The SELinux configuration file is /etc/selinux/config file.

Update the configuration file as follows:

• SELINUX=enforcing : Enforcing is the default mode which will enable and enforce the SELinux security policy on the Linux. It will also deny unauthorized access and log actions in a log file.
• SELINUXTYPE=targeted : Only targeted network daemons (such as DNS, Apache and others) are protected.

Save and close the file. Make sure SELinux is not disabled using Grub boot loader. Search /boot/grub/grub.conf file using grep and make sure the following line DOES NOT appears:

egrep -i 'selinux=0|enforcing=0' /boot/grub/grub.conf

If you found lines with selinux=0 or enforcing=0, remove them and save the changes.

Reboot the server:

reboot