How to safely upgrade kernel ? Many times it happens that you upgrade kernel, and reboot your server and your server never comes on-line. So using the trick below, server will first boot up on the new kernel and if the server isn’t coming on-line then reboot the server again and it will boot up in old kernel.
First Upgrade the Kernel
root@justgeek~]# yum install kernel
Edit grub configuration by editing /boot/grub/grub.conf and change default=0 to default=1 (Or your working kernel)
Go to grub prompt using grub command.
Probing devices to guess BIOS drives. This may take a long time.
Unknown partition table signature
GNU GRUB version 0.97 (640K lower / 3072K upper memory)
[Minimal BASH-like line editing is supported.For first word,TAB listspossible command completions.Anywhere else TAB lists the possible
completions of a device/filename.]
grub> savedefault --default=0 --once
Reboot the server and make sure that you booted with latest kernel
Once the Server is booted with new kernel edit /boot/grub/grub.conf and change default=1 to default=0 (i.e. your new kernel)