Hi Tomas,

[ For those that have not already seen it, this is in reply to:
https://blog.fai-project.org/posts/extending-iso-images/ ]

I've long thought that it would be great to be able to easily tweak our
ISO images, and I think this idea may well provide the means.

This could be particularly useful for enabling Debian Blends to present
users with a task list that would be tuned for their blend.

This makes me think that we may be able to publish an image with a
filesystem already appended to it, so that a blend could then create
such a thing including a preseed file that configures their preferred
selection of tasks.

Is that possible with your approach?

BTW if one did that, would it still be possible to read the filesystem
if one were to burn it to a physical CD rather than write it to a USB
stick? (just wondering -- don't really see much need to do that these
days) -- I guess it should be, even if some loop mount with offset was
required to make it work.

Another advantage of having a pre-existing FS appended is that we could
have examples in place so that people could apply common tweaks by
simply un-commenting a line in the example preseed.cfg, but it introduces
the complication of resizing things (or deleting & recreating), if the
default size is too small for one's needs.

Cheers, Phil.
--
Philip Hands -- https://hands.com/~phil

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On Tue, 19 Dec 2023 13:15:53 +0100, Philip Hands <phil@hands.com> said:

> This makes me think that we may be able to publish an image with a
> filesystem already appended to it, so that a blend could then create
> such a thing including a preseed file that configures their preferred
> selection of tasks.

> Is that possible with your approach?
Hi Phil

yes, after calling mk-data-partition an empty filesystem of a certain
size (specifiy with -s) is available in the ISO.
But the blends should take the original Deian ISO (without this file
system) and they should call mk-data-partition and add their content,
because they know which size it needs.


> BTW if one did that, would it still be possible to read the filesystem
> if one were to burn it to a physical CD rather than write it to a USB
> stick?
Nope. A quick test with qemu showed that booting the ISO as CD does
not show the additional file system.

> (just wondering -- don't really see much need to do that these
> days) -- I guess it should be, even if some loop mount with offset was
> required to make it work.
Yes, I also guess some offset would help. But I also think that booting
a CD not that important.

> Another advantage of having a pre-existing FS appended is that we could
> have examples in place so that people could apply common tweaks by
> simply un-commenting a line in the example preseed.cfg, but it introduces
> the complication of resizing things (or deleting & recreating), if the
> default size is too small for one's needs.
The scenario should not invole editing lines in a config file.
This additional file system could help blends or companies to add
their software to the Debian installer and maybe to easily add a
selection menu. A they will now which size is needed.

--
regards Thomas

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Hi!

On 2023-12-20 08:47, Roland Clobus wrote:

A few months ago another approach was presented on the live-build project: for computers that are able to boot with EFI (secure or not), preparing a live USB-stick (based on the ISO file) is nearly trivial [1]. It is called FST (File System Transposition) [2].

It requires a FAT32 formatted USB stick on which the whole (including the hidden .disk folder) content of the ISO file is copied. There is no need for magic boot sectors, update-grub or similar. (On Windows the tool Rufus can
do all this for you).
Since the files are now on a regular FAT32 partition, they can be modified
as required.

Without knowing that the method had such a cool name, a few weeks back I documented it here: https://wiki.debian.org/DebianInstaller/WritableUSBStick

ema

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A followup to my post from December

It's possible to access the data partition when booting a real CD
using mount with an offset.

offset=$(fdisk -l /dev/sr0 | awk '/p3/ { print $2 * 512 }')
mount -ooffset=$offset /dev/sr0 /data

But the partition is read-only.

On Tue, 19 Dec 2023 13:15:53 +0100, Philip Hands <phil@hands.com> said:

On Tue, 19 Dec 2023 15:58:39 +0100, Thomas Lange <lange@cs.uni-koeln.de> said:

>> BTW if one did that, would it still be possible to read the filesystem
>> if one were to burn it to a physical CD rather than write it to a USB
>> stick?
> Nope. A quick test with qemu showed that booting the ISO as CD does
> not show the additional file system.

>> (just wondering -- don't really see much need to do that these
>> days) -- I guess it should be, even if some loop mount with offset was
>> required to make it work.
> Yes, I also guess some offset would help. But I also think that booting
> a CD not that important.


--
regards Thomas

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