Changing the date of a commit in Git is not a common practice, but it can be necessary in certain situations. For example, you might need to correct the timestamp of a commit for compliance reasons, to reflect the actual time work was done, or to fix an error. This process involves rewriting Git history, which should be done with caution. This article provides a step-by-step guide on how to update the date of an old commit in Git.

Understanding Commit Dates in Git

Git records two dates for each commit:

• Author Date: The date when the original change was made.
• Committer Date: The date when the commit was added to the repository.

Both dates are stored in the commit object, and either can be changed depending on your needs.

Why Update a Commit Date?

Updating a commit date might be necessary for several reasons:

• Compliance: Aligning with project timelines or legal requirements.
• Accurate Record: Correcting a mistakenly set date to reflect the actual work done.
• Fixing Errors: Rectifying incorrect system dates that affected commit timestamps.

Methods to Update the Commit Date

Method 1: Using git commit –amend

The git commit –amend command allows you to change the most recent commit, including its date.

Steps 1: Set GIT_COMMITTER_DATE

Set the desired date using the GIT_COMMITTER_DATE environment variable.

export GIT_COMMITTER_DATE="Wed Mar 4 12:34 2022 +0100"

Adjust the date and time as needed.

Step 2: Amend the Commit

Amend the last commit to apply the new date.

git commit --amend --no-edit --date="Wed Mar 4 12:34 2022 +0100"

The –no-edit option ensures that only the date is changed without altering the commit message.

Step 3: Push Changes

Force push the updated commit.

git push origin branch-name --force

Method 2: Interactive Rebase

Interactive rebase is a powerful Git tool that allows you to edit commit history, including dates. Here’s how to update the date of an old commit using interactive rebase.

Step 1: Start Interactive Rebase

Run the following command to start an interactive rebase. Replace HEAD~N with the number of commits you want to go back from the most recent commit

git rebase -i HEAD~N

For example, to go back 3 commits, use HEAD~3.

Step 2: Select the Commit

In the text editor that opens, you’ll see a list of commits. Change the word pick to edit next to the commit you want to change the date for:

edit <commit-hash> <commit-message>

Step 3: Amend the Commit

After saving and closing the editor, Git will pause the rebase process at the specified commit. Amend the commit date with:

git commit --amend --no-edit --date="YYYY-MM-DDTHH:MM:SS"

Replace "YYYY-MM-DDTHH:MM:SS" with your desired date and time. For example:

git commit --amend --no-edit --date="2022-05-01T12:34:56"

Step 4: Continue Rebase

Continue the rebase process with:

git rebase --continue

Repeat the process if you are changing multiple commits.

Step 5: Force Push

If you are working on a remote branch, you’ll need to force push the changes:

git push --force

Be cautious with force pushes, especially on shared branches, as it rewrites history.

Best Practices

• Backup: Always backup your repository before making changes to commit history.
• Communication: Inform your team before force-pushing changes, as it can disrupt shared branches.
• Use on Personal Branches: Preferably use these methods on personal branches to avoid complications in collaborative projects.