It may be possible to restore from a su-backup if you have a su binary still in /system/bin or xbin. Even if you can't access a root prompt (#) by just typing su, read starting at page 6. Places to look for a su-backup include /system/ /system/usr/we-need-root/ and /system/bin/
I have a batch script in the works that will determine if you can re-root and take the appropriate steps to do so if possible.
I had to do a voldown wipe after my update to JB. My prime would reboot after 5-10 seconds into the homescreen after boot. After wiping, I thought for sure my root was screwed until a new exploit was found.
I accessed my device through adb, and realized that I could invoke a root prompt using the su command at the $ prompt. Using ES file explorer, I could see su in /system/bin/ but no su-backup or superuser.apk in /system/app/.
I tried simply installing superuser from the market, but it did not work. The busybox installer would not work, either.
ATTACHED ARE THE EXACT THREE FILES I USED. I do not know if using different version will affect the process!
Here is what worked for me:
1. adb shell
(# - you should see this now! This will not work without this specific prompt!)
3. type 'exit' press enter, and then 'exit' again. You will now be back at the regular command prompt.
4. adb push C:\(location of attached files)\superuser.apk /data/local/tmp
5. adb push C:\(location of attached files)\su /data/local/tmp
6. adb push C:\(location of attached files)\busybox /data/local/tmp
7. Access the adb shell again, and type su
8. chmod 644 /data/local/tmp/superuser.apk
9. chmod 755 /data/local/tmp/busybox
10. chmod 6755 /data/local/tmp/su
11. mount -o remount,rw /system
12. dd if=/data/local/tmp/Superuser.apk of=/system/app/Superuser.apk
13. dd if=/data/local/tmp/busybox of=/system/bin/busybox
14. dd if=/data/local/tmp/busybox of=/system/xbin/busybox
14a. Chmod 755 /system/bin/busybox
14b. Chmod 755 /system/xbin/busybox
16. busybox rm /system/bin/su
17. busybox cp /data/local/tmp/su /system/bin
18. type su once again to assure you still have access to the # prompt
18a. Chmod 644 /system/app/superuser.apk
18b. mount -o remount,ro /system
19. type exit, and exit again, returning to the regular windows command prompt.
20. type 'adb reboot' (without quotes)
NOTE - you will not need to install the superuser.apk app in the normal sense. It will be installed upon the reboot as a system app automatically!
21. Once your prime has rebooted, go download root checker basic or the like from the play store. Open it, and wait for your superuser prompt!
22. Get the busybox installer from the play store as well, and use that to get the newest version of busybox.
23. Get SuperSU from the market. It seems to be the safest method to keep root with JB...
ALSO! Make sure to keep a backup root with voodoo or super su after completing this guide! I have lost root (VERY WELL may have been my own fault... too much poking around) Anyway, better safe than sorry!!!
Thanks to daymz from the debugfs thread in development for the basic instructions of what needed to be done!! And also thanks to all before me who got us root in the first place!
I will answer questions to the best of my ability. I am not a developer and do not try to present myself as so... I can tinker with the best, and after losing root, I set out to see if I could figure it out!
Changes made as per tsmt971