git: 'lfs' is not a git command unclear

It looks like you haven't downloaded git-lfs on your machine, so git lfs install isn't a registered command by git.

Install git-lfs as outlined below:

1. Pre-Requisites

git-lfs requires git version 1.8.2 or later. You can check the version you have by running git --version, and update if required.
If you are installing on macOS, make sure you have Homebrew installed.

Download git-lfs by following the steps based on your operating system.

Debian / Ubuntu

$ curl -s https://packagecloud.io/install/repositories/github/git-lfs/script.deb.sh | sudo bash
$ sudo apt-get install git-lfs

MacOS (Using Homebrew)

$ brew update
$ brew install git-lfs

Windows

Download and run the latest windows installer.

Finally, run git-lfs install to install git-lfs on your system. You can always run git-lfs uninstall to uninstall.

More detailed information (such as for installation on other platforms) can be found on git-lfs's installation page.

You can't directly use

git lfs install

Instead of that, you can use these commands to download and install (you have to download it before installing).

sudo apt-get install git-lfs
git-lfs install