Install Unison 2.51.2 on Debian / Ubuntu - Used in Vagrant Guest Machines for compatibility with OSX Unison version

unison.sh

#!/bin/bash

apt-get update
apt-get install libdpkg-perl -y -f --allow-downgrades
apt-get install ocaml ocaml-native-compilers camlp4-extra opam -y -f

mkdir -p /usr/src/unison/
cd /usr/src/unison/

wget https://github.com/bcpierce00/unison/archive/refs/tags/v2.51.2.tar.gz -O unison.tar.gz
tar xzvf unison.tar.gz  --strip-components 1
make UISTYLE=text || true

chmod +x unison unison-*
rm /usr/bin/unison
rm /usr/bin/unison-*

ln -s $PWD/unison /usr/bin/
ln -s $PWD/unison-* /usr/bin/

echo "fs.inotify.max_user_watches=262144" > /etc/sysctl.d/90-unison-notify.conf
sysctl -p --system

Here was the fix that I put in place (adapted from code from @markbil)

I ended up going with 4.07.0 since that is the current version returned by unison -version -- unison version 2.51.2 (ocaml 4.07.0).

4.07.1 ended up erroring out when make tags was ran by the unison Makefile.

  # Remove current references of oCaml
  apt purge ocaml
  rm -r /usr/bin/ocaml*

  # Remove current versions of unison binaries
  apt purge unison
  rm -r /usr/bin/unison
  rm -r /usr/bin/unison-*

  # Compile OCaml from source
  mkdir -p /usr/src/ocaml
  cd /usr/src/ocaml
  wget http://caml.inria.fr/pub/distrib/ocaml-4.07/ocaml-4.07.0.tar.gz
  tar xzvf ocaml-4.07.0.tar.gz --strip-components 1
  ./configure
  make world.opt
  make install
  make clean

  # Compile Unison from source
  rm -rf /usr/src/unison/
  mkdir -p /usr/src/unison/
  cd /usr/src/unison/
  wget https://www.seas.upenn.edu/~bcpierce/unison/download/releases/unison-2.51.2/unison-2.51.2.tar.gz -O unison.tar.gz
  tar xzvf unison.tar.gz  --strip-components 1
  make UISTYLE=text || true

  chmod +x unison unison-*
  ln -s $PWD/unison /usr/bin/
  ln -s $PWD/unison-* /usr/bin/

  unison -version

I'm sure I'll need to update the original install script at some point in the near future so I'll get a new revision in then. ;)

Change the archive link
https://github.com/bcpierce00/unison/archive/refs/tags/v2.51.2.tar.gz

@Wedmal Thank you -- updated.