Read Android system update log file

Problem:

• The Android (OTA) System update fails but doesn't show the reason why.

Solution:

• Open a root explorer (e.g. ES Datei Explorer) and mount the system partition as root.
• The update log file is located at the following location: /cache/recovery/last_log
• Browse to this location and open the file with a text editor.

Context:

• Device: Nexus 7
• Status: rooted
• Android version: 4.2