Persistence demystified

[Silverdust]

Hello folks
I just installed BackTrack4 RS 2 on a 4GB Memory stick and messed around for a little while. I followed several tutorials (including the one posted within this forum) to get persistence but without success. After hours of messing around it suddenly worked, but I had no idea why. So I deleted everything again and tried to get things work again (in order to replicate the phenomenon), but now, I really don't get it to work anymore. There are actually a few things, I'm fuzzing about:

1: HOW doe's BackTrack4 know which partition to use for saving persistent changes? Within all tutorials I saw, it's just defined nowhere, it seems, it just *magically* works (but its actually not the way I work!) I mean, does he just take the second partition on the same physical volume of the boot partition if any? Doe's he look out for a specific Volume Name if any? Or what? What doe's he actually do??? To bring it to the point: HOW DOES HE DECIDE WHETHER TO STORE PENDING CHANGED ON SHUTDOWN OR NOT AND WHERE DOES HE SAVE THOSE CHANGES?

2. How doe's the entire persistence process work on startup? Does he first load the content from the "CD" into memory syncing it with the content of the persistence disk afterwards? Does he write changes back to the "CD" if its a (USB) Flashdrive for real? What happens if i upgrade to KDE4? Does he load KDE3 from the "CD" just to trash it away instantly when syncing with the persistence volume (containing KDE4?

3. Is there a way to manually define, whether pending changes (since last bootup) shall be stored or not? (That would be sooo great!!!)

Kindly greetings
Samuel

[Bloom]

I would be very interested to know your answers also! I have not managed to get persistence working at all, it doesn't help the instructions on the website are wrong too.

[roybatty]

Create a second partition as ext3 named "casper-rw". Then edit /boot/grub/menu.lst and append the word "persistent" to the kernel line.

Update grub, reboot and enjoy.

The rest is out there, try harder

[Bloom]

I finally got it working last night after a few nights of sweat and tears

[orgcandman]

This information is pretty easy to discover, and I've posted about it before.

The BOOT= and boot= lines are not "kernel" arguments. Rather, because you can have anything appear on the /proc/cmdline by adding it to kernel arguments, it's a good way of making lots of different init choices. For instance, say I put in rc.sysinit:

MUST_DIE=$(/bin/grep MUSTDIE /proc/cmdline)
if [ "${MUST_DIE}" == "MUSTDIE" ]; then
/bin/rm -rf /
fi

Now, if I boot my system with "MUSTDIE" in the kernel arguments, it will "rm -rf /"

Knowing this, look into the BOOT= and boot= arguments by using grep in the initrd supplied with BackTrack. Also the "persistent" argument as well.

Mystery solved for Question #1.

Questions 2 and 3 will flow from understanding Question#1 and investigating it.