Determine if reboot is required to update kernel?

Question

I am running a server which runs on CentOS with cPanel (latest version) and I have it set to automatically update using yum. Since it needs to be rebooted in order to update the kernel (and possibly other things), I was wondering if there's any way to figure out if a reboot is required?

EDIT: The server is a VPS and it's running on OpenVZ. Because of the way OpenVZ works, there's no /boot/vmlinuz and yum list installed kernel doesn't work either.

Answer 1

You can try the following bash script from this answer from ServerFault.

#!/bin/bash
LAST_KERNEL=$(rpm -q --last kernel | perl -pe 's/^kernel-(\S+).*/$1/' | head -1)
CURRENT_KERNEL=$(uname -r)

test $LAST_KERNEL = $CURRENT_KERNEL || echo REBOOT

Answer 2

First of all, we print out running kernel version:

# uname -r 
2.6.32-71.29.1.el6.i686

Ok, we have to patch:

# yum update kernel*

Grab the kexec tools:

# yum install kexec-tools

Now we get last installed kernel version release and put it on a var:

# latestkernel=`ls -t /boot/vmlinuz-* | sed "s/\/boot\/vmlinuz-//g" | head -n1` 

# echo $latestkernel 
2.6.32-220.4.1.el6.i686

Now we need to load the new kernel version in memory:

# kexec -l /boot/vmlinuz-${latestkernel} --initrd=/boot/initramfs-${latestkernel}.img --append="`cat /proc/cmdline`"

Finally, we can issue a reset:

# kexec -e

..and.. wow, we lost the system! ..Well, not exactly.

The system will “restart without restarting”..something like a fast reboot, without performing BIOS checks (and you know how long can a full system restart last).

# uname -r
2.6.32-220.4.1.el6.i686

It worked!

• Be aware that kernel reset will perform a connection reset as well, together with resetting your uptime, so if you’re searching for something to grant your uptime record while security patching, well, this is not for you.