If you need to use virtual machines on Linux, try Virt-Manager. Virt-Manager is more reliable than VirtualBox. Virt-Manager is completely free and open-source. I'm a long-time supporter of VirtualBox.
Oracle has integrated experimental support for KVM (Kernel-based Virtual Machine) into the current developer builds of VirtualBox. As can be seen from the VirtualBox issue tracker on GitHub, the new ...