[Acer Iconia A500] timmyDean:
I can tell you exactly how it works.

In Linux there is a command called chattr which allows you to change the attributes on a file like in Windows (readonly for example). However, in Linux it is much more powerful. So, what you do, is set the chattr bit so NOBOBY can modify a file. Not even root. If root wants to change it, then root has to remove that bit first.

So, if you want to keep root you chattr it. Then when the update.zip runs and walks through the /system folder it cannot remove the su sticky bit because it has been chattr'ed.

However, some updates delete everything in the /system/xbin folder therefore the tool makes a backup to another folder called /system/backupsu. This backup usually remains. Usually, that is, unless ACER loads a NEW /system image. Like they need to expand the size, or want to reload everything, then they lay down a NEW system image and it's gone. ALL GONE.

Some ask, why don't you chattr to another folder other then system, well most other mount points have su sticky bit turned off, therefore making su not work from another mount.

So will ACER plug the chattr hole? I don't think so, this in the kernel and part of the file system. They could walk the system mount and un-chattr everything, but then again you can just use another approach.

The chattr trick normally only works on simple OTA's. For example, I think when ACER went to 3.2 they relaid down system. I could be wrong, I'd have to check my notes. But thankfully, most vendors don't reload system that often so you'r find that chattr'ng the su file works 99% of the time.

Hope this helps,

TD

---------- Post added at 06:25 PM ---------- Previous post was at 06:10 PM ----------

Also, 411 on rooting.

To root, you find a hole and then set the 'sticky bit' on an executable so it now runs as root for example: rwsr-xr-x. Notice the 's' in the owner permissions. When this file is executed it runs with the owners permissions on the file system. So to make a simple root, just copy the ash shell to /system/xbin make the file owned by root and then set the sticky bit. Now, if you are not root, you just run /system/xbin/ash and because this version of ash is owned by root and has the sticky bit set, you get the root(#) because the ash shell is now running as root.

So, you use the exploit to gain root and then set up a program to give you root anytime you want it. Usually that program is named su. Now, when an update runs, it walks the entire /system tree resetting all files to rwxr-xr-x which removes the sticky bit and breaks root.

What is heartbreaking, is you now need to use the exploit to get root so you can set back your sticky bit. If the update patched your exploit then you have find another one.

So, the question is, once you get root, how do you keep it. Using chattr is one way therefore if the update removes your exploit, hopefully it doesn't matter because you 'locked in' your sticky bit with chattr.

This is why once any version is rooted you can root most any other version. It now becomes possible to move back and forth through OTA's while allowing you to keep root. But time traveling a root OTA is only possible into the future, you can never go back in time prior to the invention of the root. But you can always travel forward with root. This is exactly how we root the 3.2.1. We take a tablet that has 3.0.1 on it and use iconia root exploit to root it. Then we lock it, add other backdoors, and roll forward in time through the minefields of the OTA's until it stops. Hopefully, you still have root. In other words, it's the flux capacitor and is what makes future rooting possible.

So it doesn't matter, as long as you chattr (chatter), because who cares if ACER's heart goes pitter patter <<== Sounds like a Roll'n Stone lyrics <lol>

"Don't you know the crime rate is going up, up, up, up, up

To live on this forum you must be tough, tough, tough, tough, tough

You got rats at ACER dreaming of the west side

Software bugs on upgrades

What a mess, this forum says chatter (chattr), so my root won't be shattered

My brains been battered, splattered all over this forum

but what's that matter.

Ah look at me, my root is chattr'ed

I'm not wanting my root shattered

Look at me- I'm a chattr'ed, look at me

Man time to go drink heavily.