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-2.6.18-8.1.15. 100% |=========================| 207 kB    00:00
---> Package kernel-PAE.i686 0:2.6.18-8.1.15.el5 set to be installed
--> Running transaction check

Dependencies Resolved

 Package                 Arch       Version          Repository        Size
 kernel-PAE              i686       2.6.18-8.1.15.el5  updates            12 M

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

Total download size: 12 M
Is this ok [y/N]: y
Downloading Packages:
(1/1): kernel-PAE-2.6.18- 100% |=========================|  12 MB    00:12
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
  Installing: kernel-PAE                   ######################### [1/1]

Installed: kernel-PAE.i686 0:2.6.18-8.1.15.el5

Just reboot the server and make sure you boot with PAE kernel i.e. 2.6.18-8.1.15.el5PAE:
# reboot

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28 comments… add one
  • DonEstefan Sep 18, 2010 @ 15:23

    You don’t necessarily need a different Kernel.
    When you are using a Multiprocessor (Multicore) Machine you should already be using the SMP Kernel (check “uname -a”).

    The “SMP” kernel supports a maximum of 16GB of main memory. Systems with more than 16GB of main memory use the “Hugemem” kernel. In certain workload scenarios it may be advantageous to use the “Hugemem” kernel on systems with more than 12GB of main memory.”
    [/QUOTE]I can’t post URLs but if you google “Red Hat Enterprise Server Version comparison chart” you will find the information in Note 5 on the bottom of the page.
    Also check out the “Technology capabilities and limits” on the same page.

  • FSX Oct 14, 2010 @ 7:14

    I have recently upgraded memory from 4gb ecc to 12gb ecc on Dell PowerEdge 2950 server running RHEL 5.3.
    Its showing 12Gb memory in RHEL but on SNMP monitoring its shows total memory 12gb and used memory 4gb max, and percentage usage of memory shows 99%, which was the reason to upgrade memory from 4gb initial to 12gb.
    Any suggestions?
    i am using PAE kernel.

  • mir Mar 28, 2011 @ 5:21

    Hi, I am using RHEL 5.3 (32 Bit) on HP DL380G6. I am getting File System Read Only error on my server. please suggest on this..
    I am using PAE kernel

  • Muhammad Shakir Jul 22, 2011 @ 9:34

    I have upgraded memory from 16 gb to 64gb in CentOS 5.4 x64 bit server which is installed on Dell R710 server. In BIOS it is showing 64 GB but when i check in OS it is only showing 32 GB. Do you have any idea about this.

  • Enabled991221 Oct 25, 2011 @ 20:46


    How to PAE kernel install to FreeBSD 7.0?

  • Denilson Aug 6, 2012 @ 14:36

    It helped me a lot. Thanks.

  • wanjohi Nov 27, 2013 @ 13:46

    Hi, I have RHEL5.9 but do not have yum, which is the exact rpm I can download to install the kernel pae

  • yusuf Feb 22, 2015 @ 9:17

    Centos 6.4 Maximum memory and cpu supported.

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