A portion of /etc/grub.d/05_debian_theme in grub-pc 1.98+20100804-11 has:

# Earlier versions of grub-pc copied the default background image to /boot/grub
# during postinst. Remove those obsolete images if they haven't been touched by
# the user. They are still available under /usr/share/images/desktop-base/ if
# desktop-base is installed.
while read checksum background; do
if [ -f "${background}" ] && [ "x`sha1sum "${background}"`" = "x${checksum} ${
background}" ]; then
echo "Removing old background image: ${background}" >&2
rm "${background}"
fi
done <<EOF
648ee65dd0c157a69b019a5372cbcfea4fc754a5 debian-blueish-wallpaper-640x480.png
0431e97a6c661084c59676c4baeeb8c2f602edb8 debian-blueish-wallpaper-640x480.png
968ecf6696c5638cfe80e8e70aba239526270864 debian-blueish-wallpaper-640x480.tga
11143e8c92a073401de0b0fd42d0c052af4ccd9b moreblue-orbit-grub.png
d00d5e505ab63f2d53fa880bfac447e2d3bb197c moreblue-orbit-grub.png
f5b12c1009ec0a3b029185f6b66cd0d7e5611019 moreblue-orbit-grub.png
EOF

I understand what its purpose is but am unclear as to the meaning of

. . . if they haven't been touched by the user.

as it doesn't appear possible to alter the sha1sum of a file by touching it.

The background is that I don't have the desktop-base package installed
but do have (or, rather, did have) moreblue-orbit-grub.png from the
package in /boot/grub and am inclined to think its removal is a possible
bug.


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On Fri Dec 31, 2010 at 11:44:01 +0000, Brian wrote:

> I understand what its purpose is but am unclear as to the meaning of
>
> . . . if they haven't been touched by the user.
>
> as it doesn't appear possible to alter the sha1sum of a file by touching it.

It's a shorthand way of saying "modified" - which would clearly
change the hash.

"I didn't touch the cake", is like "I didn't eat the cake"

Steve
--
Debian GNU/Linux System Administration
http://www.debian-administration.org/


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On Fri 31 Dec 2010 at 12:23:30 +0000, Steve Kemp wrote:

> It's a shorthand way of saying "modified" - which would clearly
> change the hash.
>
> "I didn't touch the cake", is like "I didn't eat the cake"

Thanks. That was one interpretation I thought of. So it's nothing to do
with touch(1)? Changing a file's timestamp wouldn't alter the hash.


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Brian wrote:
> Steve Kemp wrote:
> > It's a shorthand way of saying "modified" - which would clearly
> > change the hash.
> >
> > "I didn't touch the cake", is like "I didn't eat the cake"
>
> Thanks. That was one interpretation I thought of. So it's nothing to do
> with touch(1)? Changing a file's timestamp wouldn't alter the hash.

Correct. As Steve said, it is a common speech idiom for "modified".
In the way it was used it had nothing to do with the 'touch' command.

Bob