I'm using virtualbox with Kali and it's working fine, however I currently only have it using 1 cpu and I'd like to add more.

However when I go to Settings → System → Processor the fields are greyed out and I can't change number of processors (this happens even when kali isn't running). Any help is appreciated

  • restart, close all processes related to virtualbox of vbox and then open vbox and then try to change. – Hunter May 12 '14 at 4:33

You can find the workaround here: How do I enable multiple cores in my virtual enviroment?.

To enable more than 1 CPU in your VM the following settings are needed in addition:

  • 64-bit virtual guest hardware in General settings tab (for 64-bit guests)

  • Enable I/O APIC in the Motherboard settings tab

  • Enable hardware virtualization (VT-x/AMD-V) in the Acceleration tab

Note that if your run your VM on all cores available you may experience a better host performance when assigning an execution cap to the CPU.

You won't be able to edit the CPU count while the VM is running or has a saved state, so make sure that it is in the powered off state.

  • What if the accelaration tab is grayed out too ? – user2284570 Feb 25 '17 at 22:13

I had a similar issue: I could not change the number of processors or the amount of RAM after I had run a new VM and installed a host OS.

The only way I found was to create a brand new virtual machine using all the new settings I want and then instead of creating a new virtual hard drive just link the drives from the first VM. As long as you make the MAC address the same as the old one it all works.

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