This video shows the process in general terms:
Installing adb tools on ubuntu worked really well:
apt-get install android-tools-adb android-tools-fastboot
I thought about installing android sdk. I didn’t go ahead.
My steps that worked:
fastboot flash recovery openrecovery-twrp-22.214.171.124-bacon.img
Setting up the ADB driver. The suggested universal ADB driver and the alternate Samsung driver did not work. And it turns out I did not need it. I just had to hold power + volume up to get to fastboot mode. No need for ADB (command: adb reboot bootloader).
Copying the supersu zip file as indicated in the video also did not work for me. I had to copy it over a second time. Maybe something about my android mtp connection.
Installing the ADB and fastboot tools for ubuntu was the main thing that worked. The steps in windows and ubuntu are quite similar.
Encountered a boot loop situation – not sure what caused it. Maybe because I tried to freeze some of the unnecessary google apps and cyanogen mod theme apps? Or was a data+cache wipe necessary before performing the root process.
– to complicate the situation I mistakenly wiped the system partition without performing a nand backup previously so I had to reinstall system.img.
– the restore of the system partition as recommended by other websites (http://www.ibtimes.co.uk/how-restore-oneplus-one-cyanogenmod-11s-stock-firmware-1468901) –i.e. by using flash-all.sh didn’t work smoothly. had to manually install system.img by extracting it from the zip and running:
fastboot flash system system.img
– flash-all returns an error about the system partition not being large enough for the image
– had to reinstall twrp because flash-all overwrote it.