On Sun, Apr 11, 2021 at 10:26:26AM -0700, Dan Hitt wrote:
> On Sun, Apr 11, 2021 at 6:41 AM Jean Louis <bugs@gnu.support> wrote:
> 
> > * Hongyi Zhao <hongyi.zhao@gmail.com> [2021-04-11 16:35]:
> > > It's well known that Emacs is an 8-bit clean editor which makes it
> > > safe to edit binary files. So, I want to whether I can fix the above
> > > destroyed disk image file with Emacs for my scenario.
> >
> > There is hexl library:
> >
> > ;; This package implements a major mode for editing binary files.  It uses
> > ;; a program called hexl, supplied with the GNU Emacs distribution, that
> > ;; can filter a binary into an editable format or from the format back into
> > ;; binary.  For full instructions, invoke `hexl-mode' on an empty buffer
> > and
> > ;; do M-x `describe-mode'.
> >
> > But I guess you need `hexl' program.
> >
> > --
> > Jean
> >
> 
> Hi Jean,
> 
> hexl-mode works for me on my xubuntu 20.04 system, and i do not have a
> program called 'hexl'.

Look around somewhere (Debian here)

  /usr/lib/emacs/<version>/x86_64-linux-gnu/hexl

Replace <version> by your Emacs version and x86_64-linux-gnu by some
appropriate architecture string.

> Of course, i don't know if my system is secretly using some other program
> which does the same thing as hexl.

It's all in the open ;-)

Hint: apt-file search finds such things, even if you haven't installed
a package. Package apt-file. Very much recommended. 

Cheers
 - t