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When I was using Virtual Box in Windows 7, I could choose how many CPU cores to assign to the guest OS. Now I'm using Linux, and when I installed Virtual Box, I couldn't find that option. System Monitor shows that when the VM is busy only one CPU core goes to 100% while the rest are near 0%. How can I make Virtual Box in Linux use multiple CPU cores?

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I think you need a 64-bit host OS and hardware virtualization to present multiple cores to the guest. Does your Linux installation meet those requirements? – coneslayer Jul 28 '10 at 11:25
I'm using a 64-bit Linux. Hardware virtualization is turned on. – OSX NINJA Jul 28 '10 at 11:28
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I can simply set that in the VMs settings - change its details, go to the "System" tab, click on "Processor" and slide the slider to the right - done.

Did you check if the Host OS can actually see the correct number of cores?

You might want to check /proc/cpuinfo for that.

Picture of the settings tab / slider on OS X:

enter image description here

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Yes, all four CPU cores are seen. The Linux version of Virtual Box does not look like that. That's how the Windows version looks. – OSX NINJA Jul 28 '10 at 11:36
Actually, that's OS X ;) (admittedly with the settings displayed for a XP Guest). Glad it now seems to work with your updated version :) – phrozen77 Jul 30 '10 at 7:04
Yeah I have it on OSX too and that's what it looks like. The newest version pretty much has the same features across Windows, OSX, and Linux. – OSX NINJA Jul 31 '10 at 12:33
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I found the solution. It turns out I was using an older version of Virtual Box. I upgraded to a newer version and I get the options for multiple CPU cores.

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