Unable to unlock/flash recovery

[irha]

I am trying to unlock the bootloader and flash TWRP for the first time. I followed the steps from here: https://wiki.lineageos.org/devices/s2/install

I turned on the unlock option in settings and unlocked via fastboot, rebooted it manually (it didn't reboot), and then tried to flash:

$ ./fastboot oem unlock-go
                                                   OKAY [  0.007s]
Finished. Total time: 0.007s
$ ./fastboot flash recovery twrp-3.3.1-0-s2.img
Sending 'recovery' (24618 KB)                      OKAY [  0.859s]
Writing 'recovery'                                 FAILED (remote: 'Partition flashing is not allowed')
fastboot: error: Command failed
$ ./fastboot reboot
Rebooting                                          OKAY [  0.001s]
Finished. Total time: 0.001s
$ ./adb reboot bootloader
$ ./fastboot flash recovery twrp-3.3.1-0-s2.img
Sending 'recovery' (24618 KB)                      OKAY [  0.779s]
Writing 'recovery'                                 FAILED (remote: 'Partition flashing is not allowed')
fastboot: error: Command failed
$ ./fastboot oem unlock-go
                                                   OKAY [  0.007s]
Finished. Total time: 0.007s
$ ./fastboot flash recovery twrp-3.3.1-0-s2.img
Sending 'recovery' (24618 KB)                      OKAY [  0.836s]
Writing 'recovery'                                 OKAY [  0.231s]
Finished. Total time: 1.071s
$ ./fastboot reboot recovery
Rebooting into recovery                            OKAY [  0.001s]
Finished. Total time: 0.001s

However, I got into the stock recovery page instead of TWRP. You can see above that the flash failed before I rebooted, but succeeded after that. Interesting observations:
- The above webpage indicates that the device should reset when I reboot, but it didn't, which means the unlock didn't work.
- When I went back to bootloader, the first attempt to flash failed, but when I ran another unlock it worked though apparently it did nothing.

Am I missing a step? I am using fastboot version 29.0.6-6198805 on Mac OS Mojave 10.14.6.

 

[kalehrl]

Don't reboot to recovery via a command after flashing it.
Try rebooting using buttons, vol-up + power.

 

[irha]

Don't reboot to recovery via a command after flashing it.
Try rebooting using buttons, vol-up + power.

Thank you! That got me into TWRP with a dialog titled "Unmodified System Partition" with a slider to allow modifications. I am googling to see what this dialogue is about and how to get TWRP to permanently get installed.

 

[kalehrl]

That's normal. Just enable modifications and that's it.

 

[irha]

That's normal. Just enable modifications and that's it.

OK, I don't remember seeing it before (I haven't flashed in at least a couple of years). I ran `adb reboot recovery` and it did go back into TWRP, so I am assuming that it did get persisted. For some reason "Never show this screen..." option didn't work, which is fine, but does it indicate that something is still readonly?

 

[kalehrl]

I don't think so.
You're good to proceed.

 

[irha]

I was able to sideload the ROM and opengapps nano and it is booting up for the first time. I skipped the optional step to install root (AddonSU), I guess I can do it later too if I feel the need to get root. Thanks a lot for your quick help.

 

[kalehrl]

No problem.
If you want to root it, do it with Magisk.
Nowadays, LineageOS team recommend it.