A simple demo how one can alter history on git server

git_demo.sh

# Creating a local git server

mkdir -p git_show/git_server
cd git_show/git_server
git init --bare

# Initiating the repo with first commit

cd ../
mkdir master_user
cd master_user
git init
git config user.name "Master User"
git config push.default matching
echo "hello" > hello.txt
git add hello.txt
git commit -m "initial"
git remote add origin ../git_server
git push origin master

# Checking out as a new user

cd ../
git clone ./git_server developer_user
cd ./developer_user
git config user.name "Developer User"

# Creating new branch

git branch temp
git push origin temp
git checkout temp

# Adding some other file

echo "buy" > buy.txt
git add buy.txt
git commit -m "Added some other file"

# Changing the initial file as a developer (not pushing to the repo!)

echo "developer says hello" > hello.txt
git add hello.txt
git commit -m "Changing initial file as a developer"

# Changing the initial file as a master, and pushing to the repo

cd ../master_user
git pull origin master

echo "master says hello" > hello.txt
git add hello.txt
git commit -m "Changing initial file as a master"
git push origin master

# Getting back to developer user, trying to pull origin master

cd ../developer_user
git pull origin master

# Oops! Conflict! Never mind, resetting hard..

git reset --hard

# Looks like it's all good, trying to push

git push

# Fail! Trying to push harder, altering history on the server

git push -f

# Ok, now let's take a look on this lost commit

git fsck --lost-found

# Ok, now cloning as some other user

cd ../
git clone ./git_server other_developer_user
cd other_developer_user

# Look! No word from our master!

cat hello.txt

# Here's our lost commit:

git fsck --lost-found

# Now do a 'git show' with hash, check the content