What is the difference between git push -u origin master and git push origin master? Why the -u switch for the git push command?

Question

git

The question is essentially to the -u switch for the git push command:

-u, --set-upstream
           For every branch that is up to date or successfully pushed, add upstream (tracking) reference, used by argument-less git-pull(1) and other commands. For more information, see branch.<name>.merge in git-config(1).

What I want to get an explanation: in what cases is the -u switch necessary?

Answer 1

In case the master branch (or branch_name) is not a tracked branch origin/master (or origin/branch_name) and you want to make it so.
By executing the git push -u origin master command , you establish a link between the branch you are on and the master branch on the remote server. The command needs to be executed once, so that later you can send / receive changes only by performing git push from the branch without specifying any aliases for the server and remote branches. This is for convenience.