Adding more CPU-cores without rebooting you Linux-server

This assumes that you are running your Linuxsystem as a virtual server on VMWare, KVM, XEN or AHV with CPU Hotplug enabled.

From time to time, I have been in need of extra CPU-power for various reasons. It might be that someone suddenly got alot of traffic to their PHP-based website, or they want to add more containers but loosing the time and uptime that comes with a reboot it not an option.

Luckily, there is solutions for that!

  1. First of all, add the cores to your VM via your hypervisor.
  2. Second, we need to tell the kernel that there is more cores available for use, we can do that by using this simple script:

for f in /sys/devices/system/cpu/cpu*/online ; do grep -v -q 0 $f || continue echo -n "Bringing $f online... " echo 1 > $f || continue echo OK done

Done, you can now verify that you have added more cores to your system, using for example – htop

Note! Some programs needs a restart in order to start using more cores