One of the reasons that I installed a custom ROM on my smartphone was so that I would be able to update the operating system and maintain some level of security. And, sure enough, the installed LineageOS 14.1 provided notifications of available updates, essentially on a weekly basis.
Navigating to Settings – About phone – LineageOS updates shows a list of the available software updates (see screenshot below). An icon – a down-arrow above a horizontal line – next to each listing indicates that the file can be downloaded. Having done this for the most recent update, I thought I had to locate the downloaded file and install it. However, the trick is really to click on the now, slightly-different arrow next to the file. Clicking on the “download” arrow – now a down-arrow inside a rectangular box – a second time causes the phone to boot into recovery mode and install the update.
I subsequently experienced a problem with booting the newly-updated system. Error messages were popping up indicating that “Google play services keeps stopping”. The real problem here was that, without Google play services running properly, Google Play Store wouldn’t download and install any apps.
None of the fixes for this issue that were posted on the Internet seemed to make any difference. These included changing the option for “WebView implementation” and installing the latest version of Google Play Store. The solution that worked for me was to download and install the latest version of Gapps (open-gapps-arm-7.1-stock-20171208.zip).
The phone rebooted more-or-less normally. A minor issue was that it booted into the Pixel Launcher. I navigated to Settings – Apps, chose the option for the Google Launcher, and set this to Always, in order to return the user interface to its previous look and feel.
I also found that the update process had removed root access such that Quick Reboot would no longer run. The fix for this was to boot into recovery mode and re-flash the LineageOS super-user file (addonsu-14.1-arm-signed.zip).
As a side note, the successful update to LineageOS also seemed to clear up a problem whereby TWRP would no longer make a new system backup. In particular, the backup process produced the error: “createTarFork() process ended with ERROR: 255 Backup Failed. Cleaning Backup Folder”.
Once again, there proved to be a dearth of useful information on the cause of this problem, and how to fix it. Simply re-installing TWRP had no effect, nor did deleting the file /addon.d. However, once I had successfully updated LineageOS as noted above, I was able to re-run TWRP recovery and make a complete system backup without any error messages appearing.