bootable USB flash memory sticks for installation

[D. Hugh Redelmeier]

Flash memory sticks seem like a great installation medium.  I know the 
adepts among us say that PXE is better, but I will ignore that for now.

I would like a variety of bootable systems, several on one stick.  (Speak 
softly and carry a big stick?)

As far as I can make out, there are several schemes for making a bootable 
USB stick from a .iso, and I don't understand why.

I think some use grub and some (more?) use syslinux.
  <http://www.syslinux.org/wiki/index.php/SYSLINUX>

(The raw bootable .iso uses grub or more likely isolinux.
  <http://www.syslinux.org/wiki/index.php/ISOLINUX>
)

I think some have a .iso file on a FAT filesystem and use loopback to
access it, some others unpack the .iso onto the USB stick in some more
expressive filesystem.

Grub2 seems to support loop devices.  But such a device cannot be
passed to Linux: the grub driver is unrelated to the Linux loop
driver.

Typically the programs to create bootable USBs don't explain what they are 
doing.  They can have mysterious failure modes too.
  <https://bugs.launchpad.net/ubuntu/+source/usb-creator/+bug/859539>

This looks intriguing but seems to only run under Windows 
  <http://www.pendrivelinux.com/yumi-multiboot-usb-creator/>

This looks a little dodgy but might be good
  <http://www.pendrivelinux.com/multiboot-create-a-multiboot-usb-from-linux/>
The writeup suggests that it requires Ubuntu, an odd limitation.
The script just installs multisystem.deb from their site -- magic.

This looks instructive.  Perhaps this recipe does manually what the
above does automatically.
  <http://www.pendrivelinux.com/boot-multiple-iso-from-usb-via-grub2-using-linux/> 

It appears that all the magic is in the grub.cfg.
And the grub entry doesn't do chain loading.
So it must mimic what the bootable CD/DVD intended to do -- in other
words, the .iso cannot be treated as a black box, parts must be copied
into the grub.cfg.

For example, any kernel flags must be put in the grub.cfg

Does grub2 provide a similar runtime environment for the booted kernel
as syslinux?

I wish grub allowed the "configfile" command inside menu entries.
Wait, reading "info grub" it looks as if it might be legal.

If so, I have a new wish.  When the grub configfile building routines
on Fedora or Ubuntu run, they also look for bootable linuxes on other
paritions.  And they craft normal menu entries for each of them, with
kernel and initrd lines WITH options suitable for this kernel, not the
one to be booted.  Since it is hard to discover the right options, and
that partition might get changed (added or deleted kernels) without
this partition's grub config update script being run, why not generate
a chaining configfile command instead?
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