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I know that Linux OS's are typically multi-programmed, which means that multiple processes can be active at the same time. Can there be multiple kernels executing at the same time?

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up vote 9 down vote accepted

Sort of. Check out User-mode Linux.

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Oh right, thanks. Got soft on the brain... – Keith Jan 2 '11 at 9:22

With most virtualization solutions (xen, virtualbox, vmware and the likes), you certainly have multiple kernels running at the same time on a single machine.

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But of course only one kernel is running "on the real hardware" as the hypervisor. – mattdm Jan 2 '11 at 12:52
Some high end servers support multiple kernels running concurrently on the same machine (a.k.a. physical domains) but I don't think Linux is supported on these boxes. Solaris definitely is. – jlliagre Jan 3 '11 at 17:21
— I believe in those cases what it really means is that there's a firmware-level hypervisor mediating access to the actual hardware. – mattdm Feb 22 '11 at 20:36
There is no such need with physical domains. The hardware resources are dispatched between the domains then are electrically isolated. Thanks to this isolation, there is no need for an underlying hypervisor layer on these kind of servers. – jlliagre Feb 22 '11 at 21:55

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