@ Michael Hudson-Doyle, @ Olivier Robert, and everybody else who is interested,


What do you think of the following idea for Ubuntu Focal Fossa?

It is possible to add the boot option

- 'persistent' in order to create a persistent live drive
or
- 'nopersistent' in order to create a live-only drive.

I am looking for a method to edit the iso file (binary edit) without loss of any current feature.

---
$ echo -n ' nopersistent '| wc -c
14
---

In order to add one of these boot options we need an unused space of 14 blank (alias 'space') characters in the iso file. I suggest that it is made so that the image contains such space in the image of grub.cfg and the corresponding file for syslinux.

So for the 'linux lines' in grub.cfg put 14 blanks (not 1 blank as it is now) after quiet splash.

'linux ... quiet splash              ---'
'linux ... quiet splash persistent   ---'
'linux ... quiet splash nopersistent ---'

and for the 'append lines' in isolinux/txt.cfg

'append ... quiet splash              ---'
'append ... quiet splash persistent   ---'
'append ... quiet splash nopersistent ---'

This way we can add those boot options without removing anything except blank characters and at the same time without offset of the code after the substitutions.

I have tested that this kind of substitution works in a straightforward way with 'sed' from the iso file. I have a method with a shellscript that 'wraps a safety belt' around the process and can write directly to the device without creating a modified file,

ubuntu.iso < sed 's/quiet splash              ---/quiet splash persistent ---/' > /dev/sdx

or

ubuntu.iso < sed 's/quiet splash              ---/quiet splash nopersistent ---/' > /dev/sdx