Reinstalling the Kernel in CentOS or RHEL

• yum does not remove the kernel entirely.
• You can remove and reinstall the kernel since it’s entirely in
  memory

Reinstalling your kernel

To see a list of installed kernels:

[root@server ~]# rpm -qa | grep kernel | sort  
kernel-2.6.18-308.11.1.el5  
kernel-2.6.18-308.13.1.el5  
kernel-2.6.18-308.4.1.el5  
kernel-2.6.18-308.8.1.el5  
kernel-2.6.18-308.8.2.el5  
kernel-headers-2.6.18-308.13.1.el5  
kernel-xen-2.6.18-308.11.1.el5  
kernel-xen-2.6.18-308.13.1.el5  
kernel-xen-2.6.18-308.4.1.el5  
kernel-xen-2.6.18-308.8.1.el5  
kernel-xen-2.6.18-308.8.2.el5

To remove specific ones,

yum remove kernel-2.6.18-308.11.1.el5 kernel-2.6.18-308.13.1.el5

And so on. Now you can

# Install the version you want   
yum install kernel-2.6.18-308.13.1.el5  
  
# or the latest version  
yum install kernel

Check /boot/grub/menu.lst, and then reboot.