[GUIDE][BOOTLOADER,TWRP, ROOT]Lenovo TAB3 8/TB3-850F

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pndwal

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wezroot2k said:
At first i used the one from the 850F but it failed, keep rebooting to recovery. then i extracted the boot.img from both the LOS 850m port and Stock 850f using MTK_ Extractor and replace the kernel and ram-disk of the LOS 850m with the stock 850F kernel and ram-disk then flash the modified boot.img with twrp and it worked flawless no loops what so ever, even after three reboots
thanks
Click to expand...
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Very interesting. You've now overtaken my knowledge of boot.img. - I assumed the two would be the same. Does boot.img contain items other than kernel and ram-disk? Or are these simply packaged differently, with identifiers that only work with a specific ROM (eg. LOS)? PW.

---------- Post added at 07:49 AM ---------- Previous post was at 07:30 AM ----------
wezroot2k said:
At first i used the one from the 850F but it failed, keep rebooting to recovery. then i extracted the boot.img from both the LOS 850m port and Stock 850f using MTK_ Extractor and replace the kernel and ram-disk of the LOS 850m with the stock 850F kernel and ram-disk then flash the modified boot.img with twrp and it worked flawless no loops what so ever, even after three reboots
thanks
Click to expand...
Click to collapse
Could you post modified boot.img here for us? And, with your permission and credit to you, may I post it on Russian 4PDA Tab3_8 thread so others (including those who already tried LOS14.1 ROM on TB3-850F) can flash and trial this?

Many thanks for your skilful efforts. PW.
 
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wezroot2k

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Sep 12, 2017
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Could you post modified boot.img here for us? And, with your permission and credit to you, may I post it on Russian 4PDA Tab3_8 thread so others (including those who already tries LOS14.1 ROM on TB3-850F) can flash and trial this?

Many thanks for your skillful efforts. PW.
Click to expand...
Click to collapse
Yes i will post the modified boot.img for sure and go ahead and Post on Russian 4pda. Anything that can help get us a proper lineage 14.1 port for the 850F. So just go ahead and do what you must.:good:
 
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wezroot2k

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re TAB3-850F -mod_boot.img

OK PW here's the boot.img and could you just give a big shout and thank you al_rus for is tremendous work on the 850m LOS 14.1 ROM:good:
 

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wezroot2k

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OK people so i tried to do some porting last night and it was a no go, there was no error in flashing ROM but it boot-looped and by that i mean it did not to boot to OS but it did not freeze or restart but just would not past the boot animation screen was on the screen for a while I try to wipe dalvik and cache and it still would not past boot animation screen so I'm gonna try again from scratch and see if i can get it to boot OK.

PS: PW seems like you and I are on the same wavelength in terms of posting the mod 850f boot.img i was considering talking to you about doing same thing until i saw your post and i am very happy that i could post it for everyone.
Thanks man

---------- Post added at 05:20 PM ---------- Previous post was at 05:00 PM ----------
Very interesting. You've now overtaken my knowledge of boot.img. - I assumed the two would be the same. Does boot.img contain items other than kernel and ram-disk? Or are these simply packaged differently, with identifiers that only work with a specific ROM (eg. LOS)? PW.
Click to expand...
Click to collapse
Yes they do. when i extracted it the file were as follows: initrd folder, bootinfo.txt, cpiolist.txt a boot-old.img,kernel .zip and ramdisk.zip.
here's the info from the boot info text file

base:0x40078000
ramdisk_addr:0x44000000
second_addr:0x40f78000
tags_addr:0x4e000000
page_size:0x800
name:1472186745
cmdline:bootopt=64S3,32N2,64N2 androidboot.selinux=permissive buildvariant=userdebug
padding_size:0x800
the above info in is from the modded boot.img
also the initrd folder there is file ueventd.rc that when porting will help with boot-loops.
 
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pndwal

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wezroot2k said:
OK people so i tried to do some porting last night and it was a no go, there was no error in flashing ROM but it boot-looped and by that i mean it did not to boot to OS but it did not freeze or restart but just would not past the boot animation screen was on the screen for a while I try to wipe dalvik and cache and it still would not past boot animation screen so I'm gonna try again from scratch and see if i can get it to boot OK.
Click to expand...
Click to collapse
What porting changes resulted in bootloop?

