i down loaded super_program.appimage
on the command line i type ./super_program.appimage
how does my debian powered device know what to do

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On Tue 12 Nov 2024 at 02:47:21 (+0000), fxkl47BF@protonmail.com wrote:

i down loaded super_program.appimage
on the command line i type ./super_program.appimage
how does my debian powered device know what to do

It looks at the file signature, or "magic number", in the first few
bytes of the file. For example, type:

$ hexdump -C /bin/cat | head -n 1
00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
$

and the 7f 45 4c 46 sequence means Executable and Linkable Format.
OTOH, in:

$ hexdump -C /bin/firefox | head -n 1
00000000 23 21 2f 62 69 6e 2f 73 68 0a 0a 46 49 52 45 46 |#!/bin/sh..FIREF|
$

the first two bytes, 23 21, indicate that the file should be passed
to the program whose name immediately follows, ie /bin/sh, which is
normally the dash shell in Debian.

See https://en.wikipedia.org/wiki/List_of_file_signatures for
loads more magic numbers.

Cheers,
David.

--- SoupGate-Win32 v1.05
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On Mon, 11 Nov 2024, David Wright wrote:

On Tue 12 Nov 2024 at 02:47:21 (+0000), fxkl47BF@protonmail.com wrote:

i down loaded super_program.appimage
on the command line i type ./super_program.appimage
how does my debian powered device know what to do

It looks at the file signature, or "magic number", in the first few
bytes of the file. For example, type:

$ hexdump -C /bin/cat | head -n 1
00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
$

and the 7f 45 4c 46 sequence means Executable and Linkable Format.
OTOH, in:

$ hexdump -C /bin/firefox | head -n 1
00000000 23 21 2f 62 69 6e 2f 73 68 0a 0a 46 49 52 45 46 |#!/bin/sh..FIREF|
$

the first two bytes, 23 21, indicate that the file should be passed
to the program whose name immediately follows, ie /bin/sh, which is
normally the dash shell in Debian.

See https://en.wikipedia.org/wiki/List_of_file_signatures for
loads more magic numbers.

Cheers,
David.

i don't see anything in that about appimage

--- SoupGate-Win32 v1.05
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On Tue, Nov 12, 2024 at 05:14:50AM +0000, fxkl47BF@protonmail.com wrote:

On Mon, 11 Nov 2024, David Wright wrote:

On Tue 12 Nov 2024 at 02:47:21 (+0000), fxkl47BF@protonmail.com wrote:

i down loaded super_program.appimage
on the command line i type ./super_program.appimage
how does my debian powered device know what to do

It looks at the file signature, or "magic number", in the first few
bytes of the file. For example, type:

$ hexdump -C /bin/cat | head -n 1
00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
$

and the 7f 45 4c 46 sequence means Executable and Linkable Format.
OTOH, in:

$ hexdump -C /bin/firefox | head -n 1
00000000 23 21 2f 62 69 6e 2f 73 68 0a 0a 46 49 52 45 46 |#!/bin/sh..FIREF|
$

the first two bytes, 23 21, indicate that the file should be passed
to the program whose name immediately follows, ie /bin/sh, which is normally the dash shell in Debian.

See https://en.wikipedia.org/wiki/List_of_file_signatures for
loads more magic numbers.

Cheers,
David.

i don't see anything in that about appimage

There are more of those patterns. Try "file":

file super_proram.appimage

pattern pattern patternsss

...what does it tell you?

Perhaps the binfmt_misc entry in the Wikipedia gives you a starting point
on how the Linux kernel decides what to do when it is told to "run" (aka "exec") a file.

Cheers

[1] https://en.wikipedia.org/wiki/Binfmt_misc
--
t

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--- SoupGate-Win32 v1.05
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fxkl47BF@protonmail.com writes:

i don't see anything in that about appimage

AppImages are ELF binaries. So the answer to your question "how does my
debian powered device know what to do", is that it knows how to run ELF
format binaries. I'd assume there are technical descriptions available
on how that works exactly, my seat of the pants feeling it's not much
more than loading the binary into RAM and jumping to the binary's start address.

As to how AppImages work, they seem to mount the AppImage file itself
while running, presumably to gain access to more ELF binaries or other executables within. I don't really know, just an observation from the
few occasions I've actually run an AppImage.

--- SoupGate-Win32 v1.05
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On Tue 12 Nov 2024 at 05:14:50 (+0000), fxkl47BF@protonmail.com wrote:

On Mon, 11 Nov 2024, David Wright wrote:

On Tue 12 Nov 2024 at 02:47:21 (+0000), fxkl47BF@protonmail.com wrote:

i down loaded super_program.appimage
on the command line i type ./super_program.appimage
how does my debian powered device know what to do

It looks at the file signature, or "magic number", in the first few
bytes of the file. For example, type:

$ hexdump -C /bin/cat | head -n 1
00000000 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 |.ELF............|
$

and the 7f 45 4c 46 sequence means Executable and Linkable Format.
OTOH, in:

$ hexdump -C /bin/firefox | head -n 1
00000000 23 21 2f 62 69 6e 2f 73 68 0a 0a 46 49 52 45 46 |#!/bin/sh..FIREF|
$

the first two bytes, 23 21, indicate that the file should be passed
to the program whose name immediately follows, ie /bin/sh, which is normally the dash shell in Debian.

See https://en.wikipedia.org/wiki/List_of_file_signatures for
loads more magic numbers.

i don't see anything in that about appimage

That's because the last component of the filename (aka extension) is
not important in what happens when you type that command. Assuming
you don't want to hear next that the device will know what to do by
executing the instructions contained in the file, I'll just say that
I know nothing about your appimage, so I don't know what it will
cause your device to do.

If you want to read about appimages and what they are in general,
perhaps start at:

https://en.wikipedia.org/wiki/AppImage

If you want to know what super_program.appimage in particular does
when you execute it, look for some documentation wherever you got
it from. I would have assumed you'd already found some, which led
to your downloading the file in the first place.

I've written and/or used programs named super… in the dim and distant
past. Typically the … bit gave /some/ indication of what the program
was designed to do, like supermix and supermap. However, super_program
means nothing at all to me. It sounds more like a placeholder for a
program in search of a name.

Cheers,
David.

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