[Oberon] Re (2): Copy or reinstall A2?

Michael Schierl schierlm at gmx.de
Wed Jul 21 20:52:03 CEST 2021

Am 21.07.2021 um 17:07 schrieb Liam Proven:

> [1] Just because something is called $filename.ISO does not mean that
> the contents are necessarily an ISO-format file.

> [2] Tools which can write an ISO file to a USB flash drive may
> completely fail when presented with an ISO file that does not contain
> an ISO 9660 filesystem.

Even worse: There are *NO* Tools whatsoever that can put an ISO file
that contains *any* ISO9660 filesystem with an El Torito NoEmulation
Boot Block to a standard USB flash drive in a way that it will boot (I
am not talking about those rare flash drives that have a physical switch
where you can switch them into "emulating" a USB CDROM drive). Ventoy,
Rufus etc. contain a list of hashes of "well-known" El Torito
bootloaders and will replace those with MBR-style bootloaders that
(hopefully) perform the same task. If your tool does not recognize the
bootloader, you are out of luck.

With EFI boot blocks or Floppy Emulation boot blocks it is easier (most
EFI boot blocks can cope with both USB and CDROM, and floppy emulation
boot blocks can be booted from USB using syslinux+memdisk).

Yet still, this bootloader will only load the operating system kernel
(and maybe some initial ramdisk) into memory. If the OS needs more files
than just the kernel + initrd, and the kernel is not prepared to scan
for USB mass storage drives (or has no appropriate driver linked in), it
will not be possible to boot it from USB as it just cannot find the
drive to boot from.

Fortunately, many people who create ISOs know that people want to boot
them from USB so they will accommondate for that by making sure that the
kernel includes the required USB drivers. Some will even create an
"isohybrid" file which contains both an El Torito Boot Block (for
booting from CD) and a classic MBR (for booting from USB), or they
contain a loopback.cfg file which can be used by those mentioned tools
to find out how to boot it from an USB key. Yet both of them are not
what I would consider a standard ISO9660 format.

So, when you want to boot exotic OSes from CD (even if they use real
ISO9660 filesystems), either get a real CD drive, get one of those flash
drives that can emulate a CD drive in hardware, or put the ISO into a
virtual machine.



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