Feb 16, 2011
Atlanta, GA
Hi guys, I just bought an unlocked M8 off amazon, good phone, great condition. I previously had an m7. I saw that marshmallow is out and checked to see if an update was available, phone said none available (up to date). Go to HTC and see there is an update for the unlocked version to Ver 6.12.1540.4 phone currently on Ver 4.21.512.5 Downloaded the RUU run it and get Error 132 Signature error. Any help would be greatly appreciated.
It's the wrong RUU. When you say the phone's unlocked did you think that meant it was a Developer edition, or was the phone just not locked to a network? The RUU you tried is for developer edition iirc, but your phone is on 4.21.512.5 so is a different variant and hence that RUU won't work.

Actually I've not come across x.x.512.x before and it doesn't seem to be very common. From a quick search this seems to be a US carrier called LRA, and from what I could find LRA seems to stand for Verizon's LTE for Rural America service - does that sound right? If so, is the phone actually a Verizon version? As it will have different hardware and may also be locked down pretty tight. We could do with getting more info on the phone and hardware - are you familiar with using fastboot?
Not really, but i can learn fast. Also have my phone working on t-mobile network, unless I read wrong verizon phones won't work with t-mobile. and the fastboot thing it booting while holding down vol down button yes?
and sorry I purchased an HTC One M8- Factory Unlocked 32GB - US Warranty (Glacial Silver) that is all I know, i even checked the IMEI to make sure it was all good.
Yep, that will boot to the bootloader. What we be useful is to get a screenshot of your bootloader screen, or boot your phone to the bootloader and post what's on the screen - specifically whether the bootloader is "Locked" or "Unlocked" and whether the phone is S-ON or S-OFF.

Get the mini-sdk tools from here:

ADB Guide (updated 2014/11/11)

along with instructions to install.

Edit: I can't remember off the top of my head if using vol down + power takes you straight to FASTBOOT mode or not. On the bootloader screen the mode is shown below the info text lines in green - this will either say FASTBOOT or HBOOT. If it says HBOOT, then to load FASTBOOT mode if you look further down the screen to the words in different colour text the top one should be Fastboot. Use the vol down button to highlight Fastboot and then press the power button to select, this will load FASTBOOT mode. If you then plug the phone in to your PC, on the phone screen you should then see FASTBOOT USB displayed if the phone is recognised ok.

Reboot phone to bootloader and plug in to PC (so you see FASTBOOT USB on bootloader screen). Open a command prompt window in the adb/fastboot folder on your PC - if in Explorer hold shift + right click, and pick "Open command window here" from context menu.

Then type:

fastboot devices (this is to check fastboot connects to phone ok, it should also return the phone serial number)

If it does, then type:

fastboot getvar all

and post the info the command returns but scrub out your IMEI number and serial number. Need to check what the CID number is plus a few other things.

Edit: I've assumed you have a Win PC or laptop available for this.
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Here you go:

:\sdk-tools\sdk-tools>fastboot getvar all
(bootloader) version: 0.5
(bootloader) version-bootloader:
(bootloader) version-baseband:
(bootloader) version-cpld: None
(bootloader) version-microp: None
(bootloader) version-main: 4.21.512.5
(bootloader) version-misc: PVT SHIP S-ON
(bootloader) serialno:
(bootloader) imei:
(bootloader) imei2: Not Support
(bootloader) meid: 99000429861529
(bootloader) product: m8_wlv
(bootloader) platform: hTCBmsm8974
(bootloader) modelid: 0P6B20000
(bootloader) cidnum: LRA__001
(bootloader) battery-status: good
(bootloader) battery-voltage: 0mV
(bootloader) partition-layout: Generic
(bootloader) security: on
(bootloader) build-mode: SHIP
(bootloader) boot-mode: FASTBOOT
(bootloader) commitno-bootloader: e7c075a3
(bootloader) hbootpreupdate: 11
(bootloader) gencheckpt: 0
all: Done!
And second line in the bootloader screen - does it say "Locked" or "Unlocked"?

As I thought you have a Verizon phone version (product: m8_wlv, modelid: 0P6B20000) and although it works with T-Mob the phone hardware is different and hence firmware requirements are also different. I suspect you will find that your bootloader is also Locked, and Verizon don't allow unlock via HTCDev.

Also, I'm in UK so don't have much experience with Verizon or Sprint devices (just so you know).

As you are also S-ON any official updates will only work if they match your CID number and your ModelID number, so you are unfortunately stuck until a suitable RUU or OTA is rolled out.

If you want to take things further then you need to investigate trying to run Sunshine to gain S-OFF and bootloader unlock, which is not something to undertake lightly without reading up and understanding what this entails, what the risk are and what you can then do with it. It will also cost $25 if your phone passes the in-built checks and Sunshine is able to run successfully. Further reading here as a start point:
So i successfully unlocked the bootloader, flashed recovery, and have S-Off. Also changed the CID to a Super CID. Was trying to make it a dev version but could not get firmware to flash for some reason. Will come back lateron tonight after work, if you could point me to a great guide on it saltire I would appreciate it. You have been very helpfulA ;)
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Ok, good stuff, not hanging about are ya! Just don't be rushing in to firmware flashing too quickly though, one wrong command and you can end up with a pretty paperweight. You've removed the inbuilt protection going s-off, so responsibility is now all on you, just saying. I can point you to some good guides for firmware and no reason you can't go for dev edition if you want but it doesn't make much difference. Tomorrow though.
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Ok, this guide is one I keep going back to as a reminder of steps to follow for firmware flashing:

You can jump straight to Section 3 (last section) since you've done all the rest.

Don't download or install any of the firmware from here though as it is strictly for international GSM versions.

As I said before I don't count myself as an expert on Verizon or Sprint phones, so it I were you I would definitely ask in the Verizon M8 forum on xda what firmware you should be using and quote the productid and modelid numbers to see what they say. Can find that here:

Make sure you post in the Q & A though - they has very strict ways over there :thinking:

I know you have T-Mob as carrier now but from the info you have posted the phone appears to be a Verizon model, and that means hardware differences and hence firmware differences. There are definitely kernel differences as well.

Once you're sure of what you need, there will likely be a thread in General or maybe Android Development with a firmware collection - plus other stuff like custom ROMs.

One more thing, do a full nandroid backup in TWRP on to your external sd card before trying anything else so you have a working setup to restore should you need it.
Saltire, (and others...)

Really appreciate your input above. I'm still missing something to really resolve my issue.

I recently let my M8 run out of power to serious levels. (Also, it had not had an SD card inserted and internal memory had been quite full for some time).
When I get it to a certain level of power, it rebooted but only to the 'htc one powered by android' screen.
It will stay there until it runs out of power (or just stay there if I leave it charging).

I have had to learn about adb and fastboot, and I can get to the fastboot and bootloader screens.

However, when I type 'adb devices' into the command line, it simply lists no devices.

I could probably fix this with a factory reset, but I would prefer to try to save my photos and videos from the past year or so (yes, I've been a silly boy and not backed up).

This has been a good learning experience but I would appreciate any tips to get me over the final hurdles...

Thanks in advance!