Redhat Enterprise 5.6 Kernel

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It is hard to be the Newbie on the block!

I have a Redhat Enterprise 5.6 server. I have to use 5.6 because the Software that runs on it requires that version. I recently upgraded the Memory from 32GB to 96GB and the change in memory is not recognized by Redhat even though when I look up 5.6 it is supposed to be to support up to 1TB. Then I find out since I have a XEN kernel 2.6ish that memory above 32GB will not be recognized. From what I understand I only need the XEN kernel if I am running a virtual machine which I am not and I am not sure why I have the XEN kernel.

The server is used for single application with a sql database. What can I do to utilized the additional memory?

Do I change the kernel? Which kernel? how?
or
Can I allocate the memory to a VM that will only get utilized by that application?

ND
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Responses

rhn-engineering-sghosh's picture Red Hat Pro 534 points
22 November 2013 7:44 PM

If you are running on bare-metal, you can swap in the regular kernel in /boot/grub/grub.conf. It will require a reboot.

1- add a new entry in grub.conf for the bare-metal kernel
2- test new entry is what you want
3- set as default

Format for new entry in grub.conf can be found at: https://access.redhat.com/site/documentation//en-US/Red_Hat_Enterprise_Linux/5/html/Deployment_Guide/s1-kernel-boot-loader.html

Use the same root disk as for the current entry
Use "kernel /vmlinuz.x.y"
Use "initrd /initrd.x.y"

No need to run a VM.

ir. Jan Gerrit Kootstra's picture Guru 6222 points
25 November 2013 2:10 PM

Subhendu,

I would not recommend this method.

Normally a kernel installation should do this already.

yum install kernel

Kind regards,

Jan Gerrit Kootstra

ND Community Member 62 points
26 November 2013 3:40 AM

If I do "yum install kernel" what kernel is going to be installed?

Thanks

ir. Jan Gerrit Kootstra's picture Guru 6222 points
26 November 2013 5:02 PM

Nick,

The latest available kernel

yum install kernel-.el5.x86_64

This will install a specific kernel version.

Kind regards,

Jan Gerrit Kootstra

james.radtke@siriusxm.com's picture Guru 6863 points
26 November 2013 4:51 PM

I would make sure that you actually have the correct kernel installed

# for KERNEL in `rpm -qa kernel | sed 's/kernel-//g'`; do grep $KERNEL /boot/grub/grub.conf; done

title Red Hat Enterprise Linux Server (2.6.18-348.6.1.el5)
    kernel /vmlinuz-2.6.18-348.6.1.el5 ro root=/dev/VolGroup00/LogVol01 rhgb quiet
    initrd /initrd-2.6.18-348.6.1.el5.img
title Red Hat Enterprise Linux Server (2.6.18-348.el5)
    kernel /vmlinuz-2.6.18-348.el5 ro root=/dev/VolGroup00/LogVol01 rhgb quiet
    initrd /initrd-2.6.18-348.el5.img

Then, I would do one of the following (probably leaning towards option b. in case things didn't work out, you technically haven't changed anything).
a.) update your /boot/grub/grub.conf to boot to a non-XEN kernel and reboot.
b.) reboot your system and select the non-XEN kernel

# yum remove <xen kernel> 
# rpm -qa | grep -i xen

The last step will update /boot/grub/grub.conf for you, make sure that the update that it made now points to the correct kernel.

A final step that I would take (but I invite others to provide feedback)
Add exclude=kernel-xen* to /etc/yum.conf

I agree with Jan Gerritt that this should not be happening, but I have seen quite a few threads lately regarding XEN showing up unexpectedly.

ir. Jan Gerrit Kootstra's picture Guru 6222 points
26 November 2013 5:06 PM

James,

Blocking yum from install kernel-xen is not my concern.

Manually editing grub.conf is a concern to me, for the next kernel update or kernel erase may undo the manual change or get corrupted.
The later most of the time if someone removed the title for old kernel releases/versions so the post script in the rpm fails.

Kind regards,

Jan Gerrit

james.radtke@siriusxm.com's picture Guru 6863 points
26 November 2013 5:13 PM

Fair enough (and I agree that manually updating grub is not a preferred approach). I did miss a step in my approach though. OP should validate there are no remaining XEN kernels installed.

ND Community Member 62 points
26 November 2013 5:33 PM

Thanks for all of your input it is going to help me out tremendously.
Recap;
The Yum install should edit the .conf files but I should check to make sure?

  1. yum install kernel-.el5.x86_64
  2. Reboot
  3. yum remove
  4. rpm -qa | grep -i xen

Thanks
Nick

ND Community Member 62 points
2 December 2013 6:52 PM

Jan and James Thanks for all of your input! I changed the Kernel without a problem and I achieved the results I needed. Once I rebooted Redhat did recognize the additional memory and everything is working. I also removed any references to the XEN which will help in the future.

My main gripe is with Redhat support not pointing out the limitations with the XEN kernel from the beginning. I ended just using support to verify the information that the very helpful gurus and experts gave to me.

os-unix's picture Active Contributor 146 points
2 December 2013 7:12 PM

Nick,

It was a learning experience for me too.

I will keep this in mind, for we have a customer running a Xen guest. Might it grow in the future we will have to recommend another solution.

Kind regards,

Jan Gerrit Kootstra

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