Real root can not change any thing on /system original files! On my rooted device running Android 4.2.2, I have following tools installed:


Terminal Emulator
BusyBox Free


On Terminal Emulator, su command successfully changes user to a real root:

root@hwH30-U10:/ # id -u
uid=0(root) gid=0(root)


Then I remount /system as R/W:

root@hwH30-U10:/ # mount | grep system
/emmc@android /system ext4 rw,realtime,noauto_da_alloc,commit=1,data=ordered 0 0


Then I even:

root@hwH30-U10:/ # chmod 777 /system


But I can not change any thing e.g. permissions or contents of /system original files like /system/build.prop!

I am sure that permissions and mounts are OK because I can create a new file, /system/tmp.prop, change it's contents and permissions by Terminal Emulator.

I really have no idea why these operations are not permitted while in Linux point of view, all things are OK for root to do these changes!

Is there any hard-coded further protection inside Android e.g. in kernel?

How to figure out this, please?
Based on my comment and Yasser's subsequent comment , I can conclude that the issue was the immutable attribute set on the file build.prop. If other files and directories also can't be edited or deleted, then they may also be having the same attribute or append-only attribute. 

The remedy is to use this command with root privilege:

chattr -i FILE_PATH    # FILE_PATH is the file which currently has immutable attribute


Use -iR followed by a directory's path to remove immutable attribute from a directory recursively.

It is to be noted that OP already has busybox installed. chattr and lsattr aren't the utilities found natively in Android.

Relevant info about the used chattr command and append-only attribute can be found in my answer here.