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/).

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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.