How to Disable SELinux

Temporarily switch off enforcement

echo 0 >/selinux/enforce

Permanently Permissive

just change SELINUX=enforcing to SELINUX=permissive in file /etc/selinux/config, and you're done. Reboot if you want to prove it.

RHEL / CentOS Support 4GB or more RAM ( memory )

RHEL / CentOS Support 4GB or more RAM ( memory )
If you have 4 GB or more RAM use the Linux kernel compiled for PAE capable machines. Your machine may not show up total 4GB ram. All you have to do is install PAE kernel package.

This package includes a version of the Linux kernel with support for up to 64GB of high memory. It requires a CPU with Physical Address Extensions (PAE).
The non-PAE kernel can only address up to 4GB of memory. Install the kernel-PAE package if your machine has more than 4GB of memory (>=4GB).

How Do I Install PAE kernel?
To install PAE kernel, use yum command:

# yum install kernel-PAE

Loading "installonlyn" plugin
Setting up Install Process
Setting up repositories
Reading repository metadata in from local files
Parsing package install arguments
Resolving Dependencies
--> Populating transaction set with selected packages. Please wait.
---> Downloading header for kernel-PAE to pack into transaction set.
kernel-PAE-2.6.18-53.1.13 100% |=========================| 259 kB 00:01
---> Package kernel-PAE.i686 0:2.6.18-53.1.13.el5 set to be installed
--> Running transaction check

Dependencies Resolved

=============================================================================
Package Arch Version Repository Size
=============================================================================
Installing:
kernel-PAE i686 2.6.18-53.1.13.el5 updates 13 M

Transaction Summary
=============================================================================
Install 1 Package(s)
Update 0 Package(s)
Remove 0 Package(s)

Total download size: 13 M
Is this ok [y/N]:
Downloading Packages:
(1/1): kernel-PAE-2.6.18- 100% |=========================| 13 MB 00:10
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
Installing: kernel-PAE ######################### [1/1]

Installed: kernel-PAE.i686 0:2.6.18-53.1.13.el5
Complete!

Just reboot the server and make sure you boot with PAE kernel i.e. 2.6.18-53.1.13.el5:

# reboot