To download the EOSIO source code, clone the eos repo and its submodules. It is adviced to create a home eosio folder first and download all the EOSIO related software there:

mkdir -p ~/eosio && cd ~/eosio
git clone --recursive https://github.com/EOSIO/eos

Update Submodules

If a repository is cloned without the --recursive flag, the submodules must be updated before starting the build process:

cd ~/eosio/eos
git submodule update --init --recursive

Pull Changes

When pulling changes, especially after switching branches, the submodules must also be updated. This can be achieved with the git submodule command as above, or using git pull directly:

[git checkout <branch>]  (optional)
git pull --recurse-submodules

[[info	What’s Next?]]
	Build EOSIO binaries