SELinux，多数发行版默认激活，对安全的重要性，但是本身有一定的复杂性，不熟悉容易产生一些莫名其妙的问题。
getenforce
sestatus 查看selinux状态
setenforce 0/1 临时修改selinux状态，重启失效
cd /etc/selinux/config
SELINUX=enforcing/disabled 重启后生效，永久
实例：
我们还需要确认系统已经安装并启动了Apache，没有的话就YUM装一个，这很简单，就不多说了，接着在root目录创建一个测试文件test.html，如下：
shell> cat /root/test.html hello, world.
然后把这个测试文件拷贝到Apache的DocumentRoot目录，我的Apache是通过YUM安装的话，缺省是/var/www/html目录，如下：
shell> cp /root/test.html /var/www/html
接着浏览一下，如果没出什么幺蛾子，应该一切都在意料之中，如下：
shell> curl http://localhost/test.html hello, world.
看到这，你可能觉得我废话连篇，别着急，下面就是见证奇迹的时候了：
同样还是那个测试文件test.html，不过这次不再是拷贝，而是移动，如下：
shell> mv /root/test.html /var/www/html
接着浏览一下，怎么样，结果很出人意料吧，竟然提示权限错误，如下：
shell> curl http://localhost/test.html <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> <html><head> <title>403 Forbidden</title> </head><body> <h1>Forbidden</h1> <p>You don't have permission to access /test.html on this server.</p> </body></html>
当然，我们现在知道这个问题是由于SELinux引起的，但还不知其所以然，实际上问题的原因此时已经被audit进程记录到了相应的日志里，可以这样查看：
shell> audit2why < /var/log/audit/audit.log
如果看不懂的话，推荐安装setroubleshoot套件：
shell> yum install setroubleshoot
它本身是一个GUI套件，不过其中包含的一个sealert命令对我们命令行用户很有用：
shell> sealert -a /var/log/audit/audit.log Summary: SELinux is preventing /usr/sbin/httpd "getattr" access to /var/www/html/test.html. Detailed Description: SELinux denied access requested by httpd. /var/www/html/test.html may be a mislabeled. /var/www/html/test.html default SELinux type is httpd_sys_content_t, but its current type is admin_home_t. Changing this file back to the default type, may fix your problem. File contexts can be assigned to a file in the following ways. * Files created in a directory receive the file context of the parent directory by default. * The SELinux policy might override the default label inherited from the parent directory by specifying a process running in context A which creates a file in a directory labeled B will instead create the file with label C. An example of this would be the dhcp client running with the dhclient_t type and creating a file in the directory /etc. This file would normally receive the etc_t type due to parental inheritance but instead the file is labeled with the net_conf_t type because the SELinux policy specifies this. * Users can change the file context on a file using tools such as chcon, or restorecon. This file could have been mislabeled either by user error, or if an normally confined application was run under the wrong domain. However, this might also indicate a bug in SELinux because the file should not have been labeled with this type. If you believe this is a bug, please file a bug report against this package. Allowing Access: You can restore the default system context to this file by executing the restorecon command. restorecon '/var/www/html/test.html', if this file is a directory, you can recursively restore using restorecon -R '/var/www/html/test.html'. Fix Command: /sbin/restorecon '/var/www/html/test.html'
这次应该看懂了吧！原因是说Apache下文件上下文类型应该是httpd_sys_content_t，但是现在是admin_home_t，所以权限错误，并且在结尾处给出了修复命令。
可httpd_sys_content_t，admin_home_t都怎么看啊？很简单，借助ls命令的-Z参数即可：
shell> ls -Z /path
回到问题的开始，拷贝之所以没出现问题，是因为cp自动修改上下文属性，而移动之所以出现问题是因为mv保留原文件的上下文属性。
注：关于SELinux和Apache的详细介绍，可以参考『man httpd_selinux』。
知道了如何解决SELinux问题，以后如果遇到类似的情况不要急着武断的关闭SELinux。
类似之前yum安装mariadb后，默认路径/var/lib/mysql，修改数据库路径为/data/mariadb，在/etc/my.cnf也修改相关配置，权限、属主都已修改，但是重启mariadb失败，也是被selinux限制。不过另外方法，从新初始化mariadb：/usr/libexec/mysqld --basedir=/usr --datadir=/data/mariadb --plugin-dir=/usr/lib64/mysql/plugin --log-error=/data/mariadb/log/mariadb.log --pid-file=/var/run/mariadb/mariadb.pid --socket=/data/mariadb/mysql.sock
