Recently I’ve got Galaxy Nexus to play with, and as soon as I’ve entered Wi-Fi password, an OTA upgrade came my way. It was very tempting to upgrade immediately, but I’ve decided to pull upgrade file from the device to see what’s inside.
Unfortunately, the phone comes from the factory locked and there’s no way to access system files except unlocking the protection.
Regarding the root access
First we need the root access to be able to access files freely.
I don’t like to permanently root my phone, so I prefer the temporary method, which keeps the phone protected, but gives me the opportunity to access what I need if I really need it (I do not delve into details about how to use adb, hoping you already know that).
Unlock the phone
Reboot into fastboot mode by switching power off, and holding all three buttons (volume up/down and power) until Android logo appears. then issue ‘fastboot oem unlock’ command from your computer. This requires full memory wipe, so be careful and make a backup of any data you care to keep.
Download the superboot
Superboot is the bootoader image, which can turn the phone into a rooted one, but only until the next reboot. Handy and safe.
Reboot into superuser-enabled mode
While still in fastboot mode, the following command will restart the phone with the boot image we have just downloaded.
fastboot boot boot.superboot.img
Wait until the update comes
Since the phone was wiped clear during unlock, we have to wait again for upgrade to come, or request the upgrade check from Settings menu, if you are impatient.
Move upgrade file into the easy to access place
Since adb can not pull system files, we have to move the upgrade file somewhere we can access easily. I chose /sdcard folder for that purpose
# cd /cache
[... file list skipped ...]
# mv signed-yakju-ICL53F-from-ITL41F.0927b42c.zip /sdcard/
In your case the file name most probably will be different, but it’s quite easy to tell based on size (90MB in my case), which file to copy.
Extract the file from the phone
Finally we can use adb to get the file:
adb pull /sdcard/signed-yakju-ICL53F-from-ITL41F.0927b42c.zip .