Build requirements:

sudo apt install git cargo libssl-dev pkg-config libpq-dev yarn curl gnupg2 git
# install yarn
curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
sudo apt update && sudo apt install yarn

Get the source code

git clone https://github.com/LemmyNet/lemmy.git
# or alternatively from gitea
# git clone https://yerbamate.dev/LemmyNet/lemmy.git

All the following commands need to be run either in lemmy/server or lemmy/ui, as indicated by the cd command.

Build the backend (Rust)

cd server
cargo build
# for development, use `cargo check` instead)

Build the frontend (Typescript)

cd ui
yarn build

Setup postgresql

sudo apt install postgresql
sudo systemctl start postgresql
# initialize postgres database
sudo -u postgres psql -c "create user lemmy with password 'password' superuser;" -U postgres
sudo -u postgres psql -c 'create database lemmy with owner lemmy;' -U postgres
export LEMMY_DATABASE_URL=postgres://lemmy:password@localhost:5432/lemmy
# or execute server/db-init.sh

Run a local development instance

# run each of these in a seperate terminal
cd server && cargo run
ui & yarn start

Then open localhost:4444 in your browser. It will auto-refresh if you edit any frontend files. For backend coding, you will have to rerun cargo run. You can use cargo check as a faster way to find compilation errors.

To speed up incremental builds, you can add the following to ~/.cargo/config:

rustflags = ["-Clink-arg=-fuse-ld=lld"]

Note that this setup doesn't include image uploads or link previews (provided by pict-rs and iframely respectively). If you want to test those, you should use the Docker development.