The MRG Realtime kernel is not automatically specified as the default boot kernel during the installation process. The recommended approach after installing the kernel replacement is to reboot, then manually select the MRG Realtime kernel in the grub menu.

Once you know that the MRG Realtime kernel is fully operational on your system you can modify grub.conf to make it the default boot kernel. The grub.conf file is located in /boot/grub/grub.conf. View the file using any text editor, it should look similar to the following:

default=1
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Red Hat Enterprise Linux (realtime) (2.6.21-43.el5rt)
	root (hd0,0)
	kernel /vmlinuz-2.6.21-43.el5rt ro root=/dev/Root rhgb quiet
	initrd /initrd-2.6.21-43.el5rt.img
title Red Hat Enterprise Linux Client (2.6.18-8.1.8.el5)
	root (hd0,0)
	kernel /vmlinuz-2.6.18-8.1.8.el5 ro root=/dev/Root rhgb quiet
	initrd /initrd-2.6.18-8.1.8.el5.img

In the example, the MRG Realtime kernel is listed first as (hd0,0). Change the value of default= to 0 as follows and save your changes.

default=0
timeout=5
splashimage=(hd0,0)/grub/splash.xpm.gz
hiddenmenu
title Red Hat Enterprise Linux (realtime) (2.6.21-43.el5rt)
	root (hd0,0)
	kernel /vmlinuz-2.6.21-43.el5rt ro root=/dev/Root rhgb quiet
	initrd /initrd-2.6.21-43.el5rt.img
title Red Hat Enterprise Linux Server (2.6.18-53.el5)
	root (hd0,0)
	kernel /vmlinuz-2.6.18-53.el5 ro root=/dev/Root rhgb quiet
	initrd /initrd-2.6.18-53.el5.img

You will also need to edit /etc/sysconfig/kernel. This will ensure that the changes you made to the grub file will remain as the default when you perform a system upgrade. To edit this file, open it in any text editor. It should look similar to this:

# UPDATEDEFAULT specifies if new-kernel-pkg should make
# new kernels the default
UPDATEDEFAULT=yes
			
# DEFAULTKERNEL specifies the default kernel package type
DEFAULTKERNEL=kernel

Simply change the DEFAULTKERNEL= parameter to read kernel-rt.

# UPDATEDEFAULT specifies if new-kernel-pkg should make
# new kernels the default
UPDATEDEFAULT=yes
			
# DEFAULTKERNEL specifies the default kernel package type
DEFAULTKERNEL=kernel-rt

You will now be able to confirm that your system is running the MRG Realtime kernel, by running the uname command as the root user at the shell prompt. Check the output for the RT designation. If it appears, the MRG Realtime kernel is running.

# uname -a
Linux server01 2.6.21-43.el5rt #1 SMP PREEMPT RT Tue Oct 16 11:05:05 EDT 2007 x86_64 x86_64 x86_64 GNU/Linux

Obtaining Kernel Crash Dump Information

MRG Realtime can be configured to provide crash dump information by enabling kexec/kdump. Further information and instructions on how to configure your system to obtain kernel crash information can be found on the MRG Realtime Wiki: Crash Dump Configuration.