The first time you get an OpenSDE working tree you can get the source like this:

$ cd somewhere
$ git clone git://git.opensde.net/opensde/opensde-nopast.git opensde
$ cd opensde
$ ./bin/sde install
$ sde up (or ./bin/sde up)

This snippet of commands that will populate the opensde source tree and the package tree.

You are supposed to have $HOME/bin in your $PATH, it's usually added by default in the Linux distributions on login when the directory exists. If sde up gives you a command not found error you may need to close the terminal and open it again.

If you already have sde in your $PATH, you only need to run

$ sde new tree my_new_tree

Our Git repository contains several extra targets, you can check them out at OpenSDE Git Repo.