Many thanks for your continued efforts with this, and for your comprehensive answers and keeping us up to speed! Hope you keep on with porting efforts. :) PW
wezroot2k said:
PS: PW seems like you and I are on the same wavelength in terms of posting the mod 850f boot.img i was considering talking to you about doing same thing until i saw your post and i am very happy that i could post it for everyone.
Thanks man
Click to expand...
Click to collapse
And thankyou too

I'll post it today.
wezroot2k said:
Yes they do. when i extracted it the file were as follows: initrd folder, bootinfo.txt, cpiolist.txt a boot-old.img,kernel .zip and ramdisk.zip.
here's the info from the boot info text file

base:0x40078000
ramdisk_addr:0x44000000
second_addr:0x40f78000
tags_addr:0x4e000000
page_size:0x800
name:1472186745
cmdline:bootopt=64S3,32N2,64N2 androidboot.selinux=permissive buildvariant=userdebug
padding_size:0x800
the above info in is from the modded boot.img
also the initrd folder there is file ueventd.rc that when porting will help with boot-loops.
Click to expand...
Click to collapse
Thanks for this info.

Is LOS booting with SELinux=permissive??? This is concerning - its enforcing in stock. PW

---------- Post added at 09:24 PM ---------- Previous post was at 09:21 PM ----------
wezroot2k said:
OK PW here's the boot.img and could you just give a big shout and thank you al_rus for is tremendous work on the 850m LOS 14.1 ROM:good:
Click to expand...
Click to collapse
Thanks, and sure, yes, I'll post and thank al_rus today. PW
 
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wezroot2k

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Thanks for this info.

Is LOS booting with SELinux=permissive??? This is concerning - its enforcing in stock. PW
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Click to collapse
could you explain why is this concerning? but i can confirm this, in the settings of the device about emulated device under phone status it says SElinux status Permissive.
 
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pndwal

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wezroot2k said:
could you explain why is concerning, but i can confirm this in the settings of the device about emulated device under phone status it says SElinux status Permissive.
Click to expand...
Click to collapse
It has serious security implications, and can cause saftey-net check, and I think Magisk hide to fail (can't use android pay, etc). Many apps got around security in past using permissive, but Google made enforcing mandatory to close security gaps / protect from malicious code, and most Devs have now made their apps and mods run in enforcing SELinux environment (it was largely root permitted apps that previously took advantage of the same security gaps to work, with permissive set) - for example, I once needed permissive to run Viper Audio (with Neon and ARISE), but these have now been fixed to work with enforcing. Further, many apps (banking etc) now require enforcing to work.

I think permissive environment can be easily changed to enforcing with SELinux Toggler and other root apps, but proper kernel setting would be more ideal. PW
 
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wezroot2k

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What porting changes resulted in boot-loop?
Click to expand...
Click to collapse
well nothing i could pinpoint right off the bat build during the porting process all did was to replace certain folder eg: xbin etc and so fourth so i can't say if it is a particular file or folder or lack thereof. but it not first this as happen before in terms of not booting to OS.
PW remember when you suggested i test stock 850f build.prop functionality with the 850m boot.img the exact same boot-loop happened just stayed on boot animation screen and not booting to OS. So my hunch is that that while porting
the build.prop needs to bee edited and ported also.
what do you guys think?
 
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pndwal

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wezroot2k said:
well nothing i could pinpoint right off the bat build during the porting process all did was to replace certain folder eg: xbin etc and so fourth so i can't say if it is a particular file or folder or lack thereof. but it not first this as happen before in terms of not booting to OS.
PW remember when you suggested i test stock 850f build.prop functionality with the 850m boot.img the exact same boot-loop happened just stayed on boot animation screen and not booting to OS. So my hunch is that that while porting
the build.prop needs to bee edited and ported also.
what do you guys think?
Click to expand...
Click to collapse
I think so too. I read somewhere re boot.img containing build.prop info which may account for failure with 850f one, so seems build.prop entries are often critical. PW
 
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pndwal

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wezroot2k

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Posted TB3850F_MOD_boot.zip and thanks to al_rus at Russian 4PDA site http://4pda.ru/forum/index.php?showtopic=764969 post #1202. Google translate to Russian just adequate.

