Friday 6 March 2015

Boot once to avoid kernel panic during upgrade

While upgrading kernel in a linux server, we will have to reboot the machine to bring up the new kernel. Now, if there is some problem with new kernel, then we may end up in kernel panic. Inorder to avoid this situation, we have boot once option.

With this option, we can bring back the machine to old kernel with the very next reboot after panic.

Step 1: Update kernel as below:
root@MANINMANOJ:~# yum update kernel

The new/updated kernel will be in 0th position in /etc/grub.conf. Then change the 'default' value to 1 in /etc/grub.conf


Step 2: - Run this at shell:
echo "savedefault --default=0 --once" | grub --batch

This means that, boot once to new kernel. In the next reboot go to the kernel at the 1 position of /etc/grub.conf.

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