How to securely use in dom0 the result of a command executed in a qube

If I may add a more specific question about it here, as I’ve been wondering whether I can use it for certain things:
How do I automate the usage of such a management vm, e.g. have it interact with a qube so I don’t have to use qvm-run --pass-io in dom0? Basically what one could do manually by using qvm-console-dispvm (which IIUC will spawn a disposable based on default-mgmt-dvm), but having the ability to pass commands via a script, similarly to how I could from dom0 do e.g. [[ "$(qvm-run --pass-io targetVM -- mycommand)" == "compareValue" ]] && otherCommand, just without having to expose dom0 to the returned and possibly malicious data.

It’s not unrelated, as I’m talking about functionality that is provided for non-automatic interaction via the qvm-console-dispvm program, which spawns an unnamed disposable from the default-mgmt-dvm DVM template, which is what this topic is about; if you don’t have an answer for me, why even reply?

In any case, your understanding is at least partially wrong, as in multiple places of the documentation qvm-console-dispvm is explicitly noted as a tool to troubleshoot different issues with qubes, so even though the default-mgmt-dvm is classified as internal in the Qube Manager, QubesOS still provides for an explicit user-exposed way to utilize it (non-internally).

Just to make it clear, as I understand it, default-mgmt-dvm don’t have any additional functionality compared to any other DVMs, it’s just a name that is used internally. If default-mgmt-dvm is based on fedora-38 template then it’ll be the same as using default_dispvm based on fedora-38 template.

In case of qvm-console-dispvm, the default-mgmt-dvm by itself is not providing any additional functionality compared to using any other DVM template.

It’s so that your question is not lost without an answer in unrelated (in my opinion) topic.

This does not make sense to me. qvm-console-dispvm will use the default-mgmt-dvm to spawn disposables, because it is designated in qubes-prefs as the management_dispvm; if you designate a different DVM template as the management_dispvm via qubes-prefs then you’ll have come full circle, as the function is still being fulfilled, just by a vm with a different name. The designation is what is providing the functionality.

I meant to say that if management_dispvm and default_dispvm are both based on e.g. fedora-38 template and you’ll change management_dispvm to default_dispvm in qvm-console-dispvm script then nothing will change and qvm-console-dispvm will function the same:

[user@dom0 ~]$ cat /usr/bin/qvm-console-dispvm
#!/usr/bin/bash --
set -eu
print_usage() {
cat >&2 << USAGE
Usage: $0 [--autostart] [--] vmname
Connects to VM console throught DispVM using the qubes.ShowInTerminal RPC service.
With --autostart, start the VM first.
USAGE
}

do_start=false
if [[ $# -ge 2 ]] && [[ "$1" = '--autostart' ]]; then
    do_start=:
    shift
fi
if [[ $# -eq 2 ]] && [[ "$1" = '--' ]]; then
    shift
elif [ $# -ne 1 ]; then
    print_usage
    exit 1
fi

QREXEC_REQUESTED_TARGET="$1"

[[ "$QREXEC_REQUESTED_TARGET" =~ ^[A-Za-z][A-Za-z0-9_-]*$ ]] || { printf 'Invalid qube name %q\n' "$QREXEC_REQUESTED_TARGET">&2; exit 1; }

if "$do_start"; then
    msg='cannot be started'
    qvm-start --skip-if-running -- "$QREXEC_REQUESTED_TARGET"
else
    msg='is not running'
    qvm-check --quiet --running -- "$QREXEC_REQUESTED_TARGET"
fi > /dev/null 2>&1 || { echo "Error: domain '$QREXEC_REQUESTED_TARGET' does not exist or $msg">&2; exit 1; }

DISPVM="$(qvm-prefs -- "$QREXEC_REQUESTED_TARGET" management_dispvm)"

[[ "x$DISPVM" == "x" ]] && { echo "Error: cannot determine management DispVM of domain '$QREXEC_REQUESTED_TARGET'">&2; exit 1; }

sudo qvm-run -p --localcmd="QREXEC_REQUESTED_TARGET=$QREXEC_REQUESTED_TARGET QREXEC_REMOTE_DOMAIN=dom0 /etc/qubes-rpc/admin.vm.Console" --service --dispvm="$DISPVM" -- qubes.ShowInTerminal

Or if you change management_dispvm from default-mgmt-dvm to some fedora-38-dvm.