Re: Write iso/isohybrid on pendrive:problem

[Thomas Schmitt]

Hi,

antispammbox-debian wrote:
> Then isohybrid does not produce a true hybrid file, because once written,
> cannot re-format the space free on usb!

Well, firstly the isohybrid program of ISOLINUX is The Original.
The isohybrid functionality of xorriso was implemented under the
guidance of the ISOLINUX main developer. Insofar, both are "true".

The partition offset feature is out of the reach of the isohybrid
program, because it operates on an existing ISO 9660 image and has
no means to create a second superblock and directory tree for
mounting at a non-zero partition start.
xorriso creates the ISO image and thus is able to create both
structures of meta data. Then it makes sense to move the partition
start to block 64.
(Program isohybrid could check for an existing second set of meta
data, though.)

After all, we do not yet know whether your problem is really
caused by the difference of partition start. An experiment would
be needed.
Either move partition start of the original ISO image to 0,
or move the start of the isohybrid result to 64.
This would cause a change in behavior under Gparted, if my theory
is true.

If partition start 0 is the reason for Gparted's refusal, then it
is a peculiarity of Gparted, not of isohybrid.
Gparted does have requirements towards the existing partition table
on the medium.


> But the problem then, is, how to create isohybrid file,  that
> allows  to re-format free space on usb.

This text describes how to fix a size overlap by help of sfdisk:
  http://gparted.sourceforge.net/h2-fix-msdos-pt.php

The procedure to set the partition start to 64 (not 63 !) should
be quite similar.


Have a nice day :)

Thomas


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Re: [Debburn-devel] Write iso/isohybrid on pendrive:problem

[antispammbox-debian]

Subject: Re: [Debburn-devel] Write iso/isohybrid on pendrive:problem



Hi,


[with] debian-7.2.0-i386-lxde-CD-1.iso > /dev/sdb
[...] debian-live-7.2-i386-lxde-desktop+nonfree.iso
I can re-format the free space present on usb


These two images have MBRs with partition 1 beginning at
block 64 (= 32 KB). See e.g. output of
 /sbin/fdisk -lu debian-7.2.0-i386-lxde-CD-1.iso
 
They have obviously been created with xorrisofs options

-isohybrid-mbr and -partition_offset 16.



When change file in to: isohybrid debian-7.2.0-i386-lxde-CD-1.iso


ISOLINUX program isohybrid produces an MBR with partition 1
starting at block 0. This overwrites the MBR produced by
xorriso.

There is not much other difference to be expected between
the downloaded ISO and its state after the isohybrid run.
So i assume this must be the cause.

One may test this theory by setting byte 448 of the isohybrid
result to 1 and byte 454 to 0. The ISO is prepared to work with
that start address to. But program isohybrid did not know.



cat debian-7.2.0-i386-lxde-CD-1.iso > /dev/sdb
on pendrive, with filesystem ext2 or Fat32


After that cat command, the filesystems are overwritten or at
least unreachable.


Have a nice day :)

Thomas




Ok, many thanks!

Then isohybrid does not produce a true hybrid file, because once written, 
cannot re-format the space free on usb!?



But the problem then, is, how to create isohybrid file,  that allows  
to re-format free space on usb.



Thanks 



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