Big shout and thank you @wezroot2k for tremendous work on the TB3-850F LOS 14.1 ROM too. PW
Click to expand...
Click to collapse

just view the post over Russian 4PDA just wanna says thanks again and will continue to do anything to help with this port.
also i gonna try and do some porting and tests over the next couples of days and keep you guys posted
okay:good:
 
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pndwal

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News Flash for users of TB3-850F!

We now have stable LOS14.1 for TB3-850F! :)

Simply flash TB3-850M LOS 14.1 ROM from @al_rus of Russian 4PDA, then flash TB3850F_MOD_boot.img from zip file from @wezroot2k (of XDA) to cure bootloops and instability on TB3-850F.Enjoy!

Reading: Details of efforts with this on the last two pages here.

Files:

TB3-850M LOS 14.1 ROM: https://yadi.sk/d/FKiFjn9x3Rp4MU

TB3850F_MOD_boot.zip: https://xdaforums.com/attachment.php?attachmentid=4698911&d=1549212166

A big Thank You to @al_rus (4PDA, TB3-850M firmware thread, http://4pda.ru/forum/index.php?showtopic=764969) for his tremendous work on TB3-850M LOS 14.1 ROM.

Also, Kudos to @wezroot2k (upcoming XDA developer) for TB3850F_MOD_boot.img (kernel and ramdisk port) and for continuing to make adjustments to LOS14.1 to streamline it for TB3-850F. :) PW

- Similar message (without file links) posted in following XDA TB3-850F threads:
- https://xdaforums.com/android/help/lenovo-tab-3-8-tb3-850f-unbrick-root-t3598727
- https://xdaforums.com/android/general/rom-lenovo-tab-3-8-tb3-850f-t3617594
- https://xdaforums.com/android/help/qa-lenovo-tab-3-8-tb3-850f-t3700868
- https://xdaforums.com/thinkpad-tablet/development/rom-stock-android-6-0-rom-lenovo-tab-3-t3825165
- https://xdaforums.com/android/general/rom-lenovo-tab-3-8-tb3-850f-android-6-0-t3593043
- https://xdaforums.com/android/help/lenovo-tab3-8-2016-custom-recovery-t3483454
 
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voland34

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Feb 1, 2015
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Stuck! help is appreciated

pndwal said:
News Flash for users of TB3-850F!

We now have stable LOS14.1 for TB3-850F! :)

Simply flash TB3-850M LOS 14.1 ROM from @al_rus of Russian 4PDA, then flash TB3850F_MOD_boot.img from zip file from @wezroot2k (of XDA) to cure bootloops and instability on TB3-850F.Enjoy!
Click to expand...
Click to collapse

Hi. Happy to hear this finally. So i just went ahead, did full wipe and installed LOS rom plus afterwards MOD_boot.img. Then rebooted, it went fine but setup wizrd keeps crashing after entering Wifi settings, it says the setup app cant start, and gets me in a loop. only options are power off and restart (but keeps on smae process ending in setup loop). I cant get it to go twrp with button combo (i remember it was tricky), so i'm stuck at this point in this loop...any help?

Update: i skipped wifi setup and it moved ahead.
So priblem solved. It seems fine so far.
 
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wezroot2k

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Sep 12, 2017
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Hi. Happy to hear this finally. So i just went ahead, did full wipe and installed LOS rom plus afterwards MOD_boot.img. Then rebooted, it went fine but setup wizrd keeps crashing after entering Wifi settings, it says the setup app cant start, and gets me in a loop. only options are power off and restart (but keeps on smae process ending in setup loop). I cant get it to go twrp with button combo (i remember it was tricky), so i'm stuck at this point in this loop...any help?
Click to expand...
Click to collapse

Ok voland34 and PW here's the thing sorry for not mentioning about the setup crashing because of the wifi setup, but i did not expect people to be testing so soon but i am happy to know this.
Voland34 and PW it just a minor bug that does not make this LOS port unstable what so ever or unbootable so don't worry.
The solution is simple and want everybody to read this, all that needs to done especially for Voland34 is he need to go to the wifi settings and forget the network he is connected to and then continue setup by skipping the options when it boots to the OS then you can go ahead and connect back to the your wifi network:good::good:

