The Samsung Galaxy S2 (GT-I9100) I have at hand was turned off after getting hot during standby. When trying to start it again, it was in a bootloop: Like usual, it first shows "Samsung Galaxy S2 GT-I9100", then shows the provider branding and then shows "Samsung". But at the time when it was normally asking for the PIN, it was again showing the provider branding and going into a loop.
It is possible to go into the recovery mode. Among other things (see below) it shows "E:Error in /data/log/recovery_log.txt (No space left on device)".
The phone was running the newest stock firmware (Android 4.1.2). (At least I’m quite sure it was the newest version.)
Is there something I could try to make it start again, without loosing any data? For example, it could be the case that it’s not starting because the /data partition is full. Is it possible to remove files from this partition when booting the device is not possible?
If that’s not possible, is it possible to backup all the data (including app data and the internal "USB" storage), without loosing any data?
It seems like installing a different recovery ROM makes it possible to backup the data. However, I’ve read that installing a different recovery on a S2 with a stock ROM will stop the system from booting. In this case it doesn’t boot anyway. But in case it’s possible to fix the problem by making space free on the /data partition, can the original system be restored?
Some things which I observed that may (or may not) be helpful:
The recovery mode says "Android system recovery <3e>" at the top and "# MANUAL MODE #", "-- Appling Multi-CSC...", "Applied the CSC-code : DTM", and "Successfully applied multi-CDC" in the middle, right over the out-of-space error described above.
When turning on the phone, the provider sends SMSs to everyone who has tried to call the number while the phone was off. Even though the phone is boot-looping, such notification was sent.