Document how to run the VM for builds

This includes:

- read-only / snapshot mode
- port forwarding guest 22 to host 9999
- internet access
- no visual display, serial only

1 files changed, 24 insertions, 0 deletions

diff --git a/README.md b/README.md
index 9b11592..683169a 100644
--- a/README.md
+++ b/README.md
@@ -106,3 +106,27 @@ sed -i 's|root=/dev/sda3 rw|root=/dev/vda2 rw console=ttyS0|g' /boot/syslinux/sy
 exit
 poweroff
 ```
+
+## Start Arch Linux virtual machine for automated builds
+
+The following command starts the Arch Linux QEMU virtual machine in a read-only
+mode (`snapshot=on`) to prevent altering the original image file.
+
+Furthermore the local port 22 of the VM is forwarded to the localhost port 9999
+of the host. Thus clients on the host can use SSH to connect to the VM.
+
+Again no graphical display is used and only output of the serial console is
+shown in the terminal. Since the `console=ttyS0` kernel parameter was set in
+the bootloader configuration of the VM, no manual editing of kernel parameters
+during runtime is needed (in contrast to the current Arch Linux installation
+image).
+
+```
+qemu-system-x86_64 \
+    -enable-kvm \
+    -m 4G \
+    -net nic,model=virtio -net user,hostfwd=tcp:127.0.0.1:9999-:22 \
+    -drive file=vms/archlinux.qcow2,media=disk,snapshot=on,if=virtio \
+    -smp cpus=4 \
+    -nographic
+```