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Re: debian-wheezy-amd64-efi-test3.iso does not boot from CD via BIOS


> >Further i see that fdisk -lu is once again unhappy with a xorriso
> >generated partition table. Probably because of -append_partition.
> >I will have to investigate.

Steve McIntyre:
> Hmm, OK.

I investigated further. The ISO image is properly aligned to 1 MiB.
It is the FAT partition which makes fdisk complain. Its size of 448 KiB
would destroy fdisk's theory about head_per_cyl and sectors_per_head.

A bit prematurely i declared this a bug of xorrisofs -partition_cyl_align
default mode "auto" with -isohybrid_mbr. But meanwhile i am beginning
to consider it a feature. At least the man page explanantion of
-partition_cyl_align only mentions the image size, and not appended
partitions outside of the image.

Nevertheless, the (premature) bug fix silenced fdisk's complaints:
Disk repacked.iso: 0 MB, 0 bytes
64 heads, 32 sectors/track, 0 cylinders, total 0 sectors
Units = sectors of 1 * 512 = 512 bytes

       Device Boot      Start         End      Blocks   Id  System
repacked.iso1   *          64      487423      243680   17  Hidden HPFS/NTFS
repacked.iso2          487424      489471        1024    1  FAT12

(repacked.iso is slightly larger than original because Linux mount shows
 the two hardlink instances of vmlinuz as two distinct files. So they
 became two distinct files in the repacked image.)

> >isohybrid prescribes an alignment to 1 MiB,

Steve McIntyre:
> I honestly don't know if that's needed, but it can't hurt to try.

H. Peter Anvin once told me that some BIOSes want cylinder alignment.
There was no mentioning of further partitions at that time.
On the other hand, we had several occasions when Debian images were
not aligned by my mistake. Nobody ever complained.

So it is up to you to decide whether partition 2 shall be aligned
to 1 MiB or not.
If you want it aligned, then for now append 576 * 1024 bytes to the
FAT image disk file before you hand it over by -append_partition.
I plan to introduce a -partition_cyl_align mode "all" which will
pad up appended partitions to aligned size.

Have a nice day :)


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