For everyone else considering installing this LOS port just remember do not try to connect to wifi during the initial setup but you must boot to the OS first then connect to the WIFI.
Thank you all.:good::good::good:

---------- Post added at 02:34 PM ---------- Previous post was at 02:32 PM ----------

I"m gonna try and see what causes the WIFI to crash during initial setup and keep you guys posted
 
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pndwal

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voland34 said:
Hi. Happy to hear this finally. So i just went ahead, did full wipe and installed LOS rom plus afterwards MOD_boot.img. Then rebooted, it went fine but setup wizrd keeps crashing after entering Wifi settings, it says the setup app cant start, and gets me in a loop. only options are power off and restart (but keeps on smae process ending in setup loop). I cant get it to go twrp with button combo (i remember it was tricky), so i'm stuck at this point in this loop...any help?

Update: i skipped wifi setup and it moved ahead.
So priblem solved. It seems fine so far.
Click to expand...
Click to collapse

Good to hear this.

@wezroot2k has it running "flawlessly" (meaning its stable but will have bugs), but I'm yet to flash. Just getting the word out.

See my post #66 in @Lister Of Smeg's thread: https://xdaforums.com/android/help/lenovo-tab3-8-2016-custom-recovery-t3483454 for instructions including TWRP button combo.

Posts #69 & 71 are useful too.

Regards, PW.
 
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voland34

Senior Member
Feb 1, 2015
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wezroot2k said:
The solution is simple and want everybody to read this, all that needs to done especially for Voland34 is he need to go to the wifi settings and forget the network he is connected to and then continue setup by skipping the options when it boots to the OS then you can go ahead and connect back to the your wifi network:good::good:
Click to expand...
Click to collapse
Yes, i managed to figured that out, so now it works great so far. I cant seem to get spanish evnen if i change language (only russian and english) but i can live with that.
Another question i have is if though its a rooted rom, it might be interesting to flash magisk 18.0 ...any idea? Its just about flashing magisk at twrp or that might be wrong and better leave it alone?
Thanks a lot
 
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wezroot2k

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Sep 12, 2017
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Hey Voland34 about booting Twrp with the buttons i know it kinda tricky
My suggestion though is that don't try to press the buttons all at once but try and press the vol up and down button together after the after the short vibration and logo screen or better when it boots to the boot animations press the power until it power down and immediately press vol up and down button at the same only letting go quckly after logo appears:good:
hope this helps every one:good:
 
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pndwal

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Jun 23, 2016
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wezroot2k said:
Hey Voland34 about booting Twrp with the buttons i know it kinda tricky
My suggestion though is that don't try to press the buttons all at once but try and press the vol up and down button together after the after the short vibration and logo screen or better when it boots to the boot animations press the power until it power down and immediately press vol up and down button at the same only letting go quckly after logo appears:good:
hope this helps every one:good:
Click to expand...
Click to collapse
Close, but not quite. See my post above :) PW

---------- Post added at 03:54 PM ---------- Previous post was at 03:48 PM ----------
voland34 said:
Yes, i managed to figured that out, so now it works great so far. I cant seem to get spanish evnen if i change language (only russian and english) but i can live with that.
Another question i have is if though its a rooted rom, it might be interesting to flash magisk 18.0 ...any idea? Its just about flashing magisk at twrp or that might be wrong and better leave it alone?
Thanks a lot
Click to expand...
Click to collapse
I'd try flashing Magisk from TWRP. I've flashed this over prerooted custom ROM on my Huawei Y550 phone with no problems. Magisk generally handles any cleanup well, and has now overtaken the functionality of SuperSU. PW
 
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    MotoJunkie01
    MotoJunkie01
    This guide, for the Lenovo Tab 3 8" (TB3-850F), has 3 purposes:

    1. Unlocking your bootloader;
    2. Installing TWRP custom recovery;
    3. Attaining superuser privileges (root) of the stock OS.

    NOTE:
    I can attest & confirm that this method has worked 100% on at least 7 devices of my own. Please read and re-read the instructions carefully before proceeding. If you follow this tutorial exactly as delineated, you should have no adverse issues in unlocking your bootloader, flashing custom recovery, or achieving systemless root of the stock Android OS.



