Can not install CM 13.0 / 12.1 on galaxy s2 because of missing file_contexts I am currently trying to install Cyanogenmod 13.0 via CWM on an Galaxy S2 i9100. The phone is successfully rooted and by holding Power, Home and Up I can successfully boot into the system recovery-screen. There I choose to apply update from ADB, hit adb sideload cm-13.0-20161218-NIGHTLY-i9100.zip and wait. Then I receive:

Verifying update package...
Installing update...
Warning: No file_contextsThis package is for device: galaxys2, i9100,GT-I9100,GT-I9100M,GT-I9100P,GT-I9100T,SC-O2C; this device is .
E: Error in /tmp/update.zip (Status 7)


The device is clearly an S2 i9100 (without g), and this is also displayed when I load settings -> device information.

Some sites like e.g. http://www.droidviews.com/fix-status-7-error-while-installing-ota-update-or-roms/ tell to change /META-INF/com/google/android/updater-script (and to remove the check for the correct smartphone) and then try it again. Unfortunately, with this change verification errors occur.
So I tried http://fokke.org/site/content/howto-create-android-updatezip-package (unzip everything, recreate META-INF/MANIFEST.MF, CERT.SF and CERT:RSA by runing java -classpath testsign.jar testsign update.zip update-signed.zip and then re-zip the folder), but still the verification error occurs.
Also changing in ro.product.device in /system/build.prop from GT-I9100 to i9100 did not change anything (according to http://apcmag.com/how-to-fake-an-android-device.htm/ and the assertion in the first line of /META-INF/com/google/android/updater-script, GT-I900 was correct in the first place, it rather seems like the property could not be loaded by the update script).

The same happens with different CM-versions, regardless whether they are stable or not, so I suppose the check is executed in every version. I did not find any workaround for this - is there maybe a way to set ro.product.device on my phone, skip the assertion by some argument or just get the right verification information?
After some help from the irc-channel, the solution is (like described in https://web.archive.org/web/20161224194651/https://wiki.cyanogenmod.org/w/Install_CM_for_i9100) to use the boot.img from the cm13-zip (which seems in fact to be twrp) and flash it to the device with first booting in download mode (Power + Home + Down) and then running heimdall flash --KERNEL boot.img --no-reboot (KERNEL with capital letters). Afterwards, one can normaly install the zip using sideload.