CentOS boot PHP-FPM does not use the default 9000 port permission denied

Today finally have time to think oneself took a set of LNMP development environment, as a result of the previous development environment are the company's existing, the use of the time to change the configuration on the OK, feel very relaxed, but their own hands-on from the installation of virtual machines to the last step to build lnmp, unexpectedly difficult, must be down-to-earth, absolutely can not eyes above the top.

Back to the point, in accordance with the predecessor's blog, step-by-step Yum finished nginx and PHP-FPM, want to use the FASTCGI port for the project instead of the default 90001, the strange things appear

[root@localhost ~]# Service php-fpm start  
starting php-fpm: [18-nov-2015 22:41:44] error:unable to bind listening Soc Ket for address ' 127.0.0.1:9001 ': Permission denied (a)
[18-nov-2015 22:41:44] ERROR:FPM
                                                           initialization failed [FAILED]

Obviously is the root user, obviously 9001 port is not occupied, how does not have the authority. Baffled

The reason is that SELinux is enabled in the CentOS kernel

[Root@localhost ~]# Cat/etc/sysconfig/selinux # This file controls to the state of SELinux on the    

system.
# selinux= can take one of these three values:
#     Enforcing-selinux The security policy is enforced.
#     Permissive-selinux Prints warnings instead of enforcing.
#     Disabled-no SELinux policy is loaded.
Selinux=enforcing
#SELINUX =disabled
# selinuxtype= can take one of these two values:
#     targeted- Targeted processes are protected,
#     Mls-multi level security protection.

Change the selinux=enforcing to selinux=disabled and reboot the system.

What is SELinux. When to enable SELinux and when not.