Please follow the Build Instructions document. It contains a section about building Chromium OS VM image. I will assume that you have followed them to the point where you have a virtual machine image with tweaks that you want there.
Linux KVM is a recommended virtual machine solution for Chromium OS (x86) since it is well supported by Linux community and quite fast (kernel based virtualization, also supports native virtualization for modern Intel and AMD CPUs). If present, KVM infrastructure can be utilized by QEMU as well.
In case you don't have KVM on installed on your machine yet, please run the following command:
In Ubuntu run:
Before running KVM for the first time, it's highly recommended that you reboot your machine and check that your BIOS settings has enabled native virtualization. Intel calls these technologies VT-x, on AMD machines they are called AMD-V or AMD-Virtualization. You can see the list of supported CPUs at http://en.wikipedia.org/wiki/Intel_VT-x, if you don't have one of them KVM will still work but slower.
You can run the kvm-ok helper to verify things are working:
To simplify the process of starting/stopping VMs, there are helper scripts in the Chromium OS checkout. Note: these must be executed outside of the sdk chroot.
By default, this will include graphics which can slow things down (if you want to run tests). You can use the --no_graphics option to disable that (which means you can only access the system via ssh):
When you started the VM, it told you PID file it used. Pass that to this script to stop the VM:
Please note that KVM currently does not support graphics hardware acceleration. As a result of that, you will see the red warning sign 'Unaccelerated graphics' in the upper left corner as soon as Chromium OS GUI starts.
Please note that once you click within QEMU/KVM window, it will 'grab' your mouse pointer. You can release the mouse by pressing Ctrl+Alt.
The virtual machine monitor console can be reached within the emulation window by pressing Ctrl+Alt+2. This should open a qemu command where number of useful commands can be run from. Their full description can be found at http://en.wikibooks.org/wiki/QEMU/Monitor. You can always return back to Chromium OS by pressing Ctrl+Alt+1 from the monitor screen.
Tip: to use virtual terminal in Chromium OS, enter virtual machine monitor console by Ctrl+Alt+2 then type sendkey ctrl-alt-f2 and switch back from monitor by Ctrl+Alt+1. The opposite can be done by sendkey ctrl-alt-f1.