NOTE: We have stopped maintaining the x86 book for xv6 but have switched the book to RISC-V (see https://github.com/mit-pdos/xv6-riscv-book/).

The book compiles using Heirloom Troff, an open source update of the original Unix troff.

cvs -d :pserver:anonymous@heirloom.cvs.sourceforge.net:/cvsroot/heirloom co heirloom-doctools cd heirloom-doctools make sudo make INSTALL=install STRIP=strip install # sic

This will install the binaries in /usr/ucb, but you want to install them in /usr/local/ucb, which is what the run1 script expects. Move the binaries or update PREFIX in mk.config in heirloom-doctools.