# Why 'git commit --amend' generates different HEAD sha1 each time when no content changes

3 messages from 2007-12-30 to 2007-12-30. Participants: Ping Yin.
Thread: https://gitlist.dev/t/11427

## Ping Yin, 2007-12-30 10:56

Subject: Why 'git commit --amend' generates different HEAD sha1 each time when no content changes
Message-ID: <46dff0320712300256g36e825a2g711d98b565e361f9@mail.gmail.com>
URL: https://gitlist.dev/e/46dff0320712300256g36e825a2g711d98b565e361f9%40mail.gmail.com

```
AFAIK, commit sha1 is only determined by commit object content (say
parent commit, tree sha1 and so on). So why 'git commit --amend'
changes the commit sha1 when no content changes as following shows.

$ mkdir A && cd A && echo foo >foo

$ git init && git add foo && git commit -m 'add file foo'

Created initial commit 8626800: add file foo
 1 files changed, 1 insertions(+), 0 deletions(-)
 create mode 100644 foo

$ git commit --amend
Created commit 3591035: add file foo
 1 files changed, 1 insertions(+), 0 deletions(-)
 create mode 100644 foo

$ git commit --amend
Created commit 3927d9a: add file foo
 1 files changed, 1 insertions(+), 0 deletions(-)
 create mode 100644 foo

-- 
Ping Yin

```

## Ping Yin, 2007-12-30 11:19

Subject: Re: Why 'git commit --amend' generates different HEAD sha1 each time when no content changes
Message-ID: <46dff0320712300319s72dfc865oc71463cfe4e20cd0@mail.gmail.com>
URL: https://gitlist.dev/e/46dff0320712300319s72dfc865oc71463cfe4e20cd0%40mail.gmail.com
In-Reply-To: <1199012360.15996.6.camel@futex>

```
On Dec 30, 2007 6:59 PM, Matthias Kestenholz <mk@spinlock.ch> wrote:
>
> On Sun, 2007-12-30 at 18:56 +0800, Ping Yin wrote:
> > AFAIK, commit sha1 is only determined by commit object content (say
> > parent commit, tree sha1 and so on). So why 'git commit --amend'
> > changes the commit sha1 when no content changes as following shows.
> >
>
> The full commit includes a timestamp too, which changed. Try setting the
> GIT_AUTHOR_DATE and GIT_COMMITTER_DATE environment variables, you should
> get the same SHA-1 everytime.
>



-- 
Ping Yin

```

## Ping Yin, 2007-12-30 11:20

Subject: Re: Why 'git commit --amend' generates different HEAD sha1 each time when no content changes
Message-ID: <46dff0320712300320n3d12edf9oedc36777a226528b@mail.gmail.com>
URL: https://gitlist.dev/e/46dff0320712300320n3d12edf9oedc36777a226528b%40mail.gmail.com
In-Reply-To: <1199012360.15996.6.camel@futex>

```
On Dec 30, 2007 6:59 PM, Matthias Kestenholz <mk@spinlock.ch> wrote:
>
> On Sun, 2007-12-30 at 18:56 +0800, Ping Yin wrote:
> > AFAIK, commit sha1 is only determined by commit object content (say
> > parent commit, tree sha1 and so on). So why 'git commit --amend'
> > changes the commit sha1 when no content changes as following shows.
> >
> The full commit includes a timestamp too, which changed. Try setting the
> GIT_AUTHOR_DATE and GIT_COMMITTER_DATE environment variables, you should
> get the same SHA-1 everytime.
>

Thanks. With 'git show --pretty=fuller', I find that commit date
changes each time and that author date keeps the same.



-- 
Ping Yin

```