Your CPU (Central Processor Unit) must support Intel VT-x or AMD-v hardware virtualization features which must also be enabled in UEFI/BIOS.

In order to install Ubuntu on VirtualBox, you should have a physical computer with at least 4 GB of RAM (Random Access Memory), a hard disk drive with at least 30 GB of free space (SSD is preferred due to its higher performance). Make sure that VirtualBox is installed on your physical machine before proceeding. The operating system (OS) runs on a physical machine is referred to as a host OS, and the operating system run on a VM is called a guest OS (Ubuntu in this case). Today’s blog post explains how to install Ubuntu on VirtualBox. Installing Ubuntu on VirtualBox as a virtual machine (VM) has a lot of advantages – you can create a snapshot and roll back changes to the appropriate VM state if something goes wrong, clone a VM, copy a VM to another machine easily (all VM data is stored as a set of files), or run a VM on different host operating systems that are supported by VirtualBox. Whether you are looking to try out some software, prepare for migration to Linux from Windows or macOS, test applications, network, or otherwise, you need to install Ubuntu on VirtualBox.

Ubuntu server 20.04 virtualbox image