Okay, I would start from scratch, so…
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Restart your Ubuntu PC (do not connect Phone OnePlus X to the PC)
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Now use the terminal window and enter the following commands in the correct order:
- [sudo¹] add-apt-repository ppa:phablet-team/tools
- [sudo¹] apt-get update
- [sudo¹] apt-get install phablet-tools android-tools-adb android-tools-fastboot
- Connect your OnePlus X to the Ubuntu PC .The next command should show the unique ID number of your device:
- [sudo¹] ] fastboot devices
- Now flash TWRP Recovery with the following command
- [sudo¹] fastboot flash twrp-3.3.1-0-onyx.img (twrp-3.0.2-0-onyx.img)
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the flashing process takes a few seconds.
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When the installation is complete, disconnect the OnePlus X from the Ubuntu PC and press and hold the On/Off button to exit the Quick Start mode.
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TWRP Custom Recovery should now be installed on your OnePlus X
Note: [sudo¹] is not preferred by every user