I've connected the phone via USB. The phone is rooted, USB debugging is enabled and ADB has root access. The system is a vanilla Debian 8.3.0.
lsusb:
[...]
Bus 002 Device 004: ID 04e8:685e Samsung Electronics Co., Ltd GT-I9100 Phone [Galaxy S II] (USB Debugging mode)
adb devices:
List of devices attached
adb shell:
error: device not found
The same occurs when I run the commands as root.
How can I connect to the phone with adb?