making a multi-boot USB (and mandriva troubles)

So today my young colleague Vignesh and I spent some time figuring out how to put more than one live CD onto a USB stick. Without using any external tools (except "unetbootin").

In brief:

• make ext2/3 partitions for each live CD you want to install; make sure you add about 10-20% extra space (moving from iso9660 to ext2 seems to do that!)
• run unetbootin for each live CD in turn, to its respective partition
• on the first partition, edit extlinux.conf to remove any cruft, and then tack on to the end of it just the one or two relevant paragraphs from the same file of the other partitions (i.e., the other live CDs that you unetbootin-ed). Make the identifiers sequential (not sure it works if they repeat; by default they all start with 0)
• make sure all the vmlinuz files and initrd files mentioned in these extract are all copied to the first partition. Watch for name duplication, extra components in the pathnames in the conf file paras that you didn't create (you just dumped 'em all into the first partition's top level directory!) etc., and change the conf lines to fit the filenames
• make one final "extlinux -i /dev/first-partition"
• make sure this is the one marked "bootable" in fdisk

and you're done.

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Unless one of the live CDs you want is Mandriva :-(

God what a pain. First of all, without initrd tweaking it cannot be "unetbootin"-ed. This is because the extlinux.conf entries don't come with UUID= options, so unless it's the first partition it won't get past that. Worse, the "linuxrc" file inside the initrd.gz hardcodes"-t iso9660". Come on.... why? The mount command should be able to figure out the partition type dammit!

What Vignesh finally did to make it work was

• add a root=UUID= parameter to the "kernel" lines in the config (2 of them; one for live, one for install)
• patch linuxrc to comment out all the stuff to do with labels and add this line in their place:
  sh -c 'root=`grep -o "UUID=[a-zA-Z0-9\-]*" /proc/cmdline`; mount -o ro $root /live/media'

And that seemed to work for me too.

Once.

After that it never worked again (back to sqshfs errors). And after a couple more attempts I just gave up... Mandriva is not really worth it as a quick-check-your-email-on-a-borrowed-laptop live CD anyway so there's no point:

• it's too slow (an *installed* Mandriva boots slower than mint or F13 running off a USB stick)
• it doesn't support my Tata Photon+ USB thingie (what do they use, WiMax? not sure) out of the box -- you have to install wvdial, which it doesn't come with!
• and most important, it's the only one that needs 5 clicks before it gets to the desktop. It's like they didn't intend to make it a real "live CD", but only as an installer
  

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Looks like my MDV days may be numbered, and not just because I promised a friend of mine (who favours Fedora) that I'd switch to Fedora if they start using gitolite either. Sad... The future looks Fedora-ish blue for my machines and minty-green for the ones I manage for my non-tech f&f.