How to properly factory-reset a Samsung Galaxy S2?

Question

I did a factory reset on a Samsung Galaxy S2 like this:

• switch off phone
• hold down buttons Volume Up, Home and Power until phone boots into "Android System Recovery" mode
• select wipe/factory reset and confirm all questions

As expected, after the factory reset, all apps were not installed anymore.

But this does not seem to have worked for the file system: On the file system of the internal USB memory (/storage/sdcard0), I see many folders of previously installed apps and also some which I had manually created before the factory reset. I think that a factory reset should delete all these folders, because e.g. the WhatsApp folder contains all my personal messages. I think that if a function is called a factory reset, then afterwards personal messages should be deleted. So what's wrong here?

Answer 1

A factory reset usually doesn't touch "external storage" (may sound confusing, but that includes the "internal SDcard" as well) – unless it explicitly specifies so (some devices/ROMs have a corresponding checkbox in the system menu, usually Settings → Backup & Reset, where this might be specified to be included).

What a factory reset usually does is, basically, to wipe /cache (where the application cache should be) and /data (where the userdata reside, including the apps the user installed).

Which means: Nothing is wrong here, it's "working as designed". If you want the SDcard to be wiped, you will have to do so yourself. You can e.g. use a file manager app, or connect your device to a computer. Or simply use a terminal app (or adb shell), and invoke rm -rf /storage/sdcard0/* to have all files removed from there.

See also: factory-reset tag-wiki