Hi Marquitico,
I think there is a mistake in tutorial: please use mount -o loop,ro slitaz.fs /mnt to mount your loop-type file system, and then umount -d /mnt to unmount it when not being used anymore. ;-]
You may be right to suggest mounting the loop in a read+write mode, I think as you do that it will not be possible to "un-lzma" then "un-cpio" rootfs unless you can write at specified location !
-Babaorum

Oh, thank you for confirming my thoughts! I will try this method very soon.

I've updated the online tutorial according to our conclusion ;-]

Alas, I can't get this to work. When I boot up, I'm not in the loopfile, and the flash drive it's on isn't mounted. Dmesg is no help because the error message comes very, very late. Because it goes by so fast, I cannot see whether the error refers to the mount= option or the loopfs= option (maybe both?). What would you suggest? Where would you investigate?

If I mount everything by hand after booting, the loopfile looks good. Can a switch_root be done manually after booting? Just an idea...

What boot loader has been tested as  working on those boot setup examples for loop and subdirectory installs?

 http://doc.slitaz.org/en:guides:uncommoninst

Very good question. Was wondering that myself.

Meanwhile: do we have a single page with a definitive list of SliTaz boot cheatcodes, by the way?

http://doc.slitaz.org/en:handbook:livecd

OK, I'm fairly sure that the problem is that the boot process fails to mount the flash drive. I can see it hesitate when it attempts to loopmount slitaz.fs on /mnt, because of not having first mounted the flash drive that it's hosted on, at which point it then complains "no such file". But at least it's attempting to obey the loopfs=slitaz.fs code.

@Mojo: that page is evidently incomplete. For example, it doesn't discuss the loopfs=<filename> code. Nor the mount=<device> code, either.

So I'm wondering if there are other cheatcodes that remain undocumented. What I'd like to try is to sneak a delay code, because I'm wondering whether perhaps my usb drives are too slow to register. I've tried a couple of options imitating the syntax of other distros, but no luck.

@marquitico

# mount /dev/cdrom /media/cdrom
# mount -o loop,ro slitaz.fs /media
# unlzma -c /media/cdrom/boot/rootfs.gz | ( cd /mnt; cpio -idmu )
# umount -d /mnt
# umount /media/cdrom

there is no error in those above lines ;
the 2nd mount "just over_cache" on /media , so while that 2nd mount lives on
no /media/cdrom/* is visble...until unmount the 2nd mount !
But it is correct ,and it does work !

the 3rd line needs may be "a slight modif" :
 replace unlzma with "unlzma -S gz"
to specify the suffix used by slitaz as rootfs.gz 
(which should be rootfs.lzma
or some thing unlzma recognises as defaut suffix )

And the 1st line /dev/cdrom could have been -if you just download slitaz.iso ,whithout burning it
mount -oloop slitaz.iso /media/cdrom

the result of the 4 operations above  = "rootfs inside /mnt" !!!!

not rootfs mounted on /mnt !
 true "physical files" unpacked by cpio  into the directory /mnt

the only true mistype is the 1st umount -d /mnt which should really be umount /media
since /mnt has never been mount on the above operations

HTH

I have to use rootdelay=10 on all my slitaz flash drive installs with grub.

@wangji:
Sorry to say that your advice does not work.

First problem: If I use /media, then the third line doesn't work. You yourself wrote:

so while that 2nd mount lives on
no /media/cdrom/* is visble...until unmount the 2nd mount!

On three different machines unlzma complains that it cannot find /media/cdrom/boot (No such file or directory). I must use /mnt on lines 2 & 4 instead of /media. I don't know what works for other people.

Second problem: unlzma -S gz doesn't work either because no "-S" option. SliTaz unlzma is not a "real" unlzma; it's only busybox, so only two options: -c -f.

In any case, I already have a working slitaz.fs doing it the other way. What I'm working on is making the boot process find the flash drive and loopmount the loopfile and then switch_root into it.

@mojo:
Oh, if that works here, you will have soooooo made my whole day. Will try it when I get home.

@mojo:
Alas, no joy.

After trying over and over and staring at the screen, I am fairly certain that it simply never mounts /dev/sdb1, which is the flash drive my slitaz.fs loopfile is on. But I can't tell why. The boot messages do not refer to the mount= cheatcode at all, but mojo's rootdelay has no effect either, so I'm not sure.

The loopfs= cheatcode does work, however. The boot process tries to find slitaz.fs and loopmount it on /mnt, but since the flash drive is not mounted, it produces a "no such file" error.

mojo asked a very good question: did anybody actually test the loop install method to verify it?

In the meanwhile, my poor man's alternative: after booting up, I mount the flash drive and loopmount the slitaz.fs manually, and then chroot into the loopfile. So I know that the loopfile was not only created properly, but contains a viable filesystem, just waiting to be used!

But making the chrooted filesystem usable is a little tedious since it must be done every time, so booting directly into the loopfile would be ideal. Any thoughts?

The problem could be hardware related, so you could try both grub and grub2 in addition to syslinux/isolinux.  Try these with an extreme rootdelay=80 and if that works reduce it to find the minimum.