Brian Kelsay wrote:
I went and read most of the HOWTO on User-mode Linux and I have to say, I'm not sure if it actually gives you a good impression of a new kernel being able to run on your hardware. The host kernel is still in the way. You use virtual devices and filesystems. Sure, it's safe, but it won't tell you definitively if the new kernel works on your hardware.
If you can boot to a UML kernel, you can work with whatever hardware the underlying kernel has compiled virtual device support for. The whole point is that UML doesn't work on hardware. It runs in usermode on top of a kernel which does.
Actually, I'm lying ;) One of the directions UML is moving toward is the ability to compile support for selective direct hardware access. Certain hardware resources could be dedicated to different UML instances. This would allow you to decide where you want to place the virualization performance vs. security etc. tradeoffs.
Now if you want to test other software on a specific kernel without risking crashing the system, then this appears to be the answer you've been looking for. Or if you want to test features of a new kernel, then this would work. If you want to host an app like a webserver in a controlled/limited environment, giving near root privileges to a user, then this may work also, but a chrooted jail might be better. Then again, I could be wrong.
Sure... use the right tool for the job.
I just meant to underscore that chroot isn't always the right tool for the job. It depends on what you mean by a test environment, and whether or not the test environment needs root privileges.
User-mode appears to use less resources than a Xen, VMWare or Bochs, as does chroot, but that is Linux on Linux only. Each can have its place.
You're preaching to the choir ;-)
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