On some hardware and/or software, console I/O will sometimes hang.
This is documented in a KLH10 makefile, with a workaround:
# This is a known problem on some Linux systems with high performance
# hardware. As far as I know, Ken has not found a fix for it.
#
# The workaround is to rebuild klh10 with a special configuration that
# avoids the esoteric real-time-interrupt mechanisms.
