Web Hosting Talk : Web Hosting Main Forums : Hosting Security and Technology : Hosting Security and Technology Tutorials : CentOS kernel update - [beginning at post #6]

[mouseketrips]

I have CentOS 4 running on my server, and I have been having some load issues. I have two fairly large vbulletin forums on the server (between 3k - 5k), and according to vbulletin forums, the CentOS kernel I am currently using (2.6.9-22.0.2.EL) has a major problem with vbulletin, causing hugh loads, etc.

So, I naturally want to upgrade the kernel. I have YUM on a cron, and last night, here is what I received:

=============================================================================
Package Arch Version Repository Size
=============================================================================
Updating:
yum noarch 2.4.2-2.centos4 update 383 k

Transaction Summary
=============================================================================
Install 0 Package(s)
Update 1 Package(s)
Remove 0 Package(s)
Total download size: 383 k
Downloading Packages:
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction

Updated: yum.noarch 0:2.4.2-2.centos4
Complete!

Now, I understand that 2.4.2-2 is the most current version, and according to this, it should be updated. I rebooted everything, and had my server physically restarted, and when I check, I still have the same kernel on the server.

I obviously am missing a step, but after 3 hours of searching, I can't find it. I appreciate any help you can give me. Thanks!

[Servax]

What kernel are you currently running, give us the output of 'uname -a'. If it is any of the following:

2.6.9-22.0.2.ELsmp #1 SMP
2.6.9-22.0.2.EL #1

You already have the latest kernel upgrade available from CentOS. You can either downgrade your kernel or compile it manually.

[mouseketrips]

Here you go:

Linux 2.6.9-22.0.2.EL #1 Tue Jan 17 06:51:40 CST 2006 i686 athlon i386 GNU/Linux

I asked vbulletin support, was told to upgrade to 2.6.15 or downgrade to 2.6.11. I would prefer to upgrade rather than downgrade. Maybe I am misunderstanding terms.

Oh, new server, so I think to downgrade I have to compile it manually as well.

[Steven]

Do not downgrade. You will need to hand compile it.

[mouseketrips]

Is there a guide or instructions somewhere on how to do that?

[dirtbag]

OK, Here's the revised edition. Updated to reflect the latest kernel at this time (2.6.16.1) and removed the "make mrproper" command since it was wiping out the old config and causing big issues. Also some info on "make menuconfig".


cd /usr/src/
http://www.kernel.org/pub/linux/kern....6.16.1.tar.gz
tar -zxf linux-2.6.16.1.tar.gz
cd linux-2.6.16.1

cp /boot/config-2.6.9-22.0.2.EL .config
make clean (only necessary if you compile more than once)
make oldconfig


keep hitting enter and take the defaults until you get to the CPU type. Select your CPU. Also in the SMP section select SMP if you have multiple CPUs. Oh, and select "(No Forced Preemption (server))" under that section. Everything else, just hit enter to take the defaults.

(this is the "quick and dirty" method. You can also run "make menuconfig" instead, go to the bottom of the menu, load your old config file, and then select everything in a menu individually if you wish. For most systems, the "make oldconfig" method works fine.)


Then to compile and install:

make bzImage
make modules
make modules_install
make install


Then to configure your boot loader in case of disaster:

nano /boot/grub/grub.conf

default=1
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title CentOS (2.6.16.1)
    root (hd0,0)
    kernel /vmlinuz-2.6.16.1 ro root=/dev/VolGroup00/LogVol00
    initrd /initrd-2.6.16.1.img
title CentOS (2.6.9-22.0.2.EL)
    root (hd0,0)
    kernel /vmlinuz-2.6.9-22.0.2.EL ro root=/dev/VolGroup00/LogVol00
    initrd /initrd-2.6.9-22.0.2.EL.img
title CentOS_ServerCD (2.6.9-22.EL)
    root (hd0,0)
    kernel /vmlinuz-2.6.9-22.EL ro root=/dev/VolGroup00/LogVol00
    initrd /initrd-2.6.9-22.EL.img

..make sure it looks something like this with default=1 and the new kernel (2.6.16.1) on top. (Grub starts at 0, so "default=1" is still your old kernel. You change this later if it works out ok)




..then configure grub to boot to the new kernel one time. This way if it panicks or you can't get to the machine because the network service blows up, you can have the data center do a reboot and it will default back to the last kernel. If it does boot ok and everything looks good, edit grub.conf again and change it to "default=0" and it will boot the new kernel by default after that.

grub
savedefault --default=0 --once
quit

Reboot and see what happens. If it hangs, reboot again and you'll be back to your previous kernel.
Good luck.

[dirtbag]

sorry,

cp /boot/config-2.6.9-22.0.2.EL /usr/src/linux-2.6.15.4/.config

should instead be:

cp /boot/config-2.6.9-22.0.2.EL .config


(spent too much time in windows today)

[mouseketrips]

dirtbag, thanks, just what I was looking for. I took your advice and hired someone to do it this time, didn't want to take any chance. I am going to bookmark this so that I can do it myself next time.

[dirtbag]

You're welcome. Let us know what kernel you end up with and how it performs in comparison if you could so other CentOS and RHE admins can get more info on this issue.

[eva2000]

Originally Posted by dirtbag

sorry,

cp /boot/config-2.6.9-22.0.2.EL /usr/src/linux-2.6.15.4/.config

should instead be:

cp /boot/config-2.6.9-22.0.2.EL .config


(spent too much time in windows today)

hi could you update the previous post with the correct line too

thanks

[GFuse|Kevin]

A mod would likely have to do that eva
Anyone who looks at compiling their own kernels etc sould look in depth enough to know that they sould replace the linux-2.6.15.4 with their kernel version.
Else they souldnt be compiling it yet to begin with.

[SoftWareRevue]

Originally Posted by eva2000

hi could you update the previous post with the correct line too

thanks

Post updated.

[dirtbag]

Originally Posted by TDK-Kevin

A mod would likely have to do that eva
Anyone who looks at compiling their own kernels etc sould look in depth enough to know that they sould replace the linux-2.6.15.4 with their kernel version.
Else they souldnt be compiling it yet to begin with.

Yes, I should have mentioned that, thanks. And I couldn't fix the erroneous line because you can only edit your posts in the first 15 minutes and I didn't catch that until later Basically your /boot/config-2.6.9-22.0.2.EL (or whatever version you're running) file needs to be copied into your /usr/src/linux-2.6.15.4/ (or whatever version you're using) directory and renamed ".config"

[Eser]

SSH in Commands : yum upgrade kernel

[dirtbag]

Originally Posted by Eser

SSH in Commands : yum upgrade kernel

That only gives you the stock kernel instead of compiling a new one. The current default CentOS kernels have iowait problems and need to be compiled from source.