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March 2012
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CentOS : Extending default memory limit

One of the CentOS box is not identified the exact RAM which had up-graded to 4GB. We are using CentOS 5.3 version. As a quick fix for this solution is to install new kernel which support PAE (Physical Address Extension) is a feature to allow (32-bit) x86 processors to access a physical address space (including random access memory and memory mapped devices) larger than 4 gigabytes.

So you need to install new kernel which support PAE. In CentOS install “kernel-PAE” package to do this.

Before the modification, the desktop has showing 3.2GB only

[root@rc-147 ~]# free -m
             total       used       free     shared    buffers     cached
Mem:          3286       3177        109          0        178        518
-/+ buffers/cache:       2480        806
Swap:         2000          0       2000
[root@rc-147 ~]#

1. Installing Kernel PAE package

[root@rc-147 yum.repos.d]# yum install kernel-PAE
Loaded plugins: fastestmirror
Determining fastest mirrors
My-Repo-Centos-5                                 |  951 B     00:00
primary.xml.gz                                        | 936 kB     00:00
Rain-Concert-Centos-5                                          2628/2628
Setting up Install Process
Parsing package install arguments
Resolving Dependencies
There are unfinished transactions remaining. You migh tconsider running yum-complete-transaction first to finish them.
--> Running transaction check
---> Package kernel-PAE.i686 0:2.6.18-194.el5 set to be installed
--> Finished Dependency Resolution
Dependencies Resolved
Dependencies Resolved
=============================================================================
 Package        Arch     Version             Repository                 Size
=============================================================================
Installing:
 kernel-PAE     i686     2.6.18-194.el5      My-Repo-Centos-5      17 M
Transaction Summary
=============================================================================
Install      1 Package(s)
Update       0 Package(s)
Remove       0 Package(s)
Total download size: 17 M
Is this ok [y/N]: y
Downloading Packages:
kernel-PAE-2.6.18-194.el5.i686.rpm                                |  17 MB     00:01
Running rpm_check_debug
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
  Installing     : kernel-PAE                                        [1/1]
Installed: kernel-PAE.i686 0:2.6.18-194.el5
Complete!
[root@rc-147 yum.repos.d]#

2. Enabling new kernel entry in “/etc/grub.conf”

2. Change the default boot option to 0. Note the new kernel entry listed in it (vmlinuz-2.6.18-194.el5PAE)

#cat /etc/grub.conf"
default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
password --md5 $1$SXQbd/$cg/35eLfANUf7rUxiPX0u.
hiddenmenu
title CentOS (2.6.18-194.el5PAE)
        root (hd0,0)
        kernel /vmlinuz-2.6.18-194.el5PAE ro root=LABEL=/ rhgb quiet
        initrd /initrd-2.6.18-194.el5PAE.img
title CentOS (2.6.18-128.el5)
        root (hd0,0)
        kernel /vmlinuz-2.6.18-128.el5 ro root=LABEL=/ rhgb quiet
        initrd /initrd-2.6.18-128.el5.img

3. Reboot the server.

Verify the memory status

[root@rc-1147 ~]# free -m
             total       used       free     shared    buffers     cached
Mem:          4041       2284       1756          0        258        735
-/+ buffers/cache:       1290       2750
Swap:         2047          0       2047
[root@rc-163 ~]#
[root@rc-163 ~]# uname -rmo
2.6.18-164.el5PAE i686 GNU/Linux
[root@rc-163 ~]#

That’s it -:)

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