    MENTIONS & THANKS:
    Based on XDA Senior Member @Hemphiz's groundbreaking root and custom recovery for this device, I am now revising this thread wth improved step-by-step instructions based on members' feedback and experiences. Thanks @Hemphiz for your research, assimilation of necessary files, and for breaking ground on this tablet. Thanks also for your granting me ownership of the thread. Your contributions are greatly appreciated by many. Thanks to the great @Chainfire for his flashable systemless rooting script. Thanks to @jemmini for compiling TWRP for this tablet. Finally, thanks to the many members who have tested this guide and provided much needed input & user experience.

    DISCLAIMER: As always, please be reminded of the risk involved with flashing a custom recovery and/or attempting to attain superuser privileges of your Android OS. I will not be held responsible for devices bricked or otherwise rendered inoperable as a result of this thread. You assume full responsibility for any good or bad which may result from proceeding any further. However, with that having been said, I will provide any and all support possible. Read and follow the foregoing steps thoroughly and carefully prior to proceeding. NOTE: THIS GUIDE IS INTENDED ONLY FOR THE LENOVO TAB 3 8"/TB3-850F.

    REQUIREMENTS:

    1. Minimal ADB & Fastboot v1.4 (or newer) Windows Installer;
    2. Windows PC or laptop (Mac may be used; however this guide is intended for Windows 7 and newer operating systems);
    3. Official Lenovo USB Device Driver v1.1.21;
    4. TWRP v3.0.1 for the TB3-850F;
    5. ADB Driver Installer for Windows;
    6. SuperSU v2.82-SR5 flashable zip.

    (All files, drivers & utilities for this process are available in the below download link)

    DOWNLOAD LINK: https://drive.google.com/folderview?id=1l-YN5aXmjDF3O1bHxFHVIxLKuvd847Q9




    INSTRUCTIONS:


    1. First and foremost, unlocking the bootloader is necessary. Also, this step is a good place to make some requisite preparations. Power on your Tab 3 and select SETTINGS once booted up. Go to ABOUT DEVICE, find BUILD NUMBER, and tap it 7 or 8 times until DEVELOPER OPTIONS is enabled. In DEVELOPER OPTIONS, tick OEM UNLOCKING and USB DEBUGGING. On your PC, install the Minimal ADB & Fastboot utilities, the ADB Driver Installer, and the Lenovo USB Driver Installer. Connect your Tab 3 to your PC with the supplied (or quality equivalent) OEM charging/syncing cable. Open a command window in your ADB/Fastboot directory, by holding SHIFT and right clicking in the desired path. In the command window, type: adb devices & press RETURN. If your device is connected properly, the command window will display a string of numbers/letters, which represent your device's serial number. If your serial number does not appear in the window, try changing USB ports, change syncing cables, or try reinstalling the ADB Drivers. Once properly connected, type adb reboot bootloader & press RETURN. Your tablet should boot into Fastboot Mode, which will be displayed in white bold letters on your device's display once complete. Once in Fastboot Mode, type fastboot oem unlock & press RETURN. Your device will prompt you to press Volume Up to proceed with unlocking the bootloader, or Volume Down to cancel the process. WARNING: UNLOCKING THE BOOTLOADER AUTOMATICALLY INITIATES A FACTORY DATA RESET. YOU WILL LOSE ANY UNSAVED VIDEOS, MUSIC, PERSONAL FILES, ETC.

    2. Now that your bootloader is unlocked, you are ready to flash TWRP. Download the twrp.img file from my link and save it to your PC in the ADB/Fastboot path/directory. Also, save a copy of the file on your device's internal storage or external micro SD card. Since your device underwent a factory data reset, you will again need to enable DEVELOPER OPTIONS & tick OEM UNLOCKING & USB DEBUGGING as you did in Step 1. When you have done this, again open a command window, ensure a proper connecion, & type adb reboot bootloader & press RETURN. Once in Fastboot Mode, type fastboot boot twrp.img & RETURN. EXTREMELY IMPORTANT NOTE: this device's boot image is secured with dm-verity. Leave the /system partition as read-only when prompted by TWRP. Mounting /system as read/write at this point will result in a boot loop. Flashing SuperSU, as outlined in Step 3, will patch dm-verity and fix this.
    From the TWRP main menu, select INSTALL, select the image file option in the bottom right of the screen, navigate to the location where you saved twrp.img in device storage or external storage, and commence the installation. Be certain and correctly choose "recovery" when prompted by TWRP. Now select REBOOT, then RECOVERY. Your TWRP custom recovery should now be successfully installed on your device's /recovery partition.

