Unison for Termux

Unison is a great synchronization tool, but it's not available in the Termux package manager. To use it, you must build it from source.

This guide shows you how to install Unison on your Android device using Termux. In the process, we will also install OCaml, which, to this date, is also not available in the Termux package manager.

Largely based on Compiler Unison dans Termux by jdn06.

Prerequisites

Install required build tools:

pkg update -y
pkg install -y binutils build-essential clang make git curl unzip libandroid-shmem

If running in a simulator (such as waydroid), you might need ndk-multilib as well.

Building OCaml

Unison is built using OCaml, so we will have to install it first. This process compiles OCaml specifically for the Android architecture.

Notes:

• Unison requires Ocaml 4.08 at minimum.
  • 4.13.0 to 5.3.0 (should) work
  • 5.4.0 and 5.4.1 do not work
  • 5.5.0-beta1 (latest) works
• The android api version must be at least 28. (more)
• Higher android api versions seem to have issues on aarch64 devices. (more)

Credits:

• terminatorbs: noted issues with api version and missing dependency
• engdyn: noted issues with api versions above 28 and problematic ocaml versions

OCAML_VERSION=5.3.0
TARGET="$(uname -m)-unknown-linux-android"
API=28

mkdir -p $HOME/tmp
curl -L https://github.com/ocaml/ocaml/archive/refs/tags/${OCAML_VERSION}.tar.gz \
  -o "$HOME/tmp/ocaml.tar.gz"
tar xzf "$HOME/tmp/ocaml.tar.gz" -C "$HOME/tmp"
cd "$HOME/tmp/ocaml-${OCAML_VERSION}"

# Configure OCaml for Termux/Android
# Termux provides the $PREFIX variable.
./configure --prefix=$PREFIX --disable-warn-error --without-afl CC="clang --target=${TARGET}${API}" LDFLAGS="-landroid-shmem"

# Build and install OCaml
make world
make install

Check whether ocaml was correctly installed:

ocaml --version
ocamlc --version

Building Unison

Now that OCaml is installed, you can compile Unison. This guide uses Unison 2.53.7.

UNISON_VERSION=2.53.7

mkdir -p $HOME/tmp
curl -L https://github.com/bcpierce00/unison/archive/refs/tags/v${UNISON_VERSION}.tar.gz \
  -o "$HOME/tmp/unison.tar.gz"
tar xzf "$HOME/tmp/unison.tar.gz" -C "$HOME/tmp"
cd "$HOME/tmp/unison-${UNISON_VERSION}"

# Build and install Unison
# NATIVE=false tells the build system to use the OCaml bytecode compiler,
# which makes large syncs slower but is necessary for Termux.
make NATIVE=false
make NATIVE=false install

Unison should be installed now!

You can test it by checking the version:

unison -version

Usage

If you encounter errors while running unison, try to use the options -ignorelocks and possibly -perms=0 (or -fat, which includes -perms=0) as well. Though both have downsides: With -ignorelocks, you must be careful not to start multiple sync jobs at once. When using -perms=0, no permissions will be synchronized. More information in the Unison Manual. On a rooted device, there are ways to use Unison without these flags.

Cleanup

Remove temporary build files:

cd
rm -rf $HOME/tmp/ocaml-${OCAML_VERSION} $HOME/tmp/unison-${UNISON_VERSION} $HOME/tmp/*.tar.gz

Uninstall

OCaml:

rm -f $PREFIX/lib/ocaml*
rm -rf $PREFIX/lib/ocaml $PREFIX/share/man/man1/ocaml*

Unison:

rm -f $PREFIX/bin/unison* $PREFIX/share/man/man1/unison.1