Adding custom bootup script to Android-x86 Nougat
The avc denial you have got states that:


  init is running with its context u:r:init:0, you want it to execute /system/bin/mystart (script, binary, whatever) which is labeled as u:object_r:system_file:s0. But init isn't allowed to execute system_file in sepolicy. However you have set SELinux permissive, so it's just a warning, not actual denial.


Therefore you don't need to do anything with SELinux unless you set it enforcing. There must be some other problem with your shell script. Put set -x; exec &gt;/data/media/0/mystart.log 2&gt;&amp;1 at the start of your script to see what happens when it's executed.

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