Linux上的VM

Linux有很好的VM support，如Kernel Virtual Machine (KVM), 由kernel module提供支持。QEMU （https://www.qemu.org， 一个开源的machine emulator and virtualizer）包含KVM的userspace component。如果你做过Android开发，用过Android的虚拟机AVD，那就是用QEMU实现的。KVM和QEMU是基于Linux内核的，所有有很小的footprint，效率却很高。When used as a virtualizer, QEMU achieves near native performance by executing the guest code directly on the host CPU. QEMU supports virtualization when executing under the Xen hypervisor or using the KVM kernel module in Linux. When using KVM, QEMU can virtualize x86, server and embedded PowerPC, 64-bit POWER, S390, 32-bit and 64-bit ARM, and MIPS guests. 

KVM vs VirtualBox

Both are opensource. According to this: KVM is better integrated with Linux, it's smaller and faster, and while you can use it with other guests besides Linux. Vbox supports suspends, and may be better for other guest OS such as BSD and Solaris.