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From kernel all the way up to the Desktop Environment, where does Ubuntu reside?
Linux kernel is the kernel for all distros.
The basic utilities (fdisk, ls, bash, whiptail, etc.) are mostly GNU tools and (almost) compatible to almost-all Unix-like variants.
The systems of (userspace-resident) device drivers, pamd, udev, upower, etc. are also conformant to kernel APIs and ABIs interfaces.
The X system is also not Ubuntu.
The desktop environment (Gnome, Kde, etc.) is also not Ubuntu.
So, where is Ubuntu? In particular, where is Ubuntu's source code?