Ubuntu is just a collection of software. The most important piece of software in that collection is the Linux kernel. That kernel is what is shared between dif

Ubuntu is just a collection of software. The most important piece of software in that collection is the Linux kernel. That kernel is what is shared between different containers. You can have 5 copies of Ubuntu (or Debian, or Mint) in separate containers, but they're all using the same kernel. This is what makes containers much more efficient than multiple full VMs.