TIL: macOS Serial Console Login

When using Virtualization.framework to virtualize macOS VMs, I occasionally have no use for the GUI, and even get frustrated at the slowness (especially when scrolling in Terminal.app). Since Virtualization.framework supports adding a VirtIO serial device, I decided to try doing that, but when I booted the VM, nothing showed up.

After some searching, I found that I needed to modify /etc/gettytab and add a file to LaunchDaemons to start a getty on the serial console from this answer. However, in order to get a proper login banner (from the default entry) as well as a 256 color terminal, I used this gettytab line instead:

virtio:\
        :np:sp#115200:tt=xterm-256color:

I then added a serialconsole.plist file to /Library/LaunchDaemons similar to the one in the answer, but changed it to reference the virtio gettytab entry and cu.virtio serial device:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs//
PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>KeepAlive</key>
    <true/>
    <key>Label</key>
    <string>serialconsole</string>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/libexec/getty</string>
        <string>virtio</string>
        <string>cu.virtio</string>
    </array>
</dict>
</plist>

After rebooting, I was able to log in from the serial console. At this point, I was able to remove the GUI display from the VM, and everything continued to work properly.