With this config: $ head -n2 isolinux/isolinux.cfg serial 0 9600 default vesamenu.c32 via the "Raw File Port Mode - VirtualBox" I got this: $ file /tmp/serial0.txt /tmp/serial0.txt: empty For the kernel log this in turn works OK: console=ttyS0 console=tty0 ignore_loglevel Is it really needed, exclusively a physical serial connection for the isolinux debug?