What does git pull --rebase --ff-only do?

[Edit, Dec 4, 2016: As of Git 2.6, it is git pull

no longer a script, so it is no longer easy to see what it does and the technical details below do not apply. But --ff-only

still only useful on merge, not on reboot.]

git pull

The script (you can view it yourself, for example less $(git --exec-path)/pull

) is currently allocating --ff-only

to a named variable $ff_only

, which is subsequently completely ignored if it completes the rebase:

case "$rebase" in
true)
        eval="git-rebase $diffstat $strategy_args $merge_args $rebase_args $verbosity"
        eval="$eval $gpg_sign_args"
        eval="$eval --onto $merge_head ${oldremoteref:-$merge_head}"
        ;;
*)
        eval="git-merge $diffstat $no_commit $verify_signatures $edit $squash $no_ff $ff_only"
        eval="$eval $log_arg $strategy_args $merge_args $verbosity $progress"
        eval="$eval $gpg_sign_args"
        eval="$eval FETCH_HEAD"
        ;;
esac
eval "exec $eval"

      

        
        
        
      

    

In the end, this means that your parameter is being --ff-only

ignored.

It is possible that Git may reject these as incompatible in the future, so it is probably wiser to leave explicit --ff-only

when using explicit --rebase

.