This is a bootable copy of the 9legacy branch of Plan 9 from Bell Labs. See README for the main README file.
To boot this Plan 9, install qemu, so that you have qemu-system-x86_64 in your path.
Then:
git clone https://github.com/rsc/plan9
./plan9/boot/qemu
The qemu script builds u9fs in plan9/sys/src/cmd/unix/u9fs and then runs qemu with the right options to boot diskless, using the git clone as the root file system.
Because the VM shares the files with your host machine, you can edit files in one place and see the changes instantly in the other place. For example, you can edit files in your local editor even if you are running tests in the Plan 9 VM. You can run builds of Go binaries targeting Plan 9 on your host machine and then test the binaries in the VM. And you can run more than one VM, all sharing the same file system.
At boot time, the startup disk boot/pxeboot.raw loads a minimal Plan 9 kernel
into memory, which then PXE loads a plan9.ini and new kernel over TFTP (provided by qemu).
So if you make changes to the kernel, you can boot from ether0!/sys/src/9/pc/9pc
to test an as-yet-uninstalled kernel.
The plan9.ini is loaded from /cfg/pxe/525400123456. (That number is the VM's MAC address.) Changes made to that file will be visible on the next VM boot.