How to edit init.sh file and where is it? I want to edit init.sh but I can't find it. where is the location of that file ?
I want add this to that file:


  alsa_amixer set PCM 100 unmute
I think you mean init.rc and don't.

But to answer your question, that file is in the root folder /init.rc to edit it you need root access and remount / rw and even with that you'll lose changes when you restart because it's overwritten every time by boot.img content, so you would need to extract boot.img content edit that file rebuild the image and flash it.

The right way to execute commands at start is to use init.d scripts.

In short if init.d script is supported init.rc calls a functions that search for user scripts in /system/etc/init.d/ and execute them.
You can put a script there and see if it gets executed or search for how to enable init.d scripts.

Edit
Looking for your command I found out maybe you are using android on x86. In that case looks like there is an init.sh in /system/etc/ folder.

To be able to edit files under /system you need to remount it rw using an app like ES File Explorer or running from terminal as root:

mount -o rw,remount /system