    3. Now, it is time to root this tablet. Download & save a copy of the SuperSU v2.82-SR5 zip file to the tablet's internal or external storage. In TWRP main menu, select INSTALL & navigate to the saved SuperSU zip. Commence with installation. Systemless root mode will unpack, modify, repack and flash the patched boot image. Once done, reboot system. Your Android OS should now have full systemless root, and the /system partition may now safely mount as read/write.

    TROUBLESHOOTING:

    In the event your device becomes stuck in a bootloop, or is otherwise failing to boot into the OS, the following is a link to my stock firmware images thread for this device. NOTE: the following link will be beneficial only if your device successfully boots into Recovery/Fastboot mode. This link provides stock partition images of /boot, /recovery, /logo & /system. Typically, flashing the stock boot & system images will get you up & running again, and will restore the Android OS to stock condition.
    https://xdaforums.com/android/general/rom-lenovo-tab-3-8-tb3-850f-android-6-0-t3593043/page5

    In the unfortunate event that you encounter a brick (your device fails to boot into the OS or Recovery Mode), please visit @r&xp's thread on unbricking your device & restoring it to factory stock condition. Members using his thread be sure to thank @r&xp. His collection of necessary files & comprehensive instructions has saved many, many bricked tablets. https://xdaforums.com/android/help/lenovo-tab-3-8-tb3-850f-unbrick-root-t3598727
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    pndwal
    News Flash for users of TB3-850F!

    We now have stable LOS14.1 for TB3-850F! :)

    See post above. Regards, PW.

    Alerting:
    @Hemphiz
    @Lister Of Smeg
    @mtpc
    @stonedpsycho
    @fran89
    @r&xp
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    @voland34
    @DeblaGaming
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    4
    MotoJunkie01
    MotoJunkie01
    kellogg9662 said:
    Yeah, I'm not sure how I screwed it up but I'm glad it's working. In order to get into adb I tried the method you mentioned of holding the volume+ for 5 seconds and then plugging in the usb cable. From there I used adb to reboot into the bootloader. I tried flashing the boot and recovery images from there, but it didn't seem like they took. So then I used the fastboot boot command with the TWRP image, but it wouldn't let me access the data partition for some reason. I went to reboot and then all hell broke loose and it was just rebooting through TWRP failing with openscript and then rebooting again nonstop. I couldn't manage to shut it off completely even holding the power button for 30 seconds or so. I figured I was screwed, but held the volume up, volume down (and I think power?) at the same time and suddenly it actually launched TWRP. However, it couldn't access the data partition for some reason. I threw the stock boot, recovery, and system images on an SD card and then flashed them all and that finally got it working.

    I've rooted other phones, but I've had hardly any experience with adb. Fortunately I feel like I did learn quite a bit from screwing up, which is always a plus.
    Click to expand...
    Click to collapse
    Great work. Sounds like a good learning experience for you also. These devices on a MediaTek platform are a horse of a different color indeed. I've bricked a good handful of these devices through trial & error myself. By the way, please be sure and hit the thanks button on the OP. @Hemphiz done an excellent job initiating TWRP & root for this great budget tablet.
    I am currently working on a stock based 6.0.1 ROM for this device: rooted, deodexed, debloated & zip aligned. I'll add a few baked-in features like Substratum & Viper4Android. Also I'll add a couple of tunable governors & tweaks to the stock kernel. I'm terribly tied up at work, resulting in having to take a couple weeks break from Android, but I should be up & running again in 3 weeks or so.
    Anyway, I'm very glad it worked out for you. Try this to iron out any bugs with booting TWRP. First, save a copy of the twrp.img to your internal storage or external micro SD card. Next, get your device into TWRP. Select INSTALL, then select the flash img option in the bottom right-hand corner. Navigate to the location of your TWRP.img, commence to install and select "RECOVERY" when prompted to do do. Once done, wipe Cache & Dalvik/ART. Reboot system. This should allow smooth booting of TWRP, with no loops or lags.
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    P
    pndwal
    somebody100 said:
    my tablet is tab 3-850f_S100030_161209_row

    so i guess it could be possible to root...i am little be afriad to do that...

