If you have 4 GB or more RAM on a Linux server, it may not show up the in the server. In this case you need to install PAE kernel package. This kernel package will support upto 64GB of memory. The non-PAE kernel can only address up to 4GB of memory. You can install the kernel-PAE package if you have more than 4GB of RAM. Use the yum command to install the package:
yum install kernel-PAE
This will install the package and in order for the changes to take affect, you need to reboot your server with the following command:
reboot
Once the server is online, you can check the physical memory on your server using:
free -m
