/etc/ directory. Usually it is placed in
/system/ partition which you can mount as RW:
$ ls -l /etc lrwxrwxrwx 1 root root 11 Jan 1 2009 /etc -> /system/etc $ su $ mount -o remount,rw /system $ chmod o+w /system/etc # for "adb push"
Some above steps may be replaces with:
$ adb root $ adb remount
and later remount RO:
$ chmod o-w /system/etc $ mount -o remount,ro /system
Now your task to find executable or
*rc file which you modify to achieve your goal:
$ find /etc -type f -perm +110 $ find /etc -name "*rc" $ find /etc -name "init*" $ grep -R /data /etc $ grep -R /system /etc
Google about each candidate to get know how this file was used.
Good candidate for including custom scripts are lines from:
$ grep service /init*.rc
As each device unique you may need to do own guess about search criteria...
For example I found
/etc/mkshrc which used by Korn shell. I update this file to extend
PATH env var and now each time I do
adb shell I have Busybox symlinks in my PATH!
See also hard way (if you have no luck with finding magic file): https://stackoverflow.com/questions/9768103/make-persistent-changes-to-init-rc