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

By: Enabled991221

Enabled991221 — Tue, 25 Oct 2011 20:46:40 +0000

Hi.

How to PAE kernel install to FreeBSD 7.0?

By: Muhammad Shakir

Muhammad Shakir — Fri, 22 Jul 2011 09:34:09 +0000

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.

By: mir

mir — Mon, 28 Mar 2011 05:21:53 +0000

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
Thanks.

By: FSX

FSX — Thu, 14 Oct 2010 07:14:24 +0000

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.

By: DonEstefan

DonEstefan — Sat, 18 Sep 2010 15:23:04 +0000

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”).

[QUOTE]
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.

By: Ross

Ross — Thu, 04 Feb 2010 06:26:57 +0000

We’re analysing a problem on 32 bit RHEL 5 PAE kernel (fully up-to-date) on a Dell M610 blade (4 x quad core XEON, 48GB RAM) and, although we see all 48GB in “top” and “free”, the following simple program shows that we’re still limited to 3GB of memory per process.

#include
#include
enum {
  CHUNKS = 1024 * 32,
  MEGABYTE = 1024 * 1024
};
int main (void) {
  int i, j;
  void * chunk[CHUNKS];
  for (i = 0; i < CHUNKS; i++) {
    if (NULL == (chunk[i] = (void *) calloc(MEGABYTE, 1)))
      break;
  }
  printf("Allocated %d MB\n", i);
  for (j = 0; j < i; j++) {
    free(chunk[j]);
  }
}

By: Davis

Davis — Sun, 13 Dec 2009 07:20:23 +0000

Very usefully information and easily to do ..
Now, my machine can suppot 8G ram!!
Thank you!!

By: Corben

Corben — Tue, 11 Aug 2009 17:20:12 +0000

Just replaced RAM in my HP laptop (Now, I have matched pair etc.) and my BIOS recognizes 4GB of RAM.
OS Centos 5.2 kernel 2.6.18-128.4.1.el5PAE can see only 3.5GB.
#cat /proc/meminfo
MemTotal: 3505948 kB

What should I do? My system is almost upto date.

Cheers
Corben

By: Anj Adu

Anj Adu — Thu, 16 Jul 2009 19:11:20 +0000

We have 32 Bit Red Hat Enterprise Server 5.3 with PAE and the “top” command shows 32G total (which is the amount of installed memory”..) does that imply The PAE works beyond 16G ?

By: Yuhong Bao

Yuhong Bao — Tue, 02 Jun 2009 03:36:09 +0000

Another advantage of installing a PAE kernel is that you can enable the NX support in recent CPUs to increase resistance against buffer overflow attacks. Non-PAE page tables has no space for the NX bit, thus PAE has to be enabled to get NX.

By: deeb

deeb — Mon, 06 Apr 2009 11:07:41 +0000

I’ve just been looking into this. The new RHEL5 PAE kernel does not support memory above 16G. According to RH this was due to performance problems. If your applications will run in 64bit mode (X86_64) and you’ve got more than 16G, you should go 64bit.

cheers
deeb

By: Mesut

Mesut — Sat, 01 Nov 2008 07:35:22 +0000

for rhel/centos 3.x-4.x, support 64GB memory too but kernel is not named as kernel-PAE…
check kernel-hugemem or something…

By: Sithu

Sithu — Tue, 21 Oct 2008 21:22:27 +0000

Hi,

I’ve CentOS 5.2. Upgraded RAM to 32GB from 16GB. BIOS shows the increaed memory, but the OS still shows 16GB.

Could anyone help?

Thanks and regards
sithu

By: nisha

nisha — Fri, 08 Aug 2008 10:04:45 +0000

perfect, thank you ;-)

By: vivek

vivek — Fri, 08 Aug 2008 09:58:09 +0000

Noop, 64bit kernel can address 64GB / 128GB or more. PAE kernel = 32bit OS + 4GiB or more RAM.

By: nisha

nisha — Fri, 08 Aug 2008 09:32:35 +0000

Just a quick question, is kernel-PAE required for CentOS x86_64 to recognize additional memory? I’ve been googling, but there’s no straight answer to this…from what i understand, it’s only required for x86 arch’s…i would appreciate your insight about it…thanks

*Note:apologies if this has already been answered, i would just like a second opinion, hope it’s alright :-)

By: josh

josh — Fri, 14 Mar 2008 22:54:37 +0000

older Intel chipsets (pre-965, including 945) do not support memory remapping – thus limiting access to the memory being overlapped by IO space.

By: Z. Qian

Z. Qian — Mon, 25 Feb 2008 23:33:35 +0000

my PC Bios only reports 3.2GB memory available. Does linux has its own basic IO support? Or it use standard bios support for IO?

Thanks.

By: odoylefm

odoylefm — Fri, 15 Feb 2008 14:45:54 +0000

I have a Red Hat 8, 64-Bit installation and the BIOS sees 4Gb of RAM, but Fedora only sees 3.1. It is an HP computer and the BIOS is very limited as far as configurable options. Why won’t Fedora see all the RAM?

By: ckolos

ckolos — Mon, 19 Nov 2007 19:46:53 +0000

FYI, this is only for 32bit versions of RHEL/Centos… The 64bit versions don’t supply, nor do they need these extensions