Vagrant: Use libvirt/debian

Vagrantfile

@@ -3,9 +3,17 @@
 # vi: set ft=ruby :
 
 Vagrant.configure("2") do |config|
-  config.vm.box = "ubuntu/focal64"
+  config.vm.box = "debian/buster64"
   config.vm.provider :virtualbox do |vb|
-    vb.customize ["modifyvm", :id, "--cpus", 1, "--memory", 1024]
+    vb.customize ["modifyvm", :id, "--cpus", 4, "--memory", 4096]
+  end
+  config.vm.provider :libvirt do |v|
+    v.memory = 4096
+    v.cpus = 4
+    v.nested = true
+  end
+  config.vm.provider :kvm do |kvm|
+    kvm.memory_size = '4096m'
   end
 
   # Network config: Since it's a mail server, the machine must be connected
@@ -14,13 +22,15 @@ Vagrant.configure("2") do |config|
   # machine on a private network.
   config.vm.hostname = "mailinabox.lan"
   config.vm.network "private_network", ip: "192.168.50.4"
+  config.vm.synced_folder ".", "/vagrant", nfs_version: "3"
+  #, :mount_options => ["ro"]
 
   config.vm.provision :shell, :inline => <<-SH
     # Set environment variables so that the setup script does
     # not ask any questions during provisioning. We'll let the
     # machine figure out its own public IP.
     export NONINTERACTIVE=1
-    export PUBLIC_IP=auto
+    export PUBLIC_IP=192.168.50.4
     export PUBLIC_IPV6=auto
     export PRIMARY_HOSTNAME=auto
     export SKIP_NETWORK_CHECKS=1