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I have had a constant nightmare with not being able to take OTAs on any of my (rooted) devices. They boot into TWRP, complain about the build fingerprint, and won't install, so I have to wait for a full .zip and flash my systems manually.

What is it that is preventing the OTAs from installing over a modified /system partition, and why can't it be defeated or disabled?

If it can't be defeated/disabled, why can't my modified /system lie about its build fingerprint to fool this validation into allowing the OTAs to be installed?

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OTA files work by patching files rather than replacing them will a full copy of the new version of the file. This means that it has to verify that the existing files are exactly as it expects or the patching process won't work (or could cause the file to become corrupt). If you were to fake the fingerprint and force the OTA to apply you might end up with a device that can't boot due to some files being corrupt.

Android 5.0 (i think) switched from verifying just the files it was patching to verifying the partition as a whole so any modification (even to a file that is not being patched) will cause this to fail.

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  • Do you have any idea why can't this be removed or defeated? – Ehryk Dec 18 '15 at 8:16
  • Oh, I see - you're saying the contents of the OTAs now are based off the unmodified system, hmm. In that case I'm just confused on what could be so 'different' on a /system that had been rooted, and then 'Full Unroot'ed. – Ehryk Dec 18 '15 at 8:18
  • Hi, so you think OTA's are performing dmverity-like checks now ? – moonbutt74 Dec 18 '15 at 17:12
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    @moonbutt74, it appears so. I think it is because of that removing alien files from /system during unrooting doesn't work to fool a system update because the arrangement of bits in a block before rooting and after un-rooting would certainly differ. – Firelord Dec 19 '15 at 7:57
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In addition to answer posted by @bmdixon

  1. OEMs like Samsung have Knox counter which gets tripped once you root or replace stock recovery by custom. There were work around earlier to this, but Note 4 onwards tripping Knox "burns" this information into the hardware. Only way to revert Knox status is by changing that chip on the motherboard !!(I am not aware how this is achieved but it is on record as a mail reply from Samsung ). I expect OTA to verify this first

  2. OEMs like Huawei (my current device is Honor 6), allow you to unlock boot loader and cover it by warranty allowing OTA updates if rooted but stock recovery intact. Replacing recovery fails OTA

  3. I suspect carriers which "lock-in" their customers will also employ their own means to verify before allowing OTA (probably this is one reason why there is a varying delay in carriers rolling out OTA)

So it may not be a simple solution to have the recovery trick OTA...too many tricks to learn and proprietary ones, which is NOT the purpose of TWRP

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