
systemctl start mariadb.service

添加到开机启动
systemctl enable mariadb.service

进行一些安全设置，以及修改数据库管理员密码
[zhaojq@localhost]$  mysql_secure_installation


mysql给root开启远程访问权限
use mysql；
select  User,authentication_string,Host from user；

GRANT ALL PRIVILEGES ON *.* TO 'root'@'%' IDENTIFIED BY '123456';
flush privileges;