I used to start my Android Studio emulator using
emulator -avd "mydevice" -writable-system
But suddenly now it only works if I remove the -writable-system option, otherwise it is stuck with the boot logo.
Why would that option change the outcome of booting?
And how can I understand what happened, in order to fix this and make the -writable-system option work again?
In the worst case, is there a way to reset the system image without erasing the user data?
At the end I solved the problem by myself...
The cause of the problem was a corrupted system partition.
I went in my AVD folder and renamed system image file system.img.qcow2 into BACKUP_system.img.qcow2 (I could also have deleted it, but you never know).
Then, once I ran the emulator with option -writable-system, since it could not find the system image file anymore, then it created a new one and now it is possible to write on the system partition again.
And this also allowed me to avoid erasing the user data partition, therefore I saved the data and it's like nothing bad ever happened.
The reason why it was still working without the -writable-system option:
When I removed the system.img.qcow2 file, initially I tried to run the emulator without the -writable-system. Again, it worked... and no new system image file was generated.
I tried to investigate on this, and when running:
emulator -help-disk-images
I noticed it says:
If you use a virtual device, its content directory should store
all writable images, and read-only ones will be found from the
corresponding platform/add-on directories.
So this is why the emulator was still working without the -writable-system option, although the system image file was corrupted. It's because that was a writable image file, so it's not loaded if the -writable-system option is not used, and the read-only system image, which is stored in a different place, is loaded instead.
And of course, when the emulator needs to create a new writable system partition (like in this case), it copies it from that read-only system image.