Make NetVM specifics more clear

Attempt to describe more clearly what determines which NetVM a DispVM uses; see https://github.com/QubesOS/qubes-issues/issues/2379
Also edited the first paragraph a bit.
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ubestemt 2017-04-24 18:42:35 +00:00 committed by GitHub
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@ -14,13 +14,14 @@ Disposable VMs (DispVMs)
Background
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See [this article](http://theinvisiblethings.blogspot.com/2010/06/disposable-vms.html) for a background on why would one want to use a Disposable VM and what it is.
A Disposable VM (DispVM) is a lightweight VM that can be created quickly and which will disappear when it is finished with. Usually a Disposable VM is created in order to host a single application, like a viewer or an editor. This means that you can safely work with files without risk of compromising any of your VMs. Changes made to a file opened in a disposable VM are passed back to the originating VM. See [this article](http://theinvisiblethings.blogspot.com/2010/06/disposable-vms.html) for more on why would one want to use a Disposable VM.
A DisposableVM is a lightweight VM that can be created quickly and which will disappear when it is finished with. Usually a Disposable VM is created in order to host a single application, like a viewer or an editor. This means that you can safely work with files without risk of compromising any of your VMs. Changes made to a file opened in a disposable VM are passed back to the originating VM.
By default a Disposable VM will inherit the NetVM and firewall settings of the ancestor VM, that is the VM it is launched from. Thus if an AppVM use sys-net as NetWM (instead of, say, sys-whonix), any DispVM launched from this AppVM will also have sys-net as its NetVM. You can change this behaviour for individual VMs: in the Qubes Manager open VM Settings for the VM in question and go to the "Advanced" tab. Here you can edit the "NetVM for DispVM" setting to change the NetVM of any DispVM launched from that VM.
By default a Disposable VM will inherit the netVM and firewall settings of the ancestor VM. You can change this behaviour: in the Qubes Manager go to the advanced tab of VM Settings where you can set the default netVM to be used for DisposableVMs created from that VM.
A Disposable VM launched from the Start Meny inherits the NetVM of a so-called internal TempVM, the *[DVM Template](https://www.qubes-os.org/doc/glossary/#dvm-template).* By default it is named `fedora-XX-dvm` (where `XX` is the Fedora version of the default TemplateVM) and hidden in Qubes VM Manager; it can be shown by selecting "Show/Hide internal VMs". Notice that changing the "NetVM for DispVM" setting for the DVM Template does *not* affect the NetVM of DispVMs launched from the Start Meny; only changing the DVM Template's own NetVM does.
Once a DispVM has been created it will appear in the Qubes Manager with the name "dispX", and NetVM and firewall rules can be set as for a normal VM.
Once a dispVM has been created it will appear in the Qubes Manager with the name "dispX", and NetVM and firewall rules can be set as for a normal VM.
Opening a file in a Disposable VM (via GUI)
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