[Galaxy S II Android Development] olejonbj:
EDIT: Read my latest answer at the bottom (two answers in one here).

No. I installed TWRP 3.1.1 after having had TWRP 3.1.0 AND LineageOS for a while (wanted the latest and greatest and nothing on the TWRP website says it does not work). LineageOS comes without root out of the box (as according to first post in this thread, one must flash it from here). As no flashing of IMG files is possible in TWRP 3.1.1, since it does not detect any filesystems, the GUI shows no partitions below when choosing to flash an IMG file (which TWRP 3.1.0 does), and when swiping to try anyway it just exits with an error and TWRP 3.1.0 is not installed. And no ZIP files either, but possible after mounting partitions manually. Seriously, I can flash TWRP 3.1.1 again and grab a video of it if you don't believe me. TWRP 3.1.1 isn't even able to store its own settings, because of no writeable file systems where it stores its config.

Anyway, "adb shell" and mounting partitions manually:

mkdir /efs
mkdir /preload
mount /dev/block/mmcblk0p1 /efs
mount /dev/block/mmcblk0p7 /cache
mount /dev/block/mmcblk0p9 /system
mount /dev/block/mmcblk0p10 /data
mount /dev/block/mmcblk0p12 /preload

... then I can flash ZIPs that are for LineageOS as the scripts recognize the partitions even though the TWRP GUI shows no partitions mounted under "MOUNT", but in the File Manager in TWRP or in shell (ls /path) one can clearly see that they are mounted (like /system). So flashing the addonsu-root ZIP (as according to first thread, it is not enabled out of the box and must be flashed, maybe you had it from a previous ROM) enabling root is possible under Settings > Developer options (it is NOT possible after a clean install of LineageOS). Then after using the TWRP Android app (which requires root) in Android itself and flashing the recovery back to 3.1.0 works. Then I ran the addonsu-unroot script (available on the same download page as the root script) to unroot because I need some banking apps to work.

What I don't understand is why they put TWRP 3.1.1 for i9100 on their official website when it is not supported (maybe with other ROMS?). Would be nice if they added a notice about LineageOS not working with it at least, as it is probably the most popular ROM.

Anyway as an Android Developer it is just a test phone, and also serves nice for my Spanish SIM card people can reach me depending which of my countries I'm in. Now with no roaming charges in the EU/EEA it does not matter that much, but I have 2 GB on that contract so nice to be able to use it from my home country if I run out of data on my main phone (Google phone), for example use it as router.

Again, awesome ROM for all my phones (as a dev I have quite a few). Glad I got this fixed without a full start-from-scratch.

---------- Post added at 21:19 ---------- Previous post was at 21:04 ----------

No, sorry!

Linux or whatever, the Android platform-tools are available on Linux/OS X/Windows. Yes I use Linux on main developer workstations and HTPCs, but this I did from my MacBook Air (on the go, which made me extra frustrated). Have Android Studio and the SDK on this as well if I need to develop on the go, so the whole package.

AFAIK one can not flash TWRP with ADB, but use it to reboot into bootloader and use "fastboot flash recovery <file>" to do it. I was more afraid of this solution. AFAIK this phone keeps count of how many times you have tempered from the bootloader, but I guess it would have worked without wiping my ROM. At least now I'm back to where I was, just with the new version of LineageOS and OpenGapps.

It was just that in my main thread about this it was suggested to use the TWRP Android app which requires root which I could not flash from TWRP 3.1.1.

Man this phone is so complicated to customize. So much easier with Google phones. Well, it was just a gift and the stock Samsung version, well sucks and doesn't serve for me as a testing device for apps that I develop.

Sorry again, don't be upset. I'm back to happy :)