assuming you have a apu2|apu3|apu4 from pcengines or a virtual machine running on KVM/Qemu. And you don’t have vga/dvi/hdmi whatever kind of video output. of course, you can install and run OpenBSD (or Linux) on this boxes. boot.conf if you wanna install from an USB Stick, set the correct Port and Speed before booting. boot> stty com0 115200 boot> set tty com0 or put these settings ins in the boot.conf on your tftp server.
How to Access APU “B” from APU “A” via Serial Console (USB to Serial Device) APU “A” Connect USBtoSerial Adapter Connect to Serial Console on APU “B” APU “B” /etc/ttys tty00 "/usr/libexec/getty std.115200" vt220 on secure APU “A” cu -s 115200 -l /dev/tty00 cu -s 115200 -l /dev/cuaU0 (8 Port USB2Serial Device) -> you have now Console Access to APU “B” Hardware https://www.amazon.de/LogiLink-AU0033-USB-Adapter-Serial/dp/B00BBXHOAY sha256: 61342bb512ee1ef21f21c02614a839b8654338579aaaaed6c5100e6dd89448c3