git
undo merge that hasn't been pushed
git reset --merge HEAD~1
roll back hard
git reset --hard <commit/tag>
force push of a previous commit
git push -f origin <commit_id>:<branch>
reset local branch after a forced-update (above)
git fetch
git reset origin/<branch> --hard
set username for single repo
git config user.username 'name'
set signing key for local repo
git config user.signingkey <id>
signing commits
git commit -S -m 'msg'