    this step 6

    #6 Now you need to boot to your custom recovery via the button combo for the device. (imo this tablet is a pain to boot into recovery compared to most devices) power off the phone. Wait a few seconds. Now hold the power button - then while still holding the power button press Volume up and then Volume down. Hold it for about a second then let them all go. If it worked then you will get the usual boot logo followed by the main twrp screen. Swipe to allow it to make modifications. If it boots into the Chinese recovery thing then just turn it off and try again. I would suggest getting an app that allows you to "reboot to recovery" once your all done and rooted. For root. Simply put the "Supersu sr3" zip in the storage of your tablet. Then flash it via twrp. "install - find where you put the zip - flash - reboot system" Done.

    would someone be more specific to explain...i get my tab in boot mode with holding power buton and volume down an up......and in display is simbol of android with mesage no command..its confused me...

    ---------- Post added at 01:45 PM ---------- Previous post was at 01:28 PM ----------

    i found a solution...press power button 2 seconds and quick press once volume up....

    now i am in recovery boot menu...

    so if someone to explain more specific this step 6

    thanx for advices

    regard
    Click to expand...
    Click to collapse

    See this post from Lister of Smeg's TB3-850F Thread, re root & recovery for TB3-850F. Note 'To Enter TWRP':

    filedropper.com/tb3850froot (for files)
    Quote:
    Originally Posted by mtpc
    Hey guys, It's me again. I managed to crack down the russian CAPTCHA and downloaded those files, and it just WORKS! I now have full root on my TB3-850f. I wrote down simple HOW-TO:
    [Slightly ammended by Peter Wallace (Original Post #49)]
    1) Copy SuperSU-v2.79-SR1-20161221223537.zip to the tablet
    2) Enable developer and USB debugging
    3) Open cmd (command Window) in folder with ADB and FASTBOOT
    4) Type these commands:adb reboot bootloader
    Then:fastboot oem unlock
    5) Hold down power button and reboot. Repeat 2) and enable OEM UNLOCK
    6) Repeat 3) and type:adb reboot bootloader
    7) then type:fastboot boot recovery.img (must be copied in the same folder as adb.exe and fastboot.exe)
    (Don't flash recovery yet - system will replace stock recovery before you have root)
    8) Use TWRP to install SuperSU. - Now you have ROOT (Systemless) (can update to SR3, etc)
    9) Repeat 3) and type: adb reboot bootloader
    10) Type:fastboot flash recovery recovery.img - Now your new TWRP recovery will be permanent.
    11) Use TWRP to reinstall SuperSU as lost in step 10 - Now you have ROOT (Systemless).

    To Enter TWRP:
    After powering down, press power, wait 1 sec then hold both vol up & down also (all 3 buttons) until vibrates.

    I also uploaded the files here: filedropper.com/tb3850froot

    Peter W:
    Here is link to latest 850f rom:
    http://lenovo-forums.ru/files/file/1549-lenovo-tab3-a8-tb3-850f_s100030_161209_row/
    Which takes you to https://cloud.mail.ru/public/8T5R/RWCkuBz19
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    MotoJunkie01
    MotoJunkie01
    Xecsc said:
    Thanks for the guide!
    Everything works but when I reboot into recovery I just get the dead android with no command under him..
    I tried two times with same result Fastboot reports twrp flashes ok

    Any ideas?

    Thanks
    Click to expand...
    Click to collapse
    Not to hijack the OP's thread but here are my thoughts. The dead Android indicates that TWRP did not successfully flash to your /recovery partition. Sounds like stock recovery is still installed. First, place a copy of twrp.img on your device's internal storage or on an external micro SD. Try this: instead of typing the command "fastboot flash recovery twrp.img", type " fastboot boot twrp.img" (assuming your twrp file is named twrp.img. If it isn't, rename it twrp.img for simplicity purposes). This command will temporarily boot your device into TWRP recovery. From the main menu on TWRP, select INSTALL. In the bottom right of the screen, select the option for "img" files. Navigate to where you stored "twrp.img" and select it. Install it to "RECOVERY" when prompted. Once it flashes, select REBOOT then select RECOVERY. Your device should now successfully boot into TWRP